Single step, pH induced gold nanoparticle chain formation in lecithin/water system.

PubMed

Sharma, Damyanti

2013-07-01

Gold nanoparticle (AuNP) chains have been formed by a single step method in a lecithin/water system where lecithin itself plays the role of a reductant and a template for AuNP chain formation. Two preparative strategies were explored: (1) evaporating lecithin solution with aqueous gold chloride (HAuCl4) at different pHs and (2) dispersing lecithin vesicles in aqueous HAuCl4 solutions of various pHs in the range of 2.5-11.3. In method 1, at initial pH 2.5, 20-50 nm AuNPs are found attached to lecithin vesicles. When pH is raised to 5.5 there are no vesicles present and 20 nm monodisperse particles are found aggregating. Chain formation of fine nanoparticles (3-5 nm) is observed from neutral to basic pH, between 6.5-10.3 The chains formed are hundreds of nanometers to micrometer long and are usually 2-3 nanoparticles wide. On further increasing pH to 11.3, particles form disk-like or raft-like structures. When method (ii) was used a little chain formation was observed. Most of the nanoparticles formed were found either sitting together as raft like structures or scattered on lecithin structures. Copyright © 2013 Elsevier B.V. All rights reserved.

Humid Heat Autoclaving of Hybrid Nanoparticles Achieved by Decreased Nanoparticle Concentration and Improved Nanoparticle Stability Using Medium Chain Triglycerides as a Modifier.

PubMed

Gou, Jingxin; Chao, Yanhui; Liang, Yuheng; Zhang, Ning; He, Haibing; Yin, Tian; Zhang, Yu; Xu, Hui; Tang, Xing

2016-09-01

Humid heat autoclaving is a facile technique widely used in the sterilization of injections, but the high temperature employed would destroy nanoparticles composed of biodegradable polymers. The aim of this study was to investigate whether incorporation of medium chain triglycerides (MCT) could stabilize nanoparticles composed of poly (ethylene glycol)-b-polycaprolactone (PEG-b-PCL) during autoclaving (121°C, 10 min). Polymeric nanoparticles with different MCT contents were prepared by dialysis. Block copolymer degradation was studied by GPC. The critical aggregation concentrations of nanoparticles at different temperatures were determined using pyrene fluorescence. The size, morphology and weight averaged molecular weight of pristine/autoclaved nanoparticles were studied using DLS, TEM and SLS, respectively. Drug loading content and release profile were determined using RP-HPLC. The protecting effect of MCT on nanoparticles was dependent on the amount of MCT incorporated. Nanoparticles with high MCT contents, which assumed an emulsion-like morphology, showed reduced block copolymer degradation and particle disassociation after incubation at 100°C for 24 h. Nanoparticles with high MCT content showed the lowest critical aggregation concentration (CAC) under either room temperature or 60°C and the lowest particle concentration among all samples. And the particle size, drug loading content, physical stability and release profile of nanoparticles with high MCT contents remained nearly unchanged after autoclaving. Incorporation of high amount of MCT changed the morphology of PEG-b-PCL based nanoparticles to an emulsion-like structure and the nanoparticles prepared could withstand autoclaving due to improved particle stability and decreased particle concentration caused by MCT incorporation.

Hierarchical self-assembly: Self-organized nanostructures in a nematically ordered matrix of self-assembled polymeric chains

NASA Astrophysics Data System (ADS)

Mubeena, Shaikh; Chatterji, Apratim

2015-03-01

We report many different nanostructures which are formed when model nanoparticles of different sizes (diameter σn) are allowed to aggregate in a background matrix of semiflexible self-assembled polymeric wormlike micellar chains. The different nanostructures are formed by the dynamical arrest of phase-separating mixtures of micellar monomers and nanoparticles. The different morphologies obtained are the result of an interplay of the available free volume, the elastic energy of deformation of polymers, the density (chemical potential) of the nanoparticles in the polymer matrix, and, of course, the ratio of the size of self-assembling nanoparticles and self-avoidance diameter of polymeric chains. We have used a hybrid semi-grand-canonical Monte Carlo simulation scheme to obtain the (nonequilibrium) phase diagram of the self-assembled nanostructures. We observe rodlike structures of nanoparticles which get self-assembled in the gaps between the nematically ordered chains, as well as percolating gel-like network of conjoined nanotubes. We also find a totally unexpected interlocked crystalline phase of nanoparticles and monomers, in which each crystal plane of nanoparticles is separated by planes of perfectly organized polymer chains. We identified the condition which leads to such interlocked crystal structure. We suggest experimental possibilities of how the results presented in this paper could be used to obtain different nanostructures in the laboratory.

Molecular Mechanisms of ZnO Nanoparticle Dispersion in Solution: Modeling of Surfactant Association, Electrostatic Shielding and Counter Ion Dynamics.

PubMed

Duchstein, Patrick; Milek, Theodor; Zahn, Dirk

2015-01-01

Molecular models of 5 nm sized ZnO/Zn(OH)2 core-shell nanoparticles in ethanolic solution were derived as scale-up models (based on an earlier model created from ion-by-ion aggregation and self-organization) and subjected to mechanistic analyses of surface stabilization by block-copolymers. The latter comprise a poly-methacrylate chain accounting for strong surfactant association to the nanoparticle by hydrogen bonding and salt-bridges. While dangling poly-ethylene oxide chains provide only a limited degree of sterical hindering to nanoparticle agglomeration, the key mechanism of surface stabilization is electrostatic shielding arising from the acrylates and a halo of Na+ counter ions associated to the nanoparticle. Molecular dynamics simulations reveal different solvent shells and distance-dependent mobility of ions and solvent molecules. From this, we provide a molecular rationale of effective particle size, net charge and polarizability of the nanoparticles in solution.

Molecular Mechanisms of ZnO Nanoparticle Dispersion in Solution: Modeling of Surfactant Association, Electrostatic Shielding and Counter Ion Dynamics

PubMed Central

Duchstein, Patrick; Milek, Theodor; Zahn, Dirk

2015-01-01

Molecular models of 5 nm sized ZnO/Zn(OH)2 core-shell nanoparticles in ethanolic solution were derived as scale-up models (based on an earlier model created from ion-by-ion aggregation and self-organization) and subjected to mechanistic analyses of surface stabilization by block-copolymers. The latter comprise a poly-methacrylate chain accounting for strong surfactant association to the nanoparticle by hydrogen bonding and salt-bridges. While dangling poly-ethylene oxide chains provide only a limited degree of sterical hindering to nanoparticle agglomeration, the key mechanism of surface stabilization is electrostatic shielding arising from the acrylates and a halo of Na+ counter ions associated to the nanoparticle. Molecular dynamics simulations reveal different solvent shells and distance-dependent mobility of ions and solvent molecules. From this, we provide a molecular rationale of effective particle size, net charge and polarizability of the nanoparticles in solution. PMID:25962096

Assessing the Role of Capping Molecules in Controlling Aggregative Growth of Gold Nanoparticles in Heated Solution.

PubMed

Cheng, Han-Wen; Schadt, Mark J; Zhong, Chuan-Jian

2016-01-01

This report describes findings of an investigation of the role of capping molecules in the size growth in the aggregative growth of pre-formed small-sized gold nanoparticles capped with alkanethiolate monolayers toward monodispersed larger sizes. The size controllability depends on the thiolate chain length and concentration in the thermal solution. The size evolution in solution at different concentrations of alkanethiols is analyzed in relation to adsorption isotherms and cohesive energy. The size dependence on thiolate chain length is also analyzed by considering the cohesive energy of the capping molecules, revealing the importance of cohesive energy in the capping structure. Theoretical and experimental comparisons of the surface plasmonic resonance optical properties have also provided new insights into the mechanism, thus enabling the exploitation of size-dependent nanoscale properties. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microfluidic separation of magnetic nanoparticles on an ordered array of magnetized micropillars

NASA Astrophysics Data System (ADS)

Orlandi, G.; Kuzhir, P.; Izmaylov, Y.; Alves Marins, J.; Ezzaier, H.; Robert, L.; Doutre, F.; Noblin, X.; Lomenech, C.; Bossis, G.; Meunier, A.; Sandoz, G.; Zubarev, A.

2016-06-01

Microfluidic separation of magnetic particles is based on their capture by magnetized microcollectors while the suspending fluid flows past the microcollectors inside a microchannel. Separation of nanoparticles is often challenging because of strong Brownian motion. Low capture efficiency of nanoparticles limits their applications in bioanalysis. However, at some conditions, magnetic nanoparticles may undergo field-induced aggregation that amplifies the magnetic attractive force proportionally to the aggregate volume and considerably increases nanoparticle capture efficiency. In this paper, we have demonstrated the role of such aggregation on an efficient capture of magnetic nanoparticles (about 80 nm in diameter) in a microfluidic channel equipped with a nickel micropillar array. This array was magnetized by an external uniform magnetic field, of intensity as low as 6-10 kA/m, and experiments were carried out at flow rates ranging between 0.3 and 30 μ L /min . Nanoparticle capture is shown to be mostly governed by the Mason number Ma, while the dipolar coupling parameter α does not exhibit a clear effect in the studied range, 1.4 < α < 4.5. The capture efficiency Λ shows a strongly decreasing Mason number behavior, Λ ∝M a-1.78 within the range 32 ≤ Ma ≤ 3250. We have proposed a simple theoretical model which considers destructible nanoparticle chains and gives the scaling behavior, Λ ∝M a-1.7 , close to the experimental findings.

Phase separation of comb polymer nanocomposite melts.

PubMed

Xu, Qinzhi; Feng, Yancong; Chen, Lan

2016-02-07

In this work, the spinodal phase demixing of branched comb polymer nanocomposite (PNC) melts is systematically investigated using the polymer reference interaction site model (PRISM) theory. To verify the reliability of the present method in characterizing the phase behavior of comb PNCs, the intermolecular correlation functions of the system for nonzero particle volume fractions are compared with our molecular dynamics simulation data. After verifying the model and discussing the structure of the comb PNCs in the dilute nanoparticle limit, the interference among the side chain number, side chain length, nanoparticle-monomer size ratio and attractive interactions between the comb polymer and nanoparticles in spinodal demixing curves is analyzed and discussed in detail. The results predict two kinds of distinct phase separation behaviors. One is called classic fluid phase boundary, which is mediated by the entropic depletion attraction and contact aggregation of nanoparticles at relatively low nanoparticle-monomer attraction strength. The second demixing transition occurs at relatively high attraction strength and involves the formation of an equilibrium physical network phase with local bridging of nanoparticles. The phase boundaries are found to be sensitive to the side chain number, side chain length, nanoparticle-monomer size ratio and attractive interactions. As the side chain length is fixed, the side chain number has a large effect on the phase behavior of comb PNCs; with increasing side chain number, the miscibility window first widens and then shrinks. When the side chain number is lower than a threshold value, the phase boundaries undergo a process from enlarging the miscibility window to narrowing as side chain length increases. Once the side chain number overtakes this threshold value, the phase boundary shifts towards less miscibility. With increasing nanoparticle-monomer size ratio, a crossover of particle size occurs, above which the phase separation is consistent with that of chain PNCs. The miscibility window for this condition gradually narrows while the other parameters of the PNCs system are held constant. These results indicate that the present PRISM theory can give molecular-level details of the underlying mechanisms of the comb PNCs. It is hoped that the results can be used to provide useful guidance for the future design control of novel, thermodynamically stable comb PNCs.

Precisely Size-Tunable Monodisperse Hairy Plasmonic Nanoparticles via Amphiphilic Star-Like Block Copolymers.

PubMed

Chen, Yihuang; Yoon, Young Jun; Pang, Xinchang; He, Yanjie; Jung, Jaehan; Feng, Chaowei; Zhang, Guangzhao; Lin, Zhiqun

2016-12-01

In situ precision synthesis of monodisperse hairy plasmonic nanoparticles with tailored dimensions and compositions by capitalizing on amphiphilic star-like diblock copolymers as nanoreactors are reported. Such hairy plasmonic nanoparticles comprise uniform noble metal nanoparticles intimately and perpetually capped by hydrophobic polymer chains (i.e., "hairs") with even length. Interestingly, amphiphilic star-like diblock copolymer nanoreactors retain the spherical shape under reaction conditions, and the diameter of the resulting plasmonic nanoparticles and the thickness of polymer chains situated on the surface of the nanoparticle can be readily and precisely tailored. These hairy nanoparticles can be regarded as hard/soft core/shell nanoparticles. Notably, the polymer "hairs" are directly and permanently tethered to the noble metal nanoparticle surface, thereby preventing the aggregation of nanoparticles and rendering their dissolution in nonpolar solvents and the homogeneous distribution in polymer matrices with long-term stability. This amphiphilic star-like block copolymer nanoreactor-based strategy is viable and robust and conceptually enables the design and synthesis of a rich variety of hairy functional nanoparticles with new horizons for fundamental research on self-assembly and technological applications in plasmonics, catalysis, energy conversion and storage, bioimaging, and biosensors. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Visual Detection of Human Antibodies Using Sugar Chain-Immobilized Fluorescent Nanoparticles: Application as a Point of Care Diagnostic Tool for Guillain-Barré Syndrome.

PubMed

Shinchi, Hiroyuki; Yuki, Nobuhiro; Ishida, Hideharu; Hirata, Koichi; Wakao, Masahiro; Suda, Yasuo

2015-01-01

Sugar chain binding antibodies have gained substantial attention as biomarkers due to their crucial roles in various disorders. In this study, we developed simple and quick detection method of anti-sugar chain antibodies in sera using our previously developed sugar chain-immobilized fluorescent nanoparticles (SFNPs) for the point-of-care diagnostics. Sugar chain structure on SFNPs was modified with the sugar moieties of the GM1 ganglioside via our original linker molecule to detect anti-GM1 antibodies. The structures and densities of the sugar moieties immobilized on the nanoparticles were evaluated in detail using lectins and sera containing anti-GM1 antibodies from patients with Guillain-Barré syndrome, a neurological disorder, as an example of disease involving anti-sugar chain antibodies. When optimized SFNPs were added to sera from patients with Guillain-Barré syndrome, fluorescent aggregates were able to visually detect under UV light in three hours. The sensitivity of the detection method was equivalent to that of the current ELISA method used for the diagnosis of Guillain-Barré syndrome. These results suggest that our method using SFNPs is suitable for the point-of-care diagnostics of diseases involving anti-sugar chain antibodies.

Aggregation behavior of TiO2 nanoparticles in municipal effluent: Influence of ionic strengthen and organic compounds.

PubMed

Ren, Meijie; Horn, Harald; Frimmel, Fritz H

2017-10-15

The influence of ionic strengthen and dissolved organic matter (DOM) on the aggregation of TiO 2 nanoparticles (NPs) in municipal effluent was investigated. The results demonstrated that DOM promoted the mobility of NPs in aquatic system by synergism between static repulsion and steric effect, while electrolytes were opposite by charge-neutralization. The physical-chemical characteristics of DOM played the major role on the mobility of NPs. Bovine serum albumin (BSA) showed the strongest enhancement on the mobility of TiO 2 NPs. High adsorption of BSA introduced vast negative charges on the TiO 2 NPs' surface, leading to static repulsion and neutralizing positive charges of electrolytes in surrounding as well. By contrast, another protein α-amylase retarded the aggregation rate of TiO 2 NPs through steric repulsion of the long-chain construction. Humic substances (Fulvic acid and alginate) also reflected the combination of static repulsion and steric effect. However, in the high electrolytes concentration (especially Ca 2+ ), the long-chain aliphatic compounds were prone to form calcium bridge which increased the hydrodynamic diameter of TiO 2 aggregates consequently. Sodium dodecylbenzene sulfonate (SDBS) showed low adsorption capacity, while the unabsorbed SDBS retarded the aggregates caused by the changes of pH and electrolytes. These data indicated that decreasing of DOC concentration in aqueous system was important to reduce the mobility and potential risk of NPs in aqueous system. Copyright © 2017 Elsevier Ltd. All rights reserved.

Nanoparticle-Reinforced Associative Network Hydrogels

PubMed Central

Agrawal, Sarvesh K.; Sanabria-DeLong, Naomi; Tew, Gregory N.; Bhatia, Surita R.

2009-01-01

ABA triblock copolymers in solvents selective for the midblock are known to form associative micellar gels. We have modified the structure and rheology of ABA triblock copolymer gels comprising poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) through addition of a clay nanoparticle, laponite. Addition of laponite particles resulted in additional junction points in the gel via adsorption of the PEO corona chains onto the clay surfaces. Rheological measurements showed that this strategy led to a significant enhancement of the gel elastic modulus with small amounts of nanoparticles. Further characterization using SAXS and DLS confirmed that nanoparticles increase the intermicellar attraction and result in aggregation of PLA-PEO-PLA micelles. PMID:18947244

Let there be light: photo-cross-linked block copolymer nanoparticles.

PubMed

Roy, Debashish; Sumerlin, Brent S

2014-01-01

Polymeric nanoparticles are prepared by selectively cross-linking a photo-sensitive dimethylmaleimide-containing block of a diblock copolymer via UV irradiation. A well-defined photo-cross-linkable block copolymer is prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization of a dimethylmaleimide-functional acrylamido monomer containing photoreactive pendant groups with a poly(N,N-dimethylacrylamide) (PDMA) macro-chain transfer agent. The resulting amphiphilic block copolymers form micelles in water with a hydrophilic PDMA shell and a hydrophobic photo-cross-linkable dimethylmaleimide-containing core. UV irradiation results in photodimerization of the dimethylmaleimide groups within the micelle cores to yield core-cross-linked aggregates. Alternatively, UV irradiation of homogeneous solutions of the block copolymer in a non-selective solvent leads to in situ nanoparticle formation. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of chain rigidity on the conformation of model lipid membranes in the presence of cylindrical nanoparticle inclusions

NASA Astrophysics Data System (ADS)

Diloreto, Chris; Wickham, Robert

2012-02-01

We employ real-space self-consistent field theory to study the conformation of model lipid membranes in the presence of solvent and cylindrical nanoparticle inclusions (''peptides''). Whereas it is common to employ a polymeric Gaussian chain model for the lipids, here we model the lipids as persistent, worm-like chains. Our motivation is to develop a more realistic field theory to describe the action of pore-forming anti-microbial peptides that disrupt the bacterial cell membrane. We employ operator-splitting and a pseudo-spectral algorithm, using SpharmonicKit for the chain tangent degrees of freedom, to solve for the worm-like chain propagator. The peptides, modelled using a mask function, have a surface patterned with hydrophobic and hydrophillic patches, but no charge. We examine the role chain rigidity plays in the hydrophobic mismatch, the membrane-mediated interaction between two peptides, the size and structure of pores formed by peptide aggregates, and the free-energy barrier for peptide insertion into the membrane. Our results suggest that chain rigidity influences both the pore structure and the mechanism of pore formation.

Polymer Nanocomposites: Insights from Theory and Molecular Simulations

NASA Astrophysics Data System (ADS)

Pani, Rakhee

Advantages of polymer nanocomposites have attracted great industrial attention due to their multifunctionality and innovative technological properties. Addition of small amount of nanoparticle (nanospheres, nanotubes, nanorods, nanoplatelets, or sheets) to polymer matrix cause dramatic improvement in structural and functional properties, which is difficult to attain from those of individual components. The interaction between polymer and nanoparticle create bulk materials dominated by solid state physics at the nanoscale. Furthermore, morphology of nanocomposites depends on structural arrangements of nanoparticles. Thus, for achievement of optimized functionality like electrical, optical, mechanical and thermal properties control over the dispersion of the nanoparticle is essential. However, properties of polymer nanocomposites depend on morphology control and nature of interfacial interactions. In order to control the morphology it is necessary to understand how the processing conditions, shape and size of nanoparticle influence the structure of composite. Molecular simulations can help us to predict the parameters that control the structural changes and we could design polymer nanocomposite entailing their end-use. In this work, we addressed the following research questions: (1) the dependence of nanoparticle ligand corona structure on solvent quality and (2) the role of interfacial energy and interactions on the dispersion of molecules and nanoparticles. Specifically, this research assessed the effect of solvent interactions on the structure of nanoparticles on the example of redox core encapsulating dendrimer and ligand functionalized gold nanoparticles, role of chemical interaction on solubility of glucose in ionic liquids, diffusion of fullerene nanoparticles in polymer matrix and influence of solubility parameters on the compatibility of gold nanoparticles with diblock copolymers. Computational methods allow quantifying the structure and flexibility of the polymer chains, how energetics and surface tension change with chemical composition of the polymer/dendrimer blocks, influence of nanoparticle on structural properties of polymer and factors which may contribute to the phase separation of the polymer from nanoparticle. Interfacial characteristics are not only determined by the size-induced properties, but also the surface chemistry of the particles. Presence of solvent and the resultant interactions with the solvent are known to influence the morphology and prevent or induce aggregation of nanoparticles in polymers. We found that surface chemistry can induce change in the structure of dendrimers encapsulating a redox active core and change the solubility of the nanoparticles. The interactions between nanoparticles and polymers can also influence the morphology. We performed investigation on the role of orientation of fullerene derivatives and surface energy of polymer surface which may induce the aggregation of the fullerene nanoparticles. Furthermore, we used quantitative measurements like cluster analysis to understand the most probable orientation of the fullerene derivative with respect to the polymer chains and the diffusion of the fullerene nanoparticle, which is related to the efficiency of solar cells, can change on presence of regiorandom and regioregular polymer chains. Furthermore, we have also used different solvents based on their Hildebrand solubility parameters to investigate factors governing the morphology of polymer nanocomposite via solvent interactions. We showed that change in solvent interactions affect the compatibility, aggregation/dispersion of the gold nanoparticles, which will directly affect the morphology of polymer matrix and structural aspects which can impact their functionality. Overall, our research indicated that solvent interaction play a role in controlling the morphology of polymer nanocomposite and solubility parameter can help us to predict the resulting morphology.

Switchable nanoassembly from an azobenzene-containing dye.

PubMed

Wang, Jing; Ha, Chang-Sik

2011-07-01

In this work, we investigated optical properties and the morphology of the amphiphilic azobenzene dye 1 containing hydroxyl azobenzene and C10 alkyl chains. Since the hydroxyl group on 1 has a pKa of 9.38, the deprotonation of the hydroxyl group occurs at pH > pKa (9.38) and thus the 1 nanoparticles are negatively charged. The deprotonated hydroxyl group is hydrophilic relative to the long alkyl chain that is hydrophobic, while the hydrophobic and hydrophilic parts are connected by covalent bonds. When such an azobenzene molecule 1 with both hydrophobic and hydrophilic groups exists in solution, "self-aggregation" may occur due to the hydrophobic interaction between the long alkyl chains. The scattered morphology at pH 7.0 (neutral state) and the aggregated morphology at pH 10.5 (anionic state) of 1 were demostrated by transmission electron microscopy (TEM) and atomic force microscopy (AFM) images. Formation of supramolecular aggregation-induced vesicular-like structures are highly interesting due to the ability to respond to external triggers, pH. The pH value can be reversed by adding acid or base to the system, that is, switching the aggregation "on" and "off" can be repeated.

Retention of ferrofluid aggregates at the target site during magnetic drug targeting

NASA Astrophysics Data System (ADS)

Asfer, Mohammed; Saroj, Sunil Kumar; Panigrahi, Pradipta Kumar

2017-08-01

The present study reports the retention dynamics of a ferrofluid aggregate localized at the target site inside a glass capillary (500 × 500 μm2 square cross section) against a bulk flow of DI water (Re = 0.16 and 0.016) during the process of magnetic drug targeting (MDT). The dispersion dynamics of iron oxide nanoparticles (IONPs) into bulk flow for different initial size of aggregate at the target site is reported using the brightfield visualization technique. The flow field around the aggregate during the retention is evaluated using the μPIV technique. IONPs at the outer boundary experience a higher shear force as compared to the magnetic force, resulting in dispersion of IONPs into the bulk flow downstream to the aggregate. The blockage effect and the roughness of the outer boundary of the aggregate resulting from chain like clustering of IONPs contribute to the flow recirculation at the downstream region of the aggregate. The entrapment of seeding particles inside the chain like clusters of IONPs at the outer boundary of the aggregate reduces the degree of roughness resulting in a streamlined aggregate at the target site at later time. The effect of blockage, structure of the aggregate, and disturbed flow such as recirculation around the aggregate are the primary factors, which must be investigated for the effectiveness of the MDT process for in vivo applications.

Self-catalyzed photo-initiated RAFT polymerization for fabrication of fluorescent polymeric nanoparticles with aggregation-induced emission feature.

PubMed

Zeng, Guangjian; Liu, Meiying; Jiang, Ruming; Huang, Qiang; Huang, Long; Wan, Qing; Dai, Yanfeng; Wen, Yuanqing; Zhang, Xiaoyong; Wei, Yen

2018-02-01

In recent years, the fluorescent polymeric nanoparticles (FPNs) with aggregation-induced emission (AIE) feature have been extensively exploited in various biomedical fields owing to their advantages, such as low toxicity, biodegradation, excellent biocompatibility, good designability and optical properties. Therefore, development of a facile, efficient and well designable strategy should be of great importance for the biomedical applications of these AIE-active FPNs. In this work, a novel method for the fabrication of AIE-active FPNs has been developed through the self-catalyzed photo-initiated reversible addition fragmentation chain transfer (RAFT) polymerization using an AIE dye containing chain transfer agent (CTA), which could initiate the RAFT polymerization under light irradiation. The results suggested that the final AIE-active FPNs (named as TPE-poly(St-PEGMA)) showed great potential for biomedical applications owing to their optical and biological properties. More importantly, the method described in the work is rather simple and effective and can be further extended to prepare many other different AIE-active FPNs owing to the good monomer adoptability of RAFT polymerization. Copyright © 2017 Elsevier B.V. All rights reserved.

Coupling of demixing and magnetic ordering phase transitions probed by turbidimetric measurements in a binary mixture doped with magnetic nanoparticles.

PubMed

Hernández-Díaz, Lorenzo; Hernández-Reta, Juan Carlos; Encinas, Armando; Nahmad-Molinari, Yuri

2010-05-19

We present a novel study on the effect of a magnetic field applied on a binary mixture doped with magnetic nanoparticles close to its demixing transition. Turbidity measurements in the Faraday configuration show that the effect of applying an external field produces changes in the critical opalescence of the mixture that allow us to track an aggregation produced by critical Casimir forces and a reversible aggregation due to the formation of chain-like flocks in response to the external magnetic field. The observation of a crossover of the aggregation curves through optical signals is interpreted as the evolution from low to high power dispersion nuclei due to an increase in the radius of the condensation seed brought about by Casimir or magnetic interactions. Finally, evidence of an enhanced magnetocaloric effect due to the coupling between mixing and ordering phase transitions is presented which opens up a nonsolid state approach of designing refrigerating cycles and devices.

The fate of silver nanoparticles in soil solution--Sorption of solutes and aggregation.

PubMed

Klitzke, Sondra; Metreveli, George; Peters, Andre; Schaumann, Gabriele E; Lang, Friederike

2015-12-01

Nanoparticles enter soils through various pathways. In the soil, they undergo various interactions with the solution and the solid phase. We tested the following hypotheses using batch experiments: i) the colloidal stability of Ag NP increases through sorption of soil-borne dissolved organic matter (DOM) and thus inhibits aggregation; ii) the presence of DOM suppresses Ag oxidation; iii) the surface charge of Ag NP governs sorption onto soil particles. Citrate-stabilized and bare Ag NPs were equilibrated with (colloid-free) soil solution extracted from a floodplain soil for 24h. Nanoparticles were removed through centrifugation. Concentrations of free Ag ions and DOC, the specific UV absorbance at a wavelength of 254 nm, and the absorption ratio α254/α410 were determined in the supernatant. Nanoparticle aggregation was studied using time-resolved dynamic light scattering (DLS) measurement following the addition of soil solution and 1.5mM Ca(2+) solution. To study the effect of surface charge on the adsorption of Ag NP onto soil particles, bare and citrate-stabilized Ag NP, differing in the zeta potential, were equilibrated with silt at a solid-to-solution ratio of 1:10 and an initial Ag concentration range of 30 to 320 μg/L. Results showed that bare Ag NPs sorb organic matter, with short-chained organic matter being preferentially adsorbed over long-chained, aromatic organic matter. Stabilizing effects of organic matter only come into play at higher Ag NP concentrations. Soil solution inhibits the release of Ag(+) ions, presumably due to organic matter coatings. Sorption to silt particles was very similar for the two particle types, suggesting that the surface charge does not control Ag NP sorption. Besides, sorption was much lower than in comparable studies with sand and glass surfaces. Copyright © 2014. Published by Elsevier B.V.

Anisotropic Light Scattering from Ferrofluids

NASA Astrophysics Data System (ADS)

Rablau, Corneliu; Vaishnava, Prem; Naik, Ratna; Lawes, Gavin; Tackett, Ron; Sudakar, C.

2008-03-01

We have investigated the light scattering in DC magnetic fields from aqueous suspensions of Fe3O4 nanoparticles coated with tetra methyl ammonium hydroxide and γ-Fe2O3 nanoparticles embedded in alginate hydrogel. For Fe3O4 ferrofluid, anomalous light scattering behavior was observed when light propagated both parallel and perpendicular to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanoparticles in chain-like structures. A very different light scattering behavior was observed for γ-Fe2O3 alginate sample where, under the similar conditions, the application of the magnetic field produced no structured change in scattering. We attribute this difference to the absence of chain-like structures and constrained mobility of iron nanoparticles in the alginate sample. The observation is in agreement with our relaxation and dissipative heating results^1 where both samples exhibited Neel relaxation but only the Fe3O4 ferrofluid showed Brownian relaxation. The results suggest that Brownian relaxation and nanoparticle mobility are important for producing non-linear light scattering in such systems. ^1P.P. Vaishnava, R. Tackett, A. Dixit, C. Sudakar, R. Naik, and G. Lawes, J. Appl. Phys. 102, 063914 (2007).

Molecular Simulation Studies of Covalently and Ionically Grafted Nanoparticles

NASA Astrophysics Data System (ADS)

Hong, Bingbing

Solvent-free covalently- or ionically-grafted nanoparticles (CGNs and IGNs) are a new class of organic-inorganic hybrid composite materials exhibiting fluid-like behaviors around room temperature. With similar structures to prior systems, e.g. nanocomposites, neutral or charged colloids, ionic liquids, etc, CGNs and IGNs inherit the functionality of inorganic nanopariticles, the facile processibility of polymers, as well as conductivity and nonvolatility from their constituent materials. In spite of the extensive prior experimental research having covered synthesis and measurements of thermal and dynamic properties, little progress in understanding of these new materials at the molecular level has been achieved, because of the lack of simulation work in this new area. Atomistic and coarse-grained molecular dynamics simulations have been performed in this thesis to investigate the thermodynamics, structure, and dynamics of these systems and to seek predictive methods predictable for their properties. Starting from poly(ethylene oxide) oligomers (PEO) melts, we established atomistic models based on united-atom representations of methylene. The Green-Kubo and Einstein-Helfand formulas were used to calculate the transport properties. The simulations generate densities, viscosities, diffusivities, in good agreement with experimental data. The chain-length dependence of the transport properties suggests that neither Rouse nor reptation models are applicable in the short-chain regime investigated. Coupled with thermodynamic integration methods, the models give good predictions of pressure-composition-density relations for CO 2 + PEO oligomers. Water effects on the Henry's constant of CO 2 in PEO have also been investigated. The dependence of the calculated Henry's constants on the weight percentage of water falls on a temperature-dependent master curve, irrespective of PEO chain length. CGNs are modeled by the inclusion of solid-sphere nanoparticles into the atomistic oligomers. The calculated viscosities from Green-Kubo relationships and temperature extrapolation are of the same order of magnitude as experimental values, but show a smaller activation energy relative to real CGNs systems. Grafted systems have higher viscosities, smaller diffusion coefficients, and slower chain dynamics than the ungrafted counterparts - nanocomposites - at high temperatures. At lower temperatures, grafted systems exhibit faster dynamics for both nanoparticles and chains relative to ungrafted systems, because of lower aggregation of nanoparticles and enhanced correlations between nanoparticles and chains. This agrees with the experimental observation that the new materials have liquid-like behavior in the absence of a solvent. To lower the simulated temperatures into the experimental range, we established a coarse-grained CGNs model by matching structural distribution functions to atomistic simulation data. In contrast with linear polymer systems, for which coarse-graining always accelerate dynamics, coarse-graining of grafted nanoparticles can either accelerate or slowdown the core motions, depending on the length of the grafted chains. This can be qualitatively predicted by a simple transition-state theory. Similar atomistic models to CGNs were developed for IGNs, with ammonium counterions described by an explicit-hydrogen way; these were in turn compared with "generic" coarse-grained IGNs. The elimination of chemical details in the coarse-grained models does not bring in qualitative changes to the radial distribution functions and diffusion of atomistic IGNs, but saves considerable simulation resources and make simulations near room temperatures affordable. The chain counterions in both atomistic and coarse-grained models are mobile, moving from site to site and from nanoparticle to nanoparticle. At the same temperature and the same core volume fractions, the nanoparticle diffusivities in coarse-grained IGNs are slower by a factor ten than the cores of CGNs. The coarse-grained IGNs models are later used to investigate the system dynamics through analysis of the dependence on temperature and structural parameters of the transport properties (self-diffusion coefficients, viscosities and conductivities). Further, migration kinetics of oligomeric counterions is analyzed in a manner analogous to unimer exchange between micellar aggregates. The counterion migrations follow the "double-core" mechanism and are kinetically controlled by neighboring-core collisions. (Abstract shortened by UMI.)

Particle stabilized aqueous foams at different length scales: synergy between silica particles and alkylamines.

PubMed

Carl, Adrian; Bannuscher, Anne; von Klitzing, Regine

2015-02-10

Nanoparticles can be efficient foaming agents. Yet, the detailed mechanisms of foam stabilization by these particles remain unclear. In most cases, the foamability and foam stability of a system have to be determined empirically. We used a multiscale approach to reveal how the microscopic properties of the nanoparticle dispersion are translated into their foaming behavior at the macroscopic scale. As a model system we used silica nanoparticles that were hydrophobized by the in situ adsorption of short-chain alkylamines of chain length C5 to C8. We used fluorescence spectroscopy and electrophoretic mobility measurements to characterize the bulk behavior of the nanoparticles with adsorbed amines. The interfacial behavior was probed by compressing particle monolayers while monitoring the surface tension. The macroscopic foamability and foam stability were evaluated. There are strong correlations between the system properties at all length scales. The most prominent effects are observed at a critical bulk concentration of amines at which the nanoparticles start to aggregate due to hydrophobic interactions. Our study shows how the foam properties are related to the features of the bulk dispersions and to the ordering of particles at the air/water interface. The present results help to understand the surfactant concentration dependent stages of foaming behavior of in situ hydrophobized nanoparticles.

Effect of amphiphilic polyurethane nanoparticles on sorption-desorption of phenanthrene in aquifer material.

PubMed

Kim, Ju-Young; Shim, Sun-Bo; Shim, Jin-Kie

2003-03-17

Micelle-like amphiphilic nano-sized polyurethane (APU) nanoparticles were synthesized via chemical cross-linking reaction of nano-aggregates of urethane acrylate nonionomer (UAN) chain and were tested for extraction efficiency of sorbed phenanthrene from aquifer material. Even though the solubilizing performance and interfacial activity of APU nanoparticles were inferior to that of Triton X-100, in the low concentration region, APU nanoparticles could effectively reduce phenanthrene sorption on the aquifer material and extracted sorbed phenanthrene from the aquifer material, whereas Triton X-100 could not extract sorbed phenanthrene and rather increased phenanthrene sorption onto the aquifer materials. At higher concentrations, APU nanoparticles and Triton X-100 had almost the same soil washing effectiveness. This interesting result is mainly due to a lower degree of sorption of APU nanoparticles onto the aquifer material. The sorption of APU nanoparticles onto aquifer sand is largely hindered by their chemically cross-linked nature, resulting in better soil-washing performance of APU nanoparticles than Triton X-100. Copyright 2003 Elsevier Science B.V.

Kinetics of aggregation in charged nanoparticle solutions driven by different mechanisms

NASA Astrophysics Data System (ADS)

Abbas, S.; Yadav, I.; Kumar, Sugam; Aswal, V. K.; Kohlbrecher, J.

2017-05-01

The structure and kinetics during aggregation of anionic silica nanoparticles as induced through different mechanisms have been studied by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Three different additives, namely an electrolyte (NaCl), cationic protein (lysozyme) and non-ionic surfactant (C12E10) were used to initiate nanoparticle aggregation. Electrolyte induced aggregation can be explained by DLVO interaction, whereas depletion interaction (non-DLVO interaction) is found responsible for nanoparticle aggregation in case of non-ionic surfactant. Unlike these two cases, strong electrostatic attraction between nanoparticle and oppositely charged protein results into protein-mediated nanoparticle aggregation. The electrolyte induced aggregation show quite slow aggregation rate whereas protein mediated as well as surfactant induced aggregation takes place almost instantaneously. The significant differences observed in the kinetics are explained based on range of interactions responsible for the aggregation. In spite of differences in mechanism and kinetics, the nanoparticle clusters are found to have similar fractal morphology (fractal dimension ˜ 2.5) in all the three cases.

Molecular dynamics simulation study of the early stages of nucleation of iron oxyhydroxide nanoparticles in aqueous solutions

DOE PAGES

Zhang, Hengzhong; Waychunas, Glenn A.; Banfield, Jillian F.

2015-07-29

Nucleation is a fundamental step in crystal growth. Of environmental and materials relevance are reactions that lead to nucleation of iron oxyhydroxides in aqueous solutions. These reactions are difficult to study experimentally due to their rapid kinetics. Here, we used classical molecular dynamics simulations to investigate nucleation of iron hydroxide/oxyhydroxide nanoparticles in aqueous solutions. Results show that in a solution containing ferric ions and hydroxyl groups, iron–hydroxyl molecular clusters form by merging ferric monomers, dimers, and other oligomers, driven by strong affinity of ferric ions to hydroxyls. When deprotonation reactions are not considered in the simulations, these clusters aggregate tomore » form small iron hydroxide nanocrystals with a six-membered ring-like layered structure allomeric to gibbsite. By comparison, in a solution containing iron chloride and sodium hydroxide, the presence of chlorine drives cluster assembly along a different direction to form long molecular chains (rather than rings) composed of Fe–O octahedra linked by edge sharing. Further, in chlorine-free solutions, when deprotonation reactions are considered, the simulations predict ultimate formation of amorphous iron oxyhydroxide nanoparticles with local atomic structure similar to that of ferrihydrite nanoparticles. Overall, our simulation results reveal that nucleation of iron oxyhydroxide nanoparticles proceeds via a cluster aggregation-based nonclassical pathway.« less

Influence of structure of iron nanoparticles in aggregates on their magnetic properties

PubMed Central

2011-01-01

Zero-valent iron nanoparticles rapidly aggregate. One of the reasons is magnetic forces among the nanoparticles. Magnetic field around particles is caused by composition of the particles. Their core is formed from zero-valent iron, and shell is a layer of magnetite. The magnetic forces contribute to attractive forces among the nanoparticles and that leads to increasing of aggregation of the nanoparticles. This effect is undesirable for decreasing of remediation properties of iron particles and limited transport possibilities. The aggregation of iron nanoparticles was established for consequent processes: Brownian motion, sedimentation, velocity gradient of fluid around particles and electrostatic forces. In our previous work, an introduction of influence of magnetic forces among particles on the aggregation was presented. These forces have significant impact on the rate of aggregation. In this article, a numerical computation of magnetic forces between an aggregate and a nanoparticle and between two aggregates is shown. It is done for random position of nanoparticles in an aggregate and random or arranged directions of magnetic polarizations and for structured aggregates with arranged vectors of polarizations. Statistical computation by Monte Carlo is done, and range of dominant area of magnetic forces around particles is assessed. PMID:21917152

Structure and Dynamics of Polymer/Polymer grafted nanoparticle composite

NASA Astrophysics Data System (ADS)

Archer, Lynden

Addition of nanoparticles to polymers is a well-practiced methodology for augmenting various properties of the polymer host, including mechanical strength, thermal stability, barrier properties, dimensional stability and wear resistance. Many of these property changes are known to arise from nanoparticle-induced modification of polymer structure and chain dynamics, which are strong functions of the dispersion state of the nanoparticles' and on their relative size (D) to polymer chain dimensions (e.g. Random coil radius Rg or entanglement mesh size a) . This talk will discuss polymer nanocomposites (PNCs) comprised of Polyethylene Glycol (PEG) tethered silica nanoparticles (SiO2-PEG) dispersed in polymers as model systems for investigating phase stability and dynamics of PNCs. On the basis of small-angle X-ray Scattering, it will be shown that favorable enthalpic interactions between particle-tethered chains and a polymer host provides an important mechanism for creating PNCs in which particle aggregation is avoided. The talk will report on polymer and particle scale dynamics in these materials and will show that grafted nanoparticles well dispersed in a polymer host strongly influence the host polymer relaxation dynamics on all timescales and the polymers in turn produce dramatic changes in the nature (from diffusive to hyperdiffusive) and speed of nano particle decorrelation dynamics at the polymer entanglement threshold. A local viscosity model capable of explaining these observations is discussed and the results compared with scaling theories for NP motions in polymers This material is based on work supported by the National Science Foundation Award Nos. DMR-1609125 and CBET-1512297.

Investigation on two abnormal phenomena about thermal conductivity enhancement of BN/EG nanofluids.

PubMed

Li, Yanjiao; Zhou, Jing'en; Luo, Zhifeng; Tung, Simon; Schneider, Eric; Wu, Jiangtao; Li, Xiaojing

2011-07-09

The thermal conductivity of boron nitride/ethylene glycol (BN/EG) nanofluids was investigated by transient hot-wire method and two abnormal phenomena was reported. One is the abnormal higher thermal conductivity enhancement for BN/EG nanofluids at very low-volume fraction of particles, and the other is the thermal conductivity enhancement of BN/EG nanofluids synthesized with large BN nanoparticles (140 nm) which is higher than that synthesized with small BN nanoparticles (70 nm). The chain-like loose aggregation of nanoparticles is responsible for the abnormal increment of thermal conductivity enhancement for the BN/EG nanofluids at very low particles volume fraction. And the difference in specific surface area and aspect ratio of BN nanoparticles may be the main reasons for the abnormal difference between thermal conductivity enhancements for BN/EG nanofluids prepared with 140- and 70-nm BN nanoparticles, respectively.

Engineered polymer nanoparticles containing hydrophobic dipeptide for inhibition of amyloid-β fibrillation.

PubMed

Skaat, Hadas; Chen, Ravit; Grinberg, Igor; Margel, Shlomo

2012-09-10

Protein aggregation into amyloid fibrils is implicated in the pathogenesis of many neurodegenerative diseases. Engineered nanoparticles have emerged as a potential approach to alter the kinetics of protein fibrillation process. Yet, there are only a few reports describing the use of nanoparticles for inhibition of amyloid-β 40 (Aβ(40)) peptide aggregation, involved in Alzheimer's disease (AD). In the present study, we designed new uniform biocompatible amino-acid-based polymer nanoparticles containing hydrophobic dipeptides in the polymer side chains. The dipeptide residues were designed similarly to the hydrophobic core sequence of Aβ. Poly(N-acryloyl-L-phenylalanyl-L-phenylalanine methyl ester) (polyA-FF-ME) nanoparticles of 57 ± 6 nm were synthesized by dispersion polymerization of the monomer A-FF-ME in 2-methoxy ethanol, followed by precipitation of the obtained polymer in aqueous solution. Cell viability assay confirmed that no significant cytotoxic effect of the polyA-FF-ME nanoparticles on different human cell lines, e.g., PC-12 and SH-SY5Y, was observed. A significantly slow secondary structure transition from random coil to β-sheets during Aβ(40) fibril formation was observed in the presence of these nanoparticles, resulting in significant inhibition of Aβ(40) fibrillation kinetics. However, the polyA-FF-ME analogous nanoparticles containing the L-alanyl-L-alanine (AA) dipeptide in the polymer side groups, polyA-AA-ME nanoparticles, accelerate the Aβ(40) fibrillation kinetics. The polyA-FF-ME nanoparticles and the polyA-AA-ME nanoparticles may therefore contribute to a mechanistic understanding of the fibrillation process, leading to the development of therapeutic strategies against amyloid-related diseases.

Development and Modeling of a Novel Self-Assembly Process for Polymer and Polymeric Composite Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sumpter, Bobby G.; Carrillo, Jan-Michael Y.; Ahn, Suk-Kyun

Extensive computational simulations and experiments have been used to investigate the structure, dynamics and resulting photophysical properties of a number para-phenylenevinylene (PPV) based polymers and oligomers. These studies have shown how the morphology and structure are controlled to a large extent by the nature of the solute-solvent interactions in the initial solution phase preparation. A good solvent such as dichloromethane generates non-compact structures with more of a defect-extended chain like morphology while a bad solvent such as toluene leads to compact organized and folded structures with rod-like morphologies. Secondary structural organization is induced by using the solution phase structures tomore » generate solvent-free single molecule nanoparticles. These nanoparticles are very compact and rod shaped, consisting of near-cofacial ordering of the conjugated PPV chain backbones between folds located at tetrahedral defects (sp3 C-C bonds). The resulting photophysical properties exhibit a significant enhancement in the photoluminescence quantum yield, lifetime, and stability. In addition, the single molecule nanoparticles have Gaussian-like emission spectra with discrete center frequencies that are correlated to a conjugation length, allowing the design of nanoparticles which luminesces at a particular frequency. We followed a similar approach and applied a comparable methodology in our recent work on polythiophenes in order to study the effect of polymer architecture on nanoscale assembly. Unlike linear chains of comparable size, we observed aggregation of the bottlebrush architecture of poly(norbornene)-g-poly(3-hexylthiophene) (PNB-g-P3HT) after the freeze-drying and dissolution processes. The behavior can be attributed to a significant enhancement in the number of π-π interactions between grafted P3HT side chains.« less

Colloidal behavior of aluminum oxide nanoparticles as affected by pH and natural organic matter.

PubMed

Ghosh, Saikat; Mashayekhi, Hamid; Pan, Bo; Bhowmik, Prasanta; Xing, Baoshan

2008-11-04

The colloidal behavior of aluminum oxide nanoparticles (NPs) was investigated as a function of pH and in the presence of two structurally different humic acids (HAs), Aldrich HA (AHA) and the seventh HA fraction extracted from Amherst peat soil (HA7). Dynamic light scattering (DLS) and atomic force microscopy (AFM) were employed to determine the colloidal behavior of the NPs. Influence of pH and HAs on the surface charges of the NPs was determined. zeta-Potential data clearly showed that the surface charge of the NPs decreased with increasing pH and reached the point of zero charge (ZPC) at pH 7.9. Surface charge of the NPs also decreased with the addition of HAs. The NPs tend to aggregate as the pH of the suspension approaches ZPC, where van der Waals attraction forces dominate over electrostatic repulsion. However, the NP colloidal suspension was stable in the pHs far from ZPC. Colloidal stability was strongly enhanced in the presence of HAs at the pH of ZPC or above it, but in acidic conditions NPs showed strong aggregation in the presence of HAs. AFM imaging revealed the presence of long-chain fractions in HA7, which entangled with the NPs to form large aggregates. The association of HA with the NP surface can be assumed to follow a two-step process, possibly the polar fractions of the HA7 sorbed on the NP surface followed by entanglement with the long-chain fractions. Thus, our study demonstrated that the hydrophobic nature of the HA molecules strongly influenced the aggregation of colloidal NPs, possibly through their conformational behavior in a particular solution condition. Therefore, various organic matter samples will result in different colloidal behavior of NPs, subsequently their environmental fate and transport.

PEGylation on mixed monolayer gold nanoparticles: Effect of grafting density, chain length, and surface curvature.

PubMed

Lin, Jiaqi; Zhang, Heng; Morovati, Vahid; Dargazany, Roozbeh

2017-10-15

PEGylation on nanoparticles (NPs) is widely used to prevent aggregation and to mask NPs from the fast clearance system in the body. Understanding the molecular details of the PEG layer could facilitate rational design of PEGylated NPs that maximize their solubility and stealth ability without significantly compromising the targeting efficiency and cellular uptake. Here, we use molecular dynamics (MD) simulation to understand the structural and dynamic the PEG coating of mixed monolayer gold NPs. Specifically, we modeled gold NPs with PEG grafting densities ranging from 0-2.76chain/nm 2 , chain length with 0-10 PEG monomers, NP core diameter from 5nm to 500nm. It is found that the area accessed by individual PEG chains gradually transits from a "mushroom" to a "brush" conformation as NP surface curvature become flatter, whereas such a transition is not evident on small NPs when grafting density increases. It is shown that moderate grafting density (∼1.0chain/nm 2 ) and short chain length are sufficient enough to prevent NPs from aggregating in an aqueous medium. The effect of grafting density on solubility is also validated by dynamic light scattering measurements of PEGylated 5nm gold NPs. With respect to the shielding ability, simulations predict that increase either grafting density, chain length, or NP diameter will reduce the accessibility of the protected content to a certain size molecule. Interestingly, reducing NP surface curvature is estimated to be most effective in promoting shielding ability. For shielding against small molecules, increasing PEG grafting density is more effective than increasing chain length. A simple model that includes these three investigated parameters is developed based on the simulations to roughly estimate the shielding ability of the PEG layer with respect to molecules of different sizes. The findings can help expand our current understanding of the PEG layer and guide rational design of PEGylated gold NPs for a particular application by tuning the PEG grafting density, chain length, and particle size. Copyright © 2017 Elsevier Inc. All rights reserved.

Aggregation in charged nanoparticles solutions induced by different interactions

NASA Astrophysics Data System (ADS)

Abbas, S.; Kumar, Sugam; Aswal, V. K.; Kohlbrecher, J.

2016-05-01

Small-angle neutron scattering (SANS) has been used to study the aggregation of anionic silica nanoparticles as induced through different interactions. The nanoparticle aggregation is induced by addition of salt (NaCl), cationic protein (lysozyme) and non-ionic surfactant (C12E10) employing different kind of interactions. The results show that the interaction in presence of salt can be explained using DLVO theory whereas non-DLVO forces play important role for interaction of nanoparticles with protein and surfactant. The presence of salt screens the repulsion between charged nanoparticles giving rise to a net attraction in the DLVO potential. On the other hand, strong electrostatic attraction between nanoparticle and oppositely charged protein leads to protein-mediated nanoparticle aggregation. In case of non-ionic surfactant, the relatively long-range attractive depletion interaction is found to be responsible for the particle aggregation. Interestingly, the completely different interactions lead to similar kind of aggregate morphology. The nanoparticle aggregates formed are found to have mass fractal nature having a fractal dimension (~2.5) consistent with diffusion limited type of fractal morphology in all three cases.

Aggregation in charged nanoparticles solutions induced by different interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbas, S.; Kumar, Sugam; Aswal, V. K., E-mail: vkaswal@barc.gov.in

2016-05-23

Small-angle neutron scattering (SANS) has been used to study the aggregation of anionic silica nanoparticles as induced through different interactions. The nanoparticle aggregation is induced by addition of salt (NaCl), cationic protein (lysozyme) and non-ionic surfactant (C12E10) employing different kind of interactions. The results show that the interaction in presence of salt can be explained using DLVO theory whereas non-DLVO forces play important role for interaction of nanoparticles with protein and surfactant. The presence of salt screens the repulsion between charged nanoparticles giving rise to a net attraction in the DLVO potential. On the other hand, strong electrostatic attraction betweenmore » nanoparticle and oppositely charged protein leads to protein-mediated nanoparticle aggregation. In case of non-ionic surfactant, the relatively long-range attractive depletion interaction is found to be responsible for the particle aggregation. Interestingly, the completely different interactions lead to similar kind of aggregate morphology. The nanoparticle aggregates formed are found to have mass fractal nature having a fractal dimension (~2.5) consistent with diffusion limited type of fractal morphology in all three cases.« less

Magnetoferritin nanoparticles for targeting and visualizing tumour tissues

NASA Astrophysics Data System (ADS)

Fan, Kelong; Cao, Changqian; Pan, Yongxin; Lu, Di; Yang, Dongling; Feng, Jing; Song, Lina; Liang, Minmin; Yan, Xiyun

2012-07-01

Engineered nanoparticles have been used to provide diagnostic, therapeutic and prognostic information about the status of disease. Nanoparticles developed for these purposes are typically modified with targeting ligands (such as antibodies, peptides or small molecules) or contrast agents using complicated processes and expensive reagents. Moreover, this approach can lead to an excess of ligands on the nanoparticle surface, and this causes non-specific binding and aggregation of nanoparticles, which decreases detection sensitivity. Here, we show that magnetoferritin nanoparticles (M-HFn) can be used to target and visualize tumour tissues without the use of any targeting ligands or contrast agents. Iron oxide nanoparticles are encapsulated inside a recombinant human heavy-chain ferritin (HFn) protein shell, which binds to tumour cells that overexpress transferrin receptor 1 (TfR1). The iron oxide core catalyses the oxidation of peroxidase substrates in the presence of hydrogen peroxide to produce a colour reaction that is used to visualize tumour tissues. We examined 474 clinical specimens from patients with nine types of cancer and verified that these nanoparticles can distinguish cancerous cells from normal cells with a sensitivity of 98% and specificity of 95%.

Freeze the Moment: High Speed Capturing of Weakly Bonded Dynamic Nanoparticle Assemblies in Solution by Ag Ion Soldering.

PubMed

Wang, Yueliang; Fang, Lingling; Chen, Gaoli; Song, Lei; Deng, Zhaoxiang

2018-02-01

Despite the versatile forms of colloidal aggregates, these spontaneously formed structures are often hard to find a suitable application in nanotechnology and materials science. A determinate reason is the lack of a suitable method to capture the transiently formed and quickly evolving colloidal structures in solution. To address this challenge, a simple but highly efficient strategy is herein reported to capture the dynamic and metastable colloidal assemblies formed in an aqueous or nonaqueous solution. This process takes advantage of a recently developed Ag ion soldering reaction to realize a rapid fixation of as-formed metastable assemblies. This method works efficiently for both solid (3D) nanoparticle aggregates and weakly bonded fractal nanoparticle chains (1D). In both cases, very high capturing speed and close to 100% efficiency are achieved to fully retain a quickly growing structure. The soldered nanochains further enable a fabrication of discrete, uniform, and functionalizable nanoparticle clusters with enriched linear conformation by mechanical shearing, which would otherwise be difficult to make. The captured products are water dispersible and mechanically robust, favoring an exploration of their properties toward possible applications. The work paves a way to previously untouched aspects of colloidal science and thus would create new chances in nanotechnology. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Mixed Stimuli-Responsive Magnetic and Gold Nanoparticle System for Rapid Purification, Enrichment, and Detection of Biomarkers

PubMed Central

Nash, Michael A.; Yager, Paul; Hoffman, Allan S.; Stayton, Patrick S.

2010-01-01

A new diagnostic system for the enrichment and detection of protein biomarkers from human plasma is presented. Gold nanoparticles (AuNPs) were surface-modified with a diblock copolymer synthesized using reversible addition fragmentation chain transfer (RAFT) polymerization. The diblock copolymer contained a thermally-responsive poly(N-isopropylacrylamide) (pNIPAAm) block, a cationic amine-containing block, and a semi-telechelic PEG2-biotin end group. When a mixed suspension of 23 nm pNIPAAm-modified AuNPs was heated with pNIPAAm-coated 10 nm iron oxide magnetic nanoparticles (mNPs) in human plasma, the thermally-responsive pNIPAAm directed the formation of mixed AuNP/mNP aggregates that could be separated efficiently with a magnet. Model studies showed that this mixed nanoparticle system could efficiently purify and strongly enrich the model biomarker protein streptavidin in spiked human plasma. A 10 ng/mL streptavidin sample was mixed with the biotinylated and pNIPAAm modified AuNP and magnetically separated in the mixed nanoparticle system with pNIPAAm mNPs. The aggregates were concentrated into a 50-fold smaller fluid volume at room temperature where the gold nanoparticle reagent redissolved with the streptavidin target still bound. The concentrated gold-labeled streptavidin could be subsequently analyzed directly using lateral flow immunochromatography. This rapid capture and enrichment module thus utilizes the mixed stimuli-responsive nanoparticle system to achieve direct concentration of a gold-labeled biomarker that can be directly analyzed using lateral flow or other rapid diagnostic strategies. PMID:21070026

"Mixed-charge self-assembled monolayers" as a facile method to design pH-induced aggregation of large gold nanoparticles for near-infrared photothermal cancer therapy.

PubMed

Li, Huan; Liu, Xiangsheng; Huang, Nan; Ren, Kefeng; Jin, Qiao; Ji, Jian

2014-01-01

The acidic microenvironment of tumor tissues has proven to be one of the major differences from other normal tissues. The near-infrared (NIR) light irradiation of aggregated gold nanoparticles in a tumor acidic pH-induced manner could then provide an effect approach to treat solid tumors with the advantage of minimizing the undesired damage to normal tissues. Although it is well-known the aggregation of larger nanoparticles will result in a better NIR photothermal effect, the preparation of pH-sensitive gold nanoparticles in large sizes remains a big challenge because of their worse dispersive stability. In this paper, we introduce a facile way to endow large gold nanoparticles with tunable pH-aggregation behaviors by modifying the nanoparticle surface with mixed-charge self-assembly monolayers compromising positively and negatively charged thiol ligands. Four different size nanoparticles were used to study the general principle of tailoring the pH-induced aggregation behaviors of mixed-charge gold nanoparticles (MC-GNPs) by adjusting the surface ligand composition. With proper surface ligand composition, the MC-GNPs in four different sizes that all exhibited aggregation at tumor acidic pH were obtained. The biggest MC-GNPs showed the most encouraging aggregation-enhanced photothermal efficacy in vitro when they formed aggregates. The mixed-charge self-assembled monolayers were then proved as a facile method to design pH-induced aggregation of large gold nanoparticles for better NIR photothermal cancer therapy.

Controlled assembly of nanoparticle structures: spherical and toroidal superlattices and nanoparticle-coated polymeric beads.

PubMed

Isojima, Tatsushi; Suh, Su Kyung; Vander Sande, John B; Hatton, T Alan

2009-07-21

The emulsion droplet solvent evaporation method has been used to prepare nanoclusters of monodisperse magnetite nanoparticles of varying morphologies depending on the temperature and rate of solvent evaporation and on the composition (solvent, presence of polymer, nanoparticle concentration, etc.) of the emulsion droplets. In the absence of a polymer, and with increasing solvent evaporation temperatures, the nanoparticles formed single- or multidomain crystalline superlattices, amorphous spherical aggregates, or toroidal clusters, as determined by the energetics and dynamics of the solvent evaporation process. When polymers that are incompatible with the nanoparticle coatings were included in the emulsion formulation, monolayer- and multilayer-coated polymer beads and partially coated Janus beads were prepared; the nanoparticles were expelled by the polymer as its concentration increased on evaporation of the solvent and accumulated on the surfaces of the beads in a well-ordered structure. The precise number of nanoparticle layers depended on the polymer/magnetic nanoparticle ratio in the oil droplet phase parent emulsion. The magnetic nanoparticle superstructures responded to the application of a modest magnetic field by forming regular chains with alignment of nonuniform structures (e.g., toroids and Janus beads) that are in accord with theoretical predictions and with observations in other systems.

X-ray photoelectron spectroscopy characterization of gold nanoparticles functionalized with amine-terminated alkanethiols

PubMed Central

Techane, Sirnegeda D.; Gamble, Lara J.; Castner, David G.

2011-01-01

Gold nanoparticles (AuNPs) functionalized with a short chain amine-terminated alkanethiol (HS-(CH2)2NH2 or C2 NH2-thiol) are prepared via a direct synthesis method and then ligand-exchanged with a long chain amine-terminated alkanethiol (HS-(CH2)11NH2 or C11 NH2-thiol). Transmission electron microscopy analysis showed the AuNPs were relatively spherical with a median diameter of 24.2±4.3 nm. X-ray photoelectron spectroscopy was used to determine surface chemistry of the functionalized and purified AuNPs. The ligand-exchange process was monitored within the time range from 30 min to 61 days. By the fourth day of exchange all the C2 NH2-thiol molecules had been replaced by C11 NH2-thiol molecules. C11 NH2-thiol molecules continued to be incorporated into the C11 NH2 self-assembled monolayer between days 4 and 14 of ligand-exchange. As the length of the exchange time increased, the functionalized AuNPs became more stable against aggregation. The samples were purified by a centrifugation and resuspension method. The C2 NH2 covered AuNPs aggregated immediately when purification was attempted. The C11 NH2 covered AuNPs could be purified with minimal or no aggregation. Small amounts of unbound thiol (∼15%) and oxidized sulfur (∼20%) species were detected on the ligand-exchanged AuNPs. Some of the unbound thiol and all of the oxidized sulfur could be removed by treating the functionalized AuNPs with HCl. PMID:21974680

Microfluidic magnetic switching valves based on aggregates of magnetic nanoparticles: Effects of aggregate length and nanoparticle sizes

NASA Astrophysics Data System (ADS)

Jiemsakul, Thanakorn; Manakasettharn, Supone; Kanharattanachai, Sivakorn; Wanna, Yongyuth; Wangsuya, Sujint; Pratontep, Sirapat

2017-01-01

We demonstrate microfluidic switching valves using magnetic nanoparticles blended within the working fluid as an alternative microfluidic flow control in microchannels. Y-shaped microchannels have been fabricated by using a CO2 laser cutter to pattern microchannels on transparent poly(methyl methacrylate) (PMMA) sheets covered with thermally bonded transparent polyvinyl chloride (PVC) sheets. To examine the performance of the microfluidic magnetic switching valves, an aqueous magnetic nanoparticle suspension was injected into the microchannels by a syringe pump. Neodymium magnets were then employed to attract magnetic nanoparticles and form an aggregate that blocked the microchannels at a required position. We have found that the maximum volumetric flow rate of the syringe pump that the magnetic nanoparticle aggregate can withstand scales with the square of the external magnetic flux density. The viscosity of the fluid exhibits dependent on the aggregate length and the size of the magnetic nanoparticles. This microfluidic switching valve based on aggregates of magnetic nanoparticles has strong potentials as an on-demand flow control, which may help simplifying microfluidic channel designs.

Fabrication and biological imaging of polyhedral oligomeric silsesquioxane cross-linked fluorescent polymeric nanoparticles with aggregation-induced emission feature

NASA Astrophysics Data System (ADS)

Mao, Liucheng; Liu, Meiying; Xu, Dazhuang; Wan, Qing; Huang, Qiang; Jiang, Ruming; Shi, Yingge; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

2017-11-01

Aggregation-induced emission (AIE) dyes based fluorescent polymeric nanoparticles (FNPs) have been intensively explored for biomedical applications. However, many of these AIE-active FNPs are relied on the self-assembly of amphiphilic copolymers, which are not stable in diluted solution. Therefore, the introduction of cross-linkages into these micelles has demonstrated to be an efficient route to overcome this stability problem and endow ultra-low critical micelle concentrations (CMC) of these AIE-active FNPs. In this work, we reported the fabrication of cross-linked AIE-active FNPs through controllable reversible addition fragmentation chain transfer polymerization by using commercially available octavinyl-T8-silsesquioxane (8-vinyl POSS) as the cross-linkage for the first time. The resultant cross-linked amphiphilic copolymers (named as PEG-POSS-PhE) are prone to self-assemble into stable core-shell nanoparticles with well water dispersity, strong red fluorescence and low CMC (0.0069 mg mL-1) in aqueous solution. More importantly, PEG-POSS-PhE FNPs possess some other properties such as high water dispersity, uniform morphology and small size, excellent biocompatibility and cellular internalization, providing great potential of PEG-POSS-PhE FNPs for biological imaging application.

Confined dynamics of grafted polymer chains in solutions of linear polymer

DOE PAGES

Poling-Skutvik, Ryan D.; Olafson, Katy N.; Narayanan, Suresh; ...

2017-09-11

Here, we measure the dynamics of high molecular weight polystyrene grafted to silica nanoparticles dispersed in semidilute solutions of linear polymer. Structurally, the linear free chains do not penetrate the grafted corona but increase the osmotic pressure of the solution, collapsing the grafted polymer and leading to eventual aggregation of the grafted particles at high matrix concentrations. Dynamically, the relaxations of the grafted polymer are controlled by the solvent viscosity according to the Zimm model on short time scales. On longer time scales, the grafted chains are confined by neighboring grafted chains, preventing full relaxation over the experimental time scale.more » Adding free linear polymer to the solution does not affect the initial Zimm relaxations of the grafted polymer but does increase the confinement of the grafted chains. Finally, our results elucidate the physics underlying the slow relaxations of grafted polymer.« less

Confined dynamics of grafted polymer chains in solutions of linear polymer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poling-Skutvik, Ryan D.; Olafson, Katy N.; Narayanan, Suresh

Here, we measure the dynamics of high molecular weight polystyrene grafted to silica nanoparticles dispersed in semidilute solutions of linear polymer. Structurally, the linear free chains do not penetrate the grafted corona but increase the osmotic pressure of the solution, collapsing the grafted polymer and leading to eventual aggregation of the grafted particles at high matrix concentrations. Dynamically, the relaxations of the grafted polymer are controlled by the solvent viscosity according to the Zimm model on short time scales. On longer time scales, the grafted chains are confined by neighboring grafted chains, preventing full relaxation over the experimental time scale.more » Adding free linear polymer to the solution does not affect the initial Zimm relaxations of the grafted polymer but does increase the confinement of the grafted chains. Finally, our results elucidate the physics underlying the slow relaxations of grafted polymer.« less

Achieving 3-D Nanoparticle Assembly in Nanocomposite Thin Films via Kinetic Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Jingyu; Xiao, Yihan; Xu, Ting

Nanocomposite thin films containing well-ordered nanoparticle (NP) assemblies are ideal candidates for the fabrication of metamaterials. Achieving 3-D assembly of NPs in nanocomposite thin films is thermodynamically challenging as the particle size gets similar to that of a single polymer chain. The entropic penalties of polymeric matrix upon NP incorporation leads to NP aggregation on the film surface or within the defects in the film. Controlling the kinetic pathways of assembly process provides an alternative path forward by arresting the system in nonequilibrium states. Here, we report the thin film 3-D hierarchical assembly of 20 nm NPs in supramolecules withmore » a 30 nm periodicity. By mediating the NP diffusion kinetics in the supramolecular matrix, surface aggregation of NPs was suppressed and NPs coassemble with supramolecules to form new 3-D morphologies in thin films. Lastly, the present studies opened a viable route to achieve designer functional composite thin films via kinetic control.« less

Achieving 3-D Nanoparticle Assembly in Nanocomposite Thin Films via Kinetic Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Jingyu; Xiao, Yihan; Xu, Ting

Nanocomposite thin films containing well-ordered nanoparticle (NP) assemblies are ideal candidates for the fabrication of metamaterials. Achieving 3-D assembly of NPs in nanocomposite thin films is thermodynamically challenging as the particle size gets similar to that of a single polymer chain. The entropic penalties of polymeric matrix upon NP incorporation leads to NP aggregation on the film surface or within the defects in the film. Controlling the kinetic pathways of assembly process provides an alternative path forward by arresting the system in nonequilibrium states. Here, we report the thin film 3-D hierarchical assembly of 20 nm NPs in supramolecules withmore » a 30 nm periodicity. By mediating the NP diffusion kinetics in the supramolecular matrix, surface aggregation of NPs was suppressed and NPs coassemble with supramolecules to form new 3-D morphologies in thin films. The present studies opened a viable route to achieve designer functional composite thin films via kinetic control.« less

Achieving 3-D Nanoparticle Assembly in Nanocomposite Thin Films via Kinetic Control

DOE PAGES

Huang, Jingyu; Xiao, Yihan; Xu, Ting

2017-02-20

Nanocomposite thin films containing well-ordered nanoparticle (NP) assemblies are ideal candidates for the fabrication of metamaterials. Achieving 3-D assembly of NPs in nanocomposite thin films is thermodynamically challenging as the particle size gets similar to that of a single polymer chain. The entropic penalties of polymeric matrix upon NP incorporation leads to NP aggregation on the film surface or within the defects in the film. Controlling the kinetic pathways of assembly process provides an alternative path forward by arresting the system in nonequilibrium states. Here, we report the thin film 3-D hierarchical assembly of 20 nm NPs in supramolecules withmore » a 30 nm periodicity. By mediating the NP diffusion kinetics in the supramolecular matrix, surface aggregation of NPs was suppressed and NPs coassemble with supramolecules to form new 3-D morphologies in thin films. Lastly, the present studies opened a viable route to achieve designer functional composite thin films via kinetic control.« less

Silver nanoparticle aggregation not triggered by an ionic strength mechanism

NASA Astrophysics Data System (ADS)

Botasini, Santiago; Méndez, Eduardo

2013-04-01

The synthesis of stable colloidal solutions of silver nanoparticles is a major goal in the industry to control their fate in aqueous solutions. The present work studies 10-20-nm silver nanoparticle aggregation triggered by the presence of chloride ions. The aggregation process was followed by UV-Vis-NIR spectroscopy and transmission electron microscopy. We found that the mechanism involved differs from the classic explanation of nanoparticle aggregation triggered by an increase in the ionic strength. Moreover, our results give evidence that even when nanoparticles are resistant to an increment of the total amount of ions, the formation of insoluble salts in the vicinity of the nanoparticle is enough to induce the aggregation. The presence of silver chloride around the silver nanoparticles was documented by an X-ray diffraction pattern and electrochemical methods because chloride anions are ubiquitous in real media; this alternative process jeopardized the development of many applications with silver nanoparticles that depend on the use of stable colloids.

Theoretical Insight into Dispersion of Silica Nanoparticles in Polymer Melts.

PubMed

Wei, Zhaoyang; Hou, Yaqi; Ning, Nanying; Zhang, Liqun; Tian, Ming; Mi, Jianguo

2015-07-30

Silica nanoparticles dispersed in polystyrene, poly(methyl methacrylate), and poly(ethylene oxide) melts have been investigated using a density functional approach. The polymers are regarded as coarse-grained semiflexible chains, and the segment sizes are represented by their Kuhn lengths. The particle-particle and particle-polymer interactions are calculated with the Hamaker theory to reflect the relationship between particles and polymer melts. The effects of particle volume fraction and size on the particle dispersion have been quantitatively determined to evaluate their dispersion/aggregation behavior in these polymer melts. It is shown that theoretical predictions are generally in good agreement with the corresponding experimental results, providing the reasonable verification of particle dispersion/agglomeration and polymer depletion.

Strong coupling-like phenomenon in single metallic nanoparticle embedded in molecular J-aggregates

NASA Astrophysics Data System (ADS)

Feng, Xin; Wang, Chen; Ma, Hongjing; Chen, Yuanyuan; Duan, Gaoyan; Zhang, Pengfei; Song, Gang

2018-02-01

Strong coupling-like phenomenon between plasmonic cavities and emitters provides a new way to realize the quantum-like effect controlling at microscale/nanoscale. We investigate the strong coupling-like phenomenon in the structure of single metallic nanoparticle embedded in molecular J-aggregates by the classical simulation method and show that the size of the metallic nanoparticle and the oscillator strength of molecular J-aggregates impact the strong coupling-like phenomenon. The strong coupling-like phenomenon is induced by the interactions between two dipoles formed by the metallic nanoparticle and molecular J-aggregates or the interactions between the dipole generated from molecular J-aggregates and the quadrupole generated from the metallic nanoparticle. The strong coupling-like phenomenon appears evidently with the increase in oscillator strength of molecular J-aggregates. The detuning energy linearly decreases with the increase in radius of the metallic nanoparticle. Our structure has potential applications in quantum networks, quantum key distributions and so on.

Polylactide based nanocomposites: Processing, structure and performance relationship

NASA Astrophysics Data System (ADS)

Karami, Shahir

The application of biodegradable polymers has been offered to the packing industry wishing to overcome the environmental consequence of employing the petroleum-based polymers. Furthermore, the unstable oil market urged the industry to look for the substitution of the renewable resources. Polylactide is known as the most popular biodegradable polymer developed on a large scale. Nevertheless, the growing contribution of polylactide to packing industry is somewhat restricted owing to its inherent brittleness and weak barrier properties. Therefore, the main objective of this thesis was defined to build a fundamental relationship between processing parameters and solid-state microstructure to improve the performance of polylactide. Polylactide nanocomposites were prepared through a multi-step melt compounding process. Dispersion of organically modified layered nanoparticles was detected by the WAXS and TEM characterizations, demonstrating the formation of intercalated nanocomposites. Relaxation spectrum exhibited the restricted dynamics of fraction of amorphous phase confined in polymer-particle interphase through dynamic rheological measurements. The fraction of rigid amorphous chains was estimated using TMDSC and DMA. This increased with nanoparticle content, levelling off upon the aggregation of nanoparticles. The annealing-induced molecular ordering was detected by FR-IR, increasing the rigid amorphous fraction. Cold crystallization was investigated during non-isothermal process using TMDSC. Crystallization kinetic was studied through the evaluation of Avrami parameters in isothermal process at the temperature range of Tg+30°C to Tg+70°C. The crystallization rate depressed with the nanoparticle content due to the enhanced fraction of rigid amorphous chains, as well as, the topological constraints derived from the formation of network structure. Nevertheless, the nanoparticles acted as heterogeneous nucleating sites upon devitrification of the rigid amorphous chains at the temperatures above Tg+60°C. The larger nucleation density resulted in the formation of larger rigid amorphous fraction along the semi-crystalline matrix. The variation of complex viscosity at molten state reflected the degradation of polylactide. The NMR characterization was conducted to investigate the effect of dispersed nanoparticle on the degradation of matrix. It was found that the degradation was accelerated with the nanoparticle content. However, the stereoregularity of polylactide chains remained unchanged in the presence of nanoparticles. Mechanical response was measured using Instron mechanical tester. The fractured surface was analyzed by SEM and SAXS. It was found that, toughness improved with the nanoparticle content due to enhanced occupation density upon multiple crazing. Structural evolutions were investigated during a hot-drawing process, at different initial strain rates and the temperatures of Tg+10°C and Tg+30°C, using WAXS and SAXS offline measurements. A mesomorphic phase was developed along the drawing direction, at Tg+10°C, composed of a bundle of parallel extended molecules with a looser lateral chain packing compared to that of the crystalline domain. The mesophase was disordered at the glass transition temperature of the bulk-like chains acting as the precursor of crystalline ordering. A lower fraction of the intermediate ordering was detected with nanoparticle content than that of the neat polymer at constant processing conditions. The slippage of frozen-in mesophase triggered strain hardening behavior during the stretching process at room temperature. This led to the significant improvement of film toughness and stress at break. Spherulitic crystalline domains were formed upon development of point-like nuclei during the drawing process at T g+30°C. No mesophase was detected at Tg+30°C, due to the enhanced contribution of chain relaxation. Line-like nuclei were observed at the highest applied strain rate, resulting in the formation of a fibrillar crystalline structure. Oxygen flux density was measured at constant temperature and relative humidity. Permeability coefficient was distinguished to the diffusivity and solubility, through the analysis of the non-steady state flux density with time by an approximate solution of the Fick's second law. The diffusivity decreased in the presence of the impermeable matters, crystalline domains and nanoparticle layers. Furthermore, the restricted dynamics of rigid amorphous fraction decreased the fraction of dynamic free volumes. Solubility increased with the nanoparticle content due to the accelerated degradation. The aggregation of nanoparticles also intensified the accessible static free volume. The chain architecture of toughening modifier was disclosed using NMR and FT-IR. It was believed to be Ethylene-Butyl Acrylate copolymer with the average sequence length of 10:1. A two-phase morphology was detected by SEM for polylactide/toughening modifier immiscible blend. DMA measurements exhibited a third glass transition, corresponding to development of polylactide-ethylene-butyl acrylate terpolymer at the interface through a transesterification reaction. The enhancement of zero shear viscosity of blends attributed to the Marangoni stresses derived from the uneven distribution of in-situ formed terpolymer at the interface. An intermeshed morphology was observed upon the incorporation of the nanoparticles. The nanoparticles were accommodated within the polylactide phase determined by the calculation of wetting parameter. The morphology connectivity led to the outstanding improvement of toughness.

Soft Landing of Bare Nanoparticles with Controlled Size, Composition, and Morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Grant E.; Colby, Robert J.; Laskin, Julia

2015-01-01

A kinetically-limited physical synthesis method based on magnetron sputtering and gas aggregation has been coupled with size-selection and ion soft landing to prepare bare metal nanoparticles on surfaces with controlled coverage, size, composition, and morphology. Employing atomic force microscopy (AFM) and scanning electron microscopy (SEM), it is demonstrated that the size and coverage of bare nanoparticles soft landed onto flat glassy carbon and silicon as well as stepped graphite surfaces may be controlled through size-selection with a quadrupole mass filter and the length of deposition, respectively. The bare nanoparticles are observed with AFM to bind randomly to the flat glassymore » carbon surface when soft landed at relatively low coverage (1012 ions). In contrast, on stepped graphite surfaces at intermediate coverage (1013 ions) the soft landed nanoparticles are shown to bind preferentially along step edges forming extended linear chains of particles. At the highest coverage (5 x 1013 ions) examined in this study the nanoparticles are demonstrated with both AFM and SEM to form a continuous film on flat glassy carbon and silicon surfaces. On a graphite surface with defects, however, it is shown with SEM that the presence of localized surface imperfections results in agglomeration of nanoparticles onto these features and the formation of neighboring depletion zones that are devoid of particles. Employing high resolution scanning transmission electron microscopy in the high angular annular dark field imaging mode (STEM-HAADF) and electron energy loss spectroscopy (EELS) it is demonstrated that the magnetron sputtering/gas aggregation synthesis technique produces single metal particles with controlled morphology as well as bimetallic alloy nanoparticles with clearly defined core-shell structure. Therefore, this kinetically-limited physical synthesis technique, when combined with ion soft landing, is a versatile complementary method for preparing a wide range of bare supported nanoparticles with selected properties that are free of the solvent, organic capping agents, and residual reactants present with nanoparticles synthesized in solution.« less

TiO2 nanoparticles aggregation and disaggregation in presence of alginate and Suwannee River humic acids. pH and concentration effects on nanoparticle stability.

PubMed

Loosli, Frédéric; Le Coustumer, Philippe; Stoll, Serge

2013-10-15

The behavior of manufactured TiO2 nanoparticles is studied in a systematic way in presence of alginate and Suwannee River humic acids at variable concentrations. TiO2 nanoparticles aggregation, disaggregation and stabilization are investigated using dynamic light scattering and electrophoretic experiments allowing the measurement of z-average hydrodynamic diameters and zeta potential values. Stability of the TiO2 nanoparticles is discussed by considering three pH-dependent electrostatic scenarios. In the first scenario, when pH is below the TiO2 nanoparticle point of zero charge, nanoparticles exhibit a positively charged surface whereas alginate and Suwannee River humic acids are negatively charged. Fast adsorption at the TiO2 nanoparticles occurs, promotes surface charge neutralization and aggregation. By increasing further alginate and Suwannee River humic acids concentrations charge inversion and stabilization of TiO2 nanoparticles are obtained. In the second electrostatic scenario, at the surface charge neutralization pH, TiO2 nanoparticles are rapidly forming aggregates. Adsorption of alginate and Suwannee River humic acids on aggregates leads to their partial fragmentation. In the third electrostatic scenario, when nanoparticles, alginate and Suwannee River humic acids are negatively charged, only a small amount of Suwannee River humic acids is adsorbed on TiO2 nanoparticles surface. It is found that the fate and behavior of individual and aggregated TiO2 nanoparticles in presence of environmental compounds are mainly driven by the complex interplay between electrostatic attractive and repulsive interactions, steric and van der Waals interactions, as well as concentration ratio. Results also suggest that environmental aquatic concentration ranges of humic acids and biopolymers largely modify the stability of aggregated or dispersed TiO2 nanoparticles. Copyright © 2013 Elsevier Ltd. All rights reserved.

Behavior of grafted polymers on nanofillers and their influence on polymer nanocomposite properties

NASA Astrophysics Data System (ADS)

Dukes, Douglas Michael

Polymer nanocomposites continue to receive wide-spread acclaim for their potential to improve composite materials beyond conventional macroscale fillers. The improvement lies both in the altered properties of the particle itself and in the interaction region surrounding the filler. As the surface area of the filler increases, a greater volume fraction of this interphase region is present in the composite. However, simply minimizing the particle size to maximize surface area introduces additional problems; the larger specific surface area promotes aggregation to reduce the surface energy. Since the composite's properties are largely tied to the morphology, aggregation prevents control over the dispersion state of the filler, and thus the properties. Therefore, disaggregation and morphology control are vital to achieving designable nanocomposites. To accomplish both tasks, this thesis focuses on the behavior of grafted polymer coatings on nanoparticles and their in uence on the macroscopic properties. Grafted chains play an integral role in both morphology control and reinforcement. To investigate the behavior of polymer brushes on nanoparticles, polystyrene was grafted on 15 nm silica particles at varying graft densities and molecular weights. Dynamic light scattering studies in dilute solution were performed to obtain the brush height as a function of both graft density and molecular weight. Three distinct regimes of behavior exist, the "mushroom", the semi-dilute polymer brush (SDPB), and the concentrated polymer brush (CPB) regimes. In the CPB regime, which is an extraordinary configuration of highly-stretched chains on densely grafted surfaces, the brush height h was found to scale as h ∝ N4/5, where N is the degree of polymerization. This result is contrary to the observed scaling of the CPB in flat interface systems, where h ∝ N1. To explore the behavior of grafted chains in the melt, molecular dynamics simulations were performed on grafted nanoparticles grafted with varying amounts of polymer chains at different curvatures. Particles as small as 15 monomers in size were found to already be in the large particle limit, a result that has many implications regarding the dispersibility of grafted fillers in composites. At low graft densities, melt chains were found to form entanglements with the brush all the way to the particle surface, implying the particle is not effectively screened by the grafted chains. The mechanical properties of these grafted silica composites were studied as a function of matrix polymer fraction. As more matrix polymer is introduced, the dominant contribution to the behavior shifts from the grafted chains to the matrix chains. This elucidates the role of grafted chains on the mechanical properties of grafted nanoparticle composites. As the graft density is increased, the wettability of grafted chains was shown to decrease, causing fewer entanglements between grafted chains and matrix chains, resulting in poorer reinforcement. Interesting behavior was observed at low graft densities; a pronounced shape memory effect occurred at high particle concentrations. It is proposed that the grafted chains entangle with adjacent grafted chains, forming a three-dimensional network of entangled brushes attached to silica cores. This structure effectively forms "cross-links" as in elastomeric systems, giving an entropic restorative force to stretched chains. Thus, above Tg, when chains have a higher degree of mobility, the composites can be stretched to over 800%. When cooled to below Tg, they retain the deformed geometry. Upon reheating above Tg, the composite is restored to its original dimensions. This work has identified means of improving theoretical models to better guide future experiments and lead to predictability in polymer composite design. Grafted chains have the demonstrated ability to control the morphology and reinforcement in polymer composites. The behavior of grafted chains were shown to demonstrate drastically different properties from their bulk polymer counterparts.

Optical characteristics of the nanoparticle coupled to a quantum molecular aggregate

NASA Astrophysics Data System (ADS)

Ropakova, I. Yu.; Zvyagin, A. A.

2017-11-01

Optical characteristics of a single nanoparticle, coupled to the one-dimensional quantum molecular aggregate is studied. Depending on the values of the coupling of the particle and its own frequency, with respect to the own frequency of the aggregated molecules, and the strength of the aggregation, the dynamical relative permittivity of the nanoparticle manifests the contribution from the exciton band, or/and the ones from the local level(s) caused by the particle. The refractive index and the extinction coefficient of the nanoparticle is also calculated.

Processing pathway dependence of amorphous silica nanoparticle toxicity - colloidal versus pyrolytic

PubMed Central

Zhang, Haiyuan; Dunphy, Darren R.; Jiang, Xingmao; Meng, Huan; Sun, Bingbing; Tarn, Derrick; Xue, Min; Wang, Xiang; Lin, Sijie; Ji, Zhaoxia; Li, Ruibin; Garcia, Fred L.; Yang, Jing; Kirk, Martin L.; Xia, Tian; Zink, Jeffrey I; Nel, Andre; Brinker, C. Jeffrey

2012-01-01

We have developed structure/toxicity relationships for amorphous silica nanoparticles (NPs) synthesized through low temperature, colloidal (e.g. Stöber silica) or high temperature pyrolysis (e.g. fumed silica) routes. Through combined spectroscopic and physical analyses, we have determined the state of aggregation, hydroxyl concentration, relative proportion of strained and unstrained siloxane rings, and potential to generate hydroxyl radicals for Stöber and fumed silica NPs with comparable primary particle sizes (16-nm in diameter). Based on erythrocyte hemolytic assays and assessment of the viability and ATP levels in epithelial and macrophage cells, we discovered for fumed silica an important toxicity relationship to post-synthesis thermal annealing or environmental exposure, whereas colloidal silicas were essentially non-toxic under identical treatment conditions. Specifically, we find for fumed silica a positive correlation of toxicity with hydroxyl concentration and its potential to generate reactive oxygen species (ROS) and cause red blood cell hemolysis. We propose fumed silica toxicity stems from its intrinsic population of strained three-membered rings (3MRs) along with its chain-like aggregation and hydroxyl content. Hydrogen-bonding and electrostatic interactions of the silanol surfaces of fumed silica aggregates with the extracellular plasma membrane cause membrane perturbations sensed by the Nalp3 inflammasome, whose subsequent activation leads to secretion of the cytokine IL-1β. Hydroxyl radicals generated by the strained 3MRs in fumed silica but largely absent in colloidal silicas may contribute to the inflammasome activation. Formation of colloidal silica into aggregates mimicking those of fumed silica had no effect on cell viability or hemolysis. This study emphasizes that not all amorphous silica is created equal and that the unusual toxicity of fumed silica compared to colloidal silica derives from its framework and surface chemistry along with its fused chain-like morphology established by high temperature synthesis (>1300°C) and rapid thermal quenching. PMID:22924492

Biophysical functionality in polysaccharides: from Lego-blocks to nano-particles.

PubMed

Cesàro, Attilio; Bellich, Barbara; Borgogna, Massimiliano

2012-04-01

The objective of the paper is to show the very important biophysical concepts that have been developed with polysaccharides. In particular, an attempt will be made to relate "a posteriori" the fundamental aspects, both experimental and theoretical, with some industrial applications of polysaccharide-based materials. The overview of chain conformational aspects includes relationships between topological features and local dynamics, exemplified for some naturally occurring carbohydrate polymers. Thus, by using simulation techniques and computational studies, the physicochemical properties of aqueous solutions of polysaccharides are interpreted. The relevance of conformational disorder-order transitions, chain aggregation, and phase separation to the underlying role of the ionic contribution to these processes is discussed. We stress the importance of combining information from analysis of experimental data with that from statistical-thermodynamic models for understanding the conformation, size, and functional stability of industrially important polysaccharides. The peculiar properties of polysaccharides in industrial applications are summarized for the particularly important example of nanoparticles production, a field of growing relevance and scientific interest.

Polymersomes from dual responsive block copolymers: drug encapsulation by heating and acid-triggered release.

PubMed

Qiao, Zeng-Ying; Ji, Ran; Huang, Xiao-Nan; Du, Fu-Sheng; Zhang, Rui; Liang, De-Hai; Li, Zi-Chen

2013-05-13

A series of well-defined thermoresponsive diblock copolymers (PEO45-b-PtNEAn, n=22, 44, 63, 91, 172) were prepared by the atom transfer radical polymerization of trans-N-(2-ethoxy-1,3-dioxan-5-yl) acrylamide (tNEA) using a poly(ethylene oxide) (PEO45) macroinitiator. All copolymers are water-soluble at low temperature, but upon quickly heating to 37 °C, laser light scattering (LLS) and transmission electron microscopy (TEM) characterizations indicate that these copolymers self-assemble into aggregates with different morphologies depending on the chain length of PtNEA and the polymer concentration; the morphologies gradually evolved from spherical solid nanoparticles to a polymersome as the degree of polymerization ("n") of PtNEA block increased from 22 to 172, with the formation of clusters with rod-like structure at the intermediate PtNEA length. Both the spherical nanoparticle and the polymersome are stable at physiological pH but susceptible to the mildly acidic medium. Acid-triggered hydrolysis behaviors of the aggregates were investigated by LLS, Nile red fluorescence, TEM, and (1)H NMR spectroscopy. The results revealed that the spherical nanoparticles formed from PEO45-b-PtNEA44 dissociated faster than the polymersomes of PEO45-b-PtNEA172, and both aggregates showed an enhanced hydrolysis under acidic conditions. Both the spherical nanoparticle and polymersome are able to efficiently load the hydrophobic doxorubicin (DOX), and water-soluble fluorescein isothiocyanate-lysozyme (FITC-Lys) can be conveniently encapsulated into the polymersome without using any organic solvent. Moreover, FITC-Lys and DOX could be coloaded in the polymersome. The drugs loaded either in the polymersome or in the spherical nanoparticle could be released by acid triggering. Finally, the DOX-loaded assemblies display concentration-dependent cytotoxicity to HepG2 cells, while the copolymers themselves are nontoxic.

Synthesis of anatase TiO2 nanoparticles with beta-cyclodextrin as a supramolecular shell.

PubMed

Li, Landong; Sun, Xiaohong; Yang, Yali; Guan, Naijia; Zhang, Fuxiang

2006-11-20

We report a novel, green hydrothermal-synthesis route to well-dispersed anatase TiO2 nanoparticles with particle sizes of 9-16 nm in the presence of beta-CD (beta-cyclodextrin). During the synthesis process, the CD-containing synthesis mixture assembled in both longitudinal and latitudinal directions. Driven by the interaction between molecules, the beta-CDs assembled in the longitudinal direction to form long-chain compounds, whereas in the latitudinal direction, they tended to form regular aggregates through coordination with the Ti species from the hydrolysis of tetrabutyl titanate. In view of the effect of the coordination and the steric hindrance of beta-CDs as a supramolecular shell, homogeneous nuclei and slow growth of TiO2 crystals during the synthesis process was observed, which was responsible for the formation of uniform TiO2 nanoparticles. The low beta-CD dosage and the high product yield (>90%) demonstrated well the potential of this synthesis route in the large-scale industrial production of anatase nanoparticles.

Studying the silver nanoparticles influence on thermodynamic behavior and antimicrobial activities of novel amide Gemini cationic surfactants.

PubMed

Shaban, Samy M; Abd-Elaal, Ali A

2017-07-01

Three novels amide Gemini cationic surfactants with various alkyl chains and their silver nanohybrid with silver nanoparticles were synthesized and a confirmation study for surfactant and their nanoparticles formation has been established using IR, 1 HNMR, TEM and UV-Vis spectroscopy. The surface-active properties of these surfactants and their nanoform were investigated through surface tension and electrical conductivity measurements and a comparative study has been established. The thermodynamic parameters of micellization and adsorption were assessed at temperatures range from 25 to 65°C. The effect of silver particles on the surface behavior of the synthesized surfactant has been discussed. The aggregation behavior of silver nanoparticles with these synthesized Gemini surfactants in water were investigated using dynamic light scattering and transmission electron microscopy. Furthermore, the antimicrobial activities of these synthesized amide Gemini surfactants and their nanostructure with silver against both Gram positive and Gram negative bacteria were also investigated. Copyright © 2017 Elsevier B.V. All rights reserved.

Tyrosine- and tryptophan-coated gold nanoparticles inhibit amyloid aggregation of insulin.

PubMed

Dubey, Kriti; Anand, Bibin G; Badhwar, Rahul; Bagler, Ganesh; Navya, P N; Daima, Hemant Kumar; Kar, Karunakar

2015-12-01

Here, we have strategically synthesized stable gold (AuNPs(Tyr), AuNPs(Trp)) and silver (AgNPs(Tyr)) nanoparticles which are surface functionalized with either tyrosine or tryptophan residues and have examined their potential to inhibit amyloid aggregation of insulin. Inhibition of both spontaneous and seed-induced aggregation of insulin was observed in the presence of AuNPs(Tyr), AgNPs(Tyr), and AuNPs(Trp) nanoparticles. These nanoparticles also triggered the disassembly of insulin amyloid fibrils. Surface functionalization of amino acids appears to be important for the inhibition effect since isolated tryptophan and tyrosine molecules did not prevent insulin aggregation. Bioinformatics analysis predicts involvement of tyrosine in H-bonding interactions mediated by its C=O, -NH2, and aromatic moiety. These results offer significant opportunities for developing nanoparticle-based therapeutics against diseases related to protein aggregation.

Comparison of characteristics of montmorillonite supported nano zero valent iron (M-nZVI) and nano zero valent iron (nZVI)

NASA Astrophysics Data System (ADS)

How, Ho Kuok; Wan Zuhairi W., Y.

2015-09-01

In this study, synthesized montmorillonite supported nano zero valent iron (M-nZVI) and nano zero valent iron (nZVI) are compared physically and chemically. The samples were prepared using chemical reduction method that includes sodium borohydride and ethanol. Due to the tendency of nZVI to aggregate, montmorillonite is used as a supporting material. TEM and FESEM images show that the M-nZVI has decreased the aggregation by dispersing the particles on the surface of montmorillonite whereas images of nZVI show chain-like particle due to aggregation. Both images also show particles synthesized are nanoparticles. With less aggregation, the surface area of the M-nZVI is greater than nZVI which is 45.46 m2/g and 10.49 m2/g respectively. XRD patterns have shown Fe0 are synthesized and small amount of iron oxides are produced. M-nZVI has the capability in reducing aggregation which might lead to the increase in reactivity of the particles thus enhancing the performance of nZVI.

In Situ Observations of Electric-Field Induced Nanoparticle Aggregation

NASA Astrophysics Data System (ADS)

Woehl, T. J.; Browning, N. D.; Ristenpart, W. D.

2010-11-01

Nanoparticles have been widely observed to aggregate laterally on electrodes in response to applied electric fields. The mechanism driving this behavior, however, is unclear. Several groups have interpreted the aggregation in terms of electrohydrodynamic or electroosmotic fluid motion, but little corroborating evidence has been presented. Notably, work to date has relied on post situ observations using electron microscopy. Here we present a fluorescence microscopy technique to track the dynamics of nanoparticle aggregation in situ. Fluorescent 20-nm polystyrene nanoparticles are observed to form optically visible aggregates in response to an applied AC field. Although single particle resolution is lost, the existence of aggregates on the electrode surface is marked by growing clusters of increasingly bright intensity. We present a systematic investigation of the effects of applied potential and frequency on the aggregation rate, and we interpret the behavior in terms of a mechanism based on electrically induced convective flow.

Micelle depletion-induced vs. micelle-mediated aggregation in nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ray, D., E-mail: debes.phys@gmail.com; Aswal, V. K.

2015-06-24

The phase behavior anionic silica nanoparticle (Ludox LS30) with non-ionic surfactants decaethylene glycol monododecylether (C12E10) and cationic dodecyltrimethyl ammonium bromide (DTAB) in aqueous electrolyte solution has been studied by small-angle neutron scattering (SANS). The measurements have been carried out for fixed concentrations of nanoparticle (1 wt%), surfactants (1 wt%) and electrolyte (0.1 M NaCl). Each of these nanoparticle–surfactant systems has been examined for different contrast conditions where individual components (nanoparticle or surfactant) are made visible. It is observed that the nanoparticle-micelle system in both the cases lead to the aggregation of nanoparticles. The aggregation is found to be micelle depletion-inducedmore » for C12E10 whereas micelle-mediated aggregation for DTAB. Interestingly, it is also found that phase behavior of mixed surfactant (C12E10 + DTAB) system is similar to that of C12E10 (unlike DTAB) micelles with nanoparticles.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raghuwanshi, Vikram Singh; Garusinghe, Uthpala Manavi; Ilavsky, Jan

Controlling nanoparticles (NPs) aggregation in cellulose/NPs composites allows to optimise NPs driven properties and their applications. Polyelectrolytes are used to control NPs aggregation and their retention within the fibrous matrix. Here in this study, we aim at evaluating how a polyelectrolyte (Cationic Polyacrylamide; CPAM, molecular weight: 13 MDa, charge: 50%, Radius of gyration: 30–36 nm) adsorbs and re-conforms onto the surface of silica(SiO 2) NPs differing in diameter (8, 22 and 74 nm) and to investigate the respective NPs aggregation in cellulose matrices. SEM shows the local area distribution of NPs in composites. Ultra-SAXS (USAXS) allows to evaluate the averagemore » NPs size distribution and the inter-particle interactions at length scale ranging from 1 to 1000 nm. USAXS data analysis reveals that CPAM covers multiple NPs of the smaller diameter (8 nm), presumably with a single chain to form large size NPs aggregates. As the NPs diameter is increased to 22 nm, CPAM re-conforms over NP surface forming a large shell of thickness 5.5 nm. For the composites with NPs of diameter 74 nm, the CPAM chain re-conforms further onto NP surface and the surrounding shell thickness decreases to 2.2 nm. Lastly, structure factor analysis reveals higher structural ordering for NPs as increases their diameter, which is caused by different conformations adopted by CPAM onto NPs surface.« less

Impact of Alkyl Spacer Length on Aggregation Pathways in Kinetically Controlled Supramolecular Polymerization.

PubMed

Ogi, Soichiro; Stepanenko, Vladimir; Thein, Johannes; Würthner, Frank

2016-01-20

We have investigated the kinetic and thermodynamic supramolecular polymerizations of a series of amide-functionalized perylene bisimide (PBI) organogelator molecules bearing alkyl spacers of varied lengths (ethylene to pentylene chains, PBI-1-C2 to PBI-1-C5) between the amide and PBI imide groups. These amide-functionalized PBIs form one-dimensional fibrous nanostructures as the thermodynamically favored states in solvents of low polarity. Our in-depth studies revealed, however, that the kinetic behavior of their supramolecular polymerization is dependent on the spacer length. Propylene- and pentylene-tethered PBIs follow a similar polymerization process as previously observed for the ethylene-tethered PBI. Thus, the monomers of these PBIs are kinetically trapped in conformationally restricted states through intramolecular hydrogen bonding between the amide and imide groups. In contrast, the intramolecularly hydrogen-bonded monomers of butylene-tethered PBI spontaneously self-assemble into nanoparticles, which constitute an off-pathway aggregate state with regard to the thermodynamically stable fibrous supramolecular polymers obtained. Thus, for this class of π-conjugated system, an unprecedented off-pathway aggregate with high kinetic stability could be realized for the first time by introducing an alkyl linker of optimum length (C4 chain) between the amide and imide groups. Our current system with an energy landscape of two competing nucleated aggregation pathways is applicable to the kinetic control over the supramolecular polymerization by the seeding approach.

Highly Sensitive Naked-Eye Assay for Enterovirus 71 Detection Based on Catalytic Nanoparticle Aggregation and Immunomagnetic Amplification.

PubMed

Xiong, Ling-Hong; He, Xuewen; Xia, Junjie; Ma, Hanwu; Yang, Fan; Zhang, Qian; Huang, Dana; Chen, Long; Wu, Chunli; Zhang, Xiaomin; Zhao, Zheng; Wan, Chengsong; Zhang, Renli; Cheng, Jinquan

2017-05-03

Development of sensitive, convenient, and cost-effective virus detection product is of great significance to meet the growing demand of clinical diagnosis at the early stage of virus infection. Herein, a naked-eye readout of immunoassay by means of virion bridged catalase-mediated in situ reduction of gold ions and growth of nanoparticles, has been successfully proposed for rapid visual detection of Enterovirus 71 (EV71). Through tailoring the morphologies of the produced gold nanoparticles (GNPs) varying between dispersion and aggregation, a distinguishing color changing was ready for observation. This colorimetric detection assay, by further orchestrating the efficient magnetic enrichment and the high catalytic activity of enzyme, is managed to realize highly sensitive detection of EV71 virions with the limit of detection (LOD) down to 0.65 ng/mL. Our proposed method showed a much lower LOD value than the commercial ELISA for EV71 virion detection. Comparing to the current clinical gold standard polymerase chain reaction (PCR) method, our strategy provided the same diagnostic outcomes after testing real clinical samples. Besides, this strategy has no need of complicated sample pretreatment or expensive instruments. Our presented naked-eye immunoassay method holds a promising prospect for the early detection of virus-infectious disease especially in resource-constrained settings.

Forced and natural convection in aggregate-laden nanofluids

NASA Astrophysics Data System (ADS)

Thajudeen, Thaseem; Hogan, Christopher J.

2011-12-01

A number of experimental and theoretical studies of convective heat transfer in nanofluids (liquid suspensions of nanoparticles, typically with features below 100 nm in size) reveal contrasting results; nanoparticles can either enhance or reduce the convective heat transfer coefficient. These disparate conclusions regarding the influence of nanoparticles on convective heat transfer may arise due to the aggregation of nanoparticles, which is often not considered in studies of nanofluids. Here, we examine theoretically forced and natural convective heat transfer of aggregate-laden nanofluids using Monte Carlo-based models to determine how the aggregate morphology influences the convective heat transfer coefficient. Specifically, in this study, it is first shown that standard heat transfer correlations should apply to nanofluids, and the main influence of the nanoparticles is to alter suspension thermal conductivity, dynamic viscosity, density, specific heat, and thermal expansion coefficient. Aggregated particles in suspension are modeled as quasi-fractal aggregates composed of individual primary particles described by the primary particle radius, number of primary particles, fractal (Hausdorff) dimension, pre-exponential factor, and degree of coalescence between primary particles. A sequential algorithm is used to computationally generate aggregates with prescribed morphological descriptors. Four types of aggregates are considered; spanning the range of aggregate morphologies observed in nanofluids. For each morphological type, the influences of aggregates on nanofluid dynamic viscosity and thermal conductivity are determined via first passage-based Brownian dynamics calculations. It is found that depending on both the material properties of the nanoparticles as well as the nanoparticle morphology, the addition of nanoparticles to a suspension can either increase or decrease both the forced and natural convective heat transfer coefficients, with both a 51% increase and a 32% decrease in the heat transfer coefficient achievable at particle volume fractions of 0.05. This study shows clearly that the influence of particle morphology needs to be accounted for in all studies of heat transfer in nanofluids.

Block versus Random Amphiphilic Glycopolymer Nanopaticles as Glucose-Responsive Vehicles.

PubMed

Guo, Qianqian; Zhang, Tianqi; An, Jinxia; Wu, Zhongming; Zhao, Yu; Dai, Xiaomei; Zhang, Xinge; Li, Chaoxing

2015-10-12

To explore the effect of polymer structure on their self-assembled aggregates and their unique characteristics, this study was devoted to developing a series of amphiphilic block and random phenylboronic acid-based glycopolymers by RAFT polymerization. The amphiphilic glycopolymers were successfully self-assembled into spherically shaped nanoparticles with narrow size distribution in aqueous solution. For block and random copolymers with similar monomer compositions, block copolymer nanoparticles exhibited a more regular transmittance change with the increasing glucose level, while a more evident variation of size and quicker decreasing tendency in I/I0 behavior in different glucose media were observed for random copolymer nanoparticles. Cell viability of all the polymer nanoparticles investigated by MTT assay was higher than 80%, indicating that both block and random copolymers had good cytocompatibility. Insulin could be encapsulated into both nanoparticles, and insulin release rate for random glycopolymer was slightly quicker than that for the block ones. We speculate that different chain conformations between block and random glycopolymers play an important role in self-assembled nanoaggregates and underlying glucose-sensitive behavior.

Colorimetric detection of mercury ion based on unmodified gold nanoparticles and target-triggered hybridization chain reaction amplification

NASA Astrophysics Data System (ADS)

Wang, Qing; Yang, Xiaohan; Yang, Xiaohai; Liu, Pei; Wang, Kemin; Huang, Jin; Liu, Jianbo; Song, Chunxia; Wang, Jingjing

2015-02-01

A novel unmodified gold nanoparticles (AuNPs)-based colorimetric strategy for label-free, specific and sensitive mercury ion (Hg2+) detection was demonstrated by using thymine-Hg2+-thymine (T-Hg2+-T) recognition mechanism and hybridization chain reaction (HCR) amplification strategy. In this protocol, a structure-switching probe (H0) was designed to recognize Hg2+ and then propagated a chain reaction of hybridization events between two other hairpin probes (H1 and H2). In the absence of Hg2+, all hairpin probes could stably coexist in solution, the exposed sticky ends of hairpin probes were capable of stabilizing AuNPs. As a result, salt-induced AuNPs aggregation could be effectively prevented. In the presence of Hg2+, thymine bases of H0 could specifically interact with Hg2+ to form stable T-Hg2+-T complex. Consequently, the hairpin structure of H0 probe was changed. As H1/H2 probes were added, the HCR process could be triggered and nicked double-helixes were formed. Since it was difficult for the formed nicked double-helixes to inhibit salt-induced AuNPs aggregation, a red-to-blue color change was observed in the colloid solution as the salt concentration increased. With the elegant amplification effect of HCR, a detection limit of around 30 nM was achieved (S/N = 3), which was about 1-2 orders of magnitudes lower than that of previous unmodified AuNPs-based colorimetric methods. By using the T-Hg2+-T recognition mechanism, high selectivity was also obtained. As an unmodified AuNPs-based colorimetric strategy, the system was simple in design, convenient in operation, and eliminated the requirements of separation processes, chemical modifications, and sophisticated instrumentations.

Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water.

PubMed

Matsumoto, Mayuko; Terashima, Takaya; Matsumoto, Kazuma; Takenaka, Mikihito; Sawamoto, Mitsuo

2017-05-31

Orthogonal self-assembly and intramolecular cross-linking of amphiphilic random block copolymers in water afforded an approach to tailor-make well-defined compartments and domains in single polymer chains and nanoaggregates. For a double compartment single-chain polymer, an amphiphilic random block copolymer bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl, benzyl, and olefin pendants was synthesized by living radical polymerization (LRP) and postfunctionalization; the dodecyl and benzyl units were incorporated into the different block segments, whereas PEG pendants were statistically attached along a chain. The copolymer self-folded via the orthogonal self-assembly of hydrophobic dodecyl and benzyl pendants in water, followed by intramolecular cross-linking, to form a single-chain polymer carrying double yet distinct hydrophobic nanocompartments. A single-chain cross-linked polymer with a chlorine terminal served as a globular macroinitiator for LRP to provide an amphiphilic tadpole macromolecule comprising a hydrophilic nanoparticle and a hydrophobic polymer tail; the tadpole thus self-assembled into multicompartment aggregates in water.

Aragonite-Associated Mollusk Shell Protein Aggregates To Form Mesoscale “Smart” Hydrogels

DOE PAGES

Perovic, Iva; Davidyants, Anastasia; Evans, John Spencer

2016-11-30

In the mollusk shell there exists a framework silk fibroin-polysaccharide hydrogel coating around nacre aragonite tablets, and this coating facilitates the synthesis and organization of mineral nanoparticles into mesocrystals. In this report, we identify that a protein component of this coating, n16.3, is a hydrogelator. Due to the presence of intrinsic disorder, aggregation-prone regions, and nearly equal balance of anionic and cationic side chains, this protein assembles to form porous mesoscale hydrogel particles in solution and on mica surfaces. These hydrogel particles change their dimensionality, organization, and internal structure in response to pH and ions, particularly Ca(II), which indicates thatmore » these behave as ion-responsive or “smart” hydrogels. Thus, in addition to silk fibroins, the gel phase of the mollusk shell nacre framework layer may actually consist of several framework hydrogelator proteins, such as n16.3, which can promote mineral nanoparticle organization and assembly during the nacre biomineralization process and also serve as a model system for designing ion-responsive, composite, and smart hydrogels.« less

Crosslinking to enhance colloidal stability and redispersity of layered double hydroxide nanoparticles.

PubMed

Zuo, Huali; Gu, Zi; Cooper, Helen; Xu, Zhi Ping

2015-12-01

This article introduces a strategy for stabilizing and redispersing layered double hydroxide (LDH) nanoparticles by crosslinking bovine serum albumin (BSA) coated onto the surface. The strategy involves optimization of the amount of the crosslinking agent glutaraldehyde (GTA) to achieve minimal aggregation and ready redispersion. LDH nanoparticles were prepared by co-precipitation and hydrothermal treatment, with subsequent BSA coating at the BSA/LDH mass ratio of 5:2. BSA coated onto LDH nanoparticles was crosslinked with different amounts of GTA. Aggregation studies using dilution assays, dynamic light scattering, and zeta potential analysis indicated that severe aggregation at lower LDH nanoparticle concentrations can be prevented by proper crosslinking of BSA with GTA. The GTA-crosslinked BSA-coated nanoparticles showed excellent redispersity compared to the non-crosslinked nanoparticles. In vitro cytotoxicity and cell uptake were found to be minimally affected by GTA-crosslinking. The new strategy therefore provides a much more effective method for the prevention of LDH nanoparticle aggregation and improved LDH nanoparticle redispersion for use in a wide variety of bio-applications in vitro and in vivo. Copyright © 2015 Elsevier Inc. All rights reserved.

Pectin-Lipid Self-Assembly: Influence on the Formation of Polyhydroxy Fatty Acids Nanoparticles

PubMed Central

Guzman-Puyol, Susana; Benítez, José Jesús; Domínguez, Eva; Bayer, Ilker Sefik; Cingolani, Roberto; Athanassiou, Athanassia; Heredia, Antonio; Heredia-Guerrero, José Alejandro

2015-01-01

Nanoparticles, named cutinsomes, have been prepared from aleuritic (9,10,16-trihidroxipalmitic) acid and tomato fruit cutin monomers (a mixture of mainly 9(10),16-dihydroxypalmitic acid (85%, w/w) and 16-hydroxyhexadecanoic acid (7.5%, w/w)) with pectin in aqueous solution. The process of formation of the nanoparticles of aleuritic acid plus pectin has been monitored by UV-Vis spectrophotometry, while their chemical and morphological characterization was analyzed by ATR-FTIR, TEM, and non-contact AFM. The structure of these nanoparticles can be described as a lipid core with a pectin shell. Pectin facilitated the formation of nanoparticles, by inducing their aggregation in branched chains and favoring the condensation between lipid monomers. Also, pectin determined the self-assembly of cutinsomes on highly ordered pyrolytic graphite (HOPG) surfaces, causing their opening and forming interconnected structures. In the case of cutin monomers, the nanoparticles are fused, and the condensation of the hydroxy fatty acids is strongly affected by the presence of the polysaccharide. The interaction of pectin with polyhydroxylated fatty acids could be related to an initial step in the formation of the plant biopolyester cutin. PMID:25915490

pH-programmable self-assembly of plasmonic nanoparticles: hydrophobic interaction versus electrostatic repulsion.

PubMed

Li, Weikun; Kanyo, Istvan; Kuo, Chung-Hao; Thanneeru, Srinivas; He, Jie

2015-01-21

We report a general strategy to conceptualize a new design for the pH-programmable self-assembly of plasmonic gold nanoparticles (AuNPs) tethered by random copolymers of poly(styrene-co-acrylic acid) (P(St-co-AA)). It is based on using pH as an external stimulus to reversibly change the surface charge of polymer tethers and to control the delicate balance of interparticle attractive and repulsive interactions. By incorporating -COOH moieties locally within PSt hydrophobic segments, the change in the ionization degree of -COOH moieties can dramatically disrupt the hydrophobic attraction within a close distance. pH acts as a key parameter to control the deprotonation of -COOH moieties and "programs" the assembled nanostructures of plasmonic nanoparticles in a stepwise manner. At a higher solution pH where -COOH groups of polymer tethers became highly deprotonated, electrostatic repulsion dominated the self-assembly and favored the formation of end-to-end, anisotropic assemblies, e.g. 1-D single-line chains. At a lower pH, the less deprotonated -COOH groups led to the decrease of electrostatic repulsion and the side-to-side aggregates, e.g. clusters and multi-line chains of AuNPs, became favorable. The pH-programmable self-assembly allowed us to engineer a "manual" program for a sequential self-assembly by changing the pH of the solution. We demonstrated that the two-step pH-programmable assembly could generate more sophisticated "multi-block" chains using two differently sized AuNPs. Our strategy offers a general means for the programmable design of plasmonic nanoparticles into the specific pre-ordained nanostructures that are potentially useful for the precise control over their plasmon coupling.

pH-dependent interaction and resultant structures of silica nanoparticles and lysozyme protein.

PubMed

Kumar, Sugam; Aswal, Vinod K; Callow, P

2014-02-18

Small-angle neutron scattering (SANS) and UV-visible spectroscopy studies have been carried out to examine pH-dependent interactions and resultant structures of oppositely charged silica nanoparticles and lysozyme protein in aqueous solution. The measurements were carried out at fixed concentration (1 wt %) of three differently sized silica nanoparticles (8, 16, and 26 nm) over a wide concentration range of protein (0-10 wt %) at three different pH values (5, 7, and 9). The adsorption curve as obtained by UV-visible spectroscopy shows exponential behavior of protein adsorption on nanoparticles. The electrostatic interaction enhanced by the decrease in the pH between the nanoparticle and protein (isoelectric point ∼11.4) increases the adsorption coefficient on nanoparticles but decreases the overall amount protein adsorbed whereas the opposite behavior is observed with increasing nanoparticle size. The adsorption of protein leads to the protein-mediated aggregation of nanoparticles. These aggregates are found to be surface fractals at pH 5 and change to mass fractals with increasing pH and/or decreasing nanoparticle size. Two different concentration regimes of interaction of nanoparticles with protein have been observed: (i) unaggregated nanoparticles coexisting with aggregated nanoparticles at low protein concentrations and (ii) free protein coexisting with aggregated nanoparticles at higher protein concentrations. These concentration regimes are found to be strongly dependent on both the pH and nanoparticle size.

Photoinduced Disaggregation of TiO2 Nanoparticles Enables Transdermal Penetration

PubMed Central

Bennett, Samuel W.; Zhou, Dongxu; Mielke, Randall; Keller, Arturo A.

2012-01-01

Under many aqueous conditions, metal oxide nanoparticles attract other nanoparticles and grow into fractal aggregates as the result of a balance between electrostatic and Van Der Waals interactions. Although particle coagulation has been studied for over a century, the effect of light on the state of aggregation is not well understood. Since nanoparticle mobility and toxicity have been shown to be a function of aggregate size, and generally increase as size decreases, photo-induced disaggregation may have significant effects. We show that ambient light and other light sources can partially disaggregate nanoparticles from the aggregates and increase the dermal transport of nanoparticles, such that small nanoparticle clusters can readily diffuse into and through the dermal profile, likely via the interstitial spaces. The discovery of photoinduced disaggregation presents a new phenomenon that has not been previously reported or considered in coagulation theory or transdermal toxicological paradigms. Our results show that after just a few minutes of light, the hydrodynamic diameter of TiO2 aggregates is reduced from ∼280 nm to ∼230 nm. We exposed pigskin to the nanoparticle suspension and found 200 mg kg−1 of TiO2 for skin that was exposed to nanoparticles in the presence of natural sunlight and only 75 mg kg−1 for skin exposed to dark conditions, indicating the influence of light on NP penetration. These results suggest that photoinduced disaggregation may have important health implications. PMID:23155401

Considering the formation of hematite spherules on Mars by freezing aqueous hematite nanoparticle suspensions

NASA Astrophysics Data System (ADS)

Sexton, M. R.; Elwood Madden, M. E.; Swindle, A. L.; Hamilton, V. E.; Bickmore, B. R.; Elwood Madden, A. S.

2017-04-01

The enigmatic and unexpected occurrence of coarse crystalline (gray) hematite spherules at Terra Meridiani on Mars in association with deposits of jarosite-rich sediments fueled a variety of hypotheses to explain their origin. In this study, we tested the hypothesis that freezing of aqueous hematite nanoparticle suspensions, possibly produced from low-temperature weathering of jarosite-bearing deposits, could produce coarse-grained hematite aggregate spherules. We synthesized four hematite nanoparticle suspensions with a range of sizes and morphologies and performed freezing experiments. All sizes of hematite nanoparticles rapidly aggregate during freezing. Regardless of the size or shape of the initial starting material, they rapidly collect into aggregates that are then too big to push in front of a stable advancing ice front, leading to incohesive masses of particles, rather than solid spherules. We also explored the effects of "seed" silicates, a matrix of sand grains, various concentrations of NaCl and CaCl2, and varying the freezing temperature on hematite nanoparticle aggregation. However, none of these factors resulted in mm-scale spherical aggregates. By comparing our measured freezing rates with empirical and theoretical values from the literature, we conclude that the spherules on Mars could not have been produced through the freezing of aqueous hematite nanoparticle suspensions; ice crystallization front instability disrupts the aggregation process and prevents the formation of mm-scale continuous aggregates.

Plasmonic colorimetric sensors based on etching and growth of noble metal nanoparticles: Strategies and applications.

PubMed

Zhang, Zhiyang; Wang, Han; Chen, Zhaopeng; Wang, Xiaoyan; Choo, Jaebum; Chen, Lingxin

2018-08-30

Plasmonic colorimetric sensors have emerged as a powerful tool in chemical and biological sensing applications due to the localized surface plasmon resonance (LSPR) extinction in the visible range. Among the plasmonic sensors, the most famous sensing mode is the "aggregation" plasmonic colorimetric sensor which is based on plasmon coupling due to nanoparticle aggregation. Herein, this review focuses on the newly-developing plasmonic colorimetric sensing mode - the etching or the growth of metal nanoparticles induces plasmon changes, namely, "non-aggregation" plasmonic colorimetric sensor. This type of sensors has attracted increasing interest because of their exciting properties of high sensitivity, multi-color changes, and applicability to make a test strip. Of particular interest, the test strip by immobilization of nanoparticles on the substrate can avoid the influence of nanoparticle auto-aggregation and increase the simplicity in storage and use. Although there are many excellent reviews available that describe the advance of plasmonic sensors, limited attention has been paid to the plasmonic colorimetric sensors based on etching or growth of metal nanoparticles. This review highlights recent progress on strategies and application of "non-aggregation" plasmonic colorimetric sensors. We also provide some personal insights into current challenges associated with "non-aggregation" plasmonic colorimetric sensors and propose future research directions. Copyright © 2018 Elsevier B.V. All rights reserved.

Nanoparticle-mediated local and remote manipulation of protein aggregation.

PubMed

Kogan, Marcelo J; Bastus, Neus G; Amigo, Roger; Grillo-Bosch, Dolors; Araya, Eyleen; Turiel, Antonio; Labarta, Amilcar; Giralt, Ernest; Puntes, Victor F

2006-01-01

The local heat delivered by metallic nanoparticles selectively attached to their target can be used as a molecular surgery to safely remove toxic and clogging aggregates. We apply this principle to protein aggregates, in particular to the amyloid beta protein (Abeta) involved in Alzheimer's disease (AD), a neurodegenerative disease where unnaturally folded Abeta proteins self-assemble and deposit forming amyloid fibrils and plaques. We show the possibility to remotely redissolve these deposits and to interfere with their growth, using the local heat dissipated by gold nanoparticles (AuNP) selectively attached to the aggregates and irradiated with low gigahertz electromagnetic fields. Simultaneous tagging and manipulation by AuNP of Abeta at different stages of aggregation allow both, noninvasive exploration and dissolution of molecular aggregates.

Controlled release of β-carotene in β-lactoglobulin-dextran-conjugated nanoparticles' in vitro digestion and transport with Caco-2 monolayers.

PubMed

Yi, Jiang; Lam, Tina I; Yokoyama, Wallace; Cheng, Luisa W; Zhong, Fang

2014-09-03

Undesirable aggregation of nanoparticles stabilized by proteins may occur at the protein's isoelectric point when the particle has zero net charge. Stability against aggregation of nanoparticles may be improved by reacting free amino groups with reducing sugars by the Maillard reaction. β-Lactoglobulin (BLG)-dextran conjugates were characterized by SDS-PAGE and CD. Nanoparticles (60-70 nm diameter) of β-carotene (BC) encapsulated by BLG or BLG-dextran were prepared by the homogenization-evaporation method. Both BLG and BLG-dextran nanoparticles appeared to be spherically shaped and uniformly dispersed by TEM. The stability and release of BC from the nanoparticles under simulated gastrointestinal conditions were evaluated. Dextran conjugation prevented the flocculation or aggregation of BLG-dextran particles at pH ∼4-5 compared to very large sized aggregates of BLG nanoparticles. The released contents of BC from BLG and BLG-dextran nanoparticles under acidic gastric conditions were 6.2 ± 0.9 and 5.4 ± 0.3%, respectively. The release of BC from BLG-dextran nanoparticles by trypsin digestion was 51.8 ± 4.3% of total encapsulated BC, and that from BLG nanoparticles was 60.9 ± 2.9%. Neither BLG-BC nanoparticles nor the Maillard-reacted BLG-dextran conjugates were cytotoxic to Caco-2 cells, even at 10 mg/mL. The apparent permeability coefficient (Papp) of Caco-2 cells to BC was improved by nanoencapsulation, compared to free BC suspension. The results indicate that BC-encapsulated β-lactoglobulin-dextran-conjugated nanoparticles are more stable to aggregation under gastric pH conditions with good release and permeability properties.

Impact of environmental conditions on aggregation kinetics of hematite and goethite nanoparticles

NASA Astrophysics Data System (ADS)

Xu, Chen-yang; Deng, Kai-ying; Li, Jiu-yu; Xu, Ren-kou

2015-10-01

Hematite and goethite nanoparticles were used as model minerals to investigate their aggregation kinetics under soil environmental conditions in the present study. The hydrodynamic diameters of hematite and goethite nanoparticles were 34.4 and 66.3 nm, respectively. The positive surface charges and zeta potential values for goethite were higher than for hematite. The effective diameter for goethite was much larger than for hematite due to anisotropic sticking of needle-shaped goethite during aggregation. Moreover, the critical coagulation concentration (CCC) values of nanoparticles in solutions of NaNO3, NaCl, NaF, and Na2SO4 were 79.2, 75.0, 7.8, and 0.5 mM for hematite and they were 54.7, 62.6, 5.5, and 0.2 mM for goethite, respectively. The disparity of anions in inducing hematite or goethite aggregation lay in the differences in interfacial interactions. NO3 - and Cl- could decrease the zeta potential and enhance aggregation mainly through increasing ionic strength and compressing electric double layers of hematite and goethite nanoparticles. F- and SO4 2- highly destabilized the suspensions of nanoparticles mainly through specific adsorption and then neutralizing the positive surface charges of nanoparticles. Specific adsorption of cations could increase positive surface charges and stabilize hematite and goethite nanoparticles. The Hamaker constants of hematite and goethite nanoparticles were calculated to be 2.87 × 10-20 and 2.29 × 10-20 J-1, respectively. The predicted CCC values based on DLVO theory were consistent well with the experimentally determined CCC values in NaNO3, NaCl, NaF, and Na2SO4 systems, which demonstrated that DLVO theory could successfully predict the aggregation kinetics even when specific adsorption of ions occurred.

Colorimetric As (V) detection based on S-layer functionalized gold nanoparticles.

PubMed

Lakatos, Mathias; Matys, Sabine; Raff, Johannes; Pompe, Wolfgang

2015-11-01

Herein, we present simple and rapid colorimetric and UV/VIS spectroscopic methods for detecting anionic arsenic (V) complexes in aqueous media. The methods exploit the aggregation of S-layer-functionalized spherical gold nanoparticles of sizes between 20 and 50 nm in the presence of arsenic species. The gold nanoparticles were functionalized with oligomers of the S-layer protein of Lysinibacillus sphaericus JG-A12. The aggregation of the nanoparticles results in a color change from burgundy-red for widely dispersed nanoparticles to blue for aggregated nanoparticles. A detailed signal analysis was achieved by measuring the shift of the particle plasmon resonance signal with UV/VIS spectroscopy. To further improve signal sensitivity, the influence of larger nanoparticles was tested. In the case of 50 nm gold nanoparticles, a concentration of the anionic arsenic (V) complex lower than 24 ppb was detectable. Copyright © 2015 Elsevier B.V. All rights reserved.

Gelling Mechanism of Aluminum Di-Soaps in Oils

NASA Astrophysics Data System (ADS)

Wang, Xiaorong; Rackaitis, Mindaugas

2009-03-01

This work demonstrates that aluminum di-soaps form nano-sized spherical micelles in the oils and that the aggregation of these micelles forms a network that gives rise to a gel formation -- thereby refuting a long-held belief that the gel formation was the result of linear polymeric chains of aluminum association. The discovery of such aluminum nano-particles could expand application of these materials to new technologies because these materials are chemically inert, odorless and nontoxic, and have been widely used in greases, paints, gels, cosmetics, drugs and foods.

Biological consequences from interaction of nanosized titanium(iv) oxides with defined human blood components

NASA Astrophysics Data System (ADS)

Stella, Aaron

The utility of engineered nanomaterials is growing, particularly the titanium(iv) oxide (titanium dioxide, TiO2) nanoparticles. TiO 2 is very useful for brightening paints, and coloring foods. Nano-sized TiO2 is also useful for sunscreens, cosmetics, and can be utilized as a photocatalyst. However, the nanometer size of the TiO2 nanoparticle is a characteristic that may contribute oxidative stress to red blood cells (RBCs) in humans. This study utilized screening methods to evaluate different forms of TiO2 nanoparticles which differ by primary particle size, specific surface area, crystalline phase, and surface polarity. RBCs are rich in the intracellular antioxidant glutathione (GSH). HPLC analysis revealed that some TiO2 nanoparticles caused oxidation of GSH to glutathione disulfide (GSSG). Vitamin E is a major membrane-bound antioxidant. Vitamin E levels were then determined by HPLC in the RBC membrane after exposure to TiO2 nanoparticles. The HPLC results showed that each nanoparticle oxidized RBC glutathione and membrane vitamin E at different rates. When hemoglobin was mixed with each TiO2 nanoparticle, hemoglobin was adsorbed at varying rates to the surface of the nanoparticles. Similarly, the aminothiol homocysteine was also adsorbed at different rates by the TiO2 nanoparticles. Using light microscopy, some TiO2 nanoparticles caused the formation of RBC aggregates which significantly changed the RBC morphology. The aggregation data was quantified using a hemacytometer. The TiO2 nanoparticles also caused hemolysis of RBCs. Hemolysis is considered to be a toxic endpoint for RBCs. Changes in the nucleated lymphocyte gene expression of certain oxidative stress genes were also observed using real-time polymerase chain reaction (qPCR). The data indicates that RBCs can ultimately be hemolyzed by biological oxidative damage resulting from a combination of oxidative mechanisms. Additionally, the TiO2 nanoparticles demonstrated the ability to adsorb biomolecules to their surface which could be useful for nanomedicine purposes or biosensing applications. The changes in lymphocyte gene expression at different doses indicate that these TiO2 nanoparticles are capable of disrupting nuclear activity. The use of multiple screening methods provided an effective approach to evaluate nano-bio interactions. The use of a biologically-relevant matrix combined with specific detection methods yielded results which accurately predict biological adversity.

Surface modification of the TiO2 nanoparticle surface enables fluorescence monitoring of aggregation and enhanced photoreactivity.

PubMed

Kamps, Kara; Leek, Rachael; Luebke, Lanette; Price, Race; Nelson, Megan; Simonet, Stephanie; Eggert, David Joeseph; Ateşin, Tülay Aygan; Brown, Eric Michael Bratsolias

2013-01-01

Chemically and biologically modified nanoparticles are increasingly considered as viable and multifunctional tools to be used in cancer theranostics. Herein, we demonstrate that coordination of alizarin blue black B (ABBB) to the TiO(2) nanoparticle surface enhances the resulting nanoparticles by (1) creating distinct fluorescence emission spectra that differentiate smaller TiO(2) nanoparticles from larger TiO(2) nanoparticle aggregates (both in vitro and intracellular) and (2) enhancing visible light activation of TiO(2) nanoparticles above previously described methods to induce in vitro and intracellular damage to DNA and other targets. ABBB-TiO(2) nanoparticles are characterized through sedimentation, spectral absorbance, and gel electrophoresis. The possible coordination modes of ABBB to the TiO(2) nanoparticle surface are modeled by computational methods. Fluorescence emission spectroscopy studies indicate that ABBB coordination on TiO(2) nanoparticles enables discernment between nanoparticles and nanoparticle aggregates both in vitro and intracellular through fluorescence confocal microscopy. Visible light activated ABBB-TiO(2) nanoparticles are capable of inflicting increased DNA cleavage through localized production of reactive oxygen species as visualized by plasmid DNA damage detected through gel electrophoresis and atomic force microscopy. Finally, visible light excited ABBB-TiO(2) nanoparticles are capable of inflicting damage upon HeLa (cervical cancer) cells by inducing alterations in DNA structure and membrane associated proteins. The multifunctional abilities of these ABBB-TiO(2) nanoparticles to visualize and monitor aggregation in real time, as well as inflict visible light triggered damage upon cancer targets will enhance the use of TiO(2) nanoparticles in cancer theranostics.

Meso-oblate spheroids of thermal-stabile linker-free aggregates with size-tunable subunits for reversible lithium storage.

PubMed

Deng, Da; Lee, Jim Yang

2014-01-22

The organization of nanoscale materials as building units into extended structures with specific geometry and functional properties is a challenging endeavor. Hereby, an environmentally benign, simple, and scalable method for preparation of stable, linker-free, self-supported, high-order 3D meso-oblate spheroids of CuO nanoparticle aggregates with size-tunable building nanounits for reversible lithium-ion storage is reported. In contrast to traditional spherical nanoparticle aggregation, a unique oblate spheroid morphology is achieved. The formation mechanism of the unusual oblate spheroid of aggregated nanoparticles is proposed. When tested for reversible lithium ion storage, the unique 3D meso-oblate spheroids of CuO nanoparticle aggregate demonstrated highly improved electrochemical performance (around ∼600 mAh/g over 20 cycles), which could be ascribed to the nanoporous aggregated mesostructure with abundant crystalline imperfection. Furthermore, the size of building units can be controlled (12 and 21 nm were tested) to further improve their electrochemical performance.

Systemic toxicity induced by aggregated layered double hydroxide nanoparticles

PubMed Central

Yan, Mina; Yang, Chanzhen; Huang, Binyao; Huang, Zeqian; Huang, Liangfeng; Zhang, Xuefei; Zhao, Chunshun

2017-01-01

Layered double hydroxide (LDH) nanoparticles are emerging as one of the promising nanomaterials for biomedical applications, but their systemic toxicity in vivo has received little attention. In the present study, the effects of inorganic nanoparticle aggregation on their systemic toxicity were examined. Remarkably, aggregation was observed after the mixing of naked LDH nanoparticles with saline or erythrocytes. Significant accumulation of the naked LDH nanoparticles in the lungs of mice was detected 1 h after intravenous administration, and the survival rate of mice was 0% after 6 repeated injections. Furthermore, flocculent precipitates in the alveoli and congestion in the lung interstitium were observed in the dead mice. However, lipid membrane-coated LDH nanoparticles would not form aggregates and could be injected intravenously >6 times without causing death. These findings suggested that repeated injections of LDH were lethal even at low dose (30 mg/kg), and lipid membrane coating can be considered as an approach for reducing this risk. PMID:29042768

Molecular dynamics simulations of aggregation of copper nanoparticles with different heating rates

NASA Astrophysics Data System (ADS)

Li, Qibin; Wang, Meng; Liang, Yunpei; Lin, Liyang; Fu, Tao; Wei, Peitang; Peng, Tiefeng

2017-06-01

Molecular dynamics simulations were employed to investigate the heating rates' effect on aggregation of two copper nanoparticles. The aggregation can be distinguished into three distinct regimes by the contacting and melting of nanoparticles. The nanoparticles contacting at a lower temperature during the sintering with lower heating rate, meanwhile, some temporary stacking fault exists at the contacting neck. The aggregation properties of the system, i.e. neck diameter, shrinkage ratio, potential energy, mean square displacement (MSD) and relative gyration radius, experience drastic changes due to the free surface annihilation. After the nanoparticles coalesced for a stable period, the shrinkage ratio, MSD, relative gyration radius and neck diameter of the system are dramatically changed during the melting process. It is shown that the shrinkage ratio and MSD have relative larger increasing ratio for a lower heating rate. While the evolution of the relative gyration radius and neck diameter is only sensitive to the temperature.

Sugar-Terminated Nanoparticle Chaperones Are 102-105 Times Better Than Molecular Sugars in Inhibiting Protein Aggregation and Reducing Amyloidogenic Cytotoxicity.

PubMed

Pradhan, Nibedita; Shekhar, Shashi; Jana, Nihar R; Jana, Nikhil R

2017-03-29

Sugar-based osmolyte molecules are known to stabilize proteins under stress, but usually they have poor chaperone performance in inhibiting protein aggregation. Here, we show that the nanoparticle form of sugars molecule can enhance their chaperone performance typically by 10 2 -10 5 times, compared to molecular sugar. Sugar-based plate-like nanoparticles of 20-40 nm hydrodynamic size have been synthesized by simple heating of acidic aqueous solution of glucose/sucrose/maltose/trehalose. These nanoparticles have excitation-dependent green/yellow/orange emission and surface chemistry identical to the respective sugar molecule. Fibrillation of lysozyme/insulin/amyloid beta in extracellular space, aggregation of mutant huntingtin protein inside model neuronal cell, and cytotoxic effect of fibrils are investigated in the presence of these sugar nanoparticles. We found that sugar nanoparticles are 10 2 -10 5 times efficient than respective sugar molecules in inhibiting protein fibrillation and preventing cytotoxicity arising of fibrils. We propose that better performance of the nanoparticle form is linked to its stronger binding with fibril structure and enhanced cell uptake. This result suggests that nanoparticle form of osmolyte can be an attractive option in prevention and curing of protein aggregation-derived diseases.

Effects of humic and fulvic acids on aggregation of aqu/nC60 nanoparticles

EPA Science Inventory

Aggregation of fullerene nanoparticles (nC60) is a fundamental process influencing its environmental fate and transport, and toxicity. Using time-resolved dynamic light scattering we systematically investigated aggregation kinetics of nC60 generated from extended mixing in water ...

Effect of bidispersity in grafted chain length on grafted chain conformations and potential of mean force between polymer grafted nanoparticles in a homopolymer matrix.

PubMed

Nair, Nitish; Wentzel, Nathaniel; Jayaraman, Arthi

2011-05-21

In efforts to produce polymeric materials with tailored physical properties, significant interest has grown around the ability to control the spatial organization of nanoparticles in polymer nanocomposites. One way to achieve controlled particle arrangement is by grafting the nanoparticle surface with polymers that are compatible with the matrix, thus manipulating the interfacial interactions between the nanoparticles and the polymer matrix. Previous work has shown that the molecular weight of the grafted polymer, both at high grafting density and low grafting density, plays a key role in dictating the effective inter-particle interactions in a polymer matrix. At high grafting density nanoparticles disperse (aggregate) if the graft molecular weight is higher (lower) than the matrix molecular weight. At low grafting density the longer grafts can better shield the nanoparticle surface from direct particle-particle contacts than the shorter grafts and lead to the dispersion of the grafted particles in the matrix. Despite the importance of graft molecular weight, and evidence of non-trivial effects of polydispersity of chains grafted on flat surfaces, most theoretical work on polymer grafted nanoparticles has only focused on monodisperse grafted chains. In this paper, we focus on how bidispersity in grafted chain lengths affects the grafted chain conformations and inter-particle interactions in an implicit solvent and in a dense homopolymer polymer matrix. We first present the effects of bidispersity on grafted chain conformations in a single polymer grafted particle using purely Monte Carlo (MC) simulations. This is followed by calculations of the potential of mean force (PMF) between two grafted particles in a polymer matrix using a self-consistent Polymer Reference Interaction Site Model theory-Monte Carlo simulation approach. Monte Carlo simulations of a single polymer grafted particle in an implicit solvent show that in the bidisperse polymer grafted particles with an equal number of short and long grafts at low to medium grafting density, the short grafts are in a more coiled up conformation (lower radius of gyration) than their monodisperse counterparts to provide a larger free volume to the longer grafts so they can gain conformational entropy. The longer grafts do not show much difference in conformation from their monodisperse counterparts at low grafting density, but at medium grafting density the longer grafts exhibit less stretched conformations (lower radius of gyration) as compared to their monodisperse counterparts. In the presence of an explicit homopolymer matrix, the longer grafts are more compressed by the matrix homopolymer chains than the short grafts. We observe that the potential of mean force between bidisperse grafted particles has features of the PMF of monodisperse grafted particles with short grafts and monodisperse grafted particles with long grafts. The value of the PMF at contact is governed by the short grafts and values at large inter-particle distances are governed by the longer grafts. Further comparison of the PMF for bidisperse and monodisperse polymer grafted particles in a homopolymer matrix at varying parameters shows that the effects of matrix chain length, matrix packing fraction, grafting density, and particle curvature on the PMF between bidisperse polymer grafted particles are similar to those seen between monodisperse polymer grafted particles. © 2011 American Institute of Physics.

Ionic liquid-induced aggregate formation and their applications.

PubMed

Dutta, Rupam; Kundu, Sangita; Sarkar, Nilmoni

2018-06-01

In the last two decades, researchers have extensively studied highly stable and ordered supramolecular assembly formation using oppositely charged surfactants. Thereafter, surface-active ionic liquids (SAILs), a special class of room temperature ionic liquids (RTILs), replace the surfactants to form various supramolecular aggregates. Therefore, in the last decade, the building blocks of the supramolecular aggregates (micelle, mixed micelle, and vesicular assemblies) have changed from oppositely charged surfactant/surfactant pair to surfactant/SAIL and SAIL/SAIL pair. It is also found that various biomolecules can also interact with SAILs to construct biologically important supramolecular assemblies. The very latest addition to this combination of ion pairs is the dye molecules having a long hydrophobic chain part along with a hydrophilic ionic head group. Thus, dye/surfactant or dye/SAIL pair also produces different assemblies through electrostatic, hydrophobic, and π-π stacking interactions. Vesicles are one of the important self-assemblies which mimic cellular membranes, and thus have biological application as a drug carrier. Moreover, vesicles can act as a suitable microreactor for nanoparticle synthesis.

From helical supramolecular arrays to gel-forming networks: lattice restructuring and aggregation control in peptide-based sulfamides to integrate new functional attributes.

PubMed

Raghava, Saripalli V; Srivastava, Bhartendu K; Ramshad, Kalluruttimmal; Antharjanam, Sudhadevi; Varghese, Babu; Muraleedharan, Kannoth M

2018-03-28

While supramolecular organisation is central to both crystallization and gelation, the latter is more complex considering its dynamic nature and multifactorial dependence. This makes the rational design of gelators an extremely difficult task. In this report, the assembly preference of a group of peptide-based sulfamides was modulated by making them part of an acid-amine two-component system to drive the tendency from crystallization to gelation. Here, the peptide core directed the assembly while the long-chain amines, introduced through salt-bridges, promoted layering and anisotropic development of primary aggregates. This proved to be very successful, leading to gelation of a number of solvents. Apart from this, it was possible to fine-tune their aggregation using an amphiphilic polymer like F-127 as an additive to get honey-comb-like 3D molecular architectures. These gels also proved to be excellent matrices for entrapping silver nanoparticles with superior emissive properties.

Synthesis and applications of novel silver nanoparticle structures

NASA Astrophysics Data System (ADS)

Dukes, Kyle

The field of nanotechnology is rapidly expanding across disciplines as each new development is realized. New exciting technologies are being driven by advances in the application of nanotechnology; including biochemical, optical, and semiconductors research. This thesis will focus on the use of silver nanoparticles as optical labels on cells, methods of forming different small structures of silver nanoparticles, as well as the use of silver nanoparticles in the development of a photovoltaic cell. Silver nanoparticles have been modified with self-assembled monolayers of hydroxyl-terminated long chain thiols and encapsulated with a silica shell. The resulting core-shell nanoparticles were used as optical labels for cell analysis using flow cytometry and microscopy. The excitation of plasmon resonances in nanoparticles results in strong depolarized scattering of visible light permitting detection at the single nanoparticle level. The nanoparticles were modified with neutravidin via epoxide-azide coupling chemistry and biotinylated antibodies targeting cell surface receptors were bound to the nanoparticle surface. The nanoparticle labels exhibited long-term stability under physiological conditions without aggregation or silver ion leaching. Labeled cells exhibited two orders of magnitude enhancement of the scattering intensity compared to unlabeled cells. Dimers of silver nanoparticles have been fabricated by first immobilizing a monolayer of single silver nanoparticles onto poly(4-vinylpyridine) covered glass slides. The monolayer was then exposed to adenine, which has two amines which will bind to silver. The nanoparticle monolayer, now modified with adenine, is exposed to a second suspension of nanoparticles which will bind with the amine modified monolayer. Finally, a thin silica shell is formed about the structure via solgel chemistry to prevent dissolution or aggregation upon sonication/striping. Circular arrays of silver nanoparticels are developed using a template base self assembly. A 1.5 micron silica sphere is bound to poly(4-vinylpyridine) coated glass and used as a template. a mask of silica monoxide is vacuum deposited atop the spheres/glass leaving a ring just below the sphere untouched and able to bind silver nanoparticles. Optical microscopy reveal interesting results under depolarized light conditions, but ultimate structural analysis has proven elusive. Semiconducting p-type cuprous oxide was electrochemically deposited on both silver and indium tin oxide electrodes. Silver nanoparticles were incorporated into the architecture either atop the cuprous oxide or sandwiched between cuprous oxide and n-type material. Increases in photocurrent were observed in both cases and further work must be conducted to optimize a solid state device for photovoltaic applications.

Aggregation of TiO2-graphene nanocomposites in aqueous environment: Influence of environmental factors and UV irradiation.

PubMed

Hua, Zulin; Zhang, Jianan; Bai, Xue; Ye, Zhengfang; Tang, Zhiqiang; Liang, Lu; Liu, Yuqi

2016-01-01

The aggregation kinetics of TiO2-graphene nanocomposites in aqueous solution affected by solution pH, salt types (NaCl, CaCl2) and concentrations of electrolytes, and stability induced by UV irradiation was investigated in this study. The zeta potentials and hydrodynamic diameter of the nanoparticles were used as bases to assess the aggregation behavior, and stability of nanocomposites exposed to UV irradiation was expressed in terms of supernatant concentration. The aggregation of TiO2-graphene nanoparticles in aqueous media followed the colloidal theory. TiO2-graphene nanoparticles were significantly aggregated in the presence of a diavalent cation compared with monovalent cation because the former was more capable of effective charge screening and neutralization. The calculated Hamaker constant of the TiO2-graphene nanocomposites in aqueous solution prepared in the lab was 2.31×10(-20)J. The stability of this composite nanoparticles was between those of pure TiO2 and graphene. A known intensity of UV irradiation was beneficial in the formation of TiO2-graphene nanoparticle aggregates. However, prolonged UV irradiation may stabilize the nanoparticles. These results provided critical information about the colloidal properties of the new TiO2-graphene nanocomposites and were useful in predicting the fate and transport of TiO2-graphene nanocomposites in natural water environments. Copyright © 2015 Elsevier B.V. All rights reserved.

Green synthesis of xanthan conformation-based silver nanoparticles: antibacterial and catalytic application.

PubMed

Xu, Wei; Jin, Weiping; Lin, Liufeng; Zhang, Chunlan; Li, Zhenshun; Li, Yan; Song, Rong; Li, Bin

2014-01-30

Silver nanoparticles (Ag NPs) were green synthetized using xanthan gum (XG) dissolved in water as reducing and capping agent for the first time. The structure, morphology, and size of Ag NPs in XG aqueous solutions were investigated with UV-vis spectroscopy, transmission electron microscopy and Fourier transform infrared. The results indicated Ag NPs were integrated successfully in the XG matrix and the optical properties and morphology of Ag NPs could be regulated by the synthesis condition. The aggregation of the XG-bonded Ag NPs increased with storage, whereas the size barely changed. The assemble behavior was related to the XG conformation transition of denaturation and renaturation. The one spot formed Ag NPs showed favorable antibacterial effect on Escherichia coli and Staphyloccocus aureus and excellent catalytic capability of 4-nitrophenol reduction. This work provided a feasible method to detect the biopolymer space structure transition through the intensity of metal nanoparticles labeled on the chain. Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.

Kinetic control of block copolymer self-assembly into multicompartment and novel geometry nanoparticles

NASA Astrophysics Data System (ADS)

Chen, Yingchao; Wang, Xiaojun; Zhang, Ke; Wooley, Karen; Mays, Jimmy; Percec, Virgil; Pochan, Darrin

2012-02-01

Micelles with the segregation of hydrophobic blocks trapped in the same nanoparticle core have been produced through co-self-assembly of two block copolymers in THF/water dilute solution. The dissolution of two block copolymer sharing the same polyacrylic acid PAA blocks in THF undergoes consequent aggregation and phase separation through either slow water titration or quick water addition that triggers the micellar formation. The combination and comparison of the two water addition kinetic pathways are the keys of forming multicompartment structures at high water content. Importantly, the addition of organic diamine provides for acid-base complexation with the PAA side chains which, in turn, plays the key role of trapping unlike hydrophobic blocks from different block copolymers into one nanoparticle core. The kinetic control of solution assembly can be applied to other molecular systems such as dendrimers as well as other block copolymer molecules. Transmission electron microscopy, cryogenic transmission electron microscopy, light scattering have been applied to characterize the micelle structures.

Influence of gold nanoparticles on platelets functional activity in vitro

NASA Astrophysics Data System (ADS)

Akchurin, Garif G.; Akchurin, George G.; Ivanov, Alexey N.; Kirichuk, Vyacheslav F.; Terentyuk, George S.; Khlebtsov, Boris N.; Khlebtsov, Nikolay G.

2008-02-01

Now in the leading biomedical centers of the world approved new technology of laser photothermal destruction of cancer cells using plasmon gold nanoparticles. Investigations of influence of gold nanoparticles on white rat platelets aggregative activity in vitro have been made. Platelet aggregation was investigated in platelet rich plasma (PRP) with help of laser analyzer 230 LA <>, Russia). Aggregation inductor was ADP solution in terminal concentration 2.5 micromole (<>, Russia). Gold nanoshells soluted in salt solution were used for experiments. Samples of PRP were incubated with 50 or 100 μl gold nanoshells solution in 5 minute, after that we made definition ADP induced platelet aggregation. We found out increase platelet function activity after incubation with nanoparticles solution which shown in maximum ADP-induced aggregation degree increase. Increase platelet function activity during intravenous nanoshells injection can be cause of thrombosis on patients. That's why before clinical application of cancer cell destruction based on laser photothermal used with plasmon gold nanoparticles careful investigations of thrombosis process and detail analyze of physiological blood parameters are very necessary.

Smart polyaniline nanoparticles with thermal and photothermal sensitivity

NASA Astrophysics Data System (ADS)

Bongiovanni Abel, Silvestre; Molina, María A.; Rivarola, Claudia R.; Kogan, Marcelo J.; Barbero, Cesar A.

2014-12-01

Conductive polyaniline nanoparticles (PANI NPs) are synthesized by oxidation of aniline with persulfate in acid media, in the presence of polymeric stabilizers: polyvinilpyrrolidone (PVP), poly(N-isopropylacrylamide) (PNIPAM), and hydroxylpropylcellulose (HPC). It is observed that the size of the nanoparticles obtained depends on the polymeric stabilizer used, suggesting a mechanism where the aggregation of polyaniline molecules is arrested by adsorption of the polymeric stabilizer. Indeed, polymerization in the presence of a mixture of two polymers having different stabilizing capacity (PVP and PNIPAM) allows tuning of the size of the nanoparticles. Stabilization with biocompatible PVP, HPC and PNIPAM allows use of the nanoparticle dispersions in biological applications. The nanoparticles stabilized by thermosensitive polymers (PNIPAM and HPC) aggregate when the temperature exceeds the phase transition (coil to globule) temperature of each stabilizer (Tpt = 32 °C for PNIPAM or Tpt = 42 °C for HPC). This result suggests that an extended coil form of the polymeric stabilizer is necessary to avoid aggregation. The dispersions are reversibly restored when the temperature is lowered below Tpt. In that way, the effect could be used to separate the nanoparticles from soluble contaminants. On the other hand, the PANI NPs stabilized with PVP are unaffected by the temperature change. UV-visible spectroscopy measurements show that the nanoparticle dispersion changes their spectra with the pH of the external solution, suggesting that small molecules can easily penetrate the stabilizer shell. Near infrared radiation is absorbed by PANI NPs causing an increase of their temperature which induces the collapse of the thermosensitive polymer shell and aggregation of the NPs. The effect reveals that it is possible to locally heat the nanoparticles, a phenomenon that can be used to destroy tumor cells in cancer therapy or to dissolve protein aggregates of neurodegenerative diseases (e.g. Alzheimer). Moreover, the long range control of aggregation can be used to modulate the nanoparticle residence inside biological tissues.

Superhydrophilic nanostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Samuel S; Zormpa, Vasileia; Chen, Xiaobo

2015-05-12

An embodiment of a superhydrophilic nanostructure includes nanoparticles. The nanoparticles are formed into porous clusters. The porous clusters are formed into aggregate clusters. An embodiment of an article of manufacture includes the superhydrophilic nanostructure on a substrate. An embodiment of a method of fabricating a superhydrophilic nanostructure includes applying a solution that includes nanoparticles to a substrate. The substrate is heated to form aggregate clusters of porous clusters of the nanoparticles.

Lorentz microscopy sheds light on the role of dipolar interactions in magnetic hyperthermia

NASA Astrophysics Data System (ADS)

Campanini, M.; Ciprian, R.; Bedogni, E.; Mega, A.; Chiesi, V.; Casoli, F.; de Julián Fernández, C.; Rotunno, E.; Rossi, F.; Secchi, A.; Bigi, F.; Salviati, G.; Magén, C.; Grillo, V.; Albertini, F.

2015-04-01

Monodispersed Fe3O4 nanoparticles with comparable size distributions have been synthesized by two different synthesis routes, co-precipitation and thermal decomposition. Thanks to the different steric stabilizations, the described samples can be considered as a model system to investigate the effects of magnetic dipolar interactions on the aggregation states of the nanoparticles. Moreover, the presence of magnetic dipolar interactions can strongly affect the nanoparticle efficiency as a hyperthermic mediator. In this paper, we present a novel way to visualize and map the magnetic dipolar interactions in different kinds of nanoparticle aggregates by the use of Lorentz microscopy, an easy and reliable in-line electron holographic technique. By exploiting Lorentz microscopy, which is complementary to the magnetic measurements, it is possible to correlate the interaction degrees of magnetic nanoparticles with their magnetic behaviors. In particular, we demonstrate that Lorentz microscopy is successful in visualizing the magnetic configurations stabilized by dipolar interactions, thus paving the way to the comprehension of the power loss mechanisms for different nanoparticle aggregates.Monodispersed Fe3O4 nanoparticles with comparable size distributions have been synthesized by two different synthesis routes, co-precipitation and thermal decomposition. Thanks to the different steric stabilizations, the described samples can be considered as a model system to investigate the effects of magnetic dipolar interactions on the aggregation states of the nanoparticles. Moreover, the presence of magnetic dipolar interactions can strongly affect the nanoparticle efficiency as a hyperthermic mediator. In this paper, we present a novel way to visualize and map the magnetic dipolar interactions in different kinds of nanoparticle aggregates by the use of Lorentz microscopy, an easy and reliable in-line electron holographic technique. By exploiting Lorentz microscopy, which is complementary to the magnetic measurements, it is possible to correlate the interaction degrees of magnetic nanoparticles with their magnetic behaviors. In particular, we demonstrate that Lorentz microscopy is successful in visualizing the magnetic configurations stabilized by dipolar interactions, thus paving the way to the comprehension of the power loss mechanisms for different nanoparticle aggregates. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00273g

Adsorption of weak polyelectrolytes on charged nanoparticles. Impact of salt valency, pH, and nanoparticle charge density. Monte Carlo simulations.

PubMed

Carnal, Fabrice; Stoll, Serge

2011-10-27

Complex formation between a weak flexible polyelectrolyte chain and one positively charged nanoparticle in presence of explicit counterions and salt particles is investigated using Monte Carlo simulations. The influence of parameters such as the nanoparticle surface charge density, salt valency, and solution property such as the pH on the chain protonation/deprotonation process and monomer adsorption at the nanoparticle surface are systematically investigated. It is shown that the nanoparticle presence significantly modifies chain acid/base and polyelectrolyte conformational properties. The importance of the attractive electrostatic interactions between the chain and the nanoparticle clearly promotes the chain deprotonation leading, at high pH and nanoparticle charge density, to fully wrapped polyelectrolyte at the nanoparticle surface. When the nanoparticle bare charge is overcompensated by the polyelectrolyte charges, counterions and salt particles condense at the surface of the polyelectrolyte-nanoparticle complex to compensate for the excess of charges providing from the adsorbed polyelectrolyte chain. It is also shown that the complex formation is significantly affected by the salt valency. Indeed, with the presence of trivalent salt cations, competition is observed between the nanoparticle and the trivalent cations. As a result, the amount of adsorbed monomers is less important than in the monovalent and divalent case and chain conformations are different due to the collapse of polyelectrolyte segments around trivalent cations out of the nanoparticle adsorption layer.

Controllable g5p-Protein-Directed Aggregation of ssDNA-Gold Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, S.; Maye, M; Zhang, Y

We assembled single-stranded DNA (ssDNA) conjugated nanoparticles using the phage M13 gene 5 protein (g5p) as the molecular glue to bind two antiparallel noncomplementary ssDNA strands. The entire process was controlled tightly by the concentration of the g5p protein and the presence of double-stranded DNA. The g5p-ssDNA aggregate was disintegrated by hybridization with complementary ssDNA (C-ssDNA) that triggers the dissociation of the complex. Polyhistidine-tagged g5p was bound to nickel nitrilotriacetic acid (Ni2+-NTA) conjugated nanoparticles and subsequently used to coassemble the ssDNA-conjugated nanoparticles into multiparticle-type aggregates. Our approach offers great promise for designing biologically functional, controllable protein/nanoparticle composites.

Liquid crystals from mesogens containing gold nanoparticles

NASA Astrophysics Data System (ADS)

Lewandowski, Wiktor; Gorecka, Ewa

Long-range ordered structures made of nanoparticles are perspective materials for future optical, electronic and sensing technologies. Conspicuous physicochemical features of nanoparticle aggregates originate from distant-dependent collective interactions, therefore lately a lot of attention was put to the development of assembly strategies allowing control over nanoparticle spatial distribution. In this chapter we will focus on the assembly process based on using thermotropic liquid-crystalline molecules as surface nanoparticle ligands. First, we discuss architectural parameters that inuence structure and thermal properties of the aggregates. Then, we show that this approach enables formation of assemblies with metamaterial characteristic, gives access to dynamic materials with light-, magneto- and thermo-responsive behavior and allows formation of aggregates with unique structures, which all make this strategy an attractive object of research.

Interaction of Colloidal Gold Nanoparticles with Model Serum Proteins: The Nanoparticle-Protein 'Corona' from a PhysicoChemical Viewpoint

NASA Astrophysics Data System (ADS)

Dominguez Medina, Sergio

When nanoparticles come in contact with biological fluids they become coated with a mixture of proteins present in the media, forming what is known as the nanoparticle-protein 'corona'. This corona changes the nanoparticles' original surface properties and plays a central role in how these get screened by cellular receptors. In the context of biomedical research, this presents a bottleneck for the transition of nanoparticles from research laboratories to clinical settings. It is therefore fundamental to probe these nanoparticle-protein interactions in order to understand the different physico-chemical mechanisms involved. This thesis is aimed to investigate the exposure of colloidal gold nanoparticles to model serum proteins, particularly serum albumin, the main transporter of molecular compounds in the bloodstream of mammals. A set of experimental tools based on optical microscopy and spectroscopy were developed in order to probe these interactions in situ. First, the intrinsic photoluminescence and elastic scattering of individual gold nanoparticles were investigated in order to understand its physical origin. These optical signals were then used to measure the size of the nanoparticles while in Brownian diffusion using fluctuation correlation spectroscopy. This spectroscopic tool was then applied to detect the binding of serum albumin onto the nanoparticle surface, increasing its hydrodynamic size. By performing a binding isotherm as a function of protein concentration, it was determined that serum albumin follows an anti-cooperative binding mechanism on negatively charged gold nanoparticles. This protein monolayer substantially enhanced the stability of the colloid, preventing their aggregation in saline solutions with ionic strength higher than biological media. Cationic gold nanoparticles in contrast, aggregated when serum albumin was present at a low protein-to-nanoparticle ratio, but prevented aggregation if exposed in excess. Single-molecule fluorescence microscopy revealed that under low protein-to-nanoparticle binding ratios, serum albumin irreversibly unfolds upon adsorption and spreads across the available nanoparticle surface area. Unfolded proteins then interact with one another, triggering nanoparticle aggregation. Fibrinogen and globulin also triggered aggregation when exposed to cationic nanoparticles. In an effort to relate these physico-chemical observations to relevant biological parameters, the uptake of protein coated gold nanoparticles by a model cancer cell line was investigated under different incubation conditions. Those nanoparticles pre-incubated with bovine serum albumin before fetal bovine serum were found to be uptaken three times more than those only incubated in serum.

Fabrication of ZnS nanoparticle chains on a protein template

PubMed Central

Hulleman, J.; Kim, S. M.; Tumkur, T.; Rochet, J.-C.; Stach, E.; Stanciu, L.

2011-01-01

In the present study, we have exploited the properties of a fibrillar protein for the template synthesis of zinc sulfide (ZnS) nanoparticle chains. The diameter of the ZnS nanoparticle chains was tuned in range of ~30 to ~165 nm by varying the process variables. The nanoparticle chains were characterized by field emission scanning electron microscopy, UV–Visible spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy. The effect of incubation temperature on the morphology of the nanoparticle chains was also studied. PMID:21804765

Engineered silica nanoparticles as additives in lubricant oils

PubMed Central

López, Teresa Díaz-Faes; González, Alfonso Fernández; Del Reguero, Ángel; Matos, María; Díaz-García, Marta E; Badía-Laíño, Rosana

2015-01-01

Silica nanoparticles (SiO2 NPs) synthesized by the sol–gel approach were engineered for size and surface properties by grafting hydrophobic chains to prevent their aggregation and facilitate their contact with the phase boundary, thus improving their dispersibility in lubricant base oils. The surface modification was performed by covalent binding of long chain alkyl functionalities using lauric acid and decanoyl chloride to the SiO2 NP surface. The hybrid SiO2 NPs were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, simultaneous differential thermal analysis, nuclear magnetic resonance and dynamic light scattering, while their dispersion in two base oils was studied by static multiple light scattering at low (0.01% w/v) and high (0.50%w/v) concentrations. The nature of the functional layer and the functionalization degree seemed to be directly involved in the stability of the suspensions. The potential use of the functional SiO2 NPs as lubricant additives in base oils, specially designed for being used in hydraulic circuits, has been outlined by analyzing the tribological properties of the dispersions. The dendritic structure of the external layer played a key role in the tribological characteristics of the material by reducing the friction coefficient and wear. These nanoparticles reduce drastically the waste of energy in friction processes and are more environmentally friendly than other additives. PMID:27877840

Adsorption of bovine serum albumin on silicon dioxide nanoparticles: Impact of pH on nanoparticle-protein interactions.

PubMed

Givens, Brittany E; Diklich, Nina D; Fiegel, Jennifer; Grassian, Vicki H

2017-05-03

Bovine serum albumin (BSA) adsorbed on amorphous silicon dioxide (SiO 2 ) nanoparticles was studied as a function of pH across the range of 2 to 8. Aggregation, surface charge, surface coverage, and protein structure were investigated over this entire pH range. SiO 2 nanoparticle aggregation is found to depend upon pH and differs in the presence of adsorbed BSA. For SiO 2 nanoparticles truncated with hydroxyl groups, the largest aggregates were observed at pH 3, close to the isoelectric point of SiO 2 nanoparticles, whereas for SiO 2 nanoparticles with adsorbed BSA, the aggregate size was the greatest at pH 3.7, close to the isoelectric point of the BSA-SiO 2 complex. Surface coverage of BSA was also the greatest at the isoelectric point of the BSA-SiO 2 complex with a value of ca. 3 ±   1 × 10 11 molecules cm -2 . Furthermore, the secondary protein structure was modified when compared to the solution phase at all pH values, but the most significant differences were seen at pH 7.4 and below. It is concluded that protein-nanoparticle interactions vary with solution pH, which may have implications for nanoparticles in different biological fluids (e.g., blood, stomach, and lungs).

Protein corona between nanoparticles and bacterial proteins in activated sludge: Characterization and effect on nanoparticle aggregation.

PubMed

Zhang, Peng; Xu, Xiao-Yan; Chen, You-Peng; Xiao, Meng-Qian; Feng, Bo; Tian, Kai-Xun; Chen, Yue-Hui; Dai, You-Zhi

2018-02-01

In this work, the protein coronas of activated sludge proteins on TiO 2 nanoparticles (TNPs) and ZnO nanoparticles (ZNPs) were characterized. The proteins with high affinity to TNPs and ZNPs were identified by shotgun proteomics, and their effects of on the distributions of TNPs and ZNPs in activated sludge were concluded. In addition, the effects of protein coronas on the aggregations of TNPs and ZNPs were evaluated. Thirty and nine proteins with high affinities to TNPs and ZNPs were identified, respectively. The proteomics and adsorption isotherms demonstrated that activated sludge had a higher affinity to TNPs than to ZNPs. The aggregation percentages of ZNPs at 35, 53, and 106 mg/L of proteins were 13%, 14%, and 18%, respectively, whereas those of TNPs were 21%, 30%, 41%, respectively. The proteins contributed to ZNPs aggregation by dissolved Zn ion-bridging, whereas the increasing protein concentrations enhanced the TNPs aggregation through macromolecule bridging flocculation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Adsorption of Small Cationic Nanoparticles onto Large Anionic Particles from Aqueous Solution: A Model System for Understanding Pigment Dispersion and the Problem of Effective Particle Density.

PubMed

North, S M; Jones, E R; Smith, G N; Mykhaylyk, O O; Annable, T; Armes, S P

2017-02-07

The present study focuses on the use of copolymer nanoparticles as a dispersant for a model pigment (silica). Reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization was used to synthesize sterically stabilized diblock copolymer nanoparticles. The steric stabilizer block was poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and the core-forming block was poly(benzyl methacrylate) (PBzMA). The mean degrees of polymerization for the PDMA and PBzMA blocks were 71 and 100, respectively. Transmission electron microscopy (TEM) studies confirmed a near-monodisperse spherical morphology, while dynamic light scattering (DLS) studies indicated an intensity-average diameter of 30 nm. Small-angle X-ray scattering (SAXS) reported a volume-average diameter of 29 ± 0.5 nm and a mean aggregation number of 154. Aqueous electrophoresis measurements confirmed that these PDMA 71 -PBzMA 100 nanoparticles acquired cationic character when transferred from ethanol to water as a result of protonation of the weakly basic PDMA chains. Electrostatic adsorption of these nanoparticles from aqueous solution onto 470 nm silica particles led to either flocculation at submonolayer coverage or steric stabilization at or above monolayer coverage, as judged by DLS. This technique indicated that saturation coverage was achieved on addition of approximately 465 copolymer nanoparticles per silica particle, which corresponds to a fractional surface coverage of around 0.42. These adsorption data were corroborated using thermogravimetry, UV spectroscopy and X-ray photoelectron spectroscopy. TEM studies indicated that the cationic nanoparticles remained intact on the silica surface after electrostatic adsorption, while aqueous electrophoresis confirmed that surface charge reversal occurred below pH 7. The relatively thick layer of adsorbed nanoparticles led to a significant reduction in the effective particle density of the silica particles from 1.99 g cm -3 to approximately 1.74 g cm -3 , as judged by disk centrifuge photosedimentometry (DCP). Combining the DCP and SAXS data suggests that essentially no deformation of the PBzMA cores occurs during nanoparticle adsorption onto the silica particles.

Modeling coupled nanoparticle aggregation and transport in porous media: A Lagrangian approach

NASA Astrophysics Data System (ADS)

Taghavy, Amir; Pennell, Kurt D.; Abriola, Linda M.

2015-01-01

Changes in nanoparticle size and shape due to particle-particle interactions (i.e., aggregation or agglomeration) may significantly alter particle mobility and retention in porous media. To date, however, few modeling studies have considered the coupling of transport and particle aggregation processes. The majority of particle transport models employ an Eulerian modeling framework and are, consequently, limited in the types of collisions and aggregate sizes that can be considered. In this work, a more general Lagrangian modeling framework is developed and implemented to explore coupled nanoparticle aggregation and transport processes. The model was verified through comparison of model simulations to published results of an experimental and Eulerian modeling study (Raychoudhury et al., 2012) of carboxymethyl cellulose (CMC)-modified nano-sized zero-valent iron particle (nZVI) transport and retention in water-saturated sand columns. A model sensitivity analysis reveals the influence of influent particle concentration (ca. 70 to 700 mg/L), primary particle size (10-100 nm) and pore water velocity (ca. 1-6 m/day) on particle-particle, and, consequently, particle-collector interactions. Model simulations demonstrate that, when environmental conditions promote particle-particle interactions, neglecting aggregation effects can lead to under- or over-estimation of nanoparticle mobility. Results also suggest that the extent to which higher order particle-particle collisions influence aggregation kinetics will increase with the fraction of primary particles. This work demonstrates the potential importance of time-dependent aggregation processes on nanoparticle mobility and provides a numerical model capable of capturing/describing these interactions in water-saturated porous media.

Modeling coupled nanoparticle aggregation and transport in porous media: a Lagrangian approach.

PubMed

Taghavy, Amir; Pennell, Kurt D; Abriola, Linda M

2015-01-01

Changes in nanoparticle size and shape due to particle-particle interactions (i.e., aggregation or agglomeration) may significantly alter particle mobility and retention in porous media. To date, however, few modeling studies have considered the coupling of transport and particle aggregation processes. The majority of particle transport models employ an Eulerian modeling framework and are, consequently, limited in the types of collisions and aggregate sizes that can be considered. In this work, a more general Lagrangian modeling framework is developed and implemented to explore coupled nanoparticle aggregation and transport processes. The model was verified through comparison of model simulations to published results of an experimental and Eulerian modeling study (Raychoudhury et al., 2012) of carboxymethyl cellulose (CMC)-modified nano-sized zero-valent iron particle (nZVI) transport and retention in water-saturated sand columns. A model sensitivity analysis reveals the influence of influent particle concentration (ca. 70 to 700 mg/L), primary particle size (10-100 nm) and pore water velocity (ca. 1-6 m/day) on particle-particle, and, consequently, particle-collector interactions. Model simulations demonstrate that, when environmental conditions promote particle-particle interactions, neglecting aggregation effects can lead to under- or over-estimation of nanoparticle mobility. Results also suggest that the extent to which higher order particle-particle collisions influence aggregation kinetics will increase with the fraction of primary particles. This work demonstrates the potential importance of time-dependent aggregation processes on nanoparticle mobility and provides a numerical model capable of capturing/describing these interactions in water-saturated porous media. Copyright © 2014 Elsevier B.V. All rights reserved.

Biocompatible Polysiloxane-Containing Diblock Copolymer PEO-b-PγMPS for Coating Magnetic Nanoparticles

PubMed Central

Chen, Hongwei; Wu, Xinying; Duan, Hongwei; Wang, Y. Andrew; Wang, Liya; Zhang, Minming; Mao, Hui

2009-01-01

We report a biocompatible polysiloxane containing amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly(γ-methacryloxypropyltrimethoxysilane) (PEO-b-PγMPS), for coating and stabilizing nanoparticles for biomedical applications. Such amphiphilic diblock copolymer which comprises both a hydrophobic segment with “surface anchoring moiety” (silane group) and a hydrophilic segment with PEO (Mn=5000 g/mol) was obtained by the reversible addition fragmentation chain transfer (RAFT) polymerization using the PEO macromolecular chain transfer agent. When used for coating paramagnetic iron oxide nanoparticles (IONPs), copolymers were mixed with hydrophobic oleic acid coated core size uniformed IONPs (D=13 nm) in co-solvent tetrahydrofuran. After being aged over a period of time, resulting monodispersed IONPs can be transferred into aqueous medium. With proper PγMPS block length (Mn=10,000 g/mol), polysiloxane containing diblock copolymers formed a thin layer of coating (~3 nm) around monocrystalline nanoparticles as measured by transmission electron microscopy (TEM). Magnetic resonance imaging (MRI) experiments showed excellent T2 weighted contrast effect from coated IONPs with a transverse relaxivity r2=98.6 mM−1s−1 (at 1.5 Tesla). Such thin coating layer has little effect on the relaxivity when compared to that of IONPs coated with conventional amphiphilic copolymer. Polysiloxane containing diblock copolymer coated IONPs are stable without aggregation or binding to proteins in serum when incubated for 24 h in culture medium containing 10% serum. Furthermore, much lower level of intracellular uptake by macrophage cells was observed with polysiloxane containing diblock copolymers coated IONPs, suggesting the reduction of non-specific cell uptakes and antibiofouling effect. PMID:20161520

Development of screening assays for nanoparticle toxicity assessment in human blood: preliminary studies with charged Au nanoparticles.

PubMed

Love, Sara A; Thompson, John W; Haynes, Christy L

2012-09-01

As nanoparticles have found increased use in both consumer and medical applications, corresponding increases in possible exposure to humans necessitate studies examining the impacts of these nanomaterials in biological systems. This article examines the effects of approximately 30-nm-diameter gold nanoparticles, with positively and negatively charged surface coatings in human blood. Here, we study the exposure effects, with up to 72 h of exposure to 5, 15, 25 and 50 µg/ml nanoparticles on hemolysis, reactive oxygen species (ROS) generation and platelet aggregation in subsets of cells from human blood. Assessing viability with hemolysis, results show significant changes in a concentration-dependent fashion. Rates of ROS generation were investigated using the dichlorofluorscein diacetate-based assay as ROS generation is a commonly suspected mechanism of nanoparticle toxicity; herein, ROS was not a significant factor. Optical monitoring of platelet aggregation revealed that none of the examined nanoparticles induced aggregation upon short-term exposure.

Lipase immobilization for catalytic applications obtained using fumed silica deposited with MAPLE technique

NASA Astrophysics Data System (ADS)

Bloisi, Francesco; Califano, Valeria; Perretta, Giuseppe; Nasti, Libera; Aronne, Antonio; Di Girolamo, Rocco; Auriemma, Finizia; De Rosa, Claudio; Vicari, Luciano R. M.

2016-06-01

Lipases are enzymes used for catalyzing reactions of acylglycerides in biodiesel production from lipids, where enzyme immobilization on a substrate is required. Silica nanoparticles in different morphologies and configurations are currently used in conjunction with biological molecules for drug delivery and catalysis applications, but up to date their use for triglycerides has been limited by the large size of long-chain lipid molecules. Matrix assisted pulsed laser evaporation (MAPLE), a laser deposition technique using a frozen solution/suspension as a target, is widely used for deposition of biomaterials and other delicate molecules. We have carried out a MAPLE deposition starting from a frozen mixture containing fumed silica and lipase in water. Deposition parameters were chosen in order to increase surface roughness and to promote the formation of complex structures. Both the target (a frozen thickened mixture of nanoparticles/catalyst in water) and the deposition configuration (a small target to substrate distance) are unusual and have been adopted in order to increase surface contact of catalyst and to facilitate access to long-chain molecules. The resulting innovative film morphology (fumed silica/lipase cluster level aggregation) and the lipase functionality (for catalytic biodiesel production) have been studied by FESEM, FTIR and transesterification tests.

Stable and Size-Tunable Aggregation-Induced Emission Nanoparticles Encapsulated with Nanographene Oxide and Applications in Three-Photon Fluorescence Bioimaging.

PubMed

Zhu, Zhenfeng; Qian, Jun; Zhao, Xinyuan; Qin, Wei; Hu, Rongrong; Zhang, Hequn; Li, Dongyu; Xu, Zhengping; Tang, Ben Zhong; He, Sailing

2016-01-26

Organic fluorescent dyes with high quantum yield are widely applied in bioimaging and biosensing. However, most of them suffer from a severe effect called aggregation-caused quenching (ACQ), which means that their fluorescence is quenched at high molecular concentrations or in the aggregation state. Aggregation-induced emission (AIE) is a diametrically opposite phenomenon to ACQ, and luminogens with this feature can effectively solve this problem. Graphene oxide has been utilized as a quencher for many fluorescent dyes, based on which biosensing can be achieved. However, using graphene oxide as a surface modification agent of fluorescent nanoparticles is seldom reported. In this article, we used nanographene oxide (NGO) to encapsulate fluorescent nanoparticles, which consisted of a type of AIE dye named TPE-TPA-FN (TTF). NGO significantly improved the stability of nanoparticles in aqueous dispersion. In addition, this method could control the size of nanoparticles' flexibly as well as increase their emission efficiency. We then used the NGO-modified TTF nanoparticles to achieve three-photon fluorescence bioimaging. The architecture of ear blood vessels in mice and the distribution of nanoparticles in zebrafish could be observed clearly. Furthermore, we extended this method to other AIE luminogens and showed it was widely feasible.

Small angle X-ray scattering analysis of the effect of cold compaction of Al/MoO3 thermite composites.

PubMed

Hammons, Joshua A; Wang, Wei; Ilavsky, Jan; Pantoya, Michelle L; Weeks, Brandon L; Vaughn, Mark W

2008-01-07

Nanothermites composed of aluminum and molybdenum trioxide (MoO(3)) have a high energy density and are attractive energetic materials. To enhance the surface contact between the spherical Al nanoparticles and the sheet-like MoO(3) particles, the mixture can be cold-pressed into a pelleted composite. However, it was found that the burn rate of the pellets decreased as the density of the pellets increased, contrary to expectation. Ultra-small angle X-ray scattering (USAXS) data and scanning electron microscopy (SEM) were used to elucidate the internal structure of the Al nanoparticles, and nanoparticle aggregate in the composite. Results from both SEM imaging and USAXS analysis indicate that as the density of the pellet increased, a fraction of the Al nanoparticles are compressed into sintered aggregates. The sintered Al nanoparticles lost contrast after forming the larger aggregates and no longer scattered X-rays as individual particles. The sintered aggregates hinder the burn rate, since the Al nanoparticles that make them up can no longer diffuse freely as individual particles during combustion. Results suggest a qualitative relationship for the probability that nanoparticles will sinter, based on the particle sizes and the initial structure of their respective agglomerates, as characterized by the mass fractal dimension.

Micelle-induced depletion interaction and resultant structure in charged colloidal nanoparticle system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ray, D.; Aswal, V. K., E-mail: vkaswal@barc.gov.in; Kohlbrecher, J.

2015-04-28

The evolution of the interaction and the resultant structure in the mixed system of anionic silica nanoparticles (Ludox LS30) and non-ionic surfactant decaethylene glycol monododecylether (C12E10), undergoing phase separation, have been studied using small-angle neutron scattering and dynamic light scattering. The measurements have been carried out for a fixed concentration of nanoparticle (1 wt. %) with varying concentration of surfactant (0 to 1 wt. %), in the absence and presence of an electrolyte. It is found that the micelles of non-ionic surfactant adsorb on the nanoparticle in the absence of electrolyte (form stable system), whereas these micelles become non-adsorbing in the presence of electrolytemore » (show phase separation). The phase separation arises because of C12E10 micelles, causing depletion interaction between nanoparticles and leading to their aggregation. The interaction is modeled by double Yukawa potential accounting for attractive depletion as well as repulsive electrostatic forces. Both the interactions (attraction and repulsion) are found to be of long-range. The nanoparticle aggregation (phase separation) is governed by the increase in the magnitude and the range of the depletion attraction with the increase in the surfactant concentration. The nanoparticle aggregates formed are quite large in size (order of micron) and are characterized by the surface fractal having simple cubic packing of nanoparticles within the aggregates.« less

Characterizing the Role of Nanoparticle Design on Tumor Transport and Stability in the Extracellular Environment

NASA Astrophysics Data System (ADS)

Albanese, Alexandre

Nanotechnology has emerged as an exciting strategy for the delivery of diagnostic and therapeutic agents into established tumors. Advancements in nanomaterial synthesis have generated an extensive number of nanoparticle designs made from different materials. Unfortunately, it remains impossible to predict a design's effectiveness for in vivo tumor accumulation. Little is known about how a nanoparticle's morphology and surface chemistry affect its interactions with cells and proteins inside the tumor tissue. This thesis focuses on the development of in vitro experimental tools to evaluate how nanoparticle design affects transport in a three-dimensional tumor tissue and stability in the tumor microenvironment. Nanoparticle transport was evaluated using a novel 'tumor-on-a-chip' system where multicellular tumor spheroids were immobilized in a microfluidic channel. This setup created a three-dimensional tumor environment displaying physiological cell density, extracellular matrix organization, and interstitial flow rates. The tumor-on-a-chip demonstrated that accumulation of nanoparticles was limited to diameters below 110 nm and was improved by receptor targeting. Nanoparticle stability in the tumor microenvironment was evaluated using media isolated from different tumor cell lines. Nanoparticle diameter and surface chemistry were important determinants of stability in cancer cell-conditioned media. Small nanoparticles with unstable surface chemistries adsorbed cellular proteins on their surface and were prone to aggregation. Nanoparticle aggregation altered cellular interactions leading to changes in cell uptake. Using a novel technique to generate different aggregate sizes possessing a uniform surface composition, it was determined that aggregation can change receptor affinity, cell internalization mechanisms and sub-cellular sequestration patterns. Data from this thesis characterize the behavior of nanoparticles within modeled tumor environments and provide some preliminary design guidelines for maximizing nanoparticle tumor accumulation. This work highlights the importance of characterizing nano-bio interactions for engineering successful nanomaterial-based delivery systems.

Real-time measurement of size-resolved elemental composition ratio for flame synthesized composite nanoparticle aggregates using a tandem SMPS-ICP-OES

PubMed Central

Reed, Nathan; Fang, Jiaxi; Chavalmane, Sanmathi; Biswas, Pratim

2017-01-01

Composite nanoparticles find application in catalysis, drug delivery, and energy storage and require increasingly fine control of their physical properties and composition. While composite nanoparticles have been widely synthesized and characterized, little work has systematically correlated the initial concentration of precursors and the final composition of flame synthesized composite nanoparticles. This relationship is explored in a diffusion flame aerosol reactor by coupling a scanning mobility particle sizer (SMPS) with an inductively coupled plasma optical emission spectrometer (ICP-OES). A framework for studying the relationship between the initial precursor concentrations of different elements and the final nanoparticle composition is explored. The size-resolved elemental composition was measured by directly injecting size-selected fractions of aggregated magnetite and silicon dioxide composite nanoparticles into the ICP-OES plasma. This work showed a correlation between precursor molar ratio and the measured elemental ratio in the mobility size range of 50 to 140 nm. Building on previous work studying size resolved elemental composition of engineered nanoparticles, the analysis is extended to flame synthesized composite nanoparticle aggregates in this work. PMID:28435179

Real-time measurement of size-resolved elemental composition ratio for flame synthesized composite nanoparticle aggregates using a tandem SMPS-ICP-OES.

PubMed

Reed, Nathan; Fang, Jiaxi; Chavalmane, Sanmathi; Biswas, Pratim

2017-01-01

Composite nanoparticles find application in catalysis, drug delivery, and energy storage and require increasingly fine control of their physical properties and composition. While composite nanoparticles have been widely synthesized and characterized, little work has systematically correlated the initial concentration of precursors and the final composition of flame synthesized composite nanoparticles. This relationship is explored in a diffusion flame aerosol reactor by coupling a scanning mobility particle sizer (SMPS) with an inductively coupled plasma optical emission spectrometer (ICP-OES). A framework for studying the relationship between the initial precursor concentrations of different elements and the final nanoparticle composition is explored. The size-resolved elemental composition was measured by directly injecting size-selected fractions of aggregated magnetite and silicon dioxide composite nanoparticles into the ICP-OES plasma. This work showed a correlation between precursor molar ratio and the measured elemental ratio in the mobility size range of 50 to 140 nm. Building on previous work studying size resolved elemental composition of engineered nanoparticles, the analysis is extended to flame synthesized composite nanoparticle aggregates in this work.

In situ SAXS study on size changes of platinum nanoparticles with temperature

NASA Astrophysics Data System (ADS)

Wang, W.; Chen, X.; Cai, Q.; Mo, G.; Jiang, L. S.; Zhang, K.; Chen, Z. J.; Wu, Z. H.; Pan, W.

2008-09-01

Poly(vinylpyrrolidone) (PVP)-coated platinum (Pt) nanoparticles were prepared in methanol-water reduction method. In situ small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) techniques were used to probe the size change of particles and crystallites with temperature. Tangent-by-tangent (TBT) method of SAXS data analysis was improved and used to get the particle size distribution (PSD) from SAXS intensity. Scherrer’s equation was used to derive the crystallite size from XRD pattern. Combining SAXS and XRD results, a step-like characteristic of the Pt nanoparticle growth has been found. Three stages (diffusion, aggregation, and agglomeration) can be used to describe the growth of the Pt nanoparticles and nanocrystallites. Aggregation was found to be the main growth mode of the Pt nanoparticles during heating. The maximum growth rates of Pt nanoparticles and Pt nanocrystallites, as well as the maximum aggregation degree of Pt nanocrystallites were found, respectively, at 250 °C, 350 °C and 300 °C. These results are helpful to understanding the growth mode of nanoparticles, as well as controlling the nanoparticle size.

Room Temperature Radiolytic Synthesized Cu@CuAlO2-Al2O3 Nanoparticles

PubMed Central

Abedini, Alam; Saion, Elias; Larki, Farhad; Zakaria, Azmi; Noroozi, Monir; Soltani, Nayereh

2012-01-01

Colloidal Cu@CuAlO2-Al2O3 bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a 60Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO2-Al2O3 nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO2-Al2O3 nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation. PMID:23109893

Room temperature radiolytic synthesized Cu@CuAlO(2)-Al(2)O(3) nanoparticles.

PubMed

Abedini, Alam; Saion, Elias; Larki, Farhad; Zakaria, Azmi; Noroozi, Monir; Soltani, Nayereh

2012-01-01

Colloidal Cu@CuAlO(2)-Al(2)O(3) bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a (60)Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO(2)-Al(2)O(3) nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO(2)-Al(2)O(3) nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation.

Physicochemical interaction mechanism between nanoparticles and tetrasaccharides (stachyose) during freeze-drying.

PubMed

Kamiya, Seitaro; Nakashima, Kenichiro

2017-12-01

Nanoparticle suspensions are thermodynamically unstable and subject to aggregation. Freeze-drying on addition of saccharides is a useful method for preventing aggregation. In the present study, tetrasaccharides (stachyose) was employed as an additive. In addition, we hypothesize the interactive mechanism between stachyose and the nanoparticles during freeze-drying for the first time. The mean particle size of the rehydrated freeze-dried stachyose-containing nanoparticles (104.7 nm) was similar to the initial particle size before freeze-drying (76.8 nm), indicating that the particle size had been maintained. The mean particle size of the rehydrated normal-dried stachyose-containing nanoparticles was 222.2 nm. The powder X-ray diffraction of the freeze-dried stachyose-containing nanoparticles revealed a halo pattern. The powder X-ray diffraction of the normally dried stachyose-containing nanoparticles produced mainly a halo pattern and a partial peak. These results suggest an interaction between the nanoparticles and stachyose, and that this relationship depends on whether the mixture is freeze-dried or dried normally. In the case of normal drying, although most molecules cannot move rapidly thereby settling irregularly, some stachyose molecules can arrange regularly leading to some degree of crystallization and potentially some aggregation. In contrast, during freeze-drying, the moisture sublimed, while the stachyose molecules and nanoparticles were immobilized in the ice. After sublimation, stachyose remained in the space occupied by water and played the role of a buffer material, thus preventing aggregation.

A predictive model of iron oxide nanoparticles flocculation tuning Z-potential in aqueous environment for biological application

NASA Astrophysics Data System (ADS)

Baldassarre, Francesca; Cacciola, Matteo; Ciccarella, Giuseppe

2015-09-01

Iron oxide nanoparticles are the most used magnetic nanoparticles in biomedical and biotechnological field because of their nontoxicity respect to the other metals. The investigation of iron oxide nanoparticles behaviour in aqueous environment is important for the biological applications in terms of polydispersity, mobility, cellular uptake and response to the external magnetic field. Iron oxide nanoparticles tend to agglomerate in aqueous solutions; thus, the stabilisation and aggregation could be modified tuning the colloids physical proprieties. Surfactants or polymers are often used to avoid agglomeration and increase nanoparticles stability. We have modelled and synthesised iron oxide nanoparticles through a co-precipitation method, in order to study the influence of surfactants and coatings on the aggregation state. Thus, we compared experimental results to simulation model data. The change of Z-potential and the clusters size were determined by Dynamic Light Scattering. We developed a suitable numerical model to predict the flocculation. The effects of Volume Mean Diameter and fractal dimension were explored in the model. We obtained the trend of these parameters tuning the Z-potential. These curves matched with the experimental results and confirmed the goodness of the model. Subsequently, we exploited the model to study the influence of nanoparticles aggregation and stability by Z-potential and external magnetic field. The highest Z-potential is reached up with a small external magnetic influence, a small aggregation and then a high suspension stability. Thus, we obtained a predictive model of Iron oxide nanoparticles flocculation that will be exploited for the nanoparticles engineering and experimental setup of bioassays.

Gold Nanoparticles-Based Barcode Analysis for Detection of Norepinephrine.

PubMed

An, Jeung Hee; Lee, Kwon-Jai; Choi, Jeong-Woo

2016-02-01

Nanotechnology-based bio-barcode amplification analysis offers an innovative approach for detecting neurotransmitters. We evaluated the efficacy of this method for detecting norepinephrine in normal and oxidative-stress damaged dopaminergic cells. Our approach use a combination of DNA barcodes and bead-based immunoassays for detecting neurotransmitters with surface-enhanced Raman spectroscopy (SERS), and provides polymerase chain reaction (PCR)-like sensitivity. This method relies on magnetic Dynabeads containing antibodies and nanoparticles that are loaded both with DNA barcords and with antibodies that can sandwich the target protein captured by the Dynabead-bound antibodies. The aggregate sandwich structures are magnetically separated from the solution and treated to remove the conjugated barcode DNA. The DNA barcodes are then identified by SERS and PCR analysis. The concentration of norepinephrine in dopaminergic cells can be readily detected using the bio-barcode assay, which is a rapid, high-throughput screening tool for detecting neurotransmitters.

Induced nanoparticle aggregation for short nucleic acid quantification by depletion isotachophoresis.

PubMed

Marczak, Steven; Senapati, Satyajyoti; Slouka, Zdenek; Chang, Hsueh-Chia

2016-12-15

A rapid (<20min) gel-membrane biochip platform for the detection and quantification of short nucleic acids is presented based on a sandwich assay with probe-functionalized gold nanoparticles and their separation into concentrated bands by depletion-generated gel isotachophoresis. The platform sequentially exploits the enrichment and depletion phenomena of an ion-selective cation-exchange membrane created under an applied electric field. Enrichment is used to concentrate the nanoparticles and targets at a localized position at the gel-membrane interface for rapid hybridization. The depletion generates an isotachophoretic zone without the need for different conductivity buffers, and is used to separate linked nanoparticles from isolated ones in the gel medium and then by field-enhanced aggregation of only the linked particles at the depletion front. The selective field-induced aggregation of the linked nanoparticles during the subsequent depletion step produces two lateral-flow like bands within 1cm for easy visualization and quantification as the aggregates have negligible electrophoretic mobility in the gel and the isolated nanoparticles are isotachophoretically packed against the migrating depletion front. The detection limit for 69-base single-stranded DNA targets is 10 pM (about 10 million copies for our sample volume) with high selectivity against nontargets and a three decade linear range for quantification. The selectivity and signal intensity are maintained in heterogeneous mixtures where the nontargets outnumber the targets 10,000 to 1. The selective field-induced aggregation of DNA-linked nanoparticles at the ion depletion front is attributed to their trailing position at the isotachophoretic front with a large field gradient. Copyright © 2016 Elsevier B.V. All rights reserved.

Monitoring of conditions inside gas aggregation cluster source during production of Ti/TiOx nanoparticles

NASA Astrophysics Data System (ADS)

Kousal, J.; Kolpaková, A.; Shelemin, A.; Kudrna, P.; Tichý, M.; Kylián, O.; Hanuš, J.; Choukourov, A.; Biederman, H.

2017-10-01

Gas aggregation sources are nowadays rather widely used in the research community for producing nanoparticles. However, the direct diagnostics of conditions inside the source are relatively scarce. In this work, we focused on monitoring the plasma parameters and the composition of the gas during the production of the TiOx nanoparticles. We studied the role of oxygen in the aggregation process and the influence of the presence of the particles on the plasma. The construction of the source allowed us to make a 2D map of the plasma parameters inside the source.

pH-Responsive Mercaptoundecanoic Acid Functionalized Gold Nanoparticles and Applications in Catalysis

PubMed Central

Ansar, Siyam M.; Chakraborty, Saptarshi

2018-01-01

Mercaptoundecanoic acid (MUA) functionalized gold nanoparticles (AuNP-MUA) were synthesized and demonstrated to possess pH-triggered aggregation and re-dispersion, as well as the capability of phase transfer between aqueous and organic phases in response to changes in pH. The pH of aggregation for AuNP-MUA is consistent with the pKa of MUA (pH ~4) in solution, while AuNP-MUA phase transition between aqueous and organic phases occurs at pH ~9. The ion pair formation between the amine group in octadecylamine (ODA), the carboxylate group in MUA, and the hydrophobic alkyl chain of ODA facilitates the phase transfer of AuNP-MUA into an organic medium. The AuNP-MUA were investigated as a reusable catalyst in the catalytic reduction of 4-nitrophenol by borohydride—a model reaction for AuNPs. It was determined that 100% MUA surface coverage completely inhibits the catalytic activity of AuNPs. Decreasing the surface coverage was shown to increase catalytic activity, but this decrease also leads to decreased colloidal stability, recoverability, and reusability in subsequent reactions. At 60% MUA surface coverage, colloidal stability and catalytic activity were achieved, but the surface coverage was insufficient to enable redispersion following pH-induced recovery. A balance between AuNP colloidal stability, recoverability, and catalytic activity with reusability was achieved at 90% MUA surface coverage. The AuNP-MUA catalyst can also be recovered at different pH ranges depending on the recovery method employed. At pH ~4, protonation of the MUA results in reduced surface charge and aggregation. At pH ~9, ODA will form an ion-pair with the MUA and induce phase transfer into an immiscible organic phase. Both the pH-triggered aggregation/re-dispersion and aqueous/organic phase transfer methods were employed for catalyst recovery and reuse in subsequent reactions. The ability to recover and reuse the AuNP-MUA catalyst by two different methods and different pH regimes is significant, based on the fact that nanoparticle-catalyzed reactions may occur under different pH conditions. PMID:29772775

Pulsed magneto-motive ultrasound imaging to detect intracellular trafficking of magnetic nanoparticles

PubMed Central

Mehrmohamamdi, Mohammad; Qu, Min; Ma, Li L.; Romanovicz, Dwight K.; Johnston, Keith P.; Sokolov, Konstantin V.; Emelianov, Stanislav Y.

2012-01-01

As applications of nanoparticles in medical imaging and biomedicine rapidly expand, the interactions of nanoparticles with living cells have become an area of active interest. For example, intracellular trafficking of nanoparticles – an important part of cell-nanoparticle interaction, has been well studied using plasmonic nanoparticles and optical or optics-based techniques due to the change in optical properties of the nanoparticle aggregates. However, magnetic nanoparticles, despite their wide range of clinical applications, do not exhibit plasmonic-resonant properties and therefore their intracellular aggregation cannot be detected by optics-based imaging techniques. In this study, we investigated the feasibility of a novel imaging technique – pulsed magneto-motive ultrasound (pMMUS), to identify intracellular trafficking of endocytosed magnetic nanoparticles. In pulsed magneto-motive ultrasound imaging a focused, high intensity, pulsed magnetic field is used to excite the cells labeled with magnetic nanoparticles, and ultrasound imaging is then used to monitor the mechanical response of the tissue. We demonstrated previously that clusters of magnetic nanoparticles amplify the pMMUS signal in comparison to signal from individual nanoparticles. Here we further demonstrate that pMMUS imaging can identify interaction between magnetic nanoparticles and living cells, i.e. intracellular aggregation of nanoparticles within the cells. The results of our study suggest that pMMUS imaging can not only detect the presence of magnetic nanoparticles but also provides information about their intracellular trafficking non-invasively and in real-time. PMID:21926454

Aggregate size and structure determination of nanomaterials in physiological media: importance of dynamic evolution

NASA Astrophysics Data System (ADS)

Afrooz, A. R. M. Nabiul; Hussain, Saber M.; Saleh, Navid B.

2014-12-01

Most in vitro nanotoxicological assays are performed after 24 h exposure. However, in determining size and shape effect of nanoparticles in toxicity assays, initial characterization data are generally used to describe experimental outcome. The dynamic size and structure of aggregates are typically ignored in these studies. This brief communication reports dynamic evolution of aggregation characteristics of gold nanoparticles. The study finds that gradual increase in aggregate size of gold nanospheres (AuNS) occurs up to 6 h duration; beyond this time period, the aggregation process deviates from gradual to a more abrupt behavior as large networks are formed. Results of the study also show that aggregated clusters possess unique structural conformation depending on nominal diameter of the nanoparticles. The differences in fractal dimensions of the AuNS samples likely occurred due to geometric differences, causing larger packing propensities for smaller sized particles. Both such observations can have profound influence on dosimetry for in vitro nanotoxicity analyses.

Nanostructured tracers for laser-based diagnostics in high-speed flows

NASA Astrophysics Data System (ADS)

Ghaemi, S.; Schmidt-Ott, A.; Scarano, F.

2010-10-01

The potential application of aggregates of nanoparticles for high-speed flow diagnostics is investigated. Aluminum nanoparticles around 10 nm in diameter are produced by spark discharge in argon gas. Through rapid coagulation and oxidation, aggregates of small effective density are formed. They are characterized by microscopy and their aerodynamics and optical properties are theoretically evaluated. The performance of the aggregates is experimentally investigated across an oblique shock wave in a supersonic wind tunnel of 3 × 3 cm2 cross-section at Mach 2. Particle image velocimetry is used to quantify the time response of the aggregates. The investigations are also carried out on compact titanium agglomerates to provide a base for comparison. The results yield a relaxation time of 0.27 µs for the nanostructured aluminum aggregates, which is an order of magnitude reduction with respect to the compact titanium nanoparticles. This work demonstrates the applicability of nanostructured aggregates for laser-based diagnostics in supersonic and hypersonic flows.

Ligand-modulated interactions between charged monolayer-protected Au144 (SR)60 gold nanoparticles in physiological saline

NASA Astrophysics Data System (ADS)

Villarreal, Oscar; Chen, Liao; Whetten, Robert; Yacaman, Miguel

2015-03-01

We studied the interactions of functionalized Au144 nanoparticles (NPs) in a near-physiological environment through all-atom molecular dynamics simulations. The AuNPs were coated with a homogeneous selection of 60 thiolates: 11-mercapto-1-undecanesulfonate, 5-mercapto-1-pentanesulfonate, 5-mercapto-1-pentane-amine, 4-mercapto-benzoate or 4-mercapto-benzamide. These ligands were selected to elucidate how the aggregation behavior depends on the ligands' sign of charge, length, and flexibility. Simulating the dynamics of a pair of identical AuNPs in a cell of saline of 150 mM NaCl in addition to 120 Na+/Cl- counter-ions, we computed the aggregation affinities from the potential of mean force as a function of the pair separation. We found that NPs coated with negatively charged, short ligands have the strongest affinities mediated by multiple Na+ counter-ions residing on a plane in-between the pair and forming ``salt bridges'' to both NPs. Positively charged NPs have weaker affinities, as Cl counter-ions form fewer and weaker salt bridges. The longer ligands' large fluctuations disfavor the forming of salt bridges, enable hydrophobic contact between the exposed hydrocarbon chains and interact at greater separations due to the fact that the screening effect is rather incomplete. Supported by the CONACYT, NIH, NSF and TACC.

Enhanced emission of nile red fluorescent nanoparticles embedded in hybrid sol-gel glasses.

PubMed

Ferrer, Maria L; del Monte, Francisco

2005-01-13

Highly fluorescent Nile Red (NR) nanoparticles embedded in a hybrid sol-gel glass are reported. The crystallite growth within the confined system created by the porous hybrid matrix results in NR nanoparticles of averaged dimensions below 36 nm. The preparation process allows for the control of both the conformation adopted by single NR molecules prior to aggregation (e.g., near planar) and the configuration of the aggregates (e.g., oblique with phi < 54.7 degrees) prior to their assembly in the supramolecular architecture which ultimately forms the nanoparticles. The full preservation of the fluorescent configuration of the aggregates in the nanoparticles is confirmed through the application of the exciton theory, and it is responsible for the significant increase of the fluorescence emission intensity (e.g., up to 525- and 70-fold as compared to that obtained for single NR molecules embedded in pure and hybrid silica glasses, respectively).

VAPOR PHASE MERCURY SORPTION BY ORGANIC SULFIDE MODIFIED BIMETALLIC IRON-COPPER NANOPARTICLE AGGREGATES

EPA Science Inventory

Novel organic sulfide modified bimetallic iron-copper nanoparticle aggregate sorbent materials have been synthesized for removing elemental mercury from vapor streams at elevated temperatures (120-140 °C). Silane based (disulfide silane and tetrasulfide silane) and alkyl sulfide ...

Initial stages of aggregation in aqueous solutions of ionic liquids: molecular dynamics studies.

PubMed

Bhargava, B L; Klein, Michael L

2009-07-16

Structures formed by 1-alkyl-3-methylimidazolium bromide aqueous solutions with decyl, dodecyl, tetradecyl, and hexadecyl chains have been studied using molecular dynamics (MD) simulations. Spontaneous self-assembly of the amphiphilic cations to form quasi-spherical polydisperse aggregates has been observed in all of the systems, with the size and nature of the aggregates varying with chain length. In all systems, the cation alkyl tails are buried deep inside the aggregates with the polar imidazolium group exposed to exploit the favorable interactions with water. Aggregation numbers steadily increase with the chain length. The hexadecyl aggregates have the most ordered internal structure of the systems studied, and the alkyl chains in these cations show the least number of gauche defects.

Biotoxicity of nickel oxide nanoparticles and bio-remediation by microalgae Chlorella vulgaris.

PubMed

Gong, Ning; Shao, Kuishuang; Feng, Wei; Lin, Zhengzhi; Liang, Changhua; Sun, Yeqing

2011-04-01

Adverse effects of manufactured nickel oxide nanoparticles on the microalgae Chlorellavulgaris were determined by algal growth-inhibition test and morphological observation via transmission electron microscopy (TEM). Results showed that the NiO nanoparticles had severe impacts on the algae, with 72 h EC(50) values of 32.28 mg NiOL(-1). Under the stress of NiO nanoparticles, C. vulgaris cells showed plasmolysis, cytomembrane breakage and thylakoids disorder. NiO nanoparticles aggregated and deposited in algal culture media. The presence of algal cells accelerated aggregation of nanoparticles. Moreover, about 0.14% ionic Ni was released when NiO NPs were added into seawater. The attachment of aggregates to algal cell surface and the presence of released ionic Ni were likely responsible for the toxic effects. Interestingly, some NiO nanoparticles were reduced to zero valence nickel as determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The maximum ratios of nickel reduction was achieved at 72 h of exposure, in accordance with the time-course of changes in soluble protein content of treated C. vulgaris, implying that some proteins of algae are involved in the process. Our results indicate that the toxicity and bioavailability of NiO nanoparticles to marine algae are reduced by aggregation and reduction of NiO. Thus, marine algae have the potential for usage in nano-pollution bio-remediation in aquatic system. Crown Copyright © 2010. Published by Elsevier Ltd. All rights reserved.

J-aggregation in porphyrin nanoparticles induced by diphenylalanine

NASA Astrophysics Data System (ADS)

Li, Fengqing; Liu, Dongzhi; Wang, Tianyang; Hu, Jianxin; Meng, Fancui; Sun, Haiya; Shang, Zhi; Li, Pingan; Feng, Wenhui; Li, Wei; Zhou, Xueqin

2017-08-01

In this report, L-diphenylalanine-decorated tetraphenylporphyrin (TPPtFFC) was synthesized and self-assembled into regular nano-architechtures. The morphology of the assemblies varied with the concentration of TPPtFFC. The absorption spectra of the nanoparticles show the Soret band merges with the Q bands and redistributes with great red-shift, indicative of the formation of J-aggregates of the porphyrin molecules. The fluorescence emission of the nanoparticles is merged and red-shifted to near-infrared region. Studies of absorption and fluorescence spectra reveal an indispensible role of diphenylalanine group in the formation of J-aggregates. The Raman spectra disclose that diprotonation of the porphyrin core contributes to delocalized coherent excited states in the nanoparticles. The positive cotton effect in circular dichroism spectra corresponding to the Soret band of TPPtFFC in solution confirms the formation of J-aggregates with right-handed chirality of the dipole moment. This report will shed light on the rational design of porphyrin-peptide conjugates to mimic naturally light-harvesting complexes.

The mechanisms for nanoparticle surface diffusion and chain self-assembly determined from real-time nanoscale kinetics in liquid

DOE PAGES

Woehl, Taylor J.; Prozorov, Tanya

2015-08-20

The mechanisms for nanoparticle self-assembly are often inferred from the morphology of the final nanostructures in terms of attractive and repulsive interparticle interactions. Understanding how nanoparticle building blocks are pieced together during self-assembly is a key missing component needed to unlock new strategies and mechanistic understanding of this process. Here we use real-time nanoscale kinetics derived from liquid cell transmission electron microscopy investigation of nanoparticle self-assembly to show that nanoparticle mobility dictates the pathway for self-assembly and final nanostructure morphology. We describe a new method for modulating nanoparticle diffusion in a liquid cell, which we employ to systematically investigate themore » effect of mobility on self-assembly of nanoparticles. We interpret the observed diffusion in terms of electrostatically induced surface diffusion resulting from nanoparticle hopping on the liquid cell window surface. Slow-moving nanoparticles self-assemble predominantly into linear 1D chains by sequential attachment of nanoparticles to existing chains, while highly mobile nanoparticles self-assemble into chains and branched structures by chain–chain attachments. Self-assembly kinetics are consistent with a diffusion-driven mechanism; we attribute the change in self-assembly pathway to the increased self-assembly rate of highly mobile nanoparticles. Furthermore, these results indicate that nanoparticle mobility can dictate the self-assembly mechanism and final nanostructure morphology in a manner similar to interparticle interactions.« less

Synthesis and biological imaging of cross-linked fluorescent polymeric nanoparticles with aggregation-induced emission characteristics based on the combination of RAFT polymerization and the Biginelli reaction.

PubMed

Dong, Jiande; Liu, Meiying; Jiang, Ruming; Huang, Hongye; Wan, Qing; Wen, Yuanqing; Tian, Jianwen; Dai, Yanfeng; Zhang, Xiaoyong; Wei, Yen

2018-05-17

Fluorescent probes have long been regarded as tools for imaging living organisms with advantages such as high sensitivity, good designability and multifunctional potential. Many fluorescent probes, especially the probes based on aggregation-induced emission (AIE) dyes, have received increasing attention since the AIE phenomenon was discovered. These AIE dye-based fluorescent probes could elegantly overcome the notorious quenching effect caused by aggregation of conventional organic dyes. However, it is still difficult to directly apply these AIE-active dyes for biomedical applications owing to their hydrophobic nature. Therefore, the development of novel and facile strategies to endow them with water dispersibility is of critical importance. In this work, we exploit an efficient and simple strategy to fabricate an AIE dye-based fluorescent copolymer through the combination of reversible addition-fragmentation chain transfer and the Biginelli reaction. Moreover, the copolymer can self-assemble to fluorescent polymeric nanoparticles (FPNs) in water solution. Hydrophilic poly(PEGMA-co-AEMA) was reacted with the AIE-active dye 4',4‴-(1,2-diphenylethene-1,2-diyl)bis([1,1'-biphenyl]-4-carbaldehyde (CHO-TPE-CHO) to form amphiphilic luminescent polymers using urea as the connection bridge. The successful synthesis of the final products (poly(PEGMA-co-AEMA-TPE) FPNs) was confirmed by various instruments. Furthermore, Transmission electron microscopy (TEM) images manifest that poly(PEGMA-co-AEMA-TPE) copolymers will self-assemble into spherical nanoparticles in aqueous environments with sizes between 100 nm and 200 nm. The cell uptake and bioimaging experiment confirm that poly(PEGMA-co-AEMA-TPE) FPNs have excellent biocompatibility and emit strong green fluorescence in a cellular environment. Thus, poly(PEGMA-co-AEMA-TPE) FPNs are excellent candidates for biomedical applications. Copyright © 2018. Published by Elsevier Inc.

Proteins aggregation and human diseases

NASA Astrophysics Data System (ADS)

Hu, Chin-Kun

2015-04-01

Many human diseases and the death of most supercentenarians are related to protein aggregation. Neurodegenerative diseases include Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), frontotemporallobar degeneration, etc. Such diseases are due to progressive loss of structure or function of neurons caused by protein aggregation. For example, AD is considered to be related to aggregation of Aβ40 (peptide with 40 amino acids) and Aβ42 (peptide with 42 amino acids) and HD is considered to be related to aggregation of polyQ (polyglutamine) peptides. In this paper, we briefly review our recent discovery of key factors for protein aggregation. We used a lattice model to study the aggregation rates of proteins and found that the probability for a protein sequence to appear in the conformation of the aggregated state can be used to determine the temperature at which proteins can aggregate most quickly. We used molecular dynamics and simple models of polymer chains to study relaxation and aggregation of proteins under various conditions and found that when the bending-angle dependent and torsion-angle dependent interactions are zero or very small, then protein chains tend to aggregate at lower temperatures. All atom models were used to identify a key peptide chain for the aggregation of insulin chains and to find that two polyQ chains prefer anti-parallel conformation. It is pointed out that in many cases, protein aggregation does not result from protein mis-folding. A potential drug from Chinese medicine was found for Alzheimer's disease.

Studies on the formation of polymeric nano-emulsions obtained via low-energy emulsification and their use as templates for drug delivery nanoparticle dispersions.

PubMed

Calderó, G; Montes, R; Llinàs, M; García-Celma, M J; Porras, M; Solans, C

2016-09-01

Ethylcellulose nanoparticles have been obtained from O/W nano-emulsions of the water/polyoxyethylene 10 oleyl ether/[ethyl acetate+4wt% ethylcellulose] system by low energy-energy emulsification at 25°C. Nano-emulsions with droplet sizes below 200nm and high kinetic stability were chosen for solubilising dexamethasone (DXM). Phase behaviour, conductivity and optical analysis studies of the system have evidenced for the first time that both, the polymer and the drug play a role on the structure of the aggregates formed along the emulsification path. Nano-emulsion formation may take place by both, phase inversion and self-emulsification. Spherical polymeric nanoparticles containing surfactant, showing sizes below 160nm have been obtained from the nano-emulsions by organic solvent evaporation. DXM loading in the nanoparticles was high (>90%). The release kinetics of nanoparticle dispersions with similar particle size and encapsulated DXM but different polymer to surfactant ratio were studied and compared to an aqueous DXM solution. Drug release from the nanoparticle dispersions was slower than from the aqueous solution. While the DXM solution showed a Fickian release pattern, the release behaviour from the nanoparticle dispersions was faster than that expected from a pure Fickian release. A coupled diffusion/relaxation model fitted the results very well, suggesting that polymer chains undergo conformational changes enhancing drug release. The contribution of diffusion and relaxation to drug transport in the nanoparticle dispersions depended on their composition and release time. Surfactant micelles present in the nanoparticle dispersion may exert a mild reservoir effect. The small particle size and the prolonged DXM release provided by the ethylcellulose nanoparticle dispersions make them suitable vehicles for controlled drug delivery applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Cytotoxicity of TiO{sub 2} nanoparticles towards freshwater sediment microorganisms at low exposure concentrations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumari, Jyoti; Kumar, Deepak; Mathur, Ankita

2014-11-15

There is a persistent need to assess the effects of TiO{sub 2} nanoparticles on the aquatic ecosystem owing to their increasing usage in consumer products and risk of environmental release. The current study is focused on TiO{sub 2} nanoparticle-induced acute toxicity at sub-ppm level (≤1 ppm) on the three different freshwater sediment bacterial isolates and their consortium under two different irradiation (visible light and dark) conditions. The consortium of the bacterial isolates was found to be less affected by the exposure to the nanoparticles compared to the individual cells. The oxidative stress contributed considerably towards the cytotoxicity under both lightmore » and dark conditions. A statistically significant increase in membrane permeability was noted under the dark conditions as compared to the light conditions. The optical and fluorescence microscopic images showed aggregation and chain formation of the bacterial cells, when exposed to the nanoparticles. The electron microscopic (SEM, TEM) observations suggested considerable damage of cells and bio-uptake of nanoparticles. The exopolysaccrides (EPS) production and biofilm formation were noted to increase in the presence of the nanoparticles, and expression of the key genes involved in biofilm formation was studied by RT-PCR. - Highlights: • Toxicity of NPs towards freshwater sediment bacteria at sub-ppm concentrations. • Decreased toxicity of the nanoparticles in the consortium of microorganisms. • Enhanced bacterial resistance through EPS and biofilm formation in the presence of NPs. • Considerable surface damage of cells and internalization of NPs. • Gene expression analyses related to biofilm formation in the presence of NPs.« less

High spatial resolution mapping of surface plasmon resonance modes in single and aggregated gold nanoparticles assembled on DNA strands

NASA Astrophysics Data System (ADS)

Diaz-Egea, Carlos; Sigle, Wilfried; van Aken, Peter A.; Molina, Sergio I.

2013-07-01

We present the mapping of the full plasmonic mode spectrum for single and aggregated gold nanoparticles linked through DNA strands to a silicon nitride substrate. A comprehensive analysis of the electron energy loss spectroscopy images maps was performed on nanoparticles standing alone, dimers, and clusters of nanoparticles. The experimental results were confirmed by numerical calculations using the Mie theory and Gans-Mie theory for solving Maxwell's equations. Both bright and dark surface plasmon modes have been unveiled.

UV Irradiation and Humic Acid Mediate Aggregation of Aqueous Fullerene (nC60) Nanoparticles

EPA Science Inventory

The transport and fate of engineered nanomaterials is affected by multiple environmental factors, including sunlight and natural organic matter. In this study, the initial aggregation kinetics of aqueous fullerene (nC60) nanoparticles before and after UVA irradiation was investig...

New, rapid method to measure dissolved silver concentration in silver nanoparticle suspensions by aggregation combined with centrifugation

NASA Astrophysics Data System (ADS)

Dong, Feng; Valsami-Jones, Eugenia; Kreft, Jan-Ulrich

2016-09-01

It is unclear whether the antimicrobial activities of silver nanoparticles (AgNPs) are exclusively mediated by the release of silver ions (Ag+) or, instead, are due to combined nanoparticle and silver ion effects. Therefore, it is essential to quantify dissolved Ag in nanosilver suspensions for investigations of nanoparticle toxicity. We developed a method to measure dissolved Ag in Ag+/AgNPs mixtures by combining aggregation of AgNPs with centrifugation. We also describe the reproducible synthesis of stable, uncoated AgNPs. Uncoated AgNPs were quickly aggregated by 2 mM Ca2+, forming large clusters that could be sedimented in a low-speed centrifuge. At 20,100g, the sedimentation time of AgNPs was markedly reduced to 30 min due to Ca2+-mediated aggregation, confirmed by the measurements of Ag content in supernatants with graphite furnace atomic absorption spectrometry. No AgNPs were detected in the supernatant by UV-Vis absorption spectra after centrifuging the aggregates. Our approach provides a convenient and inexpensive way to separate dissolved Ag from AgNPs, avoiding long ultracentrifugation times or Ag+ adsorption to ultrafiltration membranes.

In-situ suspended aggregate microextraction of gold nanoparticles from water samples and determination by electrothermal atomic absorption spectrometry.

PubMed

Choleva, Tatiana G; Kappi, Foteini A; Tsogas, George Z; Vlessidis, Athanasios G; Giokas, Dimosthenis L

2016-05-01

This work describes a new method for the extraction and determination of gold nanoparticles in environmental samples by means of in-situ suspended aggregate microextraction and electrothermal atomic absorption spectrometry. The method relies on the in-situ formation of a supramolecular aggregate phase through ion-association between a cationic surfactant and a benzene sulfonic acid derivative. Gold nanoparticles are physically entrapped into the aggregate phase which is separated from the bulk aqueous solution by vacuum filtration on the surface of a cellulose filter in the form of a thin film. The film is removed from the filter surface and is dissociated into an acidified methanolic solution which is used for analysis. Under the optimized experimental conditions, gold nanoparticles can be efficiently extracted from water samples with recovery rates between 81.0-93.3%, precision 5.4-12.0% and detection limits as low as 75femtomolL(-1) using only 20mL of sample volume. The satisfactory analytical features of the method along with the simplicity indicate the efficiency of this new approach to adequately collect and extract gold nanoparticle species from water samples. Copyright © 2016 Elsevier B.V. All rights reserved.

A plasmonic colorimetric strategy for visual miRNA detection based on hybridization chain reaction

NASA Astrophysics Data System (ADS)

Miao, Jie; Wang, Jingsheng; Guo, Jinyang; Gao, Huiguang; Han, Kun; Jiang, Chengmin; Miao, Peng

2016-08-01

In this work, a novel colorimetric strategy for miRNA analysis is proposed based on hybridization chain reaction (HCR)-mediated localized surface plasmon resonance (LSPR) variation of silver nanoparticles (AgNPs). miRNA in the sample to be tested is able to release HCR initiator from a solid interface to AgNPs colloid system by toehold exchange-mediated strand displacement, which then triggers the consumption of fuel strands with single-stranded tails for HCR. The final produced long nicked double-stranded DNA loses the ability to protect AgNPs from salt-induced aggregation. The stability variation of the colloid system can then be monitored by recording corresponding UV-vis spectrum and initial miRNA level is thus determined. This sensing system involves only four DNA strands which is quite simple. The practical utility is confirmed to be excellent by employing different biological samples.

Modeling the transport of engineered nanoparticles in saturated porous media - an experimental setup

NASA Astrophysics Data System (ADS)

Braun, A.; Neukum, C.; Azzam, R.

2011-12-01

The accelerating production and application of engineered nanoparticles is causing concerns regarding their release and fate in the environment. For assessing the risk that is posed to drinking water resources it is important to understand the transport and retention mechanisms of engineered nanoparticles in soil and groundwater. In this study an experimental setup for analyzing the mobility of silver and titanium dioxide nanoparticles in saturated porous media is presented. Batch and column experiments with glass beads and two different soils as matrices are carried out under varied conditions to study the impact of electrolyte concentration and pore water velocities. The analysis of nanoparticles implies several challenges, such as the detection and characterization and the preparation of a well dispersed sample with defined properties, as nanoparticles tend to form agglomerates when suspended in an aqueous medium. The analytical part of the experiments is mainly undertaken with Flow Field-Flow Fractionation (FlFFF). This chromatography like technique separates a particulate sample according to size. It is coupled to a UV/Vis and a light scattering detector for analyzing concentration and size distribution of the sample. The advantage of this technique is the ability to analyze also complex environmental samples, such as the effluent of column experiments including soil components, and the gentle sample treatment. For optimization of the sample preparation and for getting a first idea of the aggregation behavior in soil solutions, in sedimentation experiments the effect of ionic strength, sample concentration and addition of a surfactant on particle or aggregate size and temporal dispersion stability was investigated. In general the samples are more stable the lower the concentration of particles is. For TiO2 nanoparticles, the addition of a surfactant yielded the most stable samples with smallest aggregate sizes. Furthermore the suspension stability is increasing with electrolyte concentration. Depending on the dispersing medium the results show that TiO2 nanoparticles tend to form aggregates between 100-200 nm in diameter while the primary particle size is given as 21 nm by the manufacturer. Aggregate sizes are increasing with time. The particle size distribution of the silver nanoparticle samples is quite uniform in each medium. The fresh samples show aggregate sizes between 40 and 45 nm while the primary particle size is 15 nm according to the manufacturer. Aggregate size is only slightly increasing with time during the sedimentation experiments. These results are used as a reference when analyzing the effluent of column experiments.

Effect of surfactant concentration to aggregations of nanogold particles

NASA Astrophysics Data System (ADS)

Duangthanu, Methawee; Pattanaporkratana, Apichart

2017-09-01

This research presents a study of aggregation of colloidal gold nanoparticles using 400 nm diameter gold nanoparticles mixed with a surfactant (Plantacare 2000) at various concentrations. When observed under a microscope, we found that the nanoparticles aggregated to form nearly spherical clusters at the beginning of the formation, and then sedimented to the bottom of the container. These clusters moved with Brownian’s motion and collided with each other in the horizontal plane, forming branch-like clusters in 2D. The appearance and size of the clusters were different depending on the concentration of surfactant. The clusters’ size and appearance were rarely changed after mixing with surfactant for 90 minutes, and we found that the cluster’s shapes were nearly spherical at low surfactant concentration (c = 0.25%). At surfactant concentration between 0.50% - 5.00%, the aggregates formed branch-like clusters with skinnier branches and smaller sizes at higher surfactant concentration. Moreover, we also found that, at surfactant concentrations between 2.50% - 5.00%, nanoparticles and aggregates stuck to the bottom of the glass container quickly and rarely moved after 10 minutes. At c = 0.25%, the 2D fractal dimension of the aggregates was measured to be D = 1.88 ± 0.04, since the aggregates were nearly spherical. The fractal dimension decreased to the minimum of D = 1.50 ± 0.12 at c = 1.50%, similar to D ∼ 1.45 found in diffusion-limited cluster aggregation (DLCA). At surfactant concentration above 1.50%, the fractal dimension increased until it reached the value of D ∼ 1.66 at c = 5.00%.

Size-Selected Ag Nanoparticles with Five-Fold Symmetry

PubMed Central

2009-01-01

Silver nanoparticles were synthesized using the inert gas aggregation technique. We found the optimal experimental conditions to synthesize nanoparticles at different sizes: 1.3 ± 0.2, 1.7 ± 0.3, 2.5 ± 0.4, 3.7 ± 0.4, 4.5 ± 0.9, and 5.5 ± 0.3 nm. We were able to investigate the dependence of the size of the nanoparticles on the synthesis parameters. Our data suggest that the aggregation of clusters (dimers, trimer, etc.) into the active zone of the nanocluster source is the predominant physical mechanism for the formation of the nanoparticles. Our experiments were carried out in conditions that kept the density of nanoparticles low, and the formation of larges nanoparticles by coalescence processes was avoided. In order to preserve the structural and morphological properties, the impact energy of the clusters landing into the substrate was controlled, such that the acceleration energy of the nanoparticles was around 0.1 eV/atom, assuring a soft landing deposition. High-resolution transmission electron microscopy images showed that the nanoparticles were icosahedral in shape, preferentially oriented with a five-fold axis perpendicular to the substrate surface. Our results show that the synthesis by inert gas aggregation technique is a very promising alternative to produce metal nanoparticles when the control of both size and shape are critical for the development of practical applications. PMID:20596397

Size-selected ag nanoparticles with five-fold symmetry.

PubMed

Gracia-Pinilla, Miguelángel; Ferrer, Domingo; Mejía-Rosales, Sergio; Pérez-Tijerina, Eduardo

2009-05-15

Silver nanoparticles were synthesized using the inert gas aggregation technique. We found the optimal experimental conditions to synthesize nanoparticles at different sizes: 1.3 ± 0.2, 1.7 ± 0.3, 2.5 ± 0.4, 3.7 ± 0.4, 4.5 ± 0.9, and 5.5 ± 0.3 nm. We were able to investigate the dependence of the size of the nanoparticles on the synthesis parameters. Our data suggest that the aggregation of clusters (dimers, trimer, etc.) into the active zone of the nanocluster source is the predominant physical mechanism for the formation of the nanoparticles. Our experiments were carried out in conditions that kept the density of nanoparticles low, and the formation of larges nanoparticles by coalescence processes was avoided. In order to preserve the structural and morphological properties, the impact energy of the clusters landing into the substrate was controlled, such that the acceleration energy of the nanoparticles was around 0.1 eV/atom, assuring a soft landing deposition. High-resolution transmission electron microscopy images showed that the nanoparticles were icosahedral in shape, preferentially oriented with a five-fold axis perpendicular to the substrate surface. Our results show that the synthesis by inert gas aggregation technique is a very promising alternative to produce metal nanoparticles when the control of both size and shape are critical for the development of practical applications.

Manipulating the self-assembling process to obtain control over the morphologies of copper oxide in hydrothermal synthesis and creating pores in the oxide architecture.

PubMed

Zhong, Ziyi; Ng, Vivien; Luo, Jizhong; Teh, Siew-Pheng; Teo, Jaclyn; Gedanken, Aharon

2007-05-22

Copper oxide with various morphologies was synthesized by the hydrolysis of Cu(ac)2 with urea under mild hydrothermal conditions. In the synthesis, a series of organic amines with one or two amine groups (monoamine and diamine), including isobutylamine, octylamine (OLA), dodecylamine, octadecylamine (monoamines), ethylenediamine dihydrochloride, and hexamethylenediamine (diamines), was used as the "structure-directing agent". The monoamines led to the formation of one-dimensional (1D) aggregates of the copper oxide precursor particles (Pre-CuO), while the diamines led to the formation of two-dimensional (2D) aggregates. In both cases, the shorter carbon-chain amine molecules showed a stronger structure-directing function than that of the longer carbon-chain amine molecules. Next, in a series of syntheses, OLA was selected for further study, and the experimental parameters were systematically manipulated. When the hydrolysis was adjusted to a very slow rate by coupling the hydrolysis reaction with an esterification reaction, 1D aggregates of Pre-CuO were formed; when the hydrolysis rate was in the middle range, spherical Pre-CuO architectures composed of smaller linear aggregates were formed. However, under the high hydrolysis rates achieved by increasing the precipitation agent (urea) or by conducting the reaction at high temperatures (>/=120 degrees C), only Pre-CuO nanoparticles with a featureless morphology were formed. The formed spherical Pre-CuO architectures can be converted to a porous structure (CuOx) after removing the OLA molecules via calcination. Compared to the 1D and 2D aggregates, this porous architecture is highly thermally stable and did not collapse even after calcination at 500 degrees C. Preliminary results showed that the porous structure can be used both as a catalyst support and as a catalyst for the oxidation of CO at low temperatures.

Characterization of Nanoparticle Aggregation in Biologically Relevant Fluids

NASA Astrophysics Data System (ADS)

McEnnis, Kathleen; Lahann, Joerg

Nanoparticles (NPs) are often studied as drug delivery vehicles, but little is known about their behavior in blood once injected into animal models. If the NPs aggregate in blood, they will be shunted to the liver or spleen instead of reaching the intended target. The use of animals for these experiments is costly and raises ethical questions. Typically dynamic light scattering (DLS) is used to analyze aggregation behavior, but DLS cannot be used because the components of blood also scatter light. As an alternative, a method of analyzing NPs in biologically relevant fluids such as blood plasma has been developed using nanoparticle tracking analysis (NTA) with fluorescent filters. In this work, NTA was used to analyze the aggregation behavior of fluorescent polystyrene NPs with different surface modifications in blood plasma. It was expected that different surface chemistries on the particles will change the aggregation behavior. The effect of the surface modifications was investigated by quantifying the percentage of NPs in aggregates after addition to blood plasma. The use of this characterization method will allow for better understanding of particle behavior in the body, and potential problems, specifically aggregation, can be addressed before investing in in vivo studies.

Studies of aggregated nanoparticles steering during magnetic-guided drug delivery in the blood vessels

NASA Astrophysics Data System (ADS)

Hoshiar, Ali Kafash; Le, Tuan-Anh; Amin, Faiz Ul; Kim, Myeong Ok; Yoon, Jungwon

2017-04-01

Magnetic-guided targeted drug delivery (TDD) systems can enhance the treatment of diverse diseases. Despite the potential and promising results of nanoparticles, aggregation prevents precise particle guidance in the vasculature. In this study, we developed a simulation platform to investigate aggregation during steering of nanoparticles using a magnetic field function. The magnetic field function (MFF) comprises a positive and negative pulsed magnetic field generated by electromagnetic coils, which prevents adherence of particles to the vessel wall during magnetic guidance. A commonly used Y-shaped vessel was simulated and the performance of the MFF analyzed; the experimental data were in agreement with the simulation results. Moreover, the effects of various parameters on magnetic guidance were evaluated and the most influential identified. The simulation results presented herein will facilitate more precise guidance of nanoparticles in vivo.

Stable J-aggregation enabled dual photoacoustic and fluorescence nanoparticles for intraoperative cancer imaging

NASA Astrophysics Data System (ADS)

Shakiba, Mojdeh; Ng, Kenneth K.; Huynh, Elizabeth; Chan, Harley; Charron, Danielle M.; Chen, Juan; Muhanna, Nidal; Foster, F. Stuart; Wilson, Brian C.; Zheng, Gang

2016-06-01

J-aggregates display nanoscale optical properties which enable their use in fluorescence and photoacoustic imaging applications. However, control over their optical properties in an in vivo setting is hampered by the conformational lability of the J-aggregate structure in complex biological environments. J-aggregating nanoparticles (JNP) formed by self-assembly of bacteriopheophorbide-lipid (Bchl-lipid) in lipid nanovesicles represents a novel strategy to stabilize J-aggregates for in vivo bioimaging applications. We find that 15 mol% Bchl-lipid embedded within a saturated phospholipid bilayer vesicle was optimal in terms of maximizing Bchl-lipid dye loading, while maintaining a spherical nanoparticle morphology and retaining spectral properties characteristic of J-aggregates. The addition of cholesterol maintains the stability of the J-aggregate absorption band for up to 6 hours in the presence of 90% FBS. In a proof-of-concept experiment, we successfully applied JNPs as a fluorescence contrast agent for real-time intraoperative detection of metastatic lymph nodes in a rabbit head-and-neck cancer model. Lymph node metastasis delineation was further verified by visualizing the JNP within the excised lymph node using photoacoustic imaging. Using JNPs, we demonstrate the possibility of using J-aggregates as fluorescence and photoacoustic contrast agents and may potentially spur the development of other nanomaterials that can stably induce J-aggregation for in vivo cancer bioimaging applications.J-aggregates display nanoscale optical properties which enable their use in fluorescence and photoacoustic imaging applications. However, control over their optical properties in an in vivo setting is hampered by the conformational lability of the J-aggregate structure in complex biological environments. J-aggregating nanoparticles (JNP) formed by self-assembly of bacteriopheophorbide-lipid (Bchl-lipid) in lipid nanovesicles represents a novel strategy to stabilize J-aggregates for in vivo bioimaging applications. We find that 15 mol% Bchl-lipid embedded within a saturated phospholipid bilayer vesicle was optimal in terms of maximizing Bchl-lipid dye loading, while maintaining a spherical nanoparticle morphology and retaining spectral properties characteristic of J-aggregates. The addition of cholesterol maintains the stability of the J-aggregate absorption band for up to 6 hours in the presence of 90% FBS. In a proof-of-concept experiment, we successfully applied JNPs as a fluorescence contrast agent for real-time intraoperative detection of metastatic lymph nodes in a rabbit head-and-neck cancer model. Lymph node metastasis delineation was further verified by visualizing the JNP within the excised lymph node using photoacoustic imaging. Using JNPs, we demonstrate the possibility of using J-aggregates as fluorescence and photoacoustic contrast agents and may potentially spur the development of other nanomaterials that can stably induce J-aggregation for in vivo cancer bioimaging applications. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR08165C

Workplace exposure to nanoparticles from gas metal arc welding process

NASA Astrophysics Data System (ADS)

Zhang, Meibian; Jian, Le; Bin, Pingfan; Xing, Mingluan; Lou, Jianlin; Cong, Liming; Zou, Hua

2013-11-01

Workplace exposure to nanoparticles from gas metal arc welding (GMAW) process in an automobile manufacturing factory was investigated using a combination of multiple metrics and a comparison with background particles. The number concentration (NC), lung-deposited surface area concentration (SAC), estimated SAC and mass concentration (MC) of nanoparticles produced from the GMAW process were significantly higher than those of background particles before welding ( P < 0.01). A bimodal size distribution by mass for welding particles with two peak values (i.e., 10,000-18,000 and 560-320 nm) and a unimodal size distribution by number with 190.7-nm mode size or 154.9-nm geometric size were observed. Nanoparticles by number comprised 60.7 % of particles, whereas nanoparticles by mass only accounted for 18.2 % of the total particles. The morphology of welding particles was dominated by the formation of chain-like agglomerates of primary particles. The metal composition of these welding particles consisted primarily of Fe, Mn, and Zn. The size distribution, morphology, and elemental compositions of welding particles were significantly different from background particles. Working activities, sampling distances from the source, air velocity, engineering control measures, and background particles in working places had significant influences on concentrations of airborne nanoparticle. In addition, SAC showed a high correlation with NC and a relatively low correlation with MC. These findings indicate that the GMAW process is able to generate significant levels of nanoparticles. It is recommended that a combination of multiple metrics is measured as part of a well-designed sampling strategy for airborne nanoparticles. Key exposure factors, such as particle agglomeration/aggregation, background particles, working activities, temporal and spatial distributions of the particles, air velocity, engineering control measures, should be investigated when measuring workplace exposure to nanoparticles.

Plasmon enhanced fluorescence with aggregated shell-isolated nanoparticles.

PubMed

Osorio-Román, Igor O; Guerrero, Ariel R; Albella, Pablo; Aroca, Ricardo F

2014-10-21

Shell-isolated nanoparticles (SHINs) nanostructures provide a versatile substrate where the localized surface plasmon resonances (LSPRs) are well-defined. For SHINEF, the silver (or gold) metal core is protected by the SiO2 coating, which is thicker than the critical distance for minimum quenching by the metal. In the present work, it is shown that an increase in the SHINEF enhancement factor may be achieved by inducing SHIN aggregation with electrolytes in solution. The proof of concept is demonstrated using NaCl as aggregating agent, although other inorganic salts will also aggregate SHIN nanoparticles. As much as a 10-fold enhancement in the SHINEF enhancement factor (EF) may be achieved by tuning the electrolyte concentrations in solution. The SHINEF experiments include the study of the aggregation effect controlling gold SHIN's surface concentration via spraying. Au-SHINs are sprayed onto layer-by-layer (LbL) and Langmuir-Blodgett (LB) films, and samples are fabricated using fluorophores with low and also high quantum yield.

High surface area monodispersed Fe3O4 nanoparticles alone and on physical exfoliated graphite for improved supercapacitors

NASA Astrophysics Data System (ADS)

Sarno, Maria; Ponticorvo, Eleonora; Cirillo, Claudia

2016-12-01

Highly conductive, unsophisticated and easy to be obtained physical exfoliated graphite (PHG) supporting well dispersed magnetite, Fe3O4/PHG nanocomposite, has been prepared by a one-step chemical strategy and physico-chemical characterized. The nanocomposite, favoured by the a-polar nanoparticles (NPs) capping, results in a self-assembled monolayer of monodispersed Fe3O4, covering perfectly the hydrophobic surfaces of PHG. The nanocomposite as an electrode material was fabricated into a supercapacitor and characterized by cyclic voltammetry (CV) and galvanostatic charge-discharge measurements. It shows, after a suitable annealing, significant electrochemical properties (capacitance value of 787 F/g at 0.5 A g-1 and a Fe3O4/PHG weight ratio of 0.31) and good cycling stability (retention 91% after 30,000 cycles). Highly monodispersed very fine Fe3O4 NPs, covered by organic chains, have been also synthesized. The high surface area Fe3O4 NPs, after washing to leave a low content of organic chains able to avoid aggregation without excessively affecting the electrical properties of the material, exhibit remarkable pseudocapacitive activities, including the highest specific capacitance over reported for Fe3O4 (300 F/g at 0.5 A g-1).

Plasmonics-Based Detection of Virus Using Sialic Acid Functionalized Gold Nanoparticles.

PubMed

Lee, Changwon; Wang, Peng; Gaston, Marsha A; Weiss, Alison A; Zhang, Peng

2017-01-01

Biosensor for the detection of virus was developed by utilizing plasmonic peak shift phenomenon of the gold nanoparticles and viral infection mechanism of hemagglutinin on virus and sialic acid on animal cells. The plasmonic peak of the colloidal gold nanoparticles changes with the aggregation of the particles due to the plasmonic interaction between nearby particles and the color of the colloidal nanoparticle solution changes from wine red to purple. Sialic acid reduced and stabilized colloidal gold nanoparticle aggregation is induced by the addition of viral particles in the solution due to the hemagglutinin-sialic acid interaction. In this work, sialic acid reduced and stabilized gold nanoparticles (d = 20.1 ± 1.8 nm) were synthesized by a simple one-pot, green method without chemically modifying sialic acid. The gold nanoparticles showed target-specific aggregation with viral particles via hemagglutinin-sialic acid binding. A linear correlation was observed between the change in optical density and dilution of chemically inactivated influenza B virus species. The detection limit of the virus dilution (hemagglutinination assay titer, 512) was shown to be 0.156 vol% and the upper limit of the linearity can be extended with the use of more sialic acid-gold nanoparticles.

How Do the Size, Charge and Shape of Nanoparticles Affect Amyloid β Aggregation on Brain Lipid Bilayer?

NASA Astrophysics Data System (ADS)

Kim, Yuna; Park, Ji-Hyun; Lee, Hyojin; Nam, Jwa-Min

2016-01-01

Here, we studied the effect of the size, shape, and surface charge of Au nanoparticles (AuNPs) on amyloid beta (Aβ) aggregation on a total brain lipid-based supported lipid bilayer (brain SLB), a fluid platform that facilitates Aβ-AuNP aggregation process. We found that larger AuNPs induce large and amorphous aggregates on the brain SLB, whereas smaller AuNPs induce protofibrillar Aβ structures. Positively charged AuNPs were more strongly attracted to Aβ than negatively charged AuNPs, and the stronger interactions between AuNPs and Aβ resulted in fewer β-sheets and more random coil structures. We also compared spherical AuNPs, gold nanorods (AuNRs), and gold nanocubes (AuNCs) to study the effect of nanoparticle shape on Aβ aggregation on the brain SLB. Aβ was preferentially bound to the long axis of AuNRs and fewer fibrils were formed whereas all the facets of AuNCs interacted with Aβ to produce the fibril networks. Finally, it was revealed that different nanostructures induce different cytotoxicity on neuroblastoma cells, and, overall, smaller Aβ aggregates induce higher cytotoxicity. The results offer insight into the roles of NPs and brain SLB in Aβ aggregation on the cell membrane and can facilitate the understanding of Aβ-nanostructure co-aggregation mechanism and tuning Aβ aggregate structures.

Surface plasmon resonances in liquid metal nanoparticles

NASA Astrophysics Data System (ADS)

Ershov, A. E.; Gerasimov, V. S.; Gavrilyuk, A. P.; Karpov, S. V.

2017-06-01

We have shown significant suppression of resonant properties of metallic nanoparticles at the surface plasmon frequency during the phase transition "solid-liquid" in the basic materials of nanoplasmonics (Ag, Au). Using experimental values of the optical constants of liquid and solid metals, we have calculated nanoparticle plasmonic absorption spectra. The effect was demonstrated for single particles, dimers and trimers, as well as for the large multiparticle colloidal aggregates. Experimental verification was performed for single Au nanoparticles heated to the melting temperature and above up to full suppression of the surface plasmon resonance. It is emphasized that this effect may underlie the nonlinear optical response of composite materials containing plasmonic nanoparticles and their aggregates.

Impact of Environmental Conditions (pH, Ionic Strength, And Electrolyte Type) On The Surface Charge And Aggregation Of Silver Nanoparticles Suspensions

EPA Science Inventory

The impact of capping agents and environmental conditions (pH, ionic strength, and background electrolytes) on surface charge and aggregation potential of silver nanoparticles (AgNPs) suspensions were investigated. Capping agents are chemicals used in the synthesis of nanopartic...

Effects of Material Properties on Sedimentation and Aggregation of Titanium Dioxide Nanoparticles of Anatase and Rutile in the Aqueous Phase

EPA Science Inventory

This study investigated the sedimentation and aggregation kinetics of titanium dioxide (TiO2) nanoparticles with varying material properties (i.e., crystallinity, morphology, and chemical compositions). Used in the study were various types of commercially available TiO2 nanoparti...

Stability and Aggregation of Silver and Titanium Dioxide Nanoparticles in Seawater: Role of Salinity and Dissolved Organic Matter

EPA Science Inventory

The behavior and fate of nanoparticles (NPs) in the marine environment is largely unknown and has the potential to have important environmental and human health implications. The aggregation state and fate of NPs in the marine environment is greatly influenced by their interactio...

Tuning structure of oppositely charged nanoparticle and protein complexes

NASA Astrophysics Data System (ADS)

Kumar, Sugam; Aswal, V. K.; Callow, P.

2014-04-01

Small-angle neutron scattering (SANS) has been used to probe the structures of anionic silica nanoparticles (LS30) and cationic lyszyme protein (M.W. 14.7kD, I.P. ˜ 11.4) by tuning their interaction through the pH variation. The protein adsorption on nanoparticles is found to be increasing with pH and determined by the electrostatic attraction between two components as well as repulsion between protein molecules. We show the strong electrostatic attraction between nanoparticles and protein molecules leads to protein-mediated aggregation of nanoparticles which are characterized by fractal structures. At pH 5, the protein adsorption gives rise to nanoparticle aggregation having surface fractal morphology with close packing of nanoparticles. The surface fractals transform to open structures of mass fractal morphology at higher pH (7 and 9) on approaching isoelectric point (I.P.).

Freeze-drying of silica nanoparticles: redispersibility toward nanomedicine applications.

PubMed

Picco, Agustin S; Ferreira, Larissa F; Liberato, Michelle S; Mondo, Gabriela B; Cardoso, Mateus B

2018-01-01

To study freeze-drying of silica nanoparticles (SiO 2 NPs) in order to find suitable conditions to produce lyophilized powders with no aggregation after resuspension and storage. SiO 2 NPs were synthesized using a Stöber-based procedure, and characterized by scanning electron microscopy, dynamic light scattering and nitrogen adsorption/desorption isotherms. SiO 2 NPs hydrodynamic diameters were compared prior and after freeze-drying in the presence/absence of carbohydrate protectants. Glucose was found to be the most suitable protectant against the detrimental effects of lyophilization. The minimum concentration of carbohydrate required to effectively protect SiO 2 NPs from aggregation during freeze-drying is influenced by the nanoparticle's size and texture. Negligible aggregation was observed during storage. Carbohydrates can be used during SiO 2 NPs freeze-drying process to obtain redispersable solids that maintain original sizes without residual aggregation.

Use of near-infrared luminescent gold nanoclusters for detection of macrophages

PubMed Central

Sapozhnikova, Veronika; Willsey, Brian; Asmis, Reto; Wang, Tianyi; Jenkins, James Travis; Mancuso, Jacob; Ma, Li Leo; Kuranov, Roman; Milner, Thomas E.; Johnston, Keith

2012-01-01

Abstract. We determined the effect of aggregation and coating thickness of gold on the luminescence of nanoparticles engulfed by macrophages and in gelatin phantoms. Thin gold-coated iron oxide nanoclusters (nanoroses) have been developed to target macrophages to provide contrast enhancement for near-infrared optical imaging applications. We compare the brightness of nanoroses luminescent emissions in response to 635 nm laser excitation to other nanoparticles including nanoshells, nanorods, and Cy5 conjugated iron oxide nanoparticles. Luminescent properties of all these nanoparticles were investigated in monomeric and aggregated form in gelatin phantoms and primary macrophage cell cultures using confocal microscopy. Aggregation of the gold nanoparticles increased luminescence emission and correlated with increased surface mass of gold per nanoparticle (nanoshells 37±14.30×10−3 brightness with 1.23×10−4 wt of gold (g)/nanoparticle versus original nanorose 1.45±0.37×10−3 with 2.10×10−16 wt of gold/nanoparticle, p<0.05). Nanoshells showed greater luminescent intensity than original nanoroses or Cy5 conjugated iron oxide nanoparticles when compared as nanoparticles per macrophage (38±10 versus 11±2.8 versus 17±6.5, p<0.05, respectively, ANOVA), but showed relatively poor macrophage uptake (1025±128 versus 7549±236 versus 96,000  nanoparticles/cell, p<0.05, student t-test nanoshells versus nanoroses). Enhancement of gold fluorescent emissions by nanoparticles can be achieved by reducing the thickness of the gold coating, by clustering the gold on the surface of the nanoparticles (nanoshells), and by clustering the gold nanoparticles themselves. PMID:22463038

Fluorometric immunoassay for human serum albumin based on its inhibitory effect on the immunoaggregation of quantum dots with silver nanoparticles

NASA Astrophysics Data System (ADS)

Marukhyan, Seda S.; Gasparyan, Vardan K.

2017-02-01

Quantitative determination of HSA was conducted by competitive immunoassay. Inhibition of aggregation of antibody conjugated quantum dots (QD) with albumin conjugated silver nanoparticles (AgNPs) in the presence of HSA was conducted. If antibody-loaded CdSe QDs aggregate with HSA-coated silver nanoparticles the distance between the two kinds of nanoparticles will be reduced enough to cause fluorescence resonance energy transfer (FRET). In this case the yellow fluorescence of the Ab-QDs is quenched. However if HSA (antigen) is added to the Ab-QDs their surface will be blocked and they cannot aggregate any longer with the HSA-AgNPs. Hence, fluorescence will not be quenched. The drop of the intensity of fluorescence (peaking at 570 nm) is inversely correlated with the concentration of HSA in the sample. The method allows to determine HSA in the 30-600 ng·mL-1 concentration range.

Interaction of DNA bases with silver nanoparticles: assembly quantified through SPRS and SERS.

PubMed

Basu, Soumen; Jana, Subhra; Pande, Surojit; Pal, Tarasankar

2008-05-15

Colloidal silver nanoparticles were prepared by reducing silver nitrate with sodium borohydride. The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported here describes the interaction between nanoscale silver particles and various DNA bases (adenine, guanine, cytosine, and thymine), which are used as molecular linkers because of their biological significance. In colloidal solutions, the color of silver nanoparticles may range from red to purple to orange to blue, depending on the degree of aggregation as well as the orientation of the individual particles within the aggregates. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and absorption spectroscopy were used to characterize the assemblies. DNA base-induced differential silver nanoparticle aggregation was quantified from the peak separation (relates to color) of surface plasmon resonance spectroscopy (SPRS) and the signal intensity of surface-enhanced Raman scattering (SERS), which rationalize the extent of silver-nucleobase interactions.

Ultrafast exciton migration in an HJ-aggregate: Potential surfaces and quantum dynamics

NASA Astrophysics Data System (ADS)

Binder, Robert; Polkehn, Matthias; Ma, Tianji; Burghardt, Irene

2017-01-01

Quantum dynamical and electronic structure calculations are combined to investigate the mechanism of exciton migration in an oligothiophene HJ aggregate, i.e., a combination of oligomer chains (J-type aggregates) and stacked aggregates of such chains (H-type aggregates). To this end, a Frenkel exciton model is parametrized by a recently introduced procedure [Binder et al., J. Chem. Phys. 141, 014101 (2014)] which uses oligomer excited-state calculations to perform an exact, point-wise mapping of coupled potential energy surfaces to an effective Frenkel model. Based upon this parametrization, the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method is employed to investigate ultrafast dynamics of exciton transfer in a small, asymmetric HJ aggregate model composed of 30 sites and 30 active modes. For a partially delocalized initial condition, it is shown that a torsional defect confines the trapped initial exciton, and planarization induces an ultrafast resonant transition between an HJ-aggregated segment and a covalently bound "dangling chain" end. This model is a minimal realization of experimentally investigated mixed systems exhibiting ultrafast exciton transfer between aggregated, highly planarized chains and neighboring disordered segments.

Fabrication of Ni@Ti core-shell nanoparticles by modified gas aggregation source

NASA Astrophysics Data System (ADS)

Hanuš, J.; Vaidulych, M.; Kylián, O.; Choukourov, A.; Kousal, J.; Khalakhan, I.; Cieslar, M.; Solař, P.; Biederman, H.

2017-11-01

Ni@Ti core-shell nanoparticles were prepared by a vacuum based method using the gas aggregation source (GAS) of nanoparticles. Ni nanoparticles fabricated in the GAS were afterwards coated by a Ti shell. The Ti shell was deposited by means of magnetron sputtering. The Ni nanoparticles were decelerated in the vicinity of the magnetron to the Ar drift velocity in the second deposition chamber. X-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy analysis of the nanoparticles showed the core-shell structure. It was shown that the thickness of the shell can be easily tuned by the process parameters with a maximum achieved thickness of the Ti shell ~2.5 nm. The core-shell structure was confirmed by the STEM analysis of the particles.

Plasmonic properties and enhanced fluorescence of gold and dye-doped silica nanoparticle aggregates

NASA Astrophysics Data System (ADS)

Green, Nathaniel Scott

The development of metal-enhanced fluorescence has prompted a great interest in augmenting the photophysical properties of fluorescent molecules with noble metal nanostructures. Our research efforts, outlined in this dissertation, focus on augmenting properties of fluorophores by conjugation with gold nanostructures. The project goals are split into two separate efforts; the enhancement in brightness of fluorophores and long distance non-radiative energy transfer between fluorophores. We believe that interacting dye-doped silica nanoparticles with gold nanoparticles can facilitate both of these phenomena. Our primary research interest is focused on optimizing brightness, as this goal should open a path to studying the second goal of non-radiative energy transfer. The two major challenges to this are constructing suitable nanomaterials and functionalizing them to promote plasmonically active complexes. The synthesis of dye-doped layered silica nanoparticles allows for control over the discrete location of the dye and a substrate that can be surface functionalized. Controlling the exact location of the dye is important to create a silica spacer, which promotes productive interactions with metal nanostructures. Furthermore, the synthesis of silica nanoparticles allows for various fluorophores to be studied in similar environments (removing solvent and other chemo-sensitive issues). Functionalizing the surface of silica nanoparticles allows control over the degree of silica and gold nanoparticle aggregation in solution. Heteroaggregation in solution is useful for producing well-aggregated clusters of many gold around a single silica nanoparticle. The dye-doped surface functionalized silica nanoparticles can than be mixed efficiently with gold nanomaterials. Aggregating multiple gold nanospheres around a single dye-doped silica nanoparticle can dramatically increase the fluorescent brightness of the sample via metal-enhanced fluorescence due to increase plasmonic scattering. Our aim is to promote heteroaggregation with functionalized silica nanoparticles while minimizing homoaggregation of silica-silica or gold-gold species. Reproducible production of multiple gold nanospheres about a dye-doped silica nanoparticle should lead to dramatic fluorescence brightness enhancements in solution. Gold nanorods can potentially be used to establish radiationless energy transfer between hetero dye-doped silica nanoparticles via gold nanorod plasmon mediated FRET by aggregating two different dye-doped silica nanoparticles preferentially at opposite ends of the nanorod. End-cap binding is accomplished by tuning the strength of gold binding ligands that functionalize the surface of the silica nanoparticles. The gold nanorod can then theoretically serve as a waveguide by employing the longitudinal plasmon as a non-radiative energy transfer agent between the two different fluorophores, giving rise to a new ultrafast signaling paradigm. Heteroaggregation of dye-doped silica nanoparticles and gold nanorods can be potentially employed to as nano waveguides. Construction and aggregation of functionalized silica and gold nano-materials provides an opportunity to advance the field of fluorescence. The synthesis of gold nano-particles allows control over their size and shape, which give rise to useful optical and electronic properties. Silica nanoparticles provide a framework allowing control over a requisite distance for increasing beneficial and deceasing non-radiative dye-metal interactions as well fluorophore protection. Our aim is to take advantage of fine-tuned synthetic control of functionalized nanomaterials to realize the great potential of solution based metal-enhanced fluorescence for future applications.

Synthesis and characterization of novel thermoplastic elastomers employing polyhedral oligomeric silsesquioxane physical crosslinks

NASA Astrophysics Data System (ADS)

Seurer, Bradley

Polyhedral oligomeric silsesquioxanes (POSS) are molecularly precise isotropic particles with average diameters of 1-2 nm. A typical T 8 POSS nanoparticle has an inorganic Si8O12 core surrounded by eight aliphatic or aromatic groups attached to the silicon vertices of the polyhedron promoting solubility in conventional solvents. Previously, efficient synthetic methods have been developed whereby one of the aliphatic groups on the periphery is substituted by a functional group capable of undergoing either homo- or copolymerization. In the current investigations, preparative methods for the chemical incorporation of POSS macromonomers in a series elastomers have been developed. Analysis of the copolymers using WAXD reveals that pendant POSS groups off the polymer backbones aggregate, and can crystallize as nanocrystals. From both line-broadening of the diffraction maxima, and also the oriented diffraction in a drawn material, the individual POSS sub-units are crystallizing as anisotropically shaped crystallites. The formation of POSS particle aggregation is strongly dependent on the nature of the polymeric matrix and the POSS peripheral group. X-ray studies show aggregation of POSS in ethylene-propylene elastomers occurred only with a phenyl periphery, whereas POSS particles with isobutyl and ethyl peripheries disperse within the polymer matrix. By altering the polymer matrix to one containing chain repulsive fluorine units, aggregation is observed with both the phenyl and isobutyl peripheries. Altering the polymer chain to poly(dimethylcyclooctadiene), POSS aggregates with isobutyl, ethyl, cyclopentyl, and phenyl peripheries. The formation of POSS nanocrystals increases the mechanical properties of these novel thermoplastic elastomers, including an increase in the tensile storage modulus and formation of a rubbery plateau region. Tensile tests of these elastomers show an increase in elastic modulus with increasing POSS loading. The elongation at break was as high as 720%. Cyclic tensile test show some hysteresis of the elastomers. However, the curves show Mullins effect behavior, commonly seen in elastomers. Elastomers with POSS dispersion, however, show poor mechanical properties. These results demonstrate the novel material property gains by the incorporation and aggregation of POSS in thermoplastic elastomers, as well as the influence of the POSS periphery.

Material influence on hot spot distribution in the nanoparticle heterodimer on film

NASA Astrophysics Data System (ADS)

Chen, Fang; Huang, Yingzhou; Wei, Hua; Wang, Shuxia; Zeng, Xiping; Cao, Wenbin; Wen, Weijia

2018-04-01

The metal nanoparticle aggregated on film, as an effective plasma enhancement pathway, has been widely used in various surface plasmon-related fields. In this study, the hot spots on the metal nanoparticle dimer composed of different materials (Agsbnd Au, Agsbnd Pd, and Agsbnd Cu) on metal (Au) film were investigated with finite element method. Based on the results, the hot spot distribution affected by the material can be confirmed by the electric field distribution of the metal nanoparticle dimer on the film. The aggregation effects of Au and Ag nanoparticles in Ausbnd Ag dimer system are not significant. However, for the Pdsbnd Ag dimer system, the hot spot aggregation effect is slightly larger than that of the Pd nanoparticle under the Ag nanoparticle. Besides, the non-uniform hot spots would bring about the light focusing phenomenon that the light intensity under Ag nanoparticle is almost 100 times greater than that under Cu nanoparticle in Agsbnd Cu dimer system. These results were further confirmed by the surface charge distribution, and analyzed based on the plasmonic hybridization theory. The data about the nanoparticle dimer on the dielectric (Si) film demonstrate the importance of induced image charges on the film surface in such a light focusing phenomenon. Our findings can enhance the understanding of the surface plasmon coupling in different materials, which may have great application prospects in surface plasmon-related fields, such as SERS, plasmonic enhanced solar cell, and plasmonic sensoring, etc.

Precursor Ion–Ion Aggregation in the Brust–Schiffrin Synthesis of Alkanethiol Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, Trent R.; Renslow, Ryan; Govind, Niranjan

Tetraoctylammonium bromide is used in the Brust-Schiffrin nanoparticle synthesis to phase-transfer chloroaurate ions from the aqueous phase to the organic phase. While it is established that the quaternary ammonium complex self-associates in the organic phase, the actual self-assembled structure is debated. We have confirmed the presence of ion-ion aggregates through quantitative 1H Nuclear Magnetic Resonance spectroscopy (NMR), pulsed field gradient, diffusion-ordered NMR (DOSY-NMR) and density functional theory (DFT) based NMR shift calculations. Tetraoctylammonium complexes (TOA-X, where X = Br, Cl, AuCl4-xBrx, AuBr4/Br and AuCl4-xBrx/Br) were investigated to measure the extraction of water into the organic phase. 1H NMR and DFTmore » based NMR shielding calculations indicated that deshielding of water is due to hydration of the anion and not the formation of the aqueous core of a reverse micelle. DOSYNMR results were consistent with the formation of small aggregates at typical Brust-Schiffrin synthesis concentrations. The extent of aggregation correlated with the size and electronegativity of the anion and was analyzed with a modified, isodesmic, indefinite aggregation model. The substitution of bromoauric acid for chlororoauric acid at conditions emulating the Brust-Schiffrin synthesis increased the aggregation of the quaternary ammonium complex. The increase in aggregation corresponded with an increase in the size of the produced nanoparticles from 4.3 to 4.6 nm. Understanding the selfassembly and supramolecular structure of precursors in the Brust-Schiffrin synthesis will enable further refinement of models that predict the growth of noble metal nanoparticles.« less

Influence of shear forces on the aggregation and sedimentation behavior of cerium dioxide (CeO2) nanoparticles under different hydrochemical conditions

NASA Astrophysics Data System (ADS)

Lv, Bowen; Wang, Chao; Hou, Jun; Wang, Peifang; Miao, Lingzhan; Li, Yi; Ao, Yanhui; Yang, Yangyang; You, Guoxiang; Xu, Yi

2016-07-01

This study contributed to a better understanding of the behavior of nanoparticles (NPs) in dynamic water. First, the aggregation behavior of CeO2 NPs at different pH values in various salt solutions was examined to determine the appropriate hydrochemical conditions for hydrodynamics study. Second, the aggregation behavior of CeO2 NPs under different shear forces was investigated at pH 4 and ionic strength 0 in various salt solutions to find out whether shear forces could influence the stability of the nanoparticles and if yes, how. Also, five-stage sedimentation tests were conducted to understand the influence of shear stress on the vertical distribution of CeO2 NPs in natural waters. The aggregation test showed that the shear force could increase the collision efficiency between NPs during aggregation and cause a relatively large mass of NPs to remain in suspension. Consequently, the nanoparticles had a greater possibility of continued aggregation. The sedimentation test under static conditions indicated that a large mass of NPs (>1000 nm) sink to the bottom layer, leaving only small aggregates dispersed in the upper or middle layer of the solution. However, later sedimentation studies under stirring conditions demonstrated that shear forces can disrupt this stratification phenomenon. These results suggest that shear forces can influence the spatial distribution of NPs in natural waters, which might lead to different toxicities of CeO2 NPs to aquatic organisms distributed in the different water layers. This study contributes to a better understanding of nanomaterial toxicology and provides a way for further research.

Cross-linking gold nanoparticles aggregation method based on localised surface plasmon resonance for quantitative detection of miR-155.

PubMed

Esmaeili-Bandboni, Aghil; Amini, Seyed Mohammad; Faridi-Majidi, Reza; Bagheri, Jamshid; Mohammadnejad, Javad; Sadroddiny, Esmaeil

2018-06-01

MiR-155 plays a critical role in the formation of cancers and other diseases. In this study, the authors aimed to design and fabricate a biosensor based on cross-linking gold nanoparticles (AuNPs) aggregation for the detection and quantification of miR-155. Also, they intended to compare this method with SYBR Green real-time polymerase chain reaction (PCR). Primers for real-time PCR, and two thiolated capture probes for biosensor, complementary with miR-155, were designed. Citrate capped AuNPs (18.7 ± 3.6 nm) were synthesised and thiolated capture probes immobilised to AuNPs. The various concentrations of synthetic miR-155 were measured by this biosensor and real-time PCR method. Colorimetric changes were studied, and the calibration curves were plotted. Results showed the detection limit of 10 nM for the fabricated biosensor and real-time PCR. Also, eye detection using colour showed the weaker detection limit (1 µM), for this biosensor. MiR-133b as the non-complementary target could not cause a change in both colour and UV-visible spectrum. The increase in hydrodynamic diameter and negative zeta potential of AuNPs after the addition of probes verified the biosensor accurately fabricated. This fabricated biosensor could detect miR-155 simpler and faster than previous methods.

Rapid and PCR-free DNA detection by nanoaggregation-enhanced chemiluminescence

Treesearch

Renu Singh; Alexandra Feltmeyer; Olga Saiapina; Jennifer Juzwik; Brett Arenz; Abdennour Abbas

2017-01-01

The aggregation of gold nanoparticles (AuNPs) is known to induce an enhancement of localized surface plasmon resonance due to the coupling of plasmonic fields of adjacent nanoparticles. Here we show that AuNPs aggregation also causes a significant enhancement of chemiluminescence in the presence of luminophores. The phenomenon is used to introduce a rapid and sensitive...

Controlled release of B-carotene in B-lactoglobulin-dextran conjugates nanoparticles in vitro digestion and the transport with Caco-2 monolayers

USDA-ARS?s Scientific Manuscript database

Undesirable aggregation of nanoparticles stabilized by proteins may may occur at the protein’s isoelectric point when the particle has zero net charge. Aggregation may be reduced bychanging the isoelectric point by conjugation of free amino groups with reducing sugars (Maillard reaction). Alternativ...

Tetanus toxoid-loaded cationic non-aggregated nanostructured lipid particles triggered strong humoral and cellular immune responses.

PubMed

Kaur, Amandeep; Jyoti, Kiran; Rai, Shweta; Sidhu, Rupinder; Pandey, Ravi Shankar; Jain, Upendra Kumar; Katyal, Anju; Madan, Jitender

2016-05-01

In the present investigation, non-aggregated cationic and unmodified nanoparticles (TT-C-NLPs4 and TT-NLPs1) were prepared of about 49.2 ± 6.8-nm and 40.8 ± 8.3-nm, respectively. In addition, spherical shape, crystalline architecture and cationic charge were also noticed. Furthermore, integrity and conformational stability of TT were maintained in both TT-C-NLPs4 and TT-NLPs1, as evidenced by symmetrical position of bands and superimposed spectra, respectively in SDS-PAGE and circular dichroism. Cellular uptake in RAW264.7 cells indicating the concentration-dependent internalisation of nanoparticles. Qualitatively, CLSM exhibited enhanced cellular uptake of non-aggregated TT-C-NLPs4 owing to interaction with negatively charged plasma membrane and clevaloe mediated/independent endocytosis. In last, in vivo immunisation with non-aggregated TT-C-NLPs4 elicited strong humoral (anti-TT IgG) and cellular (IFN-γ) immune responses at day 42, as compared to non-aggregated TT-NLPs1 and TT-Alum following booster immunisation at day 14 and 28. Thus, non-aggregated cationic lipid nanoparticles may be a potent immune-adjuvant for parenteral delivery of weak antigens.

Efficient synthetic access to thermo-responsive core/shell nanoparticles

NASA Astrophysics Data System (ADS)

Dine, Enaam Jamal Al; Ferjaoui, Zied; Roques-Carmes, Thibault; Schjen, Aleksandra; Meftah, Abdelaziz; Hamieh, Tayssir; Toufaily, Joumana; Schneider, Raphaël; Gaffet, Eric; Alem, Halima

2017-03-01

Core/shell nanostructures based on silica, fluorescent ZnO quantum dots (QDs) and superparamagnetic Fe3O4 nanoparticles (NPs) were prepared and fully characterized by the combination of different techniques and the physical properties of the nanostructures were studied. We demonstrate the efficiency of the atom transfer radical polymerization with activators regenerated by electron transfer process to graft (co-)polymers of different structures and polarity at the surface of metal oxide NPs. The influence of the polymer chain configuration on the optical properties of the ZnO/polymer core/shell QDs was enlightened. Concerning the magnetic properties of the Fe3O4/polymer nanostructures, only the amount of the grafted polymer plays a role on the saturation magnetization of the NPs and no influence of the aggregation was evidenced. The simple and fast process described in this work is efficient for the grafting of copolymers from surfaces and the derived NPs display the combination of the physical properties of the core and the macromolecular behavior of the shell.

Efficient synthetic access to thermo-responsive core/shell nanoparticles.

PubMed

Dine, Enaam Jamal Al; Ferjaoui, Zied; Roques-Carmes, Thibault; Schjen, Aleksandra; Meftah, Abdelaziz; Hamieh, Tayssir; Toufaily, Joumana; Schneider, Raphaël; Gaffet, Eric; Alem, Halima

2017-03-24

Core/shell nanostructures based on silica, fluorescent ZnO quantum dots (QDs) and superparamagnetic Fe 3 O 4 nanoparticles (NPs) were prepared and fully characterized by the combination of different techniques and the physical properties of the nanostructures were studied. We demonstrate the efficiency of the atom transfer radical polymerization with activators regenerated by electron transfer process to graft (co-)polymers of different structures and polarity at the surface of metal oxide NPs. The influence of the polymer chain configuration on the optical properties of the ZnO/polymer core/shell QDs was enlightened. Concerning the magnetic properties of the Fe 3 O 4 /polymer nanostructures, only the amount of the grafted polymer plays a role on the saturation magnetization of the NPs and no influence of the aggregation was evidenced. The simple and fast process described in this work is efficient for the grafting of copolymers from surfaces and the derived NPs display the combination of the physical properties of the core and the macromolecular behavior of the shell.

TEM and SP-ICP-MS analysis of the release of silver nanoparticles from decoration of pastry.

PubMed

Verleysen, E; Van Doren, E; Waegeneers, N; De Temmerman, P-J; Abi Daoud Francisco, M; Mast, J

2015-04-08

Metallic silver is an EU approved food additive referred to as E174. It is generally assumed that silver is only present in bulk form in the food chain. This work demonstrates that a simple treatment with water of "silver pearls", meant for decoration of pastry, results in the release of a subfraction of silver nanoparticles. The number-based size and shape distributions of the single, aggregated, and/or agglomerated particles released from the silver pearls were determined by combining conventional bright-field TEM imaging with semiautomatic particle detection and analysis. In addition, the crystal structure of the particles was studied by electron diffraction and chemical information was obtained by combining HAADF-STEM imaging with EDX spectroscopy and mapping. The TEM results were confirmed by SP-ICP-MS. The representative Ag test nanomaterial NM-300 K was used as a positive control to determine the uncertainty on the measurement of the size and shape of the particles.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perovic, Iva; Davidyants, Anastasia; Evans, John Spencer

In the mollusk shell there exists a framework silk fibroin-polysaccharide hydrogel coating around nacre aragonite tablets, and this coating facilitates the synthesis and organization of mineral nanoparticles into mesocrystals. In this report, we identify that a protein component of this coating, n16.3, is a hydrogelator. Due to the presence of intrinsic disorder, aggregation-prone regions, and nearly equal balance of anionic and cationic side chains, this protein assembles to form porous mesoscale hydrogel particles in solution and on mica surfaces. These hydrogel particles change their dimensionality, organization, and internal structure in response to pH and ions, particularly Ca(II), which indicates thatmore » these behave as ion-responsive or “smart” hydrogels. Thus, in addition to silk fibroins, the gel phase of the mollusk shell nacre framework layer may actually consist of several framework hydrogelator proteins, such as n16.3, which can promote mineral nanoparticle organization and assembly during the nacre biomineralization process and also serve as a model system for designing ion-responsive, composite, and smart hydrogels.« less

Adaptive polymeric nanomaterials utilizing reversible covalent and hydrogen bonding

NASA Astrophysics Data System (ADS)

Neikirk, Colin

Adaptive materials based on stimuli responsive and reversible bonding moieties are a rapidly developing area of materials research. Advances in supramolecular chemistry are now being adapted to novel molecular architectures including supramolecular polymers to allow small, reversible changes in molecular and nanoscale structure to affect large changes in macroscale properties. Meanwhile, dynamic covalent chemistry provides a complementary approach that will also play a role in the development of smart adaptive materials. In this thesis, we present several advances to the field of adaptive materials and also provide relevant insight to the areas of polymer nanocomposites and polymer nanoparticles. First, we have utilized the innate molecular recognition and binding capabilities of the quadruple hydrogen bonding group ureidopyrimidinone (UPy) to prepare supramolecular polymer nanocomposites based on supramolecular poly(caprolactone) which show improved mechanical properties, but also an increase in particle aggregation with nanoparticle UPy functionalization. We also present further insight into the relative effects of filler-filler, filler-matrix, and matrix-matrix interactions using a UPy side-chain functional poly(butyl acrylate). These nanocomposites have markedly different behavior depending on the amount of UPy sidechain functionality. Meanwhile, our investigations of reversible photo-response showed that coumarin functionality in polymer nanoparticles not only facilitates light mediated aggregation/dissociation behavior, but also provides a substantial overall reduction in particle size and improvement in nanoparticle stability for particles prepared by Flash NanoPrecipitation. Finally, we have combined these stimuli responsive motifs as a starting point for the development of multiresponsive adaptive materials. The synthesis of a library of multifunctional materials has provided a strong base for future research in this area, although our initial investigations were ultimately unsuccessful due to photodegradation of the UPy moiety in chloroform solution. This thesis has provided the Priestley lab with a solid base for the further investigation of the diverse applications and unsolved science of stimuli responsive adaptive materials.

Impact of heat treatment on size, structure, and bioactivity of elemental selenium nanoparticles

PubMed Central

Zhang, Jinsong; Taylor, Ethan W; Wan, Xiaochun; Peng, Dungeng

2012-01-01

Background Elemental selenium nanoparticles have emerged as a novel selenium source with the advantage of reduced risk of selenium toxicity. The present work investigated whether heat treatment affects the size, structure, and bioactivity of selenium nanoparticles. Methods and results After a one-hour incubation of solution containing 80 nm selenium particles in a 90°C water bath, the nanoparticles aggregated into larger 110 nm particles and nanorods (290 nm × 70 nm), leading to significantly reduced bioavailability and phase II enzyme induction in selenium-deficient mice. When a solution containing 40 nm selenium nanoparticles was treated under the same conditions, the nanoparticles aggregated into larger 72 nm particles but did not transform into nanorods, demonstrating that the thermostability of selenium nanoparticles is size-dependent, smaller selenium nanoparticles being more resistant than larger selenium nanoparticles to transformation into nanorods during heat treatment. Conclusion The present results suggest that temperature and duration of the heat process, as well as the original nanoparticle size, should be carefully selected when a solution containing selenium nanoparticles is added to functional foods. PMID:22359458

Small-Angle Neutron Scattering Study of Interplay of Attractive and Repulsive Interactions in Nanoparticle-Polymer System.

PubMed

Kumar, Sugam; Aswal, Vinod K; Kohlbrecher, Joachim

2016-02-16

The phase behavior of nanoparticle (silica)-polymer (polyethylene glycol) system without and with an electrolyte (NaCl) has been studied. It is observed that nanoparticle-polymer system behaves very differently in the presence of electrolyte. In the absence of electrolyte, the nanoparticle-polymer system remains in one-phase even at very high polymer concentrations. On the other hand, a re-entrant phase behavior is found in the presence of electrolyte, where one-phase (individual) system undergoes two-phase (nanoparticle aggregation) and then back to one-phase with increasing polymer concentration. The regime of two-phase system has been tuned by varying the electrolyte concentration. The polymer concentration range over which the two-phase system exists is significantly enhanced with the increase in the electrolyte concentration. These systems have been characterized by small-angle neutron scattering (SANS) experiments of contrast-marching the polymer to the solvent. The data are modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The phase behavior of nanoparticle-polymer system is explained by interplay of attractive (polymer-induced attractive depletion between nanoparticles) and repulsive (nanoparticle-nanoparticle electrostatic repulsion and polymer-polymer repulsion) interactions present in the system. In the absence of electrolyte, the strong electrostatic repulsion between nanoparticles dominates over the polymer-induced depletion attraction and the nanoparticle system remains in one-phase. With addition of electrolyte, depletion attraction overcomes electrostatic repulsion at some polymer concentration, resulting into nanoparticle aggregation and two-phase system. Further addition of polymer increases the polymer-polymer repulsion which eventually reduces the strength of depletion and hence re-entrant phase behavior. The effects of varying electrolyte concentration on the phase behavior of nanoparticle-polymer system are understood in terms of modifications in nanoparticle-nanoparticle and polymer-polymer interactions. The nanoparticle aggregates in two-phase systems are found to have surface fractal morphology.

The molecular mass of dextran used to modify magnetite nanoparticles affects insulin amyloid aggregation

NASA Astrophysics Data System (ADS)

Siposova, Katarina; Pospiskova, Kristyna; Bednarikova, Zuzana; Safarik, Ivo; Safarikova, Mirka; Kubovcikova, Martina; Kopcansky, Peter; Gazova, Zuzana

2017-04-01

Protein transformation from its soluble state into amyloid aggregates is associated with amyloid-related diseases. Amyloid deposits of insulin fibrils have been found in the sites of subcutaneous insulin application in patients with prolonged diabetes. Using atomic force microscopy and ThT fluorescence assay we have investigated the interference of insulin amyloid aggregation with superparamagnetic Fe3O4-based nanoparticles (SPIONs) coated with dextran (DEX); molecular mass of dextran was equal to 15-20, 40 or 70 kDa. The obtained data indicate that all three types of dextran coated nanoparticles (NP-FeDEXs) are able to inhibit insulin fibrillization and to destroy amyloid fibrils. The extent of anti-amyloid activities depends on the properties of NP-FeDEXs, mainly on the size of nanoparticles which is determined by molecular mass of dextran molecules. The most effective inhibiting activity was observed for the smallest nanoparticles coated with 15-20 kDa dextran. Contrary, the highest destroying activity was observed for the largest NP-FeDEX (70 kDa dextran).

Bioresponsive polymer coating on nanoparticles

NASA Astrophysics Data System (ADS)

Laemthong, Tunyaboon

Nanotechnology incorporated with molecular biology became a promising way to treat cancer. The size of nanoparticles enables them to overcome the side effects noticed in cancer treatment like chemotherapy and surgery. Various types and shapes of nanoparticles have been synthesized and used in drug delivery to tumor sites. However, one of problems of using these nanoparticles is the aggregation after injecting them into human body due to flow rate of bloodstream. The coagulation and aggregation will result in clogging blood vessel and lower therapeutic efficacy. In this thesis, a solution to the aggregation problem was proposed, which is coating biopolymer on nanoparticles (NPs). The experimental sections covered synthesis and characterization of breast cancer specific targeting drug-encapsulated NPs and biopolymer coating on the surface of Au-Fe3O4 NPs for thermal therapy. Furthermore, in vitro studies of these NPs with breast cancer cells were also included. The specific targeting anticancer drug-encapsulated NRs showed significant inhibition in BT-474 breast cancer cell growth. The Au-Fe3O4 NPs has a possibility to treat cancer cells using the thermal therapy approach.

Non-linear optical response by functionalized gold nanospheres: identifying design principles to maximize the molecular photo-release.

PubMed

Bergamini, Luca; Voliani, Valerio; Cappello, Valentina; Nifosì, Riccardo; Corni, Stefano

2015-08-28

In a recent study by Voliani et al. [Small, 2011, 7, 3271], the electromagnetic field enhancement in the vicinity of the gold nanoparticle surface has been exploited to achieve photocontrolled release of a molecular cargo conjugated to the nanoparticles via 1,2,3-triazole, a photocleavable moiety. The aim of the present study is to investigate the mechanism of the photorelease by characterizing the nanoparticle aggregation status within the cells and simulating the electric field enhancement in a range of experimentally realistic geometries, such as single Au nanoparticles, dimers, trimers and random aggregates. Two plasmon-enhanced processes are examined for triazole photocleavage, i.e. three-photon excitation and third-harmonic-generation (one-photon) excitation. Taking into account the absorption cross sections of the triazole, we conclude that the latter mechanism is more efficient, and provides a photocleavage rate that explains the experimental findings. Moreover, we determine which aggregate geometries are required to maximize the field enhancement, and the dependence of such enhancement on the excitation wavelength. Our results provide design principles for maximizing the multiphoton molecular photorelease by such functionalized gold nanoparticles.

Heated probe diagnostic inside of the gas aggregation nanocluster source

NASA Astrophysics Data System (ADS)

Kolpakova, Anna; Shelemin, Artem; Kousal, Jaroslav; Kudrna, Pavel; Tichy, Milan; Biederman, Hynek; Surface; Plasma Science Team

2016-09-01

Gas aggregation cluster sources (GAS) usually operate outside common working conditions of most magnetrons and the size of nanoparticles created in GAS is below that commonly studied in dusty plasmas. Therefore, experimental data obtained inside the GAS are important for better understanding of process of nanoparticles formation. In order to study the conditions inside the gas aggregation chamber, special ``diagnostic GAS'' has been constructed. It allows simultaneous monitoring (or spatial profiling) by means of optical emission spectroscopy, mass spectrometry and probe diagnostic. Data obtained from Langmuir and heated probes map the plasma parameters in two dimensions - radial and axial. Titanium has been studied as an example of metal for which the reactive gas in the chamber starts nanoparticles production. Three basic situations were investigated: sputtering from clean titanium target in argon, sputtering from partially pre-oxidized target and sputtering with oxygen introduced into the discharge. It was found that during formation of nanoparticles the plasma parameters differ strongly from the situation without nanoparticles. These experimental data will support the efforts of more realistic modeling of the process. Czech Science Foundation 15-00863S.

Aggregation effect on absorbance spectrum of laser ablated gold nanoparticles

NASA Astrophysics Data System (ADS)

Isnaeni; Irmaniar; Herbani, Y.

2017-04-01

Plasmon of gold nanoparticles is one of the hot topics nowadays due to various possible applications. The application is determined by plasmon peak in absorbance spectrum. We have fabricated gold nanoparticles using laser ablation technique and studied the influence of CTAB (Cetyl trimethylammonium bromide) effect on the optical characterization of fabricated gold nanoparticles. We ablated a gold plate using NdYAG pulsed laser at 1064 nm wavelength, 10 Hz pulse frequency at low energy density. We found there are two distinctive plasmon peaks, i.e., primary and secondary peaks, where the secondary peak is the main interests of this work. Our simulation results have revealed that the secondary plasmon peak is affected by random aggregation of gold nanoparticles. Our research leads to good techniques on fabrication of colloidal gold nanoparticles in aqueous solution using laser ablation technique.

Long-term exposure to gold nanoparticles accelerates larval metamorphosis without affecting mass in wood frogs (Lithobates sylvaticus) at environmentally relevant concentrations.

PubMed

Fong, Peter P; Thompson, Lucas B; Carfagno, Gerardo L F; Sitton, Andrea J

2016-09-01

Nanoparticles are environmental contaminants of emerging concern. Exposure to engineered nanoparticles has been shown to have detrimental effects on aquatic organisms. The authors synthesized gold nanoparticles (18.1 ± 3.5 nm) and tested their effects on time to and weight at metamorphosis in wood frog (Lithobates sylvaticus) tadpoles, a species known to be sensitive to environmental stressors. Continuous exposure to all concentrations of gold nanoparticles (0.05 pM, 0.5 pM, and 5 pM in particles) for up to 55 d significantly reduced time to metamorphosis by as much as an average of 3 d (p < 0.05). However, exposure to gold nanoparticles had no effect on tadpole mass at metamorphosis. The approximately 18-nm gold nanoparticles used were metastable in dechlorinated tap water, resulting in a change in surface charge and aggregation over time, leading to negatively charged aggregates that were on the order of 60 nm to 110 nm. Nanoparticle aggregation could exacerbate the effect on time to metamorphosis. To the authors' knowledge, the present study is the first report on the effect of engineered nanoparticles of any kind on life-history variables in an amphibian, a taxonomic group that has been declining globally for at least 25 yr. Environ Toxicol Chem 2016;35:2304-2310. © 2016 SETAC. © 2016 SETAC.

Surface-Directed Synthesis of Erbium-Doped Yttrium Oxide Nanoparticles within Organosilane Zeptoliter Containers

PubMed Central

2015-01-01

We introduce an approach to synthesize rare earth oxide nanoparticles using high temperature without aggregation of the nanoparticles. The dispersity of the nanoparticles is controlled at the nanoscale by using small organosilane molds as reaction containers. Zeptoliter reaction vessels prepared from organosilane self-assembled monolayers (SAMs) were used for the surface-directed synthesis of rare earth oxide (REO) nanoparticles. Nanopores of octadecyltrichlorosilane were prepared on Si(111) using particle lithography with immersion steps. The nanopores were filled with a precursor solution of erbium and yttrium salts to confine the crystallization step to occur within individual zeptoliter-sized organosilane reaction vessels. Areas between the nanopores were separated by a matrix film of octadecyltrichlorosilane. With heating, the organosilane template was removed by calcination to generate a surface array of erbium-doped yttria nanoparticles. Nanoparticles synthesized by the surface-directed approach retain the periodic arrangement of the nanopores formed from mesoparticle masks. While bulk rare earth oxides can be readily prepared by solid state methods at high temperature (>900 °C), approaches for preparing REO nanoparticles are limited. Conventional wet chemistry methods are limited to low temperatures according to the boiling points of the solvents used for synthesis. To achieve crystallinity of REO nanoparticles requires steps for high-temperature processing of samples, which can cause self-aggregation and dispersity in sample diameters. The facile steps for particle lithography address the problems of aggregation and the requirement for high-temperature synthesis. PMID:25163977

Gene transcription patterns and energy reserves in Daphnia magna show no nanoparticle specific toxicity when exposed to ZnO and CuO nanoparticles.

PubMed

Adam, Nathalie; Vergauwen, Lucia; Blust, Ronny; Knapen, Dries

2015-04-01

There is still a lot of contradiction on whether metal ions are solely responsible for the observed toxicity of ZnO and CuO nanoparticles to aquatic species. While most experiments have studied nanoparticle effects at organismal levels (e.g. mortality, reproduction), effects at lower levels of biological organization may clarify the role of metal ions, nanoparticles and nanoparticle aggregates. In this study, the effect of ZnO and CuO nanoparticles was tested at two lower levels: energy reserves and gene transcription and compared with zinc and copper salts. Daphnia magna was exposed during 96h to 10% immobilization concentrations of all chemicals, after which daphnids were sampled for determination of glycogen, lipid and protein concentration and for a differential gene transcription analysis using microarray. The dissolved, nanoparticle and aggregated fraction in the medium was characterized. The results showed that ZnO nanoparticles had largely dissolved directly after addition to the test medium. The CuO nanoparticles mostly formed aggregates, while only a small fraction dissolved. The exposure to zinc (both nano and metal salt) had no effect on the available energy reserves. However, in the copper exposure, the glycogen, lipid and protein concentration in the exposed daphnids was lower than in the unexposed ones. When comparing the nanoparticle (ZnO or CuO) exposed daphnids to the metal salt (zinc or copper salt) exposed daphnids, the microarray results showed no significantly differentially transcribed gene fragments. The results indicate that under the current exposure conditions the toxicity of ZnO and CuO nanoparticles to D. magna is solely caused by toxic metal ions. Copyright © 2015 Elsevier Inc. All rights reserved.

Physicochemical properties of protein-modified silver nanoparticles in seawater

NASA Astrophysics Data System (ADS)

Zhong, Hangyue

2013-10-01

This study investigated the physicochemical properties of silver nanoparticles stabilized with casein protein in seawater. UV?vis spectrometry, dynamic light scattering (DLS), and transmission electron microscopy (TEM) were applied to measure the stability of silver nanoparticles in seawater samples. The obtained results show an increased aggregation tendency of silver nanoparticles in seawater, which could be attributed its relatively high cation concentration that could neutralize the negatively charges adsorbed on the surface of silver nanoparticles and reduce the electrostatic repulsion forces between nanoparticles. Similarly, due to the surface charge screening process, the zeta potential of silver nanoparticles in seawater decreased. This observation further supported the aggregation behavior of silver nanoparticles. This study also investigated the dissolution of silver nanoparticles in seawater. Result shows that the silver nanoparticle dissolution in DI water is lower than in seawater, which is attributed to the high Cl? concentration present in seawater. As Cl? can react with silver and form soluble AgCl complex, dissolution of silver nanoparticles was enhanced. Finally, this study demonstrated that silver nanoparticles are destabilized in seawater condition. These results may be helpful in understanding the environmental risk of discharged silver nanoparticles in seawater conditions.

Photochemical induced growth and aggregation of metal nanoparticles in diode-array spectrophotometer via excited dimethyl-sulfoxide.

PubMed

Zidki, Tomer; Cohen, Haim; Meyerstein, Dan

2010-10-21

Ag(0) and Au(0) nanoparticles suspended in dilute aqueous solutions containing (CH(3))(2)SO are photochemically unstable. The light source of a diode-array spectrophotometer induces, within less than a minute, particle growth and aggregation. The results indicate that this process is triggered by UV light absorption by the (CH(3))(2)SO.

Structure and Interaction in the pH-Dependent Phase Behavior of Nanoparticle-Protein Systems.

PubMed

Yadav, Indresh; Kumar, Sugam; Aswal, Vinod K; Kohlbrecher, Joachim

2017-02-07

The pH-dependent structure and interaction of anionic silica nanoparticles (diameter 18 nm) with two globular model proteins, lysozyme and bovine serum albumin (BSA), have been studied. Cationic lysozyme adsorbs strongly on the nanoparticles, and the adsorption follows exponential growth as a function of lysozyme concentration, where the saturation value increases as pH approaches the isoelectric point (IEP) of lysozyme. By contrast, irrespective of pH, anionic BSA does not show any adsorption. Despite having a different nature of interactions, both proteins render a similar phase behavior where nanoparticle-protein systems transform from being one-phase (clear) to two-phase (turbid) above a critical protein concentration (CPC). The measurements have been carried out for a fixed concentration of silica nanoparticles (1 wt %) with varying protein concentrations (0-5 wt %). The CPC is found to be much higher for BSA than for lysozyme and increases for lysozyme but decreases for BSA as pH approaches their respective IEPs. The structure and interaction in these systems have been examined using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The effective hydrodynamic size of the nanoparticles measured using DLS increases with protein concentration and is related to the aggregation of the nanoparticles above the CPC. The propensity of the nanoparticles to aggregate is suppressed for lysozyme and enhanced for BSA as pH approached their respective IEPs. This behavior is understood from SANS data through the interaction potential determined by the interplay of electrostatic repulsion with a short-range attraction for lysozyme and long-range attraction for BSA. The nanoparticle aggregation is caused by charge neutralization by the oppositely charged lysozyme and through depletion for similarly charged BSA. Lysozyme-mediated attractive interaction decreases as pH approaches the IEP because of a decrease in the charge on the protein. In the case of BSA, a decrease in the BSA-BSA repulsion enhances the depletion attraction between the nanoparticles as pH is shifted toward the IEP. The morphology of the nanoparticle aggregates is found to be mass fractal.

Extracellular proteins limit the dispersal of biogenic nanoparticles

USGS Publications Warehouse

Moreau, J.W.; Weber, P.K.; Martin, M.C.; Gilbert, B.; Hutcheon, I.D.; Banfield, J.F.

2007-01-01

High-spatial-resolution secondary ion microprobe spectrometry, synchrotron radiation-based Fourier-transform infrared spectroscopy, and polyacrylamide gel analysis demonstrated the intimate association of proteins with spheroidal aggregates of biogenic zinc sulfide nanocrystals, an example of extracellular biomineralization. Experiments involving synthetic zinc sulfide nanoparticles and representative amino acids indicated a driving role for cysteine in rapid nanoparticle aggregation. These findings suggest that microbially derived extracellular proteins can limit the dispersal of nanoparticulate metal-bearing phases, such as the mineral products of bioremediation, that may otherwise be transported away from their source by subsurface fluid flow.

Effects of humic substances on precipitation and aggregation of zinc sulfide nanoparticles

USGS Publications Warehouse

Deonarine, Amrika; Lau, Boris L.T.; Aiken, George R.; Ryan, Joseph N.; Hsu-Kim, Heileen

2011-01-01

Nanoparticulate metal sulfides such as ZnS can influence the transport and bioavailability of pollutant metals in anaerobic environments. The aim of this work was to investigate how the composition of dissolved natural organic matter (NOM) influences the stability of zinc sulfide nanoparticles as they nucleate and aggregate in water with dissolved NOM. We compared NOM fractions that were isolated from several surface waters and represented a range of characteristics including molecular weight, type of carbon, and ligand density. Dynamic light scattering was employed to monitor the growth and aggregation of Zn−S−NOM nanoparticles in supersaturated solutions containing dissolved aquatic humic substances. The NOM was observed to reduce particle growth rates, depending on solution variables such as type and concentration of NOM, monovalent electrolyte concentration, and pH. The rates of growth increased with increasing ionic strength, indicating that observed growth rates primarily represented aggregation of charged Zn−S−NOM particles. Furthermore, the observed rates decreased with increasing molecular weight and aromatic content of the NOM fractions, while carboxylate and reduced sulfur content had little effect. Differences between NOM were likely due to properties that increased electrosteric hindrances for aggregation. Overall, results of this study suggest that the composition and source of NOM are key factors that contribute to the stabilization and persistence of zinc sulfide nanoparticles in the aquatic environment.

Preparation and evaluation of high dispersion stable nanocrystal formulation of poorly water-soluble compounds by using povacoat.

PubMed

Yuminoki, Kayo; Seko, Fuko; Horii, Shota; Takeuchi, Haruka; Teramoto, Katsuya; Nakada, Yuichiro; Hashimoto, Naofumi

2014-11-01

In this study, we reported the application of Povacoat®, a hydrophilic polyvinylalcohol copolymer, as a dispersion stabilizer of nanoparticles of poorly water-soluble compounds. In addition, the influence of aggregation of the nanoparticles on their solubility and oral absorption was studied. Griseofulvin (GF) was used as a model compound with poor water solubility and was milled to nanoparticles by wet bead milling. The dispersion stability of GF milled with Povacoat® or the generally used polymers (polyvinylalcohol, hydroxypropylcellulose SSL, and polyvinylpyrrolidone K30) was compared. Milled GF suspended in Povacoat® aqueous solution with D-mannitol, added to improve the disintegration rate of freeze-dried GF, exhibited high dispersion stability without aggregation (D90 = ca. 0.220 μm), whereas milled GF suspended in aqueous solutions of the other polymers aggregated (D90 > 5 μm). Milled GF with Povacoat® showed improved aqueous solubility and bioavailability compared with the other polymers. The aggregation of nanoparticles had significant impact on the solubility and bioavailability of GF. Povacoat® also prevented the aggregation of the various milled poorly water-soluble compounds (hydrochlorothiazide and tolbutamide, etc.) more effectively than the other polymers. These results showed that Povacoat® could have wide applicability to the development of nanoformulations of poorly water-soluble compounds. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Glutathione-Capped Gold Nanoparticles-Based Photoacoustic Sensor for Label-Free Detection of Lead Ions

NASA Astrophysics Data System (ADS)

Shi, R.; Liu, X.-J.; Ying, Y.

2017-07-01

The photoacoustic signal generated by laser-induced nanobubbles (PA-LINB) proved to be a sensitive tool to monitor the aggregation of gold nanoparticles. Here, a simple and label-free photoacoustic method for the rapid detection of Pb2+ in the aqueous phase was developed. Due to the high affinity of Pb2+ ions to glutathione, the presence of Pb2+ led to the aggregation of glutathione-conjugated gold nanoparticles (GSH-GNPs). Hence, by measuring the variation of the PA-LINB signal after the aggregation of GSH-GNPs, Pb2+ can be quantified. A low detection limit for Pb2+ (42 nM) and a wide linear working range ( 42-1000 nM) were achieved. Furthermore, the proposed method showed good selectivity against other metal ions.

Aggregation of gold nanoparticles followed by methotrexate release enables Raman imaging of drug delivery into cancer cells

NASA Astrophysics Data System (ADS)

Durgadas, C. V.; Sharma, C. P.; Paul, W.; Rekha, M. R.; Sreenivasan, K.

2012-09-01

This study refers an aqueous synthesis of methotrexate (MTX)-conjugated gold nanoparticles (GNPs), their interaction with HepG2 cells, and the use of Raman imaging to observe cellular internalization and drug delivery. GNPs of average size 3.5-5 nm were stabilized using the amine terminated bifunctional biocompatible copolymer and amended by conjugating MTX, an anticancer drug. The nanoparticles were released MTX at a faster rate in acidic pH and subsequently found to form aggregates. The Raman signals of cellular components were found to be enhanced by the aggregated particles enabling the mapping to visualize site-specific drug delivery. The methodology seems to have potential in optimizing the characteristics of nanodrug carriers for emptying the cargo precisely at specified sites.

A gold nanoparticle-based immunochromatographic assay: the influence of nanoparticulate size.

PubMed

Lou, Sha; Ye, Jia-ying; Li, Ke-qiang; Wu, Aiguo

2012-03-07

Four different sized gold nanoparticles (14 nm, 16 nm, 35 nm and 38 nm) were prepared to conjugate an antibody for a gold nanoparticle-based immunochromatographic assay which has many applications in both basic research and clinical diagnosis. This study focuses on the conjugation efficiency of the antibody with different sized gold nanoparticles. The effect of factors such as pH value and concentration of antibody has been quantificationally discussed using spectra methods after adding 1 wt% NaCl which induced gold nanoparticle aggregation. It was found that different sized gold nanoparticles had different conjugation efficiencies under different pH values and concentrations of antibody. Among the four sized gold nanoparticles, the 16 nm gold nanoparticles have the minimum requirement for antibody concentrations to avoid aggregation comparing to other sized gold nanoparticles but are less sensitive for detecting the real sample compared to the 38 nm gold nanoparticles. Consequently, different sized gold nanoparticles should be labeled with antibody under optimal pH value and optimal concentrations of antibody. It will be helpful for the application of antibody-labeled gold nanoparticles in the fields of clinic diagnosis, environmental analysis and so on in future.

Structural organization of surfactant aggregates in vacuo: a molecular dynamics and well-tempered metadynamics study.

PubMed

Longhi, Giovanna; Fornili, Sandro L; Turco Liveri, Vincenzo

2015-07-07

Experimental investigations using mass spectrometry have established that surfactant molecules are able to form aggregates in the gas phase. However, there is no general consensus on the organization of these aggregates and how it depends on the aggregation number and surfactant molecular structure. In the present paper we investigate the structural organization of some surfactants in vacuo by molecular dynamics and well-tempered metadynamics simulations to widely explore the space of their possible conformations in vacuo. To study how the specific molecular features of such compounds affect their organization, we have considered as paradigmatic surfactants, the anionic single-chain sodium dodecyl sulfate (SDS), the anionic double-chain sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and the zwitterionic single-chain dodecyl phosphatidyl choline (DPC) within a wide aggregation number range (from 5 to 100). We observe that for low aggregation numbers the aggregates show in vacuo the typical structure of reverse micelles, while for large aggregation numbers a variety of globular aggregates occur that are characterized by the coexistence of interlaced domains formed by the polar or ionic heads and by the alkyl chains of the surfactants. Well-tempered metadynamics simulations allows us to confirm that the structural organizations obtained after 50 ns of molecular dynamics simulations are practically the equilibrium ones. Similarities and differences of surfactant aggregates in vacuo and in apolar media are also discussed.

The role of nanoparticle rigidity on the diffusion of linear polystyrene in a polymer nanocomposite

DOE PAGES

Miller, Brad; Imel, Adam E.; Holley, Wade; ...

2015-11-12

The impact of the inclusion of a nanoparticle in a polymer matrix on the dynamics of the polymer chains is an area of recent interest. In this article, we describe the role of nanoparticle rigidity or softness on the impact of the presence of that nanoparticle on the diffusive behavior of linear polymer chains. The neutron reflectivity results clearly show that the inclusion of 10 nm soft nanoparticles in a polymer matrix (R g ~ 20 nm) increases the diffusion coefficient of the linear polymer chain. Surprisingly, thermal analysis shows that these nanocomposites exhibit an increase in their glass transitionmore » temperature, which is incommensurate with an increase in free volume. Therefore, it appears that this effect is more complex than a simple plasticizing effect. Results from small-angle neutron scattering of the nanoparticles in solution show a structure that consists of a gel like core with a corona of free chain ends and loops. Furthermore, the increase in linear polymer diffusion may be related to an increase in constraint release mechanisms in the reptation of the polymer chain, in a similar manner to that which has been reported for the diffusion of linear polymer chains in the presence of star polymers.« less

The role of nanoparticle rigidity on the diffusion of linear polystyrene in a polymer nanocomposite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Brad; Imel, Adam E.; Holley, Wade

The impact of the inclusion of a nanoparticle in a polymer matrix on the dynamics of the polymer chains is an area of recent interest. In this article, we describe the role of nanoparticle rigidity or softness on the impact of the presence of that nanoparticle on the diffusive behavior of linear polymer chains. The neutron reflectivity results clearly show that the inclusion of 10 nm soft nanoparticles in a polymer matrix (R g ~ 20 nm) increases the diffusion coefficient of the linear polymer chain. Surprisingly, thermal analysis shows that these nanocomposites exhibit an increase in their glass transitionmore » temperature, which is incommensurate with an increase in free volume. Therefore, it appears that this effect is more complex than a simple plasticizing effect. Results from small-angle neutron scattering of the nanoparticles in solution show a structure that consists of a gel like core with a corona of free chain ends and loops. Furthermore, the increase in linear polymer diffusion may be related to an increase in constraint release mechanisms in the reptation of the polymer chain, in a similar manner to that which has been reported for the diffusion of linear polymer chains in the presence of star polymers.« less

Heteroaggregation of Silver Nanoparticles with Clay Minerals in Aqueous System

NASA Astrophysics Data System (ADS)

Liu, J.; Burrow, E.; Hwang, Y.; Lenhart, J.

2013-12-01

Nanoparticles are increasingly being used in industrial processes and consumer products that exploit their beneficial properties and improve our daily lives. Nevertheless, they also attract attention when released into natural environment due to their potential for causing adverse effects. The fate and transport of nanoparticles in aqueous systems have been the focus of intense study. However, their interactions with other natural particles have received only limited attention. Clay minerals are ubiquitous in most aquatic systems and their variably charged surfaces can act as deposition sites that can alter the fate and transport of nanoparticles in natural aqueous environments. In this study, we investigated the homoaggregation of silver nanoparticles with different coating layers and their heteroaggregation behavior with clay minerals (illite, kaolinite, montmorillonite) in neutral pH solutions. Silver nanoparticles with a nominal diameter of 80 nm were synthesized with three different surface coating layers: uncoated, citrate-coated and Tween-coated. Illite (IMt-2), kaolinite (KGa-2), and montmorillonite (SWy-2) were purchased from the Clay Mineral Society (Indiana) and pretreated to obtain monocationic (Na-clay) and dicationic (Ca-clay) suspensions before the experiments. The change in hydrodynamic diameter as a function of time was monitored using dynamic light scattering (DLS) measurements in order to evaluate early stage aggregation as a function of electrolyte concentration in both the homo- and heteroaggregation scenarios. A shift in the critical coagulation concentration (CCC) values to lower electrolyte concentrations was observed in binary systems, compared to single silver nanoparticle and clay systems. The results also suggest more rapid aggregation in binary system during the early aggregation stage when compared to the single-particle systems. The behavior of citrate-coated silver nanoparticles was similar to that of the bare particles, while the Tween-coated silver nanoparticles showed high stability in both single and binary systems. There were no significant differences in early stage aggregation kinetics observed inthe Na-clay-nanoparticle or Ca-clay-nanoparticle systems, which suggested that the CCC values of the single Na- or Ca-clay suspensions depend only on the electrolyte concentration, not the original cations on the clay surface. These results provide a basic idea for understanding the heteroaggregation of different silver nanoparticles and clays, which can be utilized in further study of fate and transport of engineered nanoparticles in natural aqueous system.

Magnetic manipulation of superparamagnetic nanoparticles in a microfluidic system for drug delivery applications

NASA Astrophysics Data System (ADS)

Agiotis, L.; Theodorakos, I.; Samothrakitis, S.; Papazoglou, S.; Zergioti, I.; Raptis, Y. S.

2016-03-01

Magnetic nanoparticles (MNPs), such as superparamagnetic iron oxide nanoparticles (SPIONS), have attracted major interest, due to their small size and unique magnetic properties, for drug delivery applications. In this context, iron oxide nanoparticles of magnetite (Fe3O4) (150 nm magnetic core diameter), were used as drug carriers, aiming to form a magnetically controlled nano-platform. The navigation capabilities of the iron oxide nanoparticles in a microfluidic channel were investigated by simulating the magnetic field and the magnetic force applied on the magnetic nanoparticles inside a microfluidic chip. The simulations have been performed using finite element method (ANSY'S software). The optimum setup which intends to simulate the magnetic navigation of the nanoparticles, by the use of MRI-type fields, in the human circulatory system, consists of two parallel permanent magnets to produce a homogeneous magnetic field, in order to ensure the maximum magnetization of the magnetic nanoparticles, an electromagnet for the induction of the magnetic gradients and the creation of the magnetic force and a microfluidic setup so as to simulate the blood flow inside the human blood vessels. The magnetization of the superparamagnetic nanoparticles and the consequent magnetic torque developed by the two permanent magnets, together with the mutual interactions between the magnetized nanoparticles lead to the creation of rhabdoid aggregates in the direction of the homogeneous field. Additionally, the magnetic gradients introduced by the operation of the electromagnet are capable of directing the aggregates, as a whole, to the desired direction. By removing the magnetic fields, the aggregates are disrupted, due to the super paramagnetic nature of the nanoparticles, avoiding thus the formation of undesired thrombosis.

In-situ formation of nanoparticles within a silicon-based matrix

DOEpatents

Thoma, Steven G [Albuquerque, NM; Wilcoxon, Jess P [Albuquerque, NM; Abrams, Billie L [Albuquerque, NM

2008-06-10

A method for encapsulating nanoparticles with an encapsulating matrix that minimizes aggregation and maintains favorable properties of the nanoparticles. The matrix comprises silicon-based network-forming compounds such as ormosils and polysiloxanes. The nanoparticles are synthesized from precursors directly within the silicon-based matrix.

Ultra-small rhenium nanoparticles immobilized on DNA scaffolds: An excellent material for surface enhanced Raman scattering and catalysis studies.

PubMed

Anantharaj, S; Sakthikumar, K; Elangovan, Ayyapan; Ravi, G; Karthik, T; Kundu, Subrata

2016-12-01

Highly Sensitive and ultra-small Rhenium (Re) metal nanoparticles (NPs) were successfully stabilized in water by the staging and fencing action of the versatile biomolecule DNA that resulted in two distinct aggregated chain-like morphologies with average grain sizes of 1.1±0.1nm and 0.7±0.1nm for the very first time within a minute of reaction time. Re NPs are formed by the borohydride reduction of ammonium perrhenate (NH4ReO4) in the presence of DNA at room temperature (RT) under stirring. The morphologies were controlled by carefully monitoring the molar ratio of NH4ReO4 and DNA. The synthesized material was employed in two potential applications: as a substrate for surface enhanced Raman scattering (SERS) studies and as a catalyst for the reduction of aromatic nitro compounds. SERS study was carried out by taking methylene blue (MB) as the probe and the highest SERS enhancement factor (EF) of 2.07×10(7) was found for the aggregated chain-like having average grain size of 0.7±0.1nm. Catalytic reduction of 4-nitro phenol (4-NP), 2-nitro phenol (2-NP) and 4-nitroaniline (4-NA) with a rate constant value of 6×10(-2)min(-1), 33.83×10(-2)min(-1) and 37.4×10(-2)min(-1) have testified the excellent catalytic performance of our Re NPs immobilized on DNA. The overall study have revealed the capability of DNA in stabilizing the highly reactive Re metal at nanoscale and made them applicable in practice. The present route can also be extended to prepare one dimensional (1-D), self-assembled NPs of other reactive metals, mixed metals or even metal oxides for specific applications in water based solutions. Copyright © 2016 Elsevier Inc. All rights reserved.

Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles.

PubMed

Hernández-Castillo, M I; Zaca-Morán, O; Zaca-Morán, P; Orduña-Diaz, A; Delgado-Macuil, R; Rojas-López, M

2015-01-01

The absorption of pesticide endosulfan on the surface of gold nanoparticles results from the formation of micrometric structures (1-10 μm) with irregular shape because of the aggregation of individual particles. Such aggregation of gold nanoparticles after absorption of pesticide shows a surface-enhanced Raman scattering (SERS) spectrum, whose intensity depends on the concentration of endosulfan. In addition, the discoloration of the colloidal solution and a diminishing of the intensity of the surface plasmon resonance absorption from individual particles were observed by UV-visible spectroscopy. At the same time, a second band between 638 and 700 nm confirms the formation of aggregates of gold nanoparticles as the concentration of endosulfan increases. Finally, we used the SERS intensity of the S-O stretching vibration at 1239 cm(-1) from the SO3 group as a measure of concentration of pesticide endosulfan. This method could be used to estimate the level of pollution in water by endosulfan in a simple and practical form.

Adsorption energies of poly(ethylene oxide)-based surfactants and nanoparticles on an air-water surface.

PubMed

Zell, Zachary A; Isa, Lucio; Ilg, Patrick; Leal, L Gary; Squires, Todd M

2014-01-14

The self-assembly of polymer-based surfactants and nanoparticles on fluid-fluid interfaces is central to many applications, including dispersion stabilization, creation of novel 2D materials, and surface patterning. Very often these processes involve compressing interfacial monolayers of particles or polymers to obtain a desired material microstructure. At high surface pressures, however, even highly interfacially active objects can desorb from the interface. Methods of directly measuring the energy which keeps the polymer or particles bound to the interface (adsorption/desorption energies) are therefore of high interest for these processes. Moreover, though a geometric description linking adsorption energy and wetting properties through the definition of a contact angle can be established for rigid nano- or microparticles, such a description breaks down for deformable or aggregating objects. Here, we demonstrate a technique to quantify desorption energies directly, by comparing surface pressure-density compression measurements using a Wilhelmy plate and a custom-microfabricated deflection tensiometer. We focus on poly(ethylene oxide)-based polymers and nanoparticles. For PEO-based homo- and copolymers, the adsorption energy of PEO chains scales linearly with molecular weight and can be tuned by changing the subphase composition. Moreover, the desorption surface pressure of PEO-stabilized nanoparticles corresponds to the saturation surface pressure for spontaneously adsorbed monolayers, yielding trapping energies of ∼10(3) k(B)T.

Self-Assembled ROS-Sensitive Polymer-Peptide Therapeutics Incorporating Built-in Reporters for Evaluation of Treatment Efficacy.

PubMed

Qiao, Zeng-Ying; Zhao, Wen-Jing; Cong, Yong; Zhang, Di; Hu, Zhiyuan; Duan, Zhong-Yu; Wang, Hao

2016-05-09

One of the major challenges in current cancer therapy is to maximize therapeutic effect and evaluate tumor progression under the scheduled treatment protocol. To address these challenges, we synthesized the cytotoxic peptide (KLAKLAK)2 (named KLAK) conjugated amphiphilic poly(β-thioester)s copolymers (H-P-K) composed of reactive oxygen species (ROS) sensitive backbones and hydrophilic polyethylene glycol (PEG) side chains. H-P-K could self-assemble into micelle-like nanoparticles by hydrophobic interaction with copolymer backbones as cores and PEG and KLAK as shells. The assembled polymer-peptide nanoparticles remarkably improved cellular internalization and accumulation of therapeutic KLAK in cells. Compared to free KLAK peptide, the antitumor activity of H-P-K was significantly enhanced up to ∼400 times, suggesting the effectiveness of the nanoscaled polymer-peptide conjugation as biopharmaceuticals. The higher antitumor activity of nanoparticles was attributed to the efficient disruption of mitochondrial membranes and subsequent excessive ROS production in cells. To realize the ROS monitoring and treatment evaluation, we encapsulated squaraine (SQ) dyes as built-in reporters in ROS-sensitive H-P-K micelles. The overgenerated ROS around mitochondria stimulated the swelling of nanoparticles and subsequent release of SQ, which formed H-aggregates and significantly increased the photoacoustic (PA) signal. We believed that this self-assembled polymer-peptide nanotherapeutics incorporating built-in reporters has great potential for high antitumor performance and in situ treatment evaluation.

SERS-active silver nanoparticle aggregates produced in high-iron float glass by ion exchange process

NASA Astrophysics Data System (ADS)

Karvonen, L.; Chen, Y.; Säynätjoki, A.; Taiviola, K.; Tervonen, A.; Honkanen, S.

2011-11-01

Silver nanoparticles were produced in iron containing float glasses by silver-sodium ion exchange and post-annealing. In particular, the effect of the concentration and the oxidation state of iron in the host glass on the nanoparticle formation was studied. After the nanoparticle fabrication process, the samples were characterized by optical absorption measurements. The samples were etched to expose nanoparticle aggregates on the surface, which were studied by optical microscopy and scanning electron microscopy. The SERS-activity of these glass samples was demonstrated and compared using a dye molecule Rhodamine 6G (R6G) as an analyte. The importance of the iron oxidation level for reduction process is discussed. The glass with high concentration of Fe 2+ ions was found to be superior in SERS applications of silver nanoparticles. The optimal surface features in terms of SERS enhancement are also discussed.

Effect of Nanoparticle Core Size on Polymer-Coated Gold Nanoparticle Location in Block Copolymers

NASA Astrophysics Data System (ADS)

Petrie, J. D.; Fredrickson, G. H.; Kramer, E. J.

2009-03-01

Gold nanoparticles modified by short chain polymer thiols [Au-PS] can be designed to strongly localize either in the PS domains of a polystyrene-b-poly(2-vinylpyridine) [PS-PVP] block copolymer or at the interface. The P2VP block has a stronger attractive interaction with bare gold than the PS block. Thus, when the areal chain density σ of end-attached PS chains falls below a critical areal chain density σc the Au-PS nanoparticles adsorb to the PS-b-P2VP interface. The effect of the polymer ligand molecular weight on the σc has been shown to scale as σc˜ ((R + Rg)/(R*Rg))̂2, where R is the curvature of the Au nanoparticle core radius. To test this scaling relation for σc further we are synthesizing gold nanoparticles with different core radii and will present preliminary results on σc as a function of R.

Effect of Ligand Molecular Weight and Nanoparticle Core Size on Polymer-Coated Gold Nanoparticle Location in Block Copolymers

NASA Astrophysics Data System (ADS)

Petrie, Joshua; Kim, Bumjoon; Fredrickson, Glenn; Kramer, Ed

2008-03-01

Gold nanoparticles modified by short chain polymer thiols [Au-PS] can be designed to strongly localize in either domain of a polystyrene-b-poly(2-vinylpyridine) [PS-PVP] block copolymer or at the interface. The P2VP block has a stronger attractive interaction with bare gold than the PS block. Thus, when the areal chain density σ of end-attached PS chains falls below a critical areal chain density σc the Au-PS nanoparticles adsorb to the PS-b-P2VP interface. The effect of the polymer ligand molecular weight on the σchas been shown to scale as σc˜ ((R+Rg)/(R*Rg))̂2, where R is the curvature of the Au nanoparticle core radius. To test this scaling relation for σc further we are synthesizing gold nanoparticles with different core radii and will present preliminary results on σcas a function of R.

The effect of nanoparticles aggregation on the thermal conductivity of nanofluids at very low concentrations: Experimental and theoretical evaluations

NASA Astrophysics Data System (ADS)

Motevasel, Mohsen; Nazar, Ali Reza Solaimany; Jamialahmadi, Mohammad

2018-01-01

Nanoparticles suspended in a base fluid yield increased thermal conductivity, which in turn increases convection heat transfer rate. Prediction of suitable relations for determination of thermal conductivity results in heightened accuracy in the calculation of convection heat transfer coefficient and reduced costs. In the majority of studies performed on the prediction of thermal conductivity, some relations and models were used in which the effect of aggregation of particles, especially at low concentrations was ignored. In this research, the thermal conductivity of the nanofluid is measured experimentally at low volumetric concentrations, within the range of 0.02-0.2% for the nanoparticles of Al2O3, MgO, CuO, and SiC in the base fluid of distilled water. The results obtained from the models are compared by the available models considering and neglecting the effect of aggregation of particles. Within the range of the applied concentrations, the relative absolute average deviation ratio of the thermal conductivity models without considering the aggregation effect in relation with the models considering the aggregate, is observed to be between 2 and 6 times. Therefore, it is recommended that even at low concentrations, the effect of aggregation should be considered in the prediction of thermal conductivity.

Kinetics and pathogenesis of intracellular magnetic nanoparticle cytotoxicity

NASA Astrophysics Data System (ADS)

Giustini, Andrew J.; Gottesman, Rachel E.; Petryk, A. A.; Rauwerdink, A. M.; Hoopes, P. Jack

2011-03-01

Magnetic nanoparticles excited by alternating magnetic fields (AMF) have demonstrated effective tumor-specific hyperthermia. This treatment is effective as a monotherapy as well as a therapeutic adjuvant to chemotherapy and radiation. Iron oxide nanoparticles have been shown, so far, to be non-toxic, as are the exciting AMF fields when used at moderate levels. Although higher levels of AMF can be more effective, depending on the type of iron oxide nanoparticles use, these higher field strengths and/or frequencies can induce normal tissue heating and toxicity. Thus, the use of nanoparticles exhibiting significant heating at low AMF strengths and frequencies is desirable. Our preliminary experiments have shown that the aggregation of magnetic nanoparticles within tumor cells improves their heating effect and cytotoxicity per nanoparticle. We have used transmission electron microscopy to track the endocytosis of nanoparticles into tumor cells (both breast adenocarcinoma (MTG-B) and acute monocytic leukemia (THP-1) cells). Our preliminary results suggest that nanoparticles internalized into tumor cells demonstrate greater cytotoxicity when excited with AMF than an equivalent heat dose from excited external nanoparticles or cells exposed to a hot water bath. We have also demonstrated that this increase in SAR caused by aggregation improves the cytotoxicity of nanoparticle hyperthermia therapy in vitro.

A highly sensitive nanoscale pH-sensor using Au nanoparticles linked by a multifunctional Raman-active reporter molecule

NASA Astrophysics Data System (ADS)

Lawson, Latevi S.; Chan, James W.; Huser, Thomas

2014-06-01

Chemical sensing on the nanoscale has been breaking new ground since the discovery of surface enhanced Raman scattering (SERS). For nanoparticles, controlled particle aggregation is necessary to achieve the largest SERS enhancements. Therefore, aggregating agents such as salts or linker molecules are used in conjunction with chemically sensitive reporters in order to develop robust environmentally sensitive SERS probes. While salt-induced colloidal nanosphere aggregates have produced robust SERS signals, their variability in aggregate size contributes significantly to poor SERS signal reproducibility, which can complicate their use in in vitro cellular studies. Such systems often also lack reproducibility in spectral measurements between different nanoparticle clusters. Preaggregation of colloids via linkers followed by surface functionalization with reporter molecules results in the linker occupying valuable SERS hotspot volume which could otherwise be utilized by additional reporter molecules. Ideally, both functionalities should be obtained from a single molecule. Here, we report the use of 3,5-dimercaptobenzoic acid, a single multifunctional molecule that creates SERS hotspots via the controlled aggregation of nanoparticles, and also reports pH values. We show that 3,5-dimercaptobenzoic acid bound to Au nanospheres results in an excellent pH nanoprobe, producing very robust, and highly reproducible SERS signals that can report pH across the entire physiological range with excellent pH resolution. To demonstrate the efficacy of our novel pH reporters, these probes were also used to image both the particle and pH distribution in the cytoplasm of human induced pluripotent stem cells (hiPSCs).Chemical sensing on the nanoscale has been breaking new ground since the discovery of surface enhanced Raman scattering (SERS). For nanoparticles, controlled particle aggregation is necessary to achieve the largest SERS enhancements. Therefore, aggregating agents such as salts or linker molecules are used in conjunction with chemically sensitive reporters in order to develop robust environmentally sensitive SERS probes. While salt-induced colloidal nanosphere aggregates have produced robust SERS signals, their variability in aggregate size contributes significantly to poor SERS signal reproducibility, which can complicate their use in in vitro cellular studies. Such systems often also lack reproducibility in spectral measurements between different nanoparticle clusters. Preaggregation of colloids via linkers followed by surface functionalization with reporter molecules results in the linker occupying valuable SERS hotspot volume which could otherwise be utilized by additional reporter molecules. Ideally, both functionalities should be obtained from a single molecule. Here, we report the use of 3,5-dimercaptobenzoic acid, a single multifunctional molecule that creates SERS hotspots via the controlled aggregation of nanoparticles, and also reports pH values. We show that 3,5-dimercaptobenzoic acid bound to Au nanospheres results in an excellent pH nanoprobe, producing very robust, and highly reproducible SERS signals that can report pH across the entire physiological range with excellent pH resolution. To demonstrate the efficacy of our novel pH reporters, these probes were also used to image both the particle and pH distribution in the cytoplasm of human induced pluripotent stem cells (hiPSCs). Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06277e

Membrane fouling by extracellular polymeric substances after ozone pre-treatment: Variation of nano-particles size.

PubMed

Yu, Wenzheng; Zhang, Dizhong; Graham, Nigel J D

2017-09-01

The application of ozone pre-treatment for ultrafiltration (UF) in drinking water treatment has been studied for more than 10 years, but its performance in mitigating or exacerbating membrane fouling has been inconclusive, and sometimes contradictory. To help explain this, our study considers the significance of the influent organic matter and its interaction with ozone on membrane fouling, using solutions of two representative types of extracellular polymeric substances (EPS), alginate and bovine serum albumin (BSA), and samples of surface water. The results show that at typical ozone doses there is no measurable mineralization of alginate and BSA, but substantial changes in their structure and an increase in the size of nano-particle aggregates (micro-flocculation). The impact of ozonation on membrane fouling, as indicated by the membrane flux, was markedly different for the two types of EPS and found to be related to the size of the nano-particle aggregates formed in comparison with the UF pore size. Thus, for BSA, ozonation created aggregate sizes similar to the UF pore size (100 k Dalton) which led to an increase in fouling. In contrast, ozonation of alginate created the nano-particle aggregates greater than the UF pore size, giving reduced membrane fouling/greater flux. For solutions containing a mixture of the two species of EPS the overall impact of ozonation on UF performance depends on the relative proportion of each, and the ozone dose, and the variable behaviour has been demonstrated by the surface water. These results provide new information about the role of nano-particle aggregate size in explaining the reported ambiguity over the benefits of applying ozone as pre-treatment for ultrafiltration. Copyright © 2017. Published by Elsevier Ltd.

Size determination of gold nanoparticles in silicate glasses by UV-Vis spectroscopy

NASA Astrophysics Data System (ADS)

Ali, Shahid; Khan, Younas; Iqbal, Yaseen; Hayat, Khizar; Ali, Muhammad

2017-01-01

A relatively easier and more accurate method for the determination of average size of metal nanoparticles/aggregates in silicate glasses based on ultraviolet visible (UV-Vis) spectra fitted with the Mie and Mie-Gans models was reported. Gold ions were diffused into sodalime silicate and borosilicate glasses by field-assisted solid-state ion-exchange technique using the same experimental parameters for both glasses. Transmission electron microscopy was performed to directly investigate the morphology and distribution of the dopant nanoparticles. UV-Vis spectra of the doped glasses showed broad surface plasmon resonance peaks in their fingerprint regions, i.e., at 525 and 500 nm for sodalime silicate and borosilicate glass matrices, respectively. These spectra were fitted with the Mie model for spherical nanoparticles and the Mie-Gans model for spheroidal nanoparticles. Although both the models were developed for colloidal nanoparticles, the size of the nanoparticles/aggregates calculated was accurate to within ˜10% in both the glass matrices in comparison to the size measured directly from the transmission electron microscope images.

Synthesis of Photocrosslinkable and Amine Containing Multifunctional Nanoparticles via Polymerization-Induced Self-Assembly.

PubMed

Huang, Jianbing; Li, Decai; Liang, Hui; Lu, Jiang

2017-08-01

Photo-crosslinkable and amine-containing block copolymer nanoparticles are synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly of a multifunctional core-forming monomer, 2-((3-(4-(diethylamino)phenyl)acryloyl)oxy)ethyl methacrylate (DEMA), using poly(2-hydroxypropyl methacrylate) macromolecular chain transfer agent as a steric stabilizer in methanol at 65 °C. By tuning the chain length of PDEMA, a range of nanoparticle morphologies (sphere, worm, and vesicle) can be obtained. Since cinnamate groups can easily undergo a [2 + 2] cycloaddition of the carbon-carbon double bonds upon UV irradiation, the as-prepared block copolymer nanoparticles are readily stabilized by photo-crosslinking to produce anisotropic nanoparticles. The crosslinked block copolymer nanoparticles can be used as templates for in situ formation polymer/gold hybrid nanoparticles. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Binding Preferences of Amino Acids for Gold Nanoparticles: A Molecular Simulation Study.

PubMed

Shao, Qing; Hall, Carol K

2016-08-09

A better understanding of the binding preference of amino acids for gold nanoparticles of different diameters could aid in the design of peptides that bind specifically to nanoparticles of a given diameter. Here we identify the binding preference of 19 natural amino acids for three gold nanoparticles with diameters of 1.0, 2.0, and 4.0 nm, and investigate the mechanisms that govern these preferences. We calculate potentials of mean force between 36 entities (19 amino acids and 17 side chains) and the three gold nanoparticles in explicit water using well-tempered metadynamics simulations. Comparing these potentials of mean force determines the amino acids' nanoparticle binding preferences and if these preferences are controlled by the backbone, the side chain, or both. Twelve amino acids prefer to bind to the 4.0 nm gold nanoparticle, and seven prefer to bind to the 2.0 nm one. We also use atomistic molecular dynamics simulations to investigate how water molecules near the nanoparticle influence the binding of the amino acids. The solvation shells of the larger nanoparticles have higher water densities than those of the smaller nanoparticles while the orientation distributions of the water molecules in the shells of all three nanoparticles are similar. The nanoparticle preferences of the amino acids depend on whether their binding free energy is determined mainly by their ability to replace or to reorient water molecules in the nanoparticle solvation shell. The amino acids whose binding free energy depends mainly on the replacement of water molecules are likely to prefer to bind to the largest nanoparticle and tend to have relatively simple side chain structures. Those whose binding free energy depends mainly on their ability to reorient water molecules prefer a smaller nanoparticle and tend to have more complex side chain structures.

Self Diffusion in Nano Filled Polymer Melts: a Molecular Dynamics Simulation Study

NASA Astrophysics Data System (ADS)

Desai, Tapan; Keblinski, Pawel

2003-03-01

SELF DIFFUSION IN NANO FILLED POLYMER MELTS: A MOLECULAR DYNAMICS SIMULATION STUDY* T. G. Desai,P. Keblinski, Material Science and Engineering Department, Rensselaer Polytechnic Institute, Troy, NY. Using molecular dynamics simulations, we studied the dynamics of the polymeric systems containing immobile and analytically smooth spherical nanoparticles. Each chain consisted of N monomers connected by an anharmonic springs described by the finite extendible nonlinear elastic, FENE potential. The system comprises of 3nanoparticles and the rest by freely rotating but not overlapping chains. The longest chain studied has a Radius of gyration equal to particle size radius and comparable to inter-particle distance. There is no effect on the structural characteristics such as Radius of gyration or end to end distance due to the nanoparticles. Diffusion of polymeric chains is not affected by the presence of either attractive or repulsive nanoparticles. In all cases Rouse dynamics is observed for short chains with a crossover to reptation dynamics for longer chains.

Gold Nanoparticles and Microwave Irradiation Inhibit Beta-Amyloid Amyloidogenesis

NASA Astrophysics Data System (ADS)

Araya, Eyleen; Olmedo, Ivonne; Bastus, Neus G.; Guerrero, Simón; Puntes, Víctor F.; Giralt, Ernest; Kogan, Marcelo J.

2008-11-01

Peptide-Gold nanoparticles selectively attached to β-amyloid protein (Aβ) amyloidogenic aggregates were irradiated with microwave. This treatment produces dramatic effects on the Aβ aggregates, inhibiting both the amyloidogenesis and the restoration of the amyloidogenic potential. This novel approach offers a new strategy to inhibit, locally and remotely, the amyloidogenic process, which could have application in Alzheimer’s disease therapy. We have studied the irradiation effect on the amyloidogenic process in the presence of conjugates peptide-nanoparticle by transmission electronic microscopy observations and by Thioflavine T assays to quantify the amount of fibrils in suspension. The amyloidogenic aggregates rather than the amyloid fibrils seem to be better targets for the treatment of the disease. Our results could contribute to the development of a new therapeutic strategy to inhibit the amyloidogenic process in Alzheimer’s disease.

[Effect of dilution on aggregation of nanoparticles of polycarboxylic derivative of fullerene C60].

PubMed

Bobylev, A G; Pen'kov, N V; Troshin, P A; Gudkov, S V

2015-01-01

In this work, we investigated the effect of dilution on aggregation of nanoparticles of the polycarboxylic derivative of fullerene C60. It is shown that the diminution of the concentration of PCDF-1 in aqueous medium leads to a decreased amount of aggregates of fullerene and an increased amount of single molecules. This can potentially interfere with the biological activity of a compound on one molecule basis. Addition of organic and inorganic salts to the aqueous medium with fullerene derivative leads to intense disaggregation of PCDF-1. The data obtained suggest an explanation of non-stoichiometric nature of neutralization of reactive oxygen species by derivatives of fullerenes, as well as provide new insight into the physical meaning of the work on the impact of nanoparticles at ultra-low concentrations on biological objects.

Chain Conformation near the Buried Interface in Nanoparticle-Stabilized Polymer Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barkley, Deborah A.; Jiang, Naisheng; Sen, Mani

It is known that when nanoparticles are added to polymer thin films, they often migrate to the film-substrate interface and form an “immobile interfacial layer”, which has been believed as the origin of suppression of dewetting. We here report an alternative mechanism of dewetting suppression from the structural aspect of a polymer. Dodecane thiol-functionalized gold (Au) nanoparticles embedded in PS thin films prepared on Si substrates were used as a model. It was found that thermal annealing promotes irreversible polymer adsorption onto the substrate surface along with the surface migration of the nanoparticles. We also revealed that the surface migrationmore » causes additional nanoconfined space for the adsorbed polymer chains. As a result, the self-organization process of the strongly adsorbed polymer chains on the solid surface was so hindered that the chain conformations were randomized and expanded in the film normal direction. Here, the resultant chain conformation allows the interpenetration between free chains and the adsorbed chains, promoting adhesion and hence stabilizing the thin film.« less

Chain Conformation near the Buried Interface in Nanoparticle-Stabilized Polymer Thin Films

DOE PAGES

Barkley, Deborah A.; Jiang, Naisheng; Sen, Mani; ...

2017-09-26

It is known that when nanoparticles are added to polymer thin films, they often migrate to the film-substrate interface and form an “immobile interfacial layer”, which has been believed as the origin of suppression of dewetting. We here report an alternative mechanism of dewetting suppression from the structural aspect of a polymer. Dodecane thiol-functionalized gold (Au) nanoparticles embedded in PS thin films prepared on Si substrates were used as a model. It was found that thermal annealing promotes irreversible polymer adsorption onto the substrate surface along with the surface migration of the nanoparticles. We also revealed that the surface migrationmore » causes additional nanoconfined space for the adsorbed polymer chains. As a result, the self-organization process of the strongly adsorbed polymer chains on the solid surface was so hindered that the chain conformations were randomized and expanded in the film normal direction. Here, the resultant chain conformation allows the interpenetration between free chains and the adsorbed chains, promoting adhesion and hence stabilizing the thin film.« less

Optical amplification of photothermal therapy with gold nanoparticles and nanoclusters

NASA Astrophysics Data System (ADS)

Khlebtsov, Boris; Zharov, Vladimir; Melnikov, Andrei; Tuchin, Valery; Khlebtsov, Nikolai

2006-10-01

Recently, several groups (Anderson, Halas, Zharov, and their co-workers, 2003; El-Sayed and co-workers, 2006) demonstrated, through pioneering results, the great potential of photothermal (PT) therapy for the selective treatment of cancer cells, bacteria, viruses, and DNA targeted with gold nanospheres, nanoshells, nanorods, and nanosphere clusters. However, the current understanding of the relationship between the nanoparticle/cluster parameters (size, shape, particle/cluster structure, etc) and the efficiency of PT therapy is limited. Here, we report theoretical simulations aimed at finding the optimal single-particle and cluster structures to achieve its maximal absorption, which is crucial for PT therapeutic effects. To characterize the optical amplification in laser-induced thermal effects, we introduce relevant parameters such as the ratio of the absorption cross section to the gold mass of a single-particle structure and absorption amplification, defined as the ratio of cluster absorption to the total absorption of non-interacting particles. We consider the absorption efficiency of single nanoparticles (gold spheres, rods, and silica/gold nanoshells), linear chains, 2D lattice arrays, 3D random volume clusters, and the random aggregated N-particle ensembles on the outer surface of a larger dielectric sphere, which mimic aggregation of nanosphere bioconjugates on or within cancer cells. The cluster particles are bare or biopolymer-coated gold nanospheres. The light absorption of cluster structures is studied by using the generalized multiparticle Mie solution and the T-matrix method. The gold nanoshells with (silica core diameter)/(gold shell thickness) parameters of (50-100)/(3-8) nm and nanorods with minor/major sizes of (15-20)/(50-70) nm are shown to be more efficient PT labels and sensitizers than the equivolume solid single gold spheres. In the case of nanosphere clusters, the interparticle separations and the short linear-chain fragments are the main structural parameters determining the absorption efficiency and its spectral shifting to the red. Although we have not found a noticeable dependence of absorption amplification on the cluster sphere size, 20-40 nm particles are found to be most effective, in accordance with our experimental observations. The long-wavelength absorption efficiency of random clusters increases with the cluster particle number N at small N and reveals a saturation behaviour at N>20.

Atomistic Structure of Mineral Nano-aggregates from Simulated Compaction and Dewatering.

PubMed

Ho, Tuan Anh; Greathouse, Jeffery A; Wang, Yifeng; Criscenti, Louise J

2017-11-10

The porosity of clay aggregates is an important property governing chemical reactions and fluid flow in low-permeability geologic formations and clay-based engineered barrier systems. Pore spaces in clays include interlayer and interparticle pores. Under compaction and dewatering, the size and geometry of such pore spaces may vary significantly (sub-nanometer to microns) depending on ambient physical and chemical conditions. Here we report a molecular dynamics simulation method to construct a complex and realistic clay-like nanoparticle aggregate with interparticle pores and grain boundaries. The model structure is then used to investigate the effect of dewatering and water content on micro-porosity of the aggregates. The results suggest that slow dewatering would create more compact aggregates compared to fast dewatering. Furthermore, the amount of water present in the aggregates strongly affects the particle-particle interactions and hence the aggregate structure. Detailed analyses of particle-particle and water-particle interactions provide a molecular-scale view of porosity and texture development of the aggregates. The simulation method developed here may also aid in modeling the synthesis of nanostructured materials through self-assembly of nanoparticles.

Atomistic Structure of Mineral Nano-aggregates from Simulated Compaction and Dewatering

DOE PAGES

Ho, Tuan Anh; Greathouse, Jeffery A.; Wang, Yifeng; ...

2017-11-10

The porosity of clay aggregates is an important property governing chemical reactions and fluid flow in low-permeability geologic formations and clay-based engineered barrier systems. Pore spaces in clays include interlayer and interparticle pores. Under compaction and dewatering, the size and geometry of such pore spaces may vary significantly (sub-nanometer to microns) depending on ambient physical and chemical conditions. Here we report a molecular dynamics simulation method to construct a complex and realistic clay-like nanoparticle aggregate with interparticle pores and grain boundaries. The model structure is then used to investigate the effect of dewatering and water content on micro-porosity of themore » aggregates. The results suggest that slow dewatering would create more compact aggregates compared to fast dewatering. Furthermore, the amount of water present in the aggregates strongly affects the particle-particle interactions and hence the aggregate structure. Detailed analyses of particle-particle and water-particle interactions provide a molecular-scale view of porosity and texture development of the aggregates. The simulation method developed here may also aid in modeling the synthesis of nanostructured materials through self-assembly of nanoparticles.« less

Atomistic Simulations of Hydrodynamic and Interaction Forces on Functionalized Silica Nanoparticles

NASA Astrophysics Data System (ADS)

Lane, J. Matthew D.; Ismail, Ahmed E.; Chandross, Michael; Lorenz, Christian D.; Grest, Gary S.

2009-03-01

It is often desired to prevent the flocculation and phase separation of nanoparticles in solution. This can be accomplished either by manipulating the solvent or by tailoring the surface chemistry of the nanoparticles through functionalization with a monolayer of oligomer chains. Since it is not known how these functionalized coatings affect the interactions between nanoparticles and with the surrounding solvent, we present results from a series of molecular dynamics simulations of polyethylene oxide (PEO) coated silica nanoparticles of varying size (5 to 20 nm diameter) in water. For a single nanoparticle we determined the Stokes drag on the nanoparticle as it moves through the solvent and as it approaches a wall. Due to hydrodynamic interactions there are large finite size effects which we estimate by varying the size of the simulation cell. We also determined both solvent-mediated (velocity-independent) and lubrication (velocity-dependent) forces between two nanoparticles as a function of the coverage and chain length of the PEO chains.

Ex vivo assessment of polyol coated-iron oxide nanoparticles for MRI diagnosis applications: toxicological and MRI contrast enhancement effects

NASA Astrophysics Data System (ADS)

Bomati-Miguel, Oscar; Miguel-Sancho, Nuria; Abasolo, Ibane; Candiota, Ana Paula; Roca, Alejandro G.; Acosta, Milena; Schwartz, Simó; Arus, Carles; Marquina, Clara; Martinez, Gema; Santamaria, Jesus

2014-03-01

Polyol synthesis is a promising method to obtain directly pharmaceutical grade colloidal dispersion of superparamagnetic iron oxide nanoparticles (SPIONs). Here, we study the biocompatibility and performance as T2-MRI contrast agents (CAs) of high quality magnetic colloidal dispersions (average hydrodynamic aggregate diameter of 16-27 nm) consisting of polyol-synthesized SPIONs (5 nm in mean particle size) coated with triethylene glycol (TEG) chains (TEG-SPIONs), which were subsequently functionalized to carboxyl-terminated meso-2-3-dimercaptosuccinic acid (DMSA) coated-iron oxide nanoparticles (DMSA-SPIONs). Standard MTT assays on HeLa, U87MG, and HepG2 cells revealed that colloidal dispersions of TEG-coated iron oxide nanoparticles did not induce any loss of cell viability after 3 days incubation with dose concentrations below 50 μg Fe/ml. However, after these nanoparticles were functionalized with DMSA molecules, an increase on their cytotoxicity was observed, so that particles bearing free terminal carboxyl groups on their surface were not cytotoxic only at low concentrations (<10 μg Fe/ml). Moreover, cell uptake assays on HeLa and U87MG and hemolysis tests have demonstrated that TEG-SPIONs and DMSA-SPIONs were well internalized by the cells and did not induce any adverse effect on the red blood cells at the tested concentrations. Finally, in vitro relaxivity measurements and post mortem MRI studies in mice indicated that both types of coated-iron oxide nanoparticles produced higher negative T2-MRI contrast enhancement than that measured for a similar commercial T2-MRI CAs consisting in dextran-coated ultra-small iron oxide nanoparticles (Ferumoxtran-10). In conclusion, the above attributes make both types of as synthesized coated-iron oxide nanoparticles, but especially DMSA-SPIONs, promising candidates as T2-MRI CAs for nanoparticle-enhanced MRI diagnosis applications.

Impact of agglomeration on the relaxometric properties of paramagnetic ultra-small gadolinium oxide nanoparticles

NASA Astrophysics Data System (ADS)

Faucher, Luc; Gossuin, Yves; Hocq, Aline; Fortin, Marc-André

2011-07-01

Ultra-small gadolinium oxide nanoparticles (US-Gd2O3) are used to provide 'positive' contrast effects in magnetic resonance imaging (MRI), and are being considered for molecular and cellular imaging applications. However, these nanoparticles can aggregate over time in aqueous medium, as well as when internalized into cells. This study is aimed at measuring in vitro, in aqueous medium, the impact of aggregation on the relaxometric properties of paramagnetic US-Gd2O3 particles. First, the nanoparticle core size as well as aggregation behaviour was assessed by HRTEM. DLS (hydrodynamic diameter) was used to measure the hydrodynamic diameter of nanoparticles and nanoaggregates. The relaxometric properties were measured by NMRD profiling, as well as with 1H NMR relaxometers. Then, the positive contrast enhancement effect was assessed by using magnetic resonance scanners (at 1.5 and 7 T). At every magnetic field, the longitudinal relaxivity (r1) decreased upon agglomeration, while remaining high enough to provide positive contrast. On the other hand, the transverse relaxivity (r2) slightly decreased at 0.47 and 1.41 T, but it was enhanced at higher fields (7 and 11.7 T) upon agglomeration. All NMRD profiles revealed a characteristic relaxivity peak in the range 60-100 MHz, suggesting the possibility to use US-Gd2O3 as an efficient 'positive-T1' contrast agent at clinical magnetic fields (1-3 T), in spite of aggregation.

Nylon-sputtered nanoparticles: fabrication and basic properties

NASA Astrophysics Data System (ADS)

Polonskyi, O.; Kylián, O.; Solař, P.; Artemenko, A.; Kousal, J.; Slavínská, D.; Choukourov, A.; Biederman, H.

2012-12-01

Nylon-sputtered nanoparticles were prepared using a simple gas aggregation cluster source based on a planar magnetron (Haberland type) and equipped with a nylon target. Plasma polymer particles originated in an aggregation chamber and travelled to a main (deposition) chamber with a gas flow through an orifice. The deposited nanoparticles were observed to have a cauliflower-like structure. The nanoparticles were found to be nitrogen-rich with N/C ratio close to 0.5. An increase in rf power from 60 to 100 W resulted in a decrease in mean particle size from 210 to 168 nm whereas an increase in their residence time in the cluster source from 0.7 to 4.6 s resulted in an increase in the size from 73 to 231 nm.

Light-responsive expansion-contraction of spherical nanoparticle grafted with azopolymers

NASA Astrophysics Data System (ADS)

Fu, Jie; Zhang, Xinghua; Miao, Bing; Yan, Dadong

2017-04-01

Due to the very importance for both fundamental research and technological applications, smart materials with stimuli-responsive properties have been studied intensively. Theoretical investigation contributes to this endeavor through constructing and analyzing a model system which captures main features of the corresponding complex material, wherefrom useful insight can be provided to the trial-and-error experiments. We here report a theoretical study on the smart spherical nanoparticle grafted with light-responsive azobenzene-containing polymers. Utilizing the photoisomerization ability of the azobenzene group, nanoparticles can undergo a light-induced expansion-contraction transition. The wormlike chain based single chain in mean field theory, which has been developed by us recently, is used to investigate this transition in detail. Exploring a large parameter space, our results definitely determine the parameters, including the chain length and effective Kuhn length of grafted chain, nanoparticle radius, grafting density, and position of the azobenzene group along the chain contour, to admit optimum light-responsive behavior of the smart nanoparticle, which provides a guide for experimentalists to design this type of material in a rational manner.

Direct visualization of nanoparticle dynamics at liquid interfaces

NASA Astrophysics Data System (ADS)

Gao, Yige; Kim, Paul; Hoagland, David; Russell, Tom

Ionic liquids, because of their negligible vapor pressures and moderate viscosities, are suitable media to investigate the dynamics of different types of dispersed nanoparticles by scanning electron microscopy. No liquid cell is necessary. Here, Brownian motions of nanoparticles partially wetted at the vacuum-liquid interface are visualized by low voltage SEM under conditions that allow single particle tracking for tens-of-minutes or longer. Conductive, nonconductive, semiconductive, and core-shell conductive-nonconductive nanoparticles have all been studied, and their interactions with each other in one- and two-component layers, as manifested in particle trajectories, differ significantly. For example, Au-coated silica nanoparticles aggregate above a threshold current, whereas aggregated silica-coated Au nanoparticles disaggregate at the same conditions. The impacts of surface concentration of nanoparticle dynamics were observed for one-component and two-component layers, with both global and localized motions visualized for single particles even in dense environments. As the surface concentration increases, the diffusion coefficient drops, and when the concentration reaches a critical threshold, the nanoparticles are essentially frozen. Financial support from NSF DMR-1619651 is acknowledged.

Stability of polyelectrolyte-coated iron nanoparticles for T2-weighted magnetic resonance imaging

NASA Astrophysics Data System (ADS)

McGrath, Andrew J.; Dolan, Ciaran; Cheong, Soshan; Herman, David A. J.; Naysmith, Briar; Zong, Fangrong; Galvosas, Petrik; Farrand, Kathryn J.; Hermans, Ian F.; Brimble, Margaret; Williams, David E.; Jin, Jianyong; Tilley, Richard D.

2017-10-01

Iron nanoparticles are highly-effective magnetic nanoparticles for T2 magnetic resonance imaging (MRI). However, the stability of their magnetic properties is dependent on good protection of the iron core from oxidation in aqueous media. Here we report the synthesis of custom-synthesized phosphonate-grafted polyelectrolytes (PolyM3) of various chain lengths, for efficient coating of iron nanoparticles with a native iron oxide shell. The size of the nanoparticle-polyelectrolyte assemblies was investigated by transmission electron microscopy and dynamic light scattering, while surface attachment was confirmed by Fourier transform infrared spectroscopy. Low cytotoxicity was observed for each of the nanoparticle-polyelectrolyte ("Fe-PolyM3") assemblies, with good cell viability (>80%) remaining up to 100 μg mL-1 Fe in HeLa cells. When applied in T2-weighted MRI, corresponding T2 relaxivities (r2) of the Fe-PolyM3 assemblies were found to be dependent on the chain length of the polyelectrolyte. A significant increase in contrast was observed when polyelectrolyte chain length was increased from 6 to 65 repeating units, implying a critical chain length required for stabilization of the α-Fe nanoparticle core.

Dynamics in Polymer Nanocomposites

NASA Astrophysics Data System (ADS)

Clarke, Nigel

2015-03-01

Since nanoparticles are increasingly being added to polymers to impart mechanical and functional properties, we are exploring how nanoparticles impact polymer dynamics with a focus on the diffusion coefficients. In high molecular weight polymer melts, chain diffusion is well described by the reptation model. Motion proceeds as a snake-like diffusion of the chain as a whole, along the contour of a tube that mimics the role of physical entanglements, or topological constraints, with other chains. In polymer nanocomposites there are additional constraints due to the dispersed nanoparticles in the polymer matrix. Chain motion can be altered by nanoparticle size, shape , aspect ratio, surface area, loading and the nature of the interactions between the nanoparticles and the polymer matrix. We have observed a minimum in the diffusion coefficient as a function of nanoparticle concentration when the nanoparticles are rod-like and a collapse of the diffusion coefficient onto a master curve when the nanoparticles are spherical. We are simulating the dynamics using molecular and dissipative particle simulations in order to provide physical insight into the local structure and dynamics, and have also carried out highly coarse grained Monte Carlo simulations of entangled polymers to explore how reptation is affected by the presence of larger scale obstacles. We acknowledge support from the NSF/EPSRC Materials World Network Program.

Nonlinear optical properties of interconnected gold nanoparticles on silicon

NASA Astrophysics Data System (ADS)

Lesuffleur, Antoine; Gogol, Philippe; Beauvillain, Pierre; Guizal, B.; Van Labeke, D.; Georges, P.

2008-12-01

We report second harmonic generation (SHG) measurements in reflectivity from chains of gold nanoparticles interconnected with metallic bridges. We measured more than 30 times a SHG enhancement when a surface plasmon resonance was excited in the chains of nanoparticles, which was influenced by coupling due to the electrical connectivity of the bridges. This enhancement was confirmed by rigorous coupled wave method calculations and came from high localization of the electric field at the bridge. The introduction of 10% random defects into the chains of nanoparticles dropped the SHG by a factor of 2 and was shown to be very sensitive to the fundamental wavelength.

Albumin-based nanoparticle trehalose lyophilisation stress-down to preserve structure/function and enhanced binding.

PubMed

Siri, Macarena; Grasselli, Mariano; Alonso, Silvia Del V

2016-07-15

The aim of this study was to preserve albumin nanoparticle structure/function during the lyophilisation process. Bovine serum albumin nanoparticles were obtained by γ-irradiation. Nanoparticles were lyophilised in buffer, miliQ water or in trehalose/miliQ solution. The size and charge of the nanoparticles were tested after lyophilisation by light scattering and Z potential. The most relevant results in size of BSA nanoparticle were those lyophilised in PBS between 20 and 350nm, assembled in different aggregates, and negative Z potential obtained was 37±8mV in all, and those nanoparticles lyophilised with trehalose had a size range of 70±2nm and a negative Z potential of 20±5mV. Structure determination of surface aminoacids SH groups in the BSA NP lyophilised in PBS showed an increase in the free SH groups. Different aggregates had different amount of SH groups exposure from 55 to 938 (from smaller to bigger aggregates), whereas BSA NP lyophilised with trehalose showed no significant difference if compared with BSA NP. The binding properties of the BSA nanoparticle with a theragnostic probe (merocyanine 540) were studied after lyophilisation. Results showed more affinity between the BSA NP lyophilised with trehalose than that observed with non lyophilised BSA NP. As a result, the lyophilisation condition in trehalose 100μM solution is the best one to preserve the BSA NP structure/function and the one with the enhance binding affinity of the BSA NP. Copyright © 2016 Elsevier B.V. All rights reserved.

Block-accelerated aggregation multigrid for Markov chains with application to PageRank problems

NASA Astrophysics Data System (ADS)

Shen, Zhao-Li; Huang, Ting-Zhu; Carpentieri, Bruno; Wen, Chun; Gu, Xian-Ming

2018-06-01

Recently, the adaptive algebraic aggregation multigrid method has been proposed for computing stationary distributions of Markov chains. This method updates aggregates on every iterative cycle to keep high accuracies of coarse-level corrections. Accordingly, its fast convergence rate is well guaranteed, but often a large proportion of time is cost by aggregation processes. In this paper, we show that the aggregates on each level in this method can be utilized to transfer the probability equation of that level into a block linear system. Then we propose a Block-Jacobi relaxation that deals with the block system on each level to smooth error. Some theoretical analysis of this technique is presented, meanwhile it is also adapted to solve PageRank problems. The purpose of this technique is to accelerate the adaptive aggregation multigrid method and its variants for solving Markov chains and PageRank problems. It also attempts to shed some light on new solutions for making aggregation processes more cost-effective for aggregation multigrid methods. Numerical experiments are presented to illustrate the effectiveness of this technique.

Naked eye detection of mutagenic DNA photodimers using gold nanoparticles.

PubMed

Kim, Joong Hyun; Chung, Bong Hyun

2011-01-15

We developed a method to detect mutagenic DNA photodimers by the naked eye using gold nanoparticles. The stability of gold nanoparticles in a high ionic strength solution is maintained by straight ssDNA adsorbed physically on the AuNPs. However, we found that UV-irradiated DNA was less adsorptive onto gold nanoparticles because of a conformational change of UV-irradiated DNA. The accumulated deformation of the DNA structure by multiple-dimer formation triggered aggregation of the gold nanoparticles mixed with the UV-irradiated DNA and thus red to purple color changes of the mixture, which allowed colorimetric detection of the DNA photodimers by the naked eye. No fragmented mass and reactive oxygen species production under the UVB irradiation confirmed that the aggregation of gold nanoparticles was solely attributed to the accumulated deformation of the UV irradiated DNA. The degree of gold nanoparticles-aggregation was dependent on the UVB irradiated time and base compositions of the UV-irradiated oligonucleotides. In addition, we successfully demonstrated how to visually qualify the photosensitizing effect of chemical compounds in parallel within only 10 min by applying this new method. Since our method does not require any chemical or biochemical treatments or special instruments for purifying and qualifying the DNA photolesions, it should provide a feasible tool for the studies of the UV-induced mutagenic or carcinogenic DNA dimers and accelerate screening of a large number of drug candidates. Crown Copyright © 2010. Published by Elsevier B.V. All rights reserved.

The effects of side-chain-induced disorder on the emission spectra and quantum yields of oligothiophene nano-aggregates. A combined experimental and MD-TDDFT study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Jiyun; Jeon, SuKyung; Kim, Janice J.

2014-07-24

Oligomeric thiophenes are commonly-used components in organic electronics and solar cells. These molecules stack and/or aggregate readily under the processing conditions used to form thin films for these applications, significantly altering their optical and charge-transport properties. To determine how these effects depend on the substitution pattern of the thiophene main chains, nano-aggregates of three sexi-thiophene (6T) oligomers having different alkyl substitution patterns were formed using solvent poisoning techniques and studied using steady-state and time-resolved emission spectroscopy. The results indicate the substantial role played by the side-chain substituents in determining the emissive properties of these species. Both the measured spectral changesmore » and their dependence on substitution are well modeled by combined quantum chemistry and molecular dynamics simulations. The simulations connect the side-chain-induced disorder, which determines the favorable chain packing configurations within the aggregates, with their measured electronic spectra.« less

SERS-activating effect of chlorides on borate-stabilized silver nanoparticles: formation of new reduced adsorption sites and induced nanoparticle fusion.

PubMed

Sloufová, Ivana; Sisková, Karolína; Vlcková, Blanka; Stepánek, Josef

2008-04-28

Changes in morphology, surface reactivity and surface-enhancement of Raman scattering induced by modification of borate-stabilized Ag nanoparticles by adsorbed chlorides have been explored using TEM, EDX analysis and SERS spectra of probing adsorbate 2,2'-bipyridine (bpy) excited at 514.5 nm and evaluated by factor analysis. At fractional coverages of the parent Ag nanoparticles by adsorbed chlorides <0.6, the Ag colloid/Cl(-)/bpy systems were found to be constituted by fractal aggregates of Ag nanoparticles fairly uniform in size (10 +/- 2 nm) and SERS spectra of Ag(+)-bpy surface species were detected. The latter result was interpreted in terms of the presence of oxidized Ag(+) and/or Ag(n)(+) adsorption sites, which have been encountered also in systems with the chemically untreated Ag nanoparticles. At chloride coverages >0.6, a fusion of fractal aggregates into the compact aggregates of touching and/or interpenetrating Ag nanoparticles has been observed and found to be accompanied by the formation of another surface species, Ag-bpy, as well as by the increase of the overall SERS enhancement of bpy by factor of 40. The same Ag-bpy surface species has been detected under the strongly reducing conditions of reduction of silver nitrate by sodium borohydride in the presence of bpy. The formation of Ag-bpy is thus interpreted in terms of the stabilization of reduced Ag(0) adsorption sites by adsorbed bpy. The formation of reduced adsorption sites on Ag nanoparticle surfaces at chloride coverages >0.6 is discussed in terms of local changes in the work function of Ag. Finally, the SERS spectral detection of Ag-bpy species is proposed as a tool for probing the presence of reduced Ag(0) adsorption sites in systems with chemically modified Ag nanoparticles.

Graphene-bonded and -encapsulated si nanoparticles for lithium ion battery anodes.

PubMed

Wen, Yang; Zhu, Yujie; Langrock, Alex; Manivannan, Ayyakkannu; Ehrman, Sheryl H; Wang, Chunsheng

2013-08-26

Silicon (Si) has been considered a very promising anode material for lithium ion batteries due to its high theoretical capacity. However, high-capacity Si nanoparticles usually suffer from low electronic conductivity, large volume change, and severe aggregation problems during lithiation and delithiation. In this paper, a unique nanostructured anode with Si nanoparticles bonded and wrapped by graphene is synthesized by a one-step aerosol spraying of surface-modified Si nanoparticles and graphene oxide suspension. The functional groups on the surface of Si nanoparticles (50-100 nm) not only react with graphene oxide and bind Si nanoparticles to the graphene oxide shell, but also prevent Si nanoparticles from aggregation, thus contributing to a uniform Si suspension. A homogeneous graphene-encapsulated Si nanoparticle morphology forms during the aerosol spraying process. The open-ended graphene shell with defects allows fast electrochemical lithiation/delithiation, and the void space inside the graphene shell accompanied by its strong mechanical strength can effectively accommodate the volume expansion of Si upon lithiation. The graphene shell provides good electronic conductivity for Si nanoparticles and prevents them from aggregating during charge/discharge cycles. The functionalized Si encapsulated by graphene sample exhibits a capacity of 2250 mAh g⁻¹ (based on the total mass of graphene and Si) at 0.1C and 1000 mAh g⁻¹ at 10C, and retains 85% of its initial capacity even after 120 charge/discharge cycles. The exceptional performance of graphene-encapsulated Si anodes combined with the scalable and one-step aerosol synthesis technique makes this material very promising for lithium ion batteries. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular design of boronic acid-functionalized squarylium cyanine dyes for multiple discriminant analysis of sialic acid in biological samples: selectivity toward monosaccharides controlled by different alkyl side chain lengths.

PubMed

Ouchi, Kazuki; Colyer, Christa L; Sebaiy, Mahmoud; Zhou, Jin; Maeda, Takeshi; Nakazumi, Hiroyuki; Shibukawa, Masami; Saito, Shingo

2015-02-03

We designed a new series of boronic acid-functionalized squarylium cyanine dyes (SQ-BA) with different lengths of alkyl chain residues, suitable for multiple discriminant analysis (MDA) of sialic acid (Neu5Ac) in biological samples. The SQ-BA dyes form aggregates based on hydrophobic interactions, which result in quenched fluorescence in aqueous solutions. When the boronic acid binds with saccharides, the fluorescence intensity increases as a result of dissociation to the emissive monomeric complex. We inferred that different dye aggregate structures (H-aggregates and J-aggregates) were induced depending on the alkyl chain length, so that monosaccharides would be recognized in different ways (especially, multipoint interaction with J-aggregates). A distinctive emission enhancement of SQ-BA dyes with shorter-alkyl-chains in the presence of Neu5Ac was observed (2.4-fold fluorescence enhancement; with formation constant 10(1.7) M(-1)), with no such enhancement for SQ-BA dyes with longer-alkyl-chain. In addition, various enhancement factors for other monosaccharides were observed depending on the alkyl chain length. Detailed thermodynamic and NMR studies of the SQ-BA complexes revealed the unique recognition mechanism: the dye aggregate with a shorter-alkyl-chain causes the slipped parallel structure and forms a stable 2:1 complex with Neu5Ac, as distinct from longer-alkyl-chain dyes, which form a 1:1 monomeric complex. MDA using the four SQ-BA dyes was performed for human urine samples, resulting in the successful discrimination between normal and abnormal Neu5Ac levels characteristic of disease. Thus, we successfully controlled various responses to similar monosaccharides with a novel approach that chemically modified not the boronic acid moiety itself but the length of the alkyl chain residue attached to the dye in order to generate specificity.

Rich complex behaviour of self-assembled nanoparticles far from equilibrium

PubMed Central

Ilday, Serim; Makey, Ghaith; Akguc, Gursoy B.; Yavuz, Özgün; Tokel, Onur; Pavlov, Ihor; Gülseren, Oguz; Ilday, F. Ömer

2017-01-01

A profoundly fundamental question at the interface between physics and biology remains open: what are the minimum requirements for emergence of complex behaviour from nonliving systems? Here, we address this question and report complex behaviour of tens to thousands of colloidal nanoparticles in a system designed to be as plain as possible: the system is driven far from equilibrium by ultrafast laser pulses that create spatiotemporal temperature gradients, inducing Marangoni flow that drags particles towards aggregation; strong Brownian motion, used as source of fluctuations, opposes aggregation. Nonlinear feedback mechanisms naturally arise between flow, aggregate and Brownian motion, allowing fast external control with minimal intervention. Consequently, complex behaviour, analogous to those seen in living organisms, emerges, whereby aggregates can self-sustain, self-regulate, self-replicate, self-heal and can be transferred from one location to another, all within seconds. Aggregates can comprise only one pattern or bifurcated patterns can coexist, compete, endure or perish. PMID:28443636

Rich complex behaviour of self-assembled nanoparticles far from equilibrium

NASA Astrophysics Data System (ADS)

Ilday, Serim; Makey, Ghaith; Akguc, Gursoy B.; Yavuz, Özgün; Tokel, Onur; Pavlov, Ihor; Gülseren, Oguz; Ilday, F. Ömer

2017-04-01

A profoundly fundamental question at the interface between physics and biology remains open: what are the minimum requirements for emergence of complex behaviour from nonliving systems? Here, we address this question and report complex behaviour of tens to thousands of colloidal nanoparticles in a system designed to be as plain as possible: the system is driven far from equilibrium by ultrafast laser pulses that create spatiotemporal temperature gradients, inducing Marangoni flow that drags particles towards aggregation; strong Brownian motion, used as source of fluctuations, opposes aggregation. Nonlinear feedback mechanisms naturally arise between flow, aggregate and Brownian motion, allowing fast external control with minimal intervention. Consequently, complex behaviour, analogous to those seen in living organisms, emerges, whereby aggregates can self-sustain, self-regulate, self-replicate, self-heal and can be transferred from one location to another, all within seconds. Aggregates can comprise only one pattern or bifurcated patterns can coexist, compete, endure or perish.

Influence of source parameters on the growth of metal nanoparticles by sputter-gas-aggregation

NASA Astrophysics Data System (ADS)

Khojasteh, Malak; Kresin, Vitaly V.

2017-11-01

We describe the production of size-selected manganese nanoclusters using a magnetron sputtering/aggregation source. Since nanoparticle production is sensitive to a range of overlapping operating parameters (in particular, the sputtering discharge power, the inert gas flow rates, and the aggregation length), we focus on a detailed map of the influence of each parameter on the average nanocluster size. In this way, it is possible to identify the main contribution of each parameter to the physical processes taking place within the source. The discharge power and argon flow supply the metal vapor, and argon also plays a crucial role in the formation of condensation nuclei via three-body collisions. However, the argon flow and the discharge power have a relatively weak effect on the average nanocluster size in the exiting beam. Here the defining role is played by the source residence time, governed by the helium supply (which raises the pressure and density of the gas column inside the source, resulting in more efficient transport of nanoparticles to the exit) and by the aggregation path length.

Solvents induced ZnO nanoparticles aggregation associated with their interfacial effect on organic solar cells.

PubMed

Li, Pandeng; Jiu, Tonggang; Tang, Gang; Wang, Guojie; Li, Jun; Li, Xiaofang; Fang, Junfeng

2014-10-22

ZnO nanofilm as a cathode buffer layer has surface defects due to the aggregations of ZnO nanoparticles, leading to poor device performance of organic solar cells. In this paper, we report the ZnO nanoparticles aggregations in solution can be controlled by adjusting the solvents ratios (chloroform vs methanol). These aggregations could influence the morphology of ZnO film. Therefore, compact and homogeneous ZnO film can be obtained to help achieve a preferable power conversion efficiency of 8.54% in inverted organic solar cells. This improvement is attributed to the decreased leakage current and the increased electron-collecting efficiency as well as the improved interface contact with the active layer. In addition, we find the enhanced maximum exciton generation rate and exciton dissociation probability lead to the improvement of device performance due to the preferable ZnO dispersion. Compared to other methods of ZnO nanofilm fabrication, it is the more convenient, moderate, and effective to get a preferable ZnO buffer layer for high-efficiency organic solar cells.

Sustainable management and supply of natural and recycled aggregates in a medium-size integrated plant.

PubMed

Faleschini, Flora; Zanini, Mariano Angelo; Pellegrino, Carlo; Pasinato, Stefano

2016-03-01

The consumption of natural aggregates in civil engineering applications can cause severe environmental impacts on a regional scale, depleting the stock of bulk resources within a territory. Several methods can improve the environmental sustainability of the whole aggregates' supply process, including natural and recycled aggregates' productive chains, for instance promoting the use of recycled aggregates (RA). However, when quarrying and recycling activities are considered as stand-alone processes, also the RA supply chain may not be as sustainable as expected, due to the high environmental loads associated to transportation, if high distances from the production to the use sites are involved. This work gives some insights on the environmental impact assessment of the aggregates' industry in the Italian context, through a comparative assessment of the environmental loads of natural and recycled aggregates' productive chains. An integrated plant for the extraction of virgin aggregates and recycling of construction and demolition waste (C&DW) was analyzed as significant case study, with the aim to identify the influence of sustainable solutions on the overall emissions of the facility. A Life Cycle Assessment (LCA) approach was used, using site-specific data and paying particular attention on transportation-related impacts, land use, avoided landfill and non-renewable resources preservation. From this work it was possible to evaluate the influence of transportation and PV energy use on the overall environmental emissions of natural and recycled aggregates' productive chains. Copyright © 2016 Elsevier Ltd. All rights reserved.

Formation of aggregated nanoparticle spheres through femtosecond laser surface processing

NASA Astrophysics Data System (ADS)

Tsubaki, Alfred T.; Koten, Mark A.; Lucis, Michael J.; Zuhlke, Craig; Ianno, Natale; Shield, Jeffrey E.; Alexander, Dennis R.

2017-10-01

A detailed structural and chemical analysis of a class of self-organized surface structures, termed aggregated nanoparticle spheres (AN-spheres), created using femtosecond laser surface processing (FLSP) on silicon, silicon carbide, and aluminum is reported in this paper. AN-spheres are spherical microstructures that are 20-100 μm in diameter and are composed entirely of nanoparticles produced during femtosecond laser ablation of material. AN-spheres have an onion-like layered morphology resulting from the build-up of nanoparticle layers over multiple passes of the laser beam. The material properties and chemical composition of the AN-spheres are presented in this paper based on scanning electron microscopy (SEM), focused ion beam (FIB) milling, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX) analysis. There is a distinct difference in the density of nanoparticles between concentric rings of the onion-like morphology of the AN-sphere. Layers of high-density form when the laser sinters nanoparticles together and low-density layers form when nanoparticles redeposit while the laser ablates areas surrounding the AN-sphere. The dynamic nature of femtosecond laser ablation creates a variety of nanoparticles that make-up the AN-spheres including Si/C core-shell, nanoparticles that directly fragmented from the base material, nanoparticles with carbon shells that retarded oxidation, and amorphous, fully oxidized nanoparticles.

"Smart" gold nanoparticles for photoacoustic imaging: an imaging contrast agent responsive to the cancer microenvironment and signal amplification via pH-induced aggregation.

PubMed

Song, Jaejung; Kim, Jeesu; Hwang, Sekyu; Jeon, Mansik; Jeong, Sanghwa; Kim, Chulhong; Kim, Sungjee

2016-07-07

'Smart' gold nanoparticles can respond to mild acidic environments, rapidly form aggregates, and shift the absorption to red and near-infrared. They were used as a photoacoustic imaging agent responsive to the cancer microenvironment, and have demonstrated the cancer-specific accumulation at the cellular level and an amplified signal which is twice higher than the control in vivo.

Effects of magnetic field strength and particle aggregation on relaxivity of ultra-small dual contrast iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Ta, Hang T.; Li, Zhen; Wu, Yuao; Cowin, Gary; Zhang, Shaohua; Yago, Anya; Whittaker, Andrew K.; Xu, Zhi Ping

2017-11-01

This study aims to compare the relaxivities of ultra-small dual positive and negative contrast iron oxide nanoparticles (DCION) at different magnetic field strengths ranging from 4.7 to 16.4 T at physiological temperatures; and to investigate the effect of particle aggregation on relaxivities. Relaxivities of DCIONs were determined by magnetic resonance imaging scanners at 4.7, 7, 9.4, and 16.4 T. Both longitudinal (T 1) and transverse relaxation times (T 2) were measured by appropriate spin-echo sequences. It has been found that both longitudinal and transverse relaxivities are significantly dependent on the magnetic field strength. Particle aggregation also strongly affects the relaxivities. Awareness of the field strength and particle colloid stability is crucial for the comparison and evaluation of relaxivity values of these ultra-small iron oxide nanoparticles, and also for their medical applications as contrast agents.

Elongated Nanoparticle Aggregates in Cancer Cells for Mechanical Destruction with Low Frequency Rotating Magnetic Field.

PubMed

Shen, Yajing; Wu, Congyu; Uyeda, Taro Q P; Plaza, Gustavo R; Liu, Bin; Han, Yu; Lesniak, Maciej S; Cheng, Yu

2017-01-01

Magnetic nanoparticles (MNPs) functionalized with targeting moieties can recognize specific cell components and induce mechanical actuation under magnetic field. Their size is adequate for reaching tumors and targeting cancer cells. However, due to the nanometric size, the force generated by MNPs is smaller than the force required for largely disrupting key components of cells. Here, we show the magnetic assembly process of the nanoparticles inside the cells, to form elongated aggregates with the size required to produce elevated mechanical forces. We synthesized iron oxide nanoparticles doped with zinc, to obtain high magnetization, and functionalized with the epidermal growth factor (EGF) peptide for targeting cancer cells. Under a low frequency rotating magnetic field at 15 Hz and 40 mT, the internalized EGF-MNPs formed elongated aggregates and generated hundreds of pN to dramatically damage the plasma and lysosomal membranes. The physical disruption, including leakage of lysosomal hydrolases into the cytosol, led to programmed cell death and necrosis. Our work provides a novel strategy of designing magnetic nanomedicines for mechanical destruction of cancer cells.

Tangeretin-loaded protein nanoparticles fabricated from zein/β-lactoglobulin: preparation, characterization, and functional performance.

PubMed

Chen, Jingjing; Zheng, Jinkai; McClements, David Julian; Xiao, Hang

2014-09-01

The aim of this study was to design a colloidal delivery system to encapsulate poor water-soluble bioactive flavonoid tangeretin so that it could be utilized in various food products as functional ingredient. Tangeretin-loaded protein nanoparticles were produced by mixing an organic phase containing zein and tangeretin with an aqueous phase containing β-lactoglobulin and then converted into powder by freeze-drying. This powder formed a colloidal suspension when dispersed in water that is relatively stable to particle aggregation and sedimentation. The influence of temperature, ionic strength, and pH on the stability of the protein nanoparticles was tested. Extensive particle aggregation occurred at high ionic strength (>100mM) and intermediate pH (4.5-5.5) due to reduced electrostatic repulsion. Extensive aggregation also occurred at temperatures exceeding 60 °C, which was presumably due to increased hydrophobic attraction. Overall, this study shows that protein-based nanoparticles can be used to encapsulate bioactive tangeretin so that it can be readily dispersed in compatible food products. Copyright © 2014 Elsevier Ltd. All rights reserved.

Elongated Nanoparticle Aggregates in Cancer Cells for Mechanical Destruction with Low Frequency Rotating Magnetic Field

PubMed Central

Shen, Yajing; Wu, Congyu; Uyeda, Taro Q. P.; Plaza, Gustavo R.; Liu, Bin; Han, Yu; Lesniak, Maciej S.; Cheng, Yu

2017-01-01

Magnetic nanoparticles (MNPs) functionalized with targeting moieties can recognize specific cell components and induce mechanical actuation under magnetic field. Their size is adequate for reaching tumors and targeting cancer cells. However, due to the nanometric size, the force generated by MNPs is smaller than the force required for largely disrupting key components of cells. Here, we show the magnetic assembly process of the nanoparticles inside the cells, to form elongated aggregates with the size required to produce elevated mechanical forces. We synthesized iron oxide nanoparticles doped with zinc, to obtain high magnetization, and functionalized with the epidermal growth factor (EGF) peptide for targeting cancer cells. Under a low frequency rotating magnetic field at 15 Hz and 40 mT, the internalized EGF-MNPs formed elongated aggregates and generated hundreds of pN to dramatically damage the plasma and lysosomal membranes. The physical disruption, including leakage of lysosomal hydrolases into the cytosol, led to programmed cell death and necrosis. Our work provides a novel strategy of designing magnetic nanomedicines for mechanical destruction of cancer cells. PMID:28529648

The ground state of metallic nano-structures in heavily irradiated NaCl-KBF4

NASA Astrophysics Data System (ADS)

Cherkasov, F. G.; L'Vov, S. G.; Tikhonov, D. A.; den Hartog, H. W.; Vainshtein, D. I.

ESR, NMR and static magnetic susceptibility measurements of heavily irradiated NaCl-K and NaCl-KBF4 are reported. Up to 10% of the NaCl-molecules are transformed into metallic Na nanoparticles and Cl-2 precipitates. In addition, there are paramagnetic F- and F-aggregates, which are coupled by exchange interactions to the conduction electrons in the nanoparticles. Above 160 K the NMR and ESR signals of NaCl-K and NaCl-KBF4 show Pauli paramagnetism and the properties of the Na nanoparticles are similar to bulk sodium. A single ESR line is observed revealing exchange interaction between conduction electrons in the nano-particles and F-aggregates. The observed decrease of the ESR susceptibility with decreasing temperature is due to a metal-insulator transition. The conduction electrons are localized below 40 K and the above mentioned F-aggregate centers contribute significantly to the overall ESR signal. For NaCl-KBF4 we observed that with decreasing temperature the ESR line shifts towards lower fields due to antiferromagnetic ordering and internal magnetic fields.

High density flux of Co nanoparticles produced by a simple gas aggregation apparatus.

PubMed

Landi, G T; Romero, S A; Santos, A D

2010-03-01

Gas aggregation is a well known method used to produce clusters of different materials with good size control, reduced dispersion, and precise stoichiometry. The cost of these systems is relatively high and they are generally dedicated apparatuses. Furthermore, the usual sample production speed of these systems is not as fast as physical vapor deposition devices posing a problem when thick samples are needed. In this paper we describe the development of a multipurpose gas aggregation system constructed as an adaptation to a magnetron sputtering system. The cost of this adaptation is negligible and its installation and operation are both remarkably simple. The gas flow for flux in the range of 60-130 SCCM (SCCM denotes cubic centimeter per minute at STP) is able to completely collimate all the sputtered material, producing spherical nanoparticles. Co nanoparticles were produced and characterized using electron microscopy techniques and Rutherford back-scattering analysis. The size of the particles is around 10 nm with around 75 nm/min of deposition rate at the center of a Gaussian profile nanoparticle beam.

Plasma based formation and deposition of metal and metal oxide nanoparticles using a gas aggregation source

NASA Astrophysics Data System (ADS)

Polonskyi, Oleksandr; Ahadi, Amir Mohammad; Peter, Tilo; Fujioka, Kenji; Abraham, Jan Willem; Vasiliauskaite, Egle; Hinz, Alexander; Strunskus, Thomas; Wolf, Sebastian; Bonitz, Michael; Kersten, Holger; Faupel, Franz

2018-05-01

Metal clusters and nanoparticles (NPs) have been studied intensively due to their unique chemical, physical, electrical, and optical properties, resulting from their dimensions, which provided host of applications in nanoscience and nanotechnology. Formation of new materials by embedding NPs into various matrices (i.e. formation of nanocomposites) further expands the horizon of possible application of such nanomaterials. In the last few decades, the focus was put on the formation of metallic and metal oxide NPs via a so-called gas aggregation nanoparticle source employing magnetron sputtering (i.e. Haberland concept). In this paper, an overview is given of the recent progress in formation and deposition of NPs by the gas aggregation method. Examples range from noble metals (Ag, Au) through reactive metals (Al, Ti) to Si and the respective oxides. Emphasis is placed on the mechanism of nanoparticle growth and the resulting properties. Moreover, kinetic Monte Carlo simulations were developed to explain the growth mechanism and dynamics of nanoparticle formation depending on the experimental conditions. In addition, the role of trace amounts of reactive gases and of pulsed operation of the plasma on the nucleation process is addressed. Finally, the treatment of the NPs in the plasma environment resulting in nanoparticle charging, morphological and chemical modifications is discussed. Contribution to the Topical Issue "Fundamentals of Complex Plasmas", edited by Jürgen Meichsner, Michael Bonitz, Holger Fehske, Alexander Piel.

Iron Oxide Nanospheres and Nanocubes for Magnetic Hyperthermia Therapy: A Comparative Study

NASA Astrophysics Data System (ADS)

Nemati, Z.; Das, R.; Alonso, J.; Clements, E.; Phan, M. H.; Srikanth, H.

2017-06-01

Improving the heating capacity of magnetic nanoparticles (MNPs) for hyperthermia therapy is an important but challenging task. Through a comparative study of the inductive heating properties of spherical and cubic Fe3O4 MNPs with two distinct average volumes (˜7000 nm3 and 80,000 nm3), we demonstrate that, for small size (˜7000 nm3), the cubic MNPs heat better compared with the spherical MNPs. However, the opposite trend is observed for larger size (˜80,000 nm3). The improvement in heating efficiency in cubic small-sized MNPs (˜7000 nm3) can be attributed to enhanced anisotropy and the formation of chain-like aggregates, whereas the decrease of the heating efficiency in cubic large-sized MNPs (˜80,000 nm3) has been attributed to stronger aggregation of particles. Physical motion is shown to contribute more to the heating efficiency in case of spherical than cubic MNPs, when dispersed in water. These findings are of crucial importance in understanding the role of shape anisotropy and optimizing the heating response of magnetic nano-structures for advanced hyperthermia.

Acoustic wave in a suspension of magnetic nanoparticle with sodium oleate coating

NASA Astrophysics Data System (ADS)

Józefczak, A.; Hornowski, T.; Závišová, V.; Skumiel, A.; Kubovčíková, M.; Timko, M.

2014-03-01

The ultrasonic propagation in the water-based magnetic fluid with doubled layered surfactant shell was studied. The measurements were carried out both in the presence as well as in the absence of the external magnetic field. The thickness of the surfactant shell was evaluated by comparing the mean size of magnetic grain extracted from magnetization curve with the mean hydrodynamic diameter obtained from differential centrifugal sedimentation method. The thickness of surfactant shell was used to estimate volume fraction of the particle aggregates consisted of magnetite grain and surfactant layer. From the ultrasonic velocity measurements in the absence of the applied magnetic field, the adiabatic compressibility of the particle aggregates was determined. In the external magnetic field, the magnetic fluid studied in this article becomes acoustically anisotropic, i.e., velocity and attenuation of the ultrasonic wave depend on the angle between the wave vector and the direction of the magnetic field. The results of the ultrasonic measurements in the external magnetic field were compared with the hydrodynamic theory of Ovchinnikov and Sokolov (velocity) and with the internal chain dynamics model of Shliomis, Mond and Morozov (attenuation).

Acoustic wave in a suspension of magnetic nanoparticle with sodium oleate coating.

PubMed

Józefczak, A; Hornowski, T; Závišová, V; Skumiel, A; Kubovčíková, M; Timko, M

2014-01-01

The ultrasonic propagation in the water-based magnetic fluid with doubled layered surfactant shell was studied. The measurements were carried out both in the presence as well as in the absence of the external magnetic field. The thickness of the surfactant shell was evaluated by comparing the mean size of magnetic grain extracted from magnetization curve with the mean hydrodynamic diameter obtained from differential centrifugal sedimentation method. The thickness of surfactant shell was used to estimate volume fraction of the particle aggregates consisted of magnetite grain and surfactant layer. From the ultrasonic velocity measurements in the absence of the applied magnetic field, the adiabatic compressibility of the particle aggregates was determined. In the external magnetic field, the magnetic fluid studied in this article becomes acoustically anisotropic, i.e., velocity and attenuation of the ultrasonic wave depend on the angle between the wave vector and the direction of the magnetic field. The results of the ultrasonic measurements in the external magnetic field were compared with the hydrodynamic theory of Ovchinnikov and Sokolov (velocity) and with the internal chain dynamics model of Shliomis, Mond and Morozov (attenuation).

pH Triggered Recovery and Reuse of Thiolated Poly(acrylic acid) Functionalized Gold Nanoparticles with Applications in Colloidal Catalysis.

PubMed

Ansar, Siyam M; Fellows, Benjamin; Mispireta, Patrick; Mefford, O Thompson; Kitchens, Christopher L

2017-08-08

Thiolated poly(acrylic acid) (PAA-SH) functionalized gold nanoparticles were explored as a colloidal catalyst with potential application as a recoverable catalyst where the PAA provides pH-responsive dispersibility and phase transfer capability between aqueous and organic media. This system demonstrates complete nanoparticle recovery and redispersion over multiple reaction cycles without changes in nanoparticle morphology or reduction in conversion. The catalytic activity (rate constant) was reduced in subsequent reactions when recovery by aggregation was employed, despite unobservable changes in morphology or dispersibility. When colloidal catalyst recovery employed a pH induced phase transfer between two immiscible solvents, the catalytic activity of the recovered nanoparticles was unchanged over four cycles, maintaining the original rate constant and 100% conversion. The ability to recover and reuse colloidal catalysts by aggregation/redispersion and phase transfer methods that occur at low and high pH, respectively, could be used for different gold nanoparticle catalyzed reactions that occur at different pH conditions.

Is It Possible To Fabricate a Nanocomposite with Excellent Mechanical Property Using Unmodified Inorganic Nanoparticles Directly?

PubMed

Zhang, Chunhua; Xia, Liangjun; Lyu, Pei; Wang, Yun; Li, Chen; Xiao, Xingfang; Dai, Fangyin; Xu, Weilin; Liu, Xin; Deng, Bo

2018-05-09

Unmodified ZrO 2 nanoparticles (ZDNPs) are used for the enhancement of polyurethane (PU) films. Optimized strain and toughness of PU/ZDNP nanocomposite at 9.09 wt % ZDNPs are up to 2714.6%, and 280.8 MJ m -3 , respectively. The unique bimodal ZDNP aggregate size distribution which exploits both interfacial positively and negatively toughening mechanisms accounts mainly for the excellent mechanical property of PU/ZDNP nanocomposite. The dependence of different toughening mechanisms on three sizes of ZDNP aggregates is summarized. These findings provide a new avenue for the industrial production of nanocomposites at low cost without surface modification of inorganic nanoparticles.

Debranching and Crystallization of Waxy Maize Starch in Relation to Enzyme Digestibility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, L.; Shi, Y; Rong, L

Molecular and crystal structures as well as morphology during debranching and crystallization of waxy maize starch at a high solid content (25%, w/w) were investigated, and the results were related to the digestibility of debranched products. The starch was cooked at 115-120 C for 10 min, cooled to 50 C and debranched by isoamylase. After 1 h of debranching, wormlike objects with 5-10 nm width and ca. 30 nm length were observed by transmission electron microscopy. Further release of linear chains and crystallization led to assembly of semi-crystalline structures in the form of nano-particles and subsequent growth of nano-particles intomore » large aggregates. After 24 h at 50 C, a debranched starch product with an A-type X-ray diffraction pattern, a high melting temperature (90-140 C), and high resistant starch content (71.4%) was obtained. Small-angle X-ray scattering results indicated that all debranched products were surface fractal in a dry state (4% moisture) but had a mass fractal structure when hydrated (e.g. 45% moisture).« less

Self-assembly and alignment of semiconductor nanoparticles on cellulose nanocrystals

Treesearch

Sonal Padalkar; Jeff R. Capadona; Stuart J. Rowan; Christoph Weder; Robert J. Moon; Lia A. Stanciu

2011-01-01

The synthesis of cadmium sulfide (CdS), zinc sulfide (ZnS), and lead sulfide (PbS) nanoparticle chains on cellulose nanocrystal (CNC) templates can be accomplished by the reaction of the precursor salts. The use of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), was critical for the synthesis of well-defined semiconductor nanoparticle chains on the...

Long Term Influence of Carbon Nanoparticles on Health and Liver Status in Rats

PubMed Central

Strojny, Barbara; Kurantowicz, Natalia; Sawosz, Ewa; Grodzik, Marta; Jaworski, Sławomir; Kutwin, Marta; Wierzbicki, Mateusz; Hotowy, Anna; Lipińska, Ludwika; Chwalibog, André

2015-01-01

Due to their excellent biocompatibility, carbon nanoparticles have been widely investigated for prospective biomedical applications. However, their impact on an organism with prolonged exposure is still not well understood. Here, we performed an experiment investigating diamond, graphene oxide and graphite nanoparticles, which were repeatedly administrated intraperitoneally into Wistar rats for four weeks. Some of the animals was sacrificed after the last injection, whereas the rest were sacrificed twelve weeks after the last exposure. We evaluated blood morphology and biochemistry, as well as the redox and inflammatory state of the liver. The results show the retention of nanoparticles within the peritoneal cavity in the form of prominent aggregates in proximity to the injection site, as well as the presence of some nanoparticles in the mesentery. Small aggregates were also visible in the liver serosa, suggesting possible transportation to the liver. However, none of the tested nanoparticles affected the health of animals. This lack of toxic effect may suggest the potential applicability of nanoparticles as drug carriers for local therapies, ensuring accumulation and slow release of drugs into a targeted tissue without harmful systemic side effects. PMID:26657282

Long Term Influence of Carbon Nanoparticles on Health and Liver Status in Rats.

PubMed

Strojny, Barbara; Kurantowicz, Natalia; Sawosz, Ewa; Grodzik, Marta; Jaworski, Sławomir; Kutwin, Marta; Wierzbicki, Mateusz; Hotowy, Anna; Lipińska, Ludwika; Chwalibog, André

2015-01-01

Due to their excellent biocompatibility, carbon nanoparticles have been widely investigated for prospective biomedical applications. However, their impact on an organism with prolonged exposure is still not well understood. Here, we performed an experiment investigating diamond, graphene oxide and graphite nanoparticles, which were repeatedly administrated intraperitoneally into Wistar rats for four weeks. Some of the animals was sacrificed after the last injection, whereas the rest were sacrificed twelve weeks after the last exposure. We evaluated blood morphology and biochemistry, as well as the redox and inflammatory state of the liver. The results show the retention of nanoparticles within the peritoneal cavity in the form of prominent aggregates in proximity to the injection site, as well as the presence of some nanoparticles in the mesentery. Small aggregates were also visible in the liver serosa, suggesting possible transportation to the liver. However, none of the tested nanoparticles affected the health of animals. This lack of toxic effect may suggest the potential applicability of nanoparticles as drug carriers for local therapies, ensuring accumulation and slow release of drugs into a targeted tissue without harmful systemic side effects.

Selective and directional actuation of elastomer films using chained magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Mishra, Sumeet R.; Dickey, Michael D.; Velev, Orlin D.; Tracy, Joseph B.

2016-01-01

We report selective and directional actuation of elastomer films utilizing magnetic anisotropy introduced by chains of Fe3O4 magnetic nanoparticles (MNPs). Under uniform magnetic fields or field gradients, dipolar interactions between the MNPs favor magnetization along the chain direction and cause selective lifting. This mechanism is described using a simple model.We report selective and directional actuation of elastomer films utilizing magnetic anisotropy introduced by chains of Fe3O4 magnetic nanoparticles (MNPs). Under uniform magnetic fields or field gradients, dipolar interactions between the MNPs favor magnetization along the chain direction and cause selective lifting. This mechanism is described using a simple model. Electronic supplementary information (ESI) available: Two videos for actuation while rotating the sample, experimental details of nanoparticle synthesis, polymer composite preparation, and alignment and bending studies, details of the theoretical model of actuation, and supplemental figures for understanding the behavior of rotating samples and results from modelling. See DOI: 10.1039/c5nr07410j

Detection of pH-induced aggregation of "smart" gold nanoparticles with photothermal optical coherence tomography.

PubMed

Xiao, Peng; Li, Qingyun; Joo, Yongjoon; Nam, Jutaek; Hwang, Sekyu; Song, Jaejung; Kim, Sungjee; Joo, Chulmin; Kim, Ki Hean

2013-11-01

We report the feasibility of a novel contrast agent, namely "smart" gold nanoparticles (AuNPs), in the detection of cancer cells with photothermal optical coherence tomography (PT-OCT). "Smart" AuNPs form aggregation in low pH condition, which is typical for cancer cells, and this aggregation results in a shift of their absorption spectrum. A PT-OCT system was developed to detect this pH-induced aggregation by combining an OCT light source and a laser with 660 nm in wavelength for photothermal excitation. Optical detection of pH-induced aggregation was tested with solution samples at two different pH conditions. An increase in optical path length (OPL) variation was measured at mild acidic condition, while there was not much change at neutral condition. Detection of cancer cells was tested with cultured cell samples. HeLa and fibroblast cells, as cancer and normal cells respectively, were incubated with "smart" gold nanoparticles and measured with PT-OCT. An elevated OPL variation signal was detected with the HeLa cells while not much of a signal was detected with the fibroblast cells. With the novel optical property of "smart" AuNPs and high sensitivity of PT-OCT, this technique is promising for cancer cell detection.

Imaging Metastasis Using an Integrin-Targeting Chain-Shaped Nanoparticle

PubMed Central

Peiris, Pubudu M.; Toy, Randall; Doolittle, Elizabeth; Pansky, Jenna; Abramowski, Aaron; Tam, Morgan; Vicente, Peter; Tran, Emily; Hayden, Elliott; Camann, Andrew; Mayer, Aaron; Erokwu, Bernadette O.; Berman, Zachary; Wilson, David; Baskaran, Harihara; Flask, Chris A.; Keri, Ruth A.; Karathanasis, Efstathios

2012-01-01

While the enhanced permeability and retention effect may promote the preferential accumulation of nanoparticles into well-vascularized primary tumors, it is ineffective in the case of metastases hidden within a large population of normal cells. Due to their small size, high dispersion to organs, and low vascularization, metastatic tumors are less accessible to targeted nanoparticles. To tackle these challenges, we designed a nanoparticle for vascular targeting based on an αvβ3 integrin-targeted nanochain particle composed of four iron oxide nanospheres chemically linked in a linear assembly. The chain-shaped nanoparticles enabled enhanced ‘sensing’ of the tumor-associated remodeling of the vascular bed offering increased likelihood of specific recognition of metastatic tumors. Compared to spherical nanoparticles, the chain-shaped nanoparticles resulted in superior targeting of αvβ3 integrin due to geometrically enhanced multivalent docking. We performed multimodal in vivo imaging (Fluorescence Molecular Tomography and Magnetic Resonance Imaging) in a non-invasive and quantitative manner, which showed that the nanoparticles targeted metastases in the liver and lungs with high specificity in a highly aggressive breast tumor model in mice. PMID:23005348

A highly sensitive nanoscale pH-sensor using Au nanoparticles linked by a multifunctional Raman-active reporter molecule.

PubMed

Lawson, Latevi S; Chan, James W; Huser, Thomas

2014-07-21

Chemical sensing on the nanoscale has been breaking new ground since the discovery of surface enhanced Raman scattering (SERS). For nanoparticles, controlled particle aggregation is necessary to achieve the largest SERS enhancements. Therefore, aggregating agents such as salts or linker molecules are used in conjunction with chemically sensitive reporters in order to develop robust environmentally sensitive SERS probes. While salt-induced colloidal nanosphere aggregates have produced robust SERS signals, their variability in aggregate size contributes significantly to poor SERS signal reproducibility, which can complicate their use in in vitro cellular studies. Such systems often also lack reproducibility in spectral measurements between different nanoparticle clusters. Preaggregation of colloids via linkers followed by surface functionalization with reporter molecules results in the linker occupying valuable SERS hotspot volume which could otherwise be utilized by additional reporter molecules. Ideally, both functionalities should be obtained from a single molecule. Here, we report the use of 3,5-dimercaptobenzoic acid, a single multifunctional molecule that creates SERS hotspots via the controlled aggregation of nanoparticles, and also reports pH values. We show that 3,5-dimercaptobenzoic acid bound to Au nanospheres results in an excellent pH nanoprobe, producing very robust, and highly reproducible SERS signals that can report pH across the entire physiological range with excellent pH resolution. To demonstrate the efficacy of our novel pH reporters, these probes were also used to image both the particle and pH distribution in the cytoplasm of human induced pluripotent stem cells (hiPSCs).

Impact of different environmental conditions on the aggregation of biogenic U(IV) nanoparticles synthesized by Desulfovibrio alaskensis G20

DOE Office of Scientific and Technical Information (OSTI.GOV)

Şengör, S. Sevinç; Singh, Gursharan; Dohnalkova, Alice

This study investigates the impact of specific environmental conditions on the formation of colloidal U(IV) nanoparticles by the sulfate reducing bacteria (SRB, Desulfovibrio alaskensis G20). The reduction of soluble U(VI) to less soluble U(IV) was quantitatively investigated under growth and non-growth conditions in bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) buffered environments. The results showed that under non-growth conditions, the majority of the reduced U nanoparticles aggregated and precipitated out of solution. High resolution transmission electron microscopy revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces in the presence of PIPES buffer, whereas inmore » the presence of bicarbonate buffer, reduced U was also observed in the cytoplasm with greater aggregation of biogenic U(IV) particles at higher initial U(VI) concentrations. The same experiments were repeated under growth conditions using two different electron donors (lactate and pyruvate) and three electron acceptors (sulfate, fumarate, and thiosulfate). In contrast to the results of the non-growth experiments, even after 0.2 m filtration, the majority of biogenic U(IV) remained in the aqueous phase resulting in potentially mobile biogenic U(IV) nanoparticles. Size fractionation results showed that U(IV) aggregates were between 18 and 200 nm in diameter, and thus could be very mobile. The findings of this study are helpful to assess the size and potential mobility of reduced U nanoparticles under different environmental conditions, and would provide insights on their potential impact affecting U(VI) bioremediation efforts at subsurface contaminated sites.« less

Enthalpic and Entropic Competition in Blends of Self-Suspended Hairy Nanoparticles

NASA Astrophysics Data System (ADS)

Choudhury, Snehashis; Agrawal, Akanksha; Archer, Lynden

Self-suspended hairy nanoparticles, where polymer chains are grafted onto nanoparticles, have attracted significant recent attention. These materials have been reported to manifest several interesting phenomena like thermal jamming, slowing-down of polymer chain dynamics, as well as small-strain stress overshoots during start-up of steady shear. The entropic penalty on tethered polymers produced by the requirement that they fill the space between the nanoparticle cores explain most of these behaviors. Here, we show that the entropic attraction between tethered polymer chains can be manipulated in mixtures of hairy nanoparticles using different polymer chemistry to design materials with unusual characteristics. Specifically, the degree of interpenetration of polymer chains can be controlled by tuning their interaction parameter (χ) . For SiO2-PEG/SiO2-PMMA blends, oscillatory rheological measurements show that the plateau modulus and yielding energy are significantly increased, while an opposite effect is seen with SiO2-PEG/SiO2-PI blends. More subtle effects of this enthalpy-entropy competition are well captured in Dielectric Spectroscopy measurements and SAXS experiments that can be used to quantify the degree of stretch and interdigitation of polymer chains.

Design and Fabrication of Tunable Nanoparticles for Biomedical Applications

NASA Astrophysics Data System (ADS)

Sun, Leming

In this dissertation, we first reviewed the naturally occurring nanoparticles and their limitations (Chapter 1). We then discussed the need and the parameters to design and fabricate bio-inspired tunable nanoparticles for wound healing, Alzheimer's disease (AD) diagnosis and progression monitoring. Tunable nanoparticles enhanced adhesive was inspired from the self-assembly processes, nanocomposite and chemical structures. Fluorescent peptide nanoparticles were inspired from the biological peptide self-assembly and naturally occurring fluorescent proteins. Then we reported the development of an in situ synthesis approach for fabricating tunable nanoparticle enhanced adhesives inspired from the strong adhesive produced by English ivy in Chapter 2. Special attention was given to tunable features of the adhesive produced by the biological process. Parameters that may be used to tune properties of the adhesive were proposed. To illustrate and validate the proposed approach, an experimental platform was presented for fabricating tunable chitosan adhesive enhanced by Au nanoparticles synthesized in situ. This study contributes to a bio-inspired approach for in situ synthesis of tunable nanocomposite adhesives by mimicking the natural biological processes of ivy adhesive synthesis. Using a bio-inspired approach, we synthesized adhesive hydrogels comprised of sodium alginate, gum arabic, and calcium ions to mimic the properties of the natural sundew-derived adhesive hydrogels in Chapter 3. We then characterized and showed that these sundew-inspired hydrogels promote wound healing through their superior adhesive strength, nanostructure, and resistance to shearing; when compared to other hydrogels in vitro. In vivo, sundew-inspired hydrogels promoted a "suturing" effect to wound sites; which was demonstrated by enhanced wound closure following topical application of the hydrogels. In combination with mouse adipose derived stem cells (ADSCs), and compared to other therapeutic biomaterials, the sundew-inspired hydrogels demonstrated superior wound healing capabilities. Collectively, our studies show that sundew-inspired hydrogels contain ideal properties that promote wound healing and suggest that sundew-inspired-ADSCs combination therapy is an efficacious approach for treating wounds without eliciting noticeable toxicity or inflammation. While tremendous efforts have been spent in investigating scalable approaches for fabricating nanoparticles, less progress has been made in scalable synthesizing cyclic peptide nanoparticles and nanotubes, despite their great potential for broader biomedical applications. In Chapter 4, tunable synthesis of self-assembled cyclic peptide nanotubes and nanoparticles using three different methods, phase equilibrium, pH-driven, and pH-sensitive methods were proposed and investigated. The goal is for scalable nano-manufacturing of cyclic peptide nanoparticles and nanotubes with different sizes in large quality by controlling multiple process parameters. The dimensions of self-assembled nanostructures were found to be strongly influenced by the cyclic peptides concentration, side chains modification, pH value, reaction time, stirring intensity, and sonication time. This study proposed an overall strategy to integrate all the parameters to achieve optimal synthesis outputs. AD is associated with the accumulation of insoluble forms of amyloid-beta (Abeta) in plaques in extracellular spaces, as well as in the walls of blood vessels, and aggregation of microtubule protein tau in neurofibrillary tangles in neurons. In Chapter 5, we designed and synthesized a series of fluorescent cyclic peptide nanoparticles that can be used to detect Abeta aggregates in both the cerebrospinal fluid (CSF) and serum, which were obtained from healthy people and AD patients in different disease stages. Our experimental studies indicate that the fluorescence intensities and wavelengths generated from the interactions between the negatively charged fluorescent cyclic peptide nanoparticles and Abeta aggregates in both the CSF and serum changed with disease status, as compared to healthy individuals. The morphological and cytotoxicity studies demonstrated a potential inhibitory effect of the negatively charged nanoparticles on amyloid fibril growth. The underlying mechanisms leading to these changes are interpreted based on the aromatic, hydrophobic, and electrostatic interactions between c-PNPs and Abeta peptides. There is a critical need to diagnose and monitor the progression of AD using blood-based biomarkers. At present, it is believed that no single biomarker can be utilized to reliably detect AD. Combined biomarkers using multimodal techniques are highly sought after for AD diagnosis and progression monitoring. For this purpose, we developed a fluorescent peptide nanoparticles arrayed microfluidic chip that is capable of detecting multiple blood-based AD biomarkers simultaneously in Chapter 6. The concentration, aggregation stages, and Young's modulus of biomarkers could be analyzed by monitoring the changes of multimodal fluorescence intensity, nano-morphological, and nano-mechanical properties of the f-PNPs array. In this study, Abeta polypeptides and tau proteins were used to verify the proposed idea. To conclude, we demonstrate that how to design and fabrication of tunable nanoparticles for biomedical applications. Inspired from English ivy and sundew nanoadhesive, tunable nanoparticles enhanced adhesive hydrogels were prepared and validated for wound healing applications. Moreover, fluorescent peptide nanoparticles were designed, synthesized, characterized, and validated for AD diagnosis and progression monitoring. (Abstract shortened by ProQuest.).

Encapsulation of antigen-loaded silica nanoparticles into microparticles for intradermal powder injection.

PubMed

Deng, Yibin; Mathaes, Roman; Winter, Gerhard; Engert, Julia

2014-10-15

Epidermal powder immunisation (EPI) is being investigated as a promising needle-free delivery methods for vaccination. The objective of this work was to prepare a nanoparticles-in-microparticles (nano-in-micro) system, integrating the advantages of nanoparticles and microparticles into one vaccine delivery system for epidermal powder immunisation. Cationic mesoporous silica nanoparticles (MSNP-NH2) were prepared and loaded with ovalbumin as a model antigen. Loading was driven by electrostatic interactions. Ovalbumin-loaded silica nanoparticles were subsequently formulated into sugar-based microparticles by spray-freeze-drying. The obtained microparticles meet the size requirement for EPI. Confocal microscopy was used to demonstrate that the nanoparticles are homogeneously distributed in the microparticles. Furthermore, the silica nanoparticles in the dry microparticles can be re-dispersed in aqueous solution showing no aggregation. The recovered ovalbumin shows integrity compared to native ovalbumin. The present nano-in-micro system allows (1) nanoparticles to be immobilized and finely distributed in microparticles, (2) microparticle formation and (3) re-dispersion of nanoparticles without subsequent aggregation. The nanoparticles inside microparticles can (1) adsorb proteins to cationic shell/surface voids in spray-dried products without detriment to ovalbumin stability, (2) deliver antigens in nano-sized modes to allow recognition by the immune system. Copyright © 2014 Elsevier B.V. All rights reserved.

Anisotropic Shape Changes of Silica Nanoparticles Induced in Liquid with Scanning Transmission Electron Microscopy.

PubMed

Zečević, Jovana; Hermannsdörfer, Justus; Schuh, Tobias; de Jong, Krijn P; de Jonge, Niels

2017-01-01

Liquid-phase transmission electron microscopy (TEM) is used for in-situ imaging of nanoscale processes taking place in liquid, such as the evolution of nanoparticles during synthesis or structural changes of nanomaterials in liquid environment. Here, it is shown that the focused electron beam of scanning TEM (STEM) brings about the dissolution of silica nanoparticles in water by a gradual reduction of their sizes, and that silica redeposites at the sides of the nanoparticles in the scanning direction of the electron beam, such that elongated nanoparticles are formed. Nanoparticles with an elongation in a different direction are obtained simply by changing the scan direction. Material is expelled from the center of the nanoparticles at higher electron dose, leading to the formation of doughnut-shaped objects. Nanoparticles assembled in an aggregate gradually fuse, and the electron beam exposed section of the aggregate reduces in size and is elongated. Under TEM conditions with a stationary electron beam, the nanoparticles dissolve but do not elongate. The observed phenomena are important to consider when conducting liquid-phase STEM experiments on silica-based materials and may find future application for controlled anisotropic manipulation of the size and the shape of nanoparticles in liquid. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, surface modification and biological imaging of aggregation-induced emission (AIE) dye doped silica nanoparticles

NASA Astrophysics Data System (ADS)

Mao, Liucheng; Liu, Meiying; Xu, Dazhuang; Wan, Qing; Huang, Qiang; Jiang, Ruming; Shi, Yingge; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

2017-05-01

Fluorescent silica nanoparticles (FSNPs) have been extensively investigated for various biomedical applications in recently years. However, the aggregation of organic dyes in silica nanoparticles also leads the significant fluorescence quenching owing to the aggregation caused quenching effects of organic dyes. Herein, we developed a rather facile strategy to fabricate FSNPs with desirable fluorescent properties through non-covalent incorporation of fluorophores with aggregation-induced emission (AIE) feature into silica nanoparticles, which were subsequently modified with functional polymers. The resultant FSNPs polymer nanocomposites (named as FSNPs-poly(IA-co-PEGMA)) exhibited uniform spherical morphology, high water dispersiity, and bright red fluorescence. Cytotoxicity results indicate that FSNPs-poly(IA-co-PEGMA) possess excellent biocompatibility. Cell uptake behavior suggests FSNPs-poly(IA-co-PEGMA) are of great potential for biological imaging applications. Taken together, we have reported a facile method for the fabrication of FSNPs through non-covalent encapsulation using an AIE-active dye. These FSNPs can be further functionalized with functional polymers through ring-opening reaction and the resultant FSNPs-poly(IA-co-PEGMA) showed great potential for biological imaging. More importantly, we believe that many other functional components could also be integrated into these FSNPs through the facile ring-opening reaction. Therefore, this method should be a facile and general tool for fabrication of polymer functionalized AIE-active FSNPs.

Sustainability in Supply Chain Management: Aggregate Planning from Sustainability Perspective.

PubMed

Türkay, Metin; Saraçoğlu, Öztürk; Arslan, Mehmet Can

2016-01-01

Supply chain management that considers the flow of raw materials, products and information has become a focal issue in modern manufacturing and service systems. Supply chain management requires effective use of assets and information that has far reaching implications beyond satisfaction of customer demand, flow of goods, services or capital. Aggregate planning, a fundamental decision model in supply chain management, refers to the determination of production, inventory, capacity and labor usage levels in the medium term. Traditionally standard mathematical programming formulation is used to devise the aggregate plan so as to minimize the total cost of operations. However, this formulation is purely an economic model that does not include sustainability considerations. In this study, we revise the standard aggregate planning formulation to account for additional environmental and social criteria to incorporate triple bottom line consideration of sustainability. We show how these additional criteria can be appended to traditional cost accounting in order to address sustainability in aggregate planning. We analyze the revised models and interpret the results on a case study from real life that would be insightful for decision makers.

Sustainability in Supply Chain Management: Aggregate Planning from Sustainability Perspective

PubMed Central

Türkay, Metin; Saraçoğlu, Öztürk; Arslan, Mehmet Can

2016-01-01

Supply chain management that considers the flow of raw materials, products and information has become a focal issue in modern manufacturing and service systems. Supply chain management requires effective use of assets and information that has far reaching implications beyond satisfaction of customer demand, flow of goods, services or capital. Aggregate planning, a fundamental decision model in supply chain management, refers to the determination of production, inventory, capacity and labor usage levels in the medium term. Traditionally standard mathematical programming formulation is used to devise the aggregate plan so as to minimize the total cost of operations. However, this formulation is purely an economic model that does not include sustainability considerations. In this study, we revise the standard aggregate planning formulation to account for additional environmental and social criteria to incorporate triple bottom line consideration of sustainability. We show how these additional criteria can be appended to traditional cost accounting in order to address sustainability in aggregate planning. We analyze the revised models and interpret the results on a case study from real life that would be insightful for decision makers. PMID:26807848

Markov chain aggregation and its applications to combinatorial reaction networks.

PubMed

Ganguly, Arnab; Petrov, Tatjana; Koeppl, Heinz

2014-09-01

We consider a continuous-time Markov chain (CTMC) whose state space is partitioned into aggregates, and each aggregate is assigned a probability measure. A sufficient condition for defining a CTMC over the aggregates is presented as a variant of weak lumpability, which also characterizes that the measure over the original process can be recovered from that of the aggregated one. We show how the applicability of de-aggregation depends on the initial distribution. The application section is devoted to illustrate how the developed theory aids in reducing CTMC models of biochemical systems particularly in connection to protein-protein interactions. We assume that the model is written by a biologist in form of site-graph-rewrite rules. Site-graph-rewrite rules compactly express that, often, only a local context of a protein (instead of a full molecular species) needs to be in a certain configuration in order to trigger a reaction event. This observation leads to suitable aggregate Markov chains with smaller state spaces, thereby providing sufficient reduction in computational complexity. This is further exemplified in two case studies: simple unbounded polymerization and early EGFR/insulin crosstalk.

Understanding the Benefits and Limitations of Magnetic Nanoparticle Heating for Improved Applications in Cancer Hyperthermia and Biomaterial Cryopreservation

NASA Astrophysics Data System (ADS)

Etheridge, Michael L.

The current work focused on the ability of magnetic nanoparticles to produce heat in the presence of an applied alternating magnetic field. Magnetic nanoparticle hyperthermia applications utilize this behavior to treat cancer and this approach has received clinical approval in the European Union, but significant developments are necessary for this technology to have a chance for wider-spread acceptance. Here then we begin by investigating some of the important limitations of the current technology. By characterizing the ability of superparamagnetic and ferromagnetic nanoparticles to heat under a range of applied fields, we are able to determine the optimal field settings for clinical application and make recommendations on the highest impact strategies to increase heating. In addition, we apply these experimentally determined limits to heating in a series of heat transfer models, to demonstrate the therapeutic impact of nanoparticle concentration, target volume, and delivery strategy. Next, we attempt to address one of the key questions facing the field- what is the impact of biological aggregation on heating? Controlled aggregate populations are produced and characterized in ionic and protein solutions and their heating is compared with nanoparticles incubated in cellular suspensions. Through this investigation we are able to demonstrate that aggregation is responsible for up to a 50% decrease in heating. However, more importantly, we are able to demonstrate that the observed reductions in heating correlate with reductions in longitudinal relaxation (T1) measured by sweep imaging with Fourier transformation (SWIFT) magnetic resonance imaging (MRI), providing a potential platform to account for these aggregation effects and directly predict heating in a clinical setting. Finally, we present a new application for magnetic nanoparticle heating, in the thawing of cryopreserved biomaterials. A number of groups have demonstrated the ability to rapidly cool and preserve tissues in the vitreous state, but crystallization and cracking failures occur upon the subsequent thaw. Magnetic nanoparticles offer a potential solution to these issues, through their ability to provide rapid, uniform heating, and we illustrate this through heating in several cryoprotectant solutions and by modeling the effects of heating at the bulk and micro-scales.

Short-Chain PEG Mixed-Monolayer Protected Gold Clusters Increase Clearance and Red Blood Cell Counts

PubMed Central

Simpson, Carrie A.; Agrawal, Amanda C.; Balinski, Andrzej; Harkness, Kellen M.; Cliffel, David E.

2011-01-01

Monolayer-protected gold nanoparticles have great potential as novel building blocks for the design of new drugs and therapeutics based on the easy ability to multifunctionalize them for biological targeting and drug activity. In order to create nanoparticles that are biocompatible in vivo, poly-ethylene glycol functional groups have been added to many previous multifunctionalized particles to eliminate non-specific binding. Recently, monolayer-protected gold nanoparticles with mercaptoglycine functionalities were shown to elicit deleterious effects on the kidney in vivo that were eliminated by incorporating a long-chain, mercapto-undecyl-tetraethylene glycol, at very high loadings into a mixed monolayer. These long-chain PEGs induced an immune response to the particle presumably generating an anti-PEG antibody as seen in other long-chain PEG-ylated nanoparticles in vivo. In the present work, we explore the in vivo effects of high and low percent ratios of a shorter chain, mercapto-tetraethylene glycol, within the monolayer using simple place-exchange reactions. The shorter chain PEG MPCs were expected to have better water solubility due to elimination of the alkyl chain, no toxicity, and long-term circulation in vivo. Shorter chain lengths at lower concentrations should not trigger the immune system into creating an anti-PEG antibody. We found that a 10% molar exchange of this short chain PEG within the monolayer met three of the desired goals: high water solubility, no toxicity, and no immune response as measured by white blood cell counts, but none of the short chain PEG mixed monolayer compositions enabled the nanoparticles to have a long circulation time within the blood as compared to mercapto-undecyl-ethylene glycol, which had a residence time of 4 weeks. We also compared the effects of a hydroxyl versus a carboxylic acid terminal functional group on the end of the PEG thiol on both clearance and immune response. The results indicate that short-chain length PEGs, regardless of termini, increase clearance rates compared to the previous long-chain PEG studies while carboxylated-termini increase red blood cell counts at high loadings. Given these findings, short-chain, alcohol-terminated PEG, exchanged at 10% was identified as a potential nanoparticle for further in vivo applications requiring short circulation lifetimes with desired features of no toxicity, no immune response, and high water solubility. PMID:21473648

Hydrolysis of short-chain phosphatidylcholines by bee venom phospholipase A2.

PubMed

Raykova, D; Blagoev, B

1986-01-01

In order to find out the aggregation state of the substrate, preferred by bee venom phospholipase A2 (EC 3.1.1.4), its action on short-chain phosphatidylcholines with two identical (C6-C10) fatty acids has been tested. The rate of hydrolysis as a function of acyl chain length showed a maximum at dioctanoylphosphatidylcholine. The effects of alcohols, NaCl and Triton X-100, which affect the aggregation state of phospholipids in water, were also studied. The addition of n-alcohol led to a significant inhibition of the hydrolysis of the substrates present in micellar form and activated the hydrolysis of substrates which form liposomes. The inhibitory effect increased with increasing length of the aliphatic carbon chain of the alcohol. Triton X-100 at low Triton/phospholipid molar ratios enhanced enzyme activity. These results do not agree with the accepted idea that bee venom phospholipase A2 hydrolyzes short-chain lecithins in their molecularly dispersed form and that micelles cannot act as substrates. The data indicate that short-chain lecithins in the aggregated state are hydrolyzed and that the requirements of bee venom phospholipase A2 for the aggregation state of the substrate are not strict.

The study of poly(L-lactide) grafted silica nanoparticles on the film blowing of poly(L-lactide)

NASA Astrophysics Data System (ADS)

Wu, Feng; Liu, Zhengying; Yang, Mingbo

2015-05-01

PLA nanocomposites are prepared by us, and to better develop the function of silica nanoparticle, the surface of silica nanoparticles are modified by introducing PLA chains via "grafting to" method in our research. According to the results of 1H NMR and TGA, it shows that the PLA grafted Silica nanoparticles are successfully synthesized by controlling the reaction condition, and the molecular weight of the grafted PLA chains is relatively as high as 22 400 g/mol. PLA Nanocomposites with modified nanoparticles are prepared using a convenient melt blending method to guarantee well-distribution of the particles. The well-dispersion state of silica nanospheres is confirmed by Scan Electrical Micrograph (SEM) technology. From the dynamic shear rheology tests, the strain and time sweep both reveal that stability networks are formed in these nanocomposites. And the frequency sweep shows that the nanoparticles with long grafted chains dramatically enhanced the storage and viscosity of the pure PLA. The rheology testing suggests that strong particle-matrix interactions between molecularly/nano-level dispersed grafted silica and PLA chains formed; and the elongational viscosity of PLA has been markedly improved with the addition of the nanoparticle. The effect of modified nanoparticles on the thermal properties of PLA has also been studied by us using Differential Scanning Calorimetry (DSC). It reveals that the crystallization rate of PLA has been improved as the long grafted chains play as the nucleation sites for PLA. Finally based on these rheology and crystallization researches, the nanocomposites are used to prepare PLA blowing films. Compared to pure PLA and PLA/unmodified silica nanocomposites, the results show that the stability of the film blowing has been greatly improved and the blow-up ratio has been increased with the addition of PLA grafted nanoparticles. The modified nanoparticles hold significant candidates to improve the thermal stability and the processability of pure PLA, especially used as special processing agent in the field of PLA stretch shaping process.

Case Western Reserve University — Treatment of Glioblastoma Using Chain-Like Nanoparticles

Cancer.gov

To overcome the limitations of current drugs to treat brain tumors, Case Western University seeks to integrate the unique features of a chain-like nanoparticle with the appropriate combination of complementary drugs.

Pure drug nanoparticles in tablets: what are the dissolution limitations?

NASA Astrophysics Data System (ADS)

Heng, Desmond; Ogawa, Keiko; Cutler, David J.; Chan, Hak-Kim; Raper, Judy A.; Ye, Lin; Yun, Jimmy

2010-06-01

There has been increasing interests for drug companies to incorporate drug nanoparticles into their existing formulations. However, technical knowledge in this area is still in its infancy and more study needs to be done to stimulate growth in this fledging field. There is a need to scrutinize the performance of pure drug nanoparticles in tablets, particularly relating formulation variables to their dissolution performance. Application of the pure form, synthesized without the use of surfactants or stabilizers, is often preferred to maximize drug loading and also to minimize toxicity. Cefuroxime axetil, a poorly water-soluble cephalosporin antibiotic, was used as the model drug in the formulation development. Drug release rate, tablet disintegration time, tensile strength and energy of failure were predominantly influenced by the amount of super-disintegrant, amount of surfactant, compression force and diluent species, respectively. The compression rate had minimal impact on the responses. The main hurdle confronting the effective use of pure drug nanoparticles in tablets is the difficulty in controlling aggregation in solution, which could potentially be aggravated by the tabletting process. Through the use of elevated levels of surfactants (8 w/w% sodium dodecyl sulphate), drug release from the nanoparticle preparation was enhanced from 58.0 ± 2.7% to 72.3 ± 0.7% in 10 min. Hence, it is recommended that physical formulations for pure drug nanoparticles be focused on the particle de-aggregation step in solution, if much higher rates are to be desired. In conclusion, even though pure drug nanoparticles could be easily synthesized, limitations from aggregation may need to be overcome, before successful application in tablets can be fully realized.

Controlled Assembly of Biocompatible Metallic Nanoaggregates Using a Small Molecule Crosslinker

PubMed Central

Van Haute, Desiree; Longmate, Julia M.; Berlin, Jacob M.

2015-01-01

By introducing a capping step and controlling reaction parameters, the assembly of metallic nanoparticle aggregates can be achieved using a small molecule crosslinker. Aggregates can be assembled from particles of varied size and composition and the size of the aggregates can be systematically adjusted. Following cell uptake of 60 nm aggregates, the aggregates are stable and non-toxic to macrophage cells up to 55mM Au. PMID:26208123

Effective heating of magnetic nanoparticle aggregates for in vivo nano-theranostic hyperthermia.

PubMed

Wang, Chencai; Hsu, Chao-Hsiung; Li, Zhao; Hwang, Lian-Pin; Lin, Ying-Chih; Chou, Pi-Tai; Lin, Yung-Ya

2017-01-01

Magnetic resonance (MR) nano-theranostic hyperthermia uses magnetic nanoparticles to target and accumulate at the lesions and generate heat to kill lesion cells directly through hyperthermia or indirectly through thermal activation and control releasing of drugs. Preclinical and translational applications of MR nano-theranostic hyperthermia are currently limited by a few major theoretical difficulties and experimental challenges in in vivo conditions. For example, conventional models for estimating the heat generated and the optimal magnetic nanoparticle sizes for hyperthermia do not accurately reproduce reported in vivo experimental results. In this work, a revised cluster-based model was proposed to predict the specific loss power (SLP) by explicitly considering magnetic nanoparticle aggregation in in vivo conditions. By comparing with the reported experimental results of magnetite Fe 3 O 4 and cobalt ferrite CoFe 2 O 4 magnetic nanoparticles, it is shown that the revised cluster-based model provides a more accurate prediction of the experimental values than the conventional models that assume magnetic nanoparticles act as single units. It also provides a clear physical picture: the aggregation of magnetic nanoparticles increases the cluster magnetic anisotropy while reducing both the cluster domain magnetization and the average magnetic moment, which, in turn, shift the predicted SLP toward a smaller magnetic nanoparticle diameter with lower peak values. As a result, the heating efficiency and the SLP values are decreased. The improvement in the prediction accuracy in in vivo conditions is particularly pronounced when the magnetic nanoparticle diameter is in the range of ~10-20 nm. This happens to be an important size range for MR cancer nano-theranostics, as it exhibits the highest efficacy against both primary and metastatic tumors in vivo. Our studies show that a relatively 20%-25% smaller magnetic nanoparticle diameter should be chosen to reach the maximal heating efficiency in comparison with the optimal size predicted by previous models.

Effective heating of magnetic nanoparticle aggregates for in vivo nano-theranostic hyperthermia

PubMed Central

Wang, Chencai; Hsu, Chao-Hsiung; Li, Zhao; Hwang, Lian-Pin; Lin, Ying-Chih; Chou, Pi-Tai; Lin, Yung-Ya

2017-01-01

Magnetic resonance (MR) nano-theranostic hyperthermia uses magnetic nanoparticles to target and accumulate at the lesions and generate heat to kill lesion cells directly through hyperthermia or indirectly through thermal activation and control releasing of drugs. Preclinical and translational applications of MR nano-theranostic hyperthermia are currently limited by a few major theoretical difficulties and experimental challenges in in vivo conditions. For example, conventional models for estimating the heat generated and the optimal magnetic nanoparticle sizes for hyperthermia do not accurately reproduce reported in vivo experimental results. In this work, a revised cluster-based model was proposed to predict the specific loss power (SLP) by explicitly considering magnetic nanoparticle aggregation in in vivo conditions. By comparing with the reported experimental results of magnetite Fe3O4 and cobalt ferrite CoFe2O4 magnetic nanoparticles, it is shown that the revised cluster-based model provides a more accurate prediction of the experimental values than the conventional models that assume magnetic nanoparticles act as single units. It also provides a clear physical picture: the aggregation of magnetic nanoparticles increases the cluster magnetic anisotropy while reducing both the cluster domain magnetization and the average magnetic moment, which, in turn, shift the predicted SLP toward a smaller magnetic nanoparticle diameter with lower peak values. As a result, the heating efficiency and the SLP values are decreased. The improvement in the prediction accuracy in in vivo conditions is particularly pronounced when the magnetic nanoparticle diameter is in the range of ~10–20 nm. This happens to be an important size range for MR cancer nano-theranostics, as it exhibits the highest efficacy against both primary and metastatic tumors in vivo. Our studies show that a relatively 20%–25% smaller magnetic nanoparticle diameter should be chosen to reach the maximal heating efficiency in comparison with the optimal size predicted by previous models. PMID:28894366

Theoretical study of nanoparticle formation in thermal plasma processing: Nucleation, coagulation and aggregation

NASA Astrophysics Data System (ADS)

Mendoza Gonzalez, Norma Yadira

This work presents a mathematical modeling study of the synthesis of nanoparticles in radio frequency (RF) inductively coupled plasma (ICP) reactors. The purpose is to further investigate the influence of process parameters on the final size and morphology of produced particles. The proposed model involves the calculation of flow and temperature fields of the plasma gas. Evaporation of raw particles is also accounted with the particle trajectory and temperature history calculated with a Lagrangian approach. The nanoparticle formation is considered by homogeneous nucleation and the growth is caused by condensation and Brownian coagulation. The growth of fractal aggregates is considered by introducing a power law exponent Df. Transport of nanoparticles occurs by convection, thermophoresis and Brownian diffusion. The method of moments is used to solve the particle dynamics equation. The model is validated using experimental results from plasma reactors at laboratory scale. The results are presented in the following manner. First, use is made of the computational fluid dynamics software (CFD), Fluent 6.1 with a commercial companion package specifically developped for aerosols named: Fine Particle Model (FPM). This package is used to study the relationship between the operating parameters effect and the properties of the end products at the laboratory scale. Secondly, a coupled hybrid model for the synthesis of spherical particles and fractal aggregates is developped in place of the FPM package. Results obtained from this model will allow to identify the importance of each parameter in defining the morphology of spherical primary particles and fractal aggregates of nanoparticles. The solution of the model was made using the geometries and operating conditions of existing reactors at the Centre de Recherche en Energie, Plasma et Electrochimie (CREPE) of the Universite de Sherbrooke, for which experimental results were obtained experimentally. Additionally, this study demonstrates the importance of the flow and temperature fields on the growth of fractal particles; namely the aggregates.

Ultrasensitive detection of target analyte-induced aggregation of gold nanoparticles using laser-induced nanoparticle Rayleigh scattering.

PubMed

Lin, Jia-Hui; Tseng, Wei-Lung

2015-01-01

Detection of salt- and analyte-induced aggregation of gold nanoparticles (AuNPs) mostly relies on costly and bulky analytical instruments. To response this drawback, a portable, miniaturized, sensitive, and cost-effective detection technique is urgently required for rapid field detection and monitoring of target analyte via the use of AuNP-based sensor. This study combined a miniaturized spectrometer with a 532-nm laser to develop a laser-induced Rayleigh scattering technique, allowing the sensitive and selective detection of Rayleigh scattering from the aggregated AuNPs. Three AuNP-based sensing systems, including salt-, thiol- and metal ion-induced aggregation of the AuNPs, were performed to examine the sensitivity of laser-induced Rayleigh scattering technique. Salt-, thiol-, and metal ion-promoted NP aggregation were exemplified by the use of aptamer-adsorbed, fluorosurfactant-stabilized, and gallic acid-capped AuNPs for probing K(+), S-adenosylhomocysteine hydrolase-induced hydrolysis of S-adenosylhomocysteine, and Pb(2+), in sequence. Compared to the reported methods for monitoring the aggregated AuNPs, the proposed system provided distinct advantages of sensitivity. Laser-induced Rayleigh scattering technique was improved to be convenient, cheap, and portable by replacing a diode laser and a miniaturized spectrometer with a laser pointer and a smart-phone. Using this smart-phone-based detection platform, we can determine whether or not the Pb(2+) concentration exceed the maximum allowable level of Pb(2+) in drinking water. Copyright © 2014 Elsevier B.V. All rights reserved.

Heparin Assisted Photochemical Synthesis of Gold Nanoparticles and Their Performance as SERS Substrates

PubMed Central

Rodríguez-Torres, Maria del Pilar; Díaz-Torres, Luis Armando; Romero-Servin, Sergio

2014-01-01

Reactive and pharmaceutical-grade heparins were used as biologically compatible reducing and stabilizing agents to photochemically synthesize colloidal gold nanoparticles. Aggregates and anisotropic shapes were obtained photochemically under UV black-light lamp irradiation (λ = 366 nm). Heparin-functionalized gold nanoparticles were characterized by Scanning Electron Microscopy and UV-Vis spectroscopy. The negatively charged colloids were used for the Surface Enhanced Raman Spectroscopy (SERS) analysis of differently charged analytes (dyes). Measurements of pH were taken to inspect how the acidity of the medium affects the colloid-analyte interaction. SERS spectra were taken by mixing the dyes and the colloidal solutions without further functionalization or addition of any aggregating agent. PMID:25342319

Functionalizing large nanoparticles for small gaps in dimer nanoantennas

NASA Astrophysics Data System (ADS)

Vietz, Carolin; Lalkens, Birka; Acuna, Guillermo P.; Tinnefeld, Philip

2016-04-01

The process of functionalizing gold nanoparticles with DNA commonly competes with nanoparticle aggregation, especially for larger particles of more than 80 nm diameter. Longer DNA strands reduce the tendency for aggregation but commonly lead to larger gaps when applied in certain geometrical arrangements such as gap nanoantennas. Here, we demonstrate that reversing the polarization of one of the strands for hybridization (yielding a zipper-like geometry) is sterically possible with uncompromised yields. Using the single dye molecule’s fluorescence lifetime as an indicator of the proximity of the nanoparticle in combination with electrodynamic simulations, we determine the distance between the nanoparticle and the dye placed in a DNA origami pillar. Importantly, compared to the common shear geometry smaller distances between the connected structures are obtained which are independent of the length of the DNA connector. Using the zipper geometry, we then arranged nanoparticles of 100 and 150 nm diameter on DNA origami and formed gap nanoantennas. We find that the previously reported trend of increased fluorescence enhancement of ATTO647N with increasing particle size for 20-100 nm nanoparticles is stopped. Gap nanoantennas built with 150 nm nanoparticles exhibit smaller enhancement than those with 100 nm nanoparticles. These results are discussed with the aid of electrodynamic simulations.

Stability of aggregates in the environment: role of solid bridging

NASA Astrophysics Data System (ADS)

Seiphoori, A.; Jerolmack, D. J.; Arratia, P. E.

2017-12-01

Colloids in suspension may form larger flocs under favorable conditions, via diffusion- or reaction-limited aggregation. In addition, the process of drying colloidal suspensions drives colloids together via hydrodynamic forces to form aggregates, that may be stable or unstable when subject to re-wetting and transport. Channel banks, shorelines and hillslopes are examples where the periodic wetting and drying results in the aggregation of muds. If aggregates disperse, the mud structure is unstable to subsequent wetting or fluid shear and can easily be detached and transported to rivers and coasts. The effective friction that governs hillslope and channel-bank soil creep rates also depends on the stability of the soil aggregates. Yet, few studies probe the particle-scale assembly or stability of aggregates subject to environmental loads, and the effects of shape or size heterogeneity have not been examined in detail. Here we investigate the formation and stability of aggregates subject to passive re-wetting (by misting) and shearing using a simple Poiseuille flow in a microfluidic device. We study the kinetics of a wide range of silicate colloids of different size and surface charge properties using in situ microscopy and particle tracking. We find that negatively charged silica microspheres are dragged by the retreating edge of an evaporating drop and are resuspended easily on re-wetting, showing that aggregates are unstable. In contrast, a bi-disperse suspension created by the addition of silica nanoparticles forms stable deposits, where nanoparticles bind larger particles by bridging the interparticle space, a mechanism similar to capillary bridging that we refer to as "solid bridging." Although aggregate structure and dynamics of the bi-disperse system changes quantitatively with surface-charge of the nanoparticles, smaller particles always conferred stability on the aggregates. Investigation of other colloids, including asbestos fibers and various clays, reveals that this solid bridging effect is robust across variations in particle shape and material composition. These experiments suggest that natural mud and soil may form more stable aggregates than would naively be expected by considering the charge effects alone, because their inherent size heterogeneity is conducive to solid bridging.

Optical Aggregation of Gold Nanoparticles for SERS Detection of Proteins and Toxins in Liquid Environment: Towards Ultrasensitive and Selective Detection

PubMed Central

Foti, Antonino; Donato, Maria Grazia; Fazio, Barbara; Maragò, Onofrio M.; Lamy de la Chapelle, Marc

2018-01-01

Optical forces are used to aggregate plasmonic nanoparticles and create SERS–active hot spots in liquid. When biomolecules are added to the nanoparticles, high sensitivity SERS detection can be accomplished. Here, we pursue studies on Bovine Serum Albumin (BSA) detection, investigating the BSA–nanorod aggregations in a range from 100 µM to 50 nM by combining light scattering, plasmon resonance and SERS, and correlating the SERS signal with the concentration. Experimental data are fitted with a simple model describing the optical aggregation process. We show that BSA–nanorod complexes can be optically printed on non-functionalized glass surfaces, designing custom patterns stable with time. Furthermore, we demonstrate that this methodology can be used to detect catalase and hemoglobin, two Raman resonant biomolecules, at concentrations of 10 nM and 1 pM, respectively, i.e., well beyond the limit of detection of BSA. Finally, we show that nanorods functionalized with specific aptamers can be used to capture and detect Ochratoxin A, a fungal toxin found in food commodities and wine. This experiment represents the first step towards the addition of molecular specificity to this novel biosensor strategy. PMID:29562606

Thick electrodes including nanoparticles having electroactive materials and methods of making same

DOEpatents

Xiao, Jie; Lu, Dongping; Liu, Jun; Zhang, Jiguang; Graff, Gordon L.

2017-02-21

Electrodes having nanostructure and/or utilizing nanoparticles of active materials and having high mass loadings of the active materials can be made to be physically robust and free of cracks and pinholes. The electrodes include nanoparticles having electroactive material, which nanoparticles are aggregated with carbon into larger secondary particles. The secondary particles can be bound with a binder to form the electrode.

Advances and challenges in the field of plasma polymer nanoparticles

PubMed Central

Pleskunov, Pavel; Nikitin, Daniil; Titov, Valerii; Shelemin, Artem; Vaidulych, Mykhailo; Kuzminova, Anna; Solař, Pavel; Hanuš, Jan; Kousal, Jaroslav; Kylián, Ondřej; Slavínská, Danka; Biederman, Hynek

2017-01-01

This contribution reviews plasma polymer nanoparticles produced by gas aggregation cluster sources either via plasma polymerization of volatile monomers or via radio frequency (RF) magnetron sputtering of conventional polymers. The formation of hydrocarbon, fluorocarbon, silicon- and nitrogen-containing plasma polymer nanoparticles as well as core@shell nanoparticles based on plasma polymers is discussed with a focus on the development of novel nanostructured surfaces. PMID:29046847

Advances and challenges in the field of plasma polymer nanoparticles.

PubMed

Choukourov, Andrei; Pleskunov, Pavel; Nikitin, Daniil; Titov, Valerii; Shelemin, Artem; Vaidulych, Mykhailo; Kuzminova, Anna; Solař, Pavel; Hanuš, Jan; Kousal, Jaroslav; Kylián, Ondřej; Slavínská, Danka; Biederman, Hynek

2017-01-01

This contribution reviews plasma polymer nanoparticles produced by gas aggregation cluster sources either via plasma polymerization of volatile monomers or via radio frequency (RF) magnetron sputtering of conventional polymers. The formation of hydrocarbon, fluorocarbon, silicon- and nitrogen-containing plasma polymer nanoparticles as well as core@shell nanoparticles based on plasma polymers is discussed with a focus on the development of novel nanostructured surfaces.

Correlation of surface enhanced Raman spectroscopy and nanoparticle aggregation with rhodamine 6G

NASA Astrophysics Data System (ADS)

Hoff, Christopher A.

Surface enhanced Raman spectroscopy (SERS) has fascinated the analytical chemistry field for decades. The SERS phenomenon has progressively leveraged the inherently insensitive Raman phenomenon from a novelty vibrational spectroscopy method into one capable of single molecule detection, with attendant molecular level selectivity and information. Yet, even after 40 years since its discovery, the core mechanism behind this phenomenon is still debated. This thesis presents results from a series of photometric titrations wherein solutions of 30 nm Au@Ag nanoparticles (NPs) were titrated with rhodamine 6G (R6G), spanning five orders of magnitude in R6G concentration, and which elucidate the conditions required for the onset of SERS by R6G in this system. The experiments illustrated the correlation between the Raman response and the plasmonic (via UV-Vis spectroscopy) properties of the nanoparticle solutions. It was found that the onset of R6G SERS was related much more closely to the aggregation of the nanoparticles in solution than to their R6G adsorbed surface coverage. However, triggering aggregation with sodium chloride appeared to enhance SERS by an independent mechanism, which is operative only at low, i.e., [NaCl] > 100 mM concentration.

Emergence of Life-Like Properties from Dissipative Self-Assembly of Nanoparticles

NASA Astrophysics Data System (ADS)

Ilday, Serim; Makey, Ghaith; Akguc, Gursoy B.; Yavuz, Ozgun; Tokel, Onur; Pavlov, Ihor; Gulseren, Oguz; Ilday, F. Omer

A profoundly fundamental question at the interface between physics and biology remains open: What are the minimum requirements for emergence of life-like properties from non-living systems? Here, we address this question and report emergent complex behavior of tens to thousands of colloidal nanoparticles in a system designed to be as plain as possible: The system is driven far from equilibrium by ultrafast laser pulses, which create spatiotemporal temperature gradients, inducing Marangoni-type flow that drags the particles towards aggregation; strong Brownian motion, used as source of fluctuations, opposes aggregation. Nonlinear feedback mechanisms naturally arise between the flow, the aggregate, and Brownian motion, allowing fast external control with minimal intervention. Consequently, complex behavior, analogous to those commonly seen in living organisms, emerges, whereby the aggregates can self-sustain, self-regulate, self-replicate, self-heal and can be transferred from one location to another, all within seconds. Aggregates can comprise of only one pattern or bifurcated patterns can co-exist, compete, survive or die.

Enhancement in volatile organic compound sensitivity of aged Ag nanoparticle aggregates by plasma exposure

NASA Astrophysics Data System (ADS)

Hosomi, Kei; Ozaki, Koichi; Nishiyama, Fumitaka; Takahiro, Katsumi

2018-01-01

Silver nanoparticles (Ag NPs) tarnish easily upon exposure to ambient air, and eventually lose their ability as a plasmonic sensor via weakened localized surface plasmon resonance (LSPR). We have demonstrated the enhancement in plasmonic sensitivity of tarnished Ag NP aggregates to vapors of volatile organic compounds (VOCs) such as ethanol and butanol by Ar plasma exposure. The response of Ag NP aggregates to the VOC vapors was examined by measuring the change in optical extinction spectra before and after exposure to the vapors. The sensitivity of Ag NP aggregates decreased gradually when stored in ambient air. The performance of tarnished Ag NPs for ethanol sensing was recovered by exposure to argon (Ar) plasma for 15 s. The reduction from oxidized Ag to metallic one was recognized, while morphological change was hardly noticeable after the plasma exposure. We conclude, therefore, that a compositional change rather than a morphological change occurred on Ag NP surfaces enhances the sensing ability of tarnished Ag NP aggregates to the VOC vapors.

Optical characterization limits of nanoparticle aggregates at different wavelengths using approximate Bayesian computation

NASA Astrophysics Data System (ADS)

Eriçok, Ozan Burak; Ertürk, Hakan

2018-07-01

Optical characterization of nanoparticle aggregates is a complex inverse problem that can be solved by deterministic or statistical methods. Previous studies showed that there exists a different lower size limit of reliable characterization, corresponding to the wavelength of light source used. In this study, these characterization limits are determined considering a light source wavelength range changing from ultraviolet to near infrared (266-1064 nm) relying on numerical light scattering experiments. Two different measurement ensembles are considered. Collection of well separated aggregates made up of same sized particles and that of having particle size distribution. Filippov's cluster-cluster algorithm is used to generate the aggregates and the light scattering behavior is calculated by discrete dipole approximation. A likelihood-free Approximate Bayesian Computation, relying on Adaptive Population Monte Carlo method, is used for characterization. It is found that when the wavelength range of 266-1064 nm is used, successful characterization limit changes from 21-62 nm effective radius for monodisperse and polydisperse soot aggregates.

Molecular simulations of assembly of functionalized spherical nanoparticles

NASA Astrophysics Data System (ADS)

Seifpour, Arezou

Precise assembly of nanoparticles is crucial for creating spatially engineered materials that can be used for photonics, photovoltaic, and metamaterials applications. One way to control nanoparticle assembly is by functionalizing the nanoparticle with ligands, such as polymers, DNA, and proteins, that can manipulate the interactions between the nanoparticles in the medium the particles are placed in. This thesis research aims to design ligands to provide a new route to the programmable assembly of nanoparticles. We first investigate using Monte Carlo simulation the effect of copolymer ligands on nanoparticle assembly. We first study a single nanoparticle grafted with many copolymer chains to understand how monomer sequence (e.g. alternating ABAB, or diblock AxBx) and chemistry of the copolymers affect the grafted chain conformation at various particle diameters, grafting densities, copolymer chain lengths, and monomer-monomer interactions in an implicit small molecule solvent. We find that the size of the grafted chain varies non-monotonically with increasing blockiness of the monomer sequence for a small particle diameter. From this first study, we selected the two sequences with the most different chain conformations---alternating and diblock---and studied the effect of the sequence and a range of monomer chemistries of the copolymer on the characteristics of assembly of multiple copolymer-functionalized nanoparticles. We find that the alternating sequence produces nanoclusters that are relatively isotropic, whereas diblock sequence tends to form anisotropic structures that are smaller and more compact when the block closer to the surface is attractive and larger loosely held together clusters when the outer block is attractive. Next, we conduct molecular dynamics simulations to study the effect of DNA ligands on nanoparticle assembly. Specifically we investigate the effect of grafted DNA strand composition (e.g. G/C content, placement and sequence) and bidispersity in DNA strand lengths on the thermodynamics and structure of assembly of functionalized nanoparticles. We find that higher G/C content increases cluster dissociation temperature for smaller particles. Placement of G/C block inward along the strand decreases number of neighbors within the assembled cluster. Finally, increased bidispersity in DNA strand lengths leads a distribution of inter-particle distances in the assembled cluster.

Iron-reducing bacteria accumulate ferric oxyhydroxide nanoparticle aggregates that may support planktonic growth

PubMed Central

Luef, Birgit; Fakra, Sirine C; Csencsits, Roseann; Wrighton, Kelly C; Williams, Kenneth H; Wilkins, Michael J; Downing, Kenneth H; Long, Philip E; Comolli, Luis R; Banfield, Jillian F

2013-01-01

Iron-reducing bacteria (FeRB) play key roles in anaerobic metal and carbon cycling and carry out biogeochemical transformations that can be harnessed for environmental bioremediation. A subset of FeRB require direct contact with Fe(III)-bearing minerals for dissimilatory growth, yet these bacteria must move between mineral particles. Furthermore, they proliferate in planktonic consortia during biostimulation experiments. Thus, a key question is how such organisms can sustain growth under these conditions. Here we characterized planktonic microbial communities sampled from an aquifer in Rifle, Colorado, USA, close to the peak of iron reduction following in situ acetate amendment. Samples were cryo-plunged on site and subsequently examined using correlated two- and three-dimensional cryogenic transmission electron microscopy (cryo-TEM) and scanning transmission X-ray microscopy (STXM). The outer membranes of most cells were decorated with aggregates up to 150 nm in diameter composed of ∼3 nm wide amorphous, Fe-rich nanoparticles. Fluorescent in situ hybridization of lineage-specific probes applied to rRNA of cells subsequently imaged via cryo-TEM identified Geobacter spp., a well-studied group of FeRB. STXM results at the Fe L2,3 absorption edges indicate that nanoparticle aggregates contain a variable mixture of Fe(II)–Fe(III), and are generally enriched in Fe(III). Geobacter bemidjiensis cultivated anaerobically in the laboratory on acetate and hydrous ferric oxyhydroxides also accumulated mixed-valence nanoparticle aggregates. In field-collected samples, FeRB with a wide variety of morphologies were associated with nano-aggregates, indicating that cell surface Fe(III) accumulation may be a general mechanism by which FeRB can grow while in planktonic suspension. PMID:23038172

Iron-reducing bacteria accumulate ferric oxyhydroxide nanoparticle aggregates that may support planktonic growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luef, Birgit; Fakra, Sirine C.; Csencsits, Roseann

2013-02-04

Iron-reducing bacteria (FeRB) play key roles in anaerobic metal and carbon cycling and carry out biogeochemical transformations that can be harnessed for environmental bioremediation. A subset of FeRB require direct contact with Fe(III) bearing minerals for dissimilatory growth, yet these bacteria must move between mineral particles. Further, they proliferate in planktonic consortia during biostimulation experiments. Thus, a key question is how such organisms can sustain growth under these conditions. Here we characterized planktonic microbial communities sampled from an aquifer in Rifle, Colorado, USA close to the peak of iron reduction following in situ acetate amendment. Samples were cryo-plunged on sitemore » and subsequently examined using correlated 2- and 3- dimensional cryogenic transmission electron microscopy (cryo-TEM) and scanning transmission X-ray microscopy (STXM). Most cells had their outer membranes decorated with up to 150 nm diameter aggregates composed of a few nm wide amorphous, Fe-rich nanoparticles. Fluorescent in situ hybridization of lineage-specific probes applied to rRNA of cells subsequently imaged via cryo-TEM identified Geobacter spp., a well studied group of FeRB. STXM results at the Fe L2,3 absorption edges indicate that nanoparticle aggregates contain a variable mixture of Fe(II)-Fe(III), and are generally enriched in Fe(III). Geobacter bemidjiensis cultivated anaerobically in the laboratory on acetate and hydrous ferric oxyhydroxides also accumulated mixed valence nanoparticle aggregates. In field-collected samples, FeRB with a wide variety of morphologies were associated with nano-aggregates, indicating that cell-surface Fe(III) accumulation may be a general mechanism by which FeRB can grow while in planktonic suspension.« less

Iron-reducing bacteria accumulate ferric oxyhydroxide nanoparticle aggregates that may support planktonic growth.

PubMed

Luef, Birgit; Fakra, Sirine C; Csencsits, Roseann; Wrighton, Kelly C; Williams, Kenneth H; Wilkins, Michael J; Downing, Kenneth H; Long, Philip E; Comolli, Luis R; Banfield, Jillian F

2013-02-01

Iron-reducing bacteria (FeRB) play key roles in anaerobic metal and carbon cycling and carry out biogeochemical transformations that can be harnessed for environmental bioremediation. A subset of FeRB require direct contact with Fe(III)-bearing minerals for dissimilatory growth, yet these bacteria must move between mineral particles. Furthermore, they proliferate in planktonic consortia during biostimulation experiments. Thus, a key question is how such organisms can sustain growth under these conditions. Here we characterized planktonic microbial communities sampled from an aquifer in Rifle, Colorado, USA, close to the peak of iron reduction following in situ acetate amendment. Samples were cryo-plunged on site and subsequently examined using correlated two- and three-dimensional cryogenic transmission electron microscopy (cryo-TEM) and scanning transmission X-ray microscopy (STXM). The outer membranes of most cells were decorated with aggregates up to 150 nm in diameter composed of ∼3 nm wide amorphous, Fe-rich nanoparticles. Fluorescent in situ hybridization of lineage-specific probes applied to rRNA of cells subsequently imaged via cryo-TEM identified Geobacter spp., a well-studied group of FeRB. STXM results at the Fe L(2,3) absorption edges indicate that nanoparticle aggregates contain a variable mixture of Fe(II)-Fe(III), and are generally enriched in Fe(III). Geobacter bemidjiensis cultivated anaerobically in the laboratory on acetate and hydrous ferric oxyhydroxides also accumulated mixed-valence nanoparticle aggregates. In field-collected samples, FeRB with a wide variety of morphologies were associated with nano-aggregates, indicating that cell surface Fe(III) accumulation may be a general mechanism by which FeRB can grow while in planktonic suspension.

Redox-responsive nanoparticles with Aggregation-Induced Emission (AIE) characteristic for fluorescence imaging.

PubMed

Cheng, Weiren; Wang, Guan; Pan, Xiaoyong; Zhang, Yong; Tang, Ben Zhong; Liu, Ye

2014-08-01

The redox environment between intracellular compartments and extracellular matrix is significantly different, and the cellular redox homeostasis determines many physiological functions. Here, redox-responsive nanoparticles with aggregation-induced emission (AIE) characteristic for fluorescence imaging are developed by encapsulation of fluorophore with redox "turn-on" AIE characteristic, TPE-MI, into the micelles of poly(ethylene glycol) (PEG)- and cholesterol (CE)-conjugated disulfide containing poly(amido amine)s. The redox-responsive fluorescence profiles of the nanoparticles are investigated after reaction with glutathione (GSH). The encapsulation of TPE-MI in micelles leads to a higher efficiency and red shift in emission, and the fluorescence intensity of the nanoparticles increases with the concentration of GSH. Confocal microscopy imaging shows that the nanoparticles can provide obvious contrast between the intracellular compartments and the extracellular matrix in MCF-7 and HepG2 cells. So the nanoparticles with PEG shells and low cytotoxicity are promising to provide fluorescence bioimaging with a high contrast and for differentiation of cellular redox environment. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Visual detection of organophosphorus pesticides represented by mathamidophos using Au nanoparticles as colorimetric probe.

PubMed

Li, Hongkun; Guo, Jiajia; Ping, Hong; Liu, Lurui; Zhang, Minwei; Guan, Fengrui; Sun, Chunyan; Zhang, Qian

2011-12-15

With citrate-coated Au nanoparticles as colorimetric probe, a novel visual method for rapid assay of organophosphorus pesticides has been developed. The assay principle is based on catalytic hydrolysis of acetylthiocholine into thiocholine by acetylcholinesterase, which induces the aggregation of Au nanoparticles and the color change from claret-red to purple or even grey. The original plasmon absorption of Au nanoparticles at 522 nm decreases, and simultaneously, a new absorption band appears at 675 nm. The irreversible inhibition of organophosphorus pesticides on acetylcholinesterase prevents aggregation of Au nanoparticles. Under optimum conditions, the absorbance at 522 nm of Au nanoparticles is related linearly to the concentration of mathamidophos in the range of 0.02-1.42 μg/mL with a detection limit of 1.40 ng/mL. This colorimetric method has been successfully utilized to detect mathamidophos in vegetables with satisfactory results. The proposed colorimetric assay exhibits good reproducibility and accuracy, providing a simple and rapid method for the analysis of organophosphorus pesticides. Copyright © 2011 Elsevier B.V. All rights reserved.

Kinetic Monte Carlo simulation of nanoparticle film formation via nanocolloid drying

NASA Astrophysics Data System (ADS)

Kameya, Yuki

2017-06-01

A kinetic Monte Carlo simulation of nanoparticle film formation via nanocolloid drying is presented. The proposed two-dimensional model addresses the dynamics of nanoparticles in the vertical plane of a drying nanocolloid film. The gas-liquid interface movement due to solvent evaporation was controlled by a time-dependent chemical potential, and the resultant particle dynamics including Brownian diffusion and aggregate growth were calculated. Simulations were performed at various Peclet numbers defined based on the rate ratio of solvent evaporation and nanoparticle diffusion. At high Peclet numbers, nanoparticles accumulated at the top layer of the liquid film and eventually formed a skin layer, causing the formation of a particulate film with a densely packed structure. At low Peclet numbers, enhanced particle diffusion led to significant particle aggregation in the bulk colloid, and the resulting film structure became highly porous. The simulated results showed some typical characteristics of a drying nanocolloid that had been reported experimentally. Finally, the potential of the model as well as the remaining challenges are discussed.

On the adsorption properties of magnetic fluids: Impact of bulk structure

NASA Astrophysics Data System (ADS)

Kubovcikova, Martina; Gapon, Igor V.; Zavisova, Vlasta; Koneracka, Martina; Petrenko, Viktor I.; Soltwedel, Olaf; Almasy, László; Avdeev, Mikhail V.; Kopcansky, Peter

2017-04-01

Adsorption of nanoparticles from magnetic fluids (MFs) on solid surface (crystalline silicon) was studied by neutron reflectometry (NR) and related to the bulk structural organization of MFs concluded from small-angle neutron scattering (SANS). The initial aqueous MF with nanomagnetite (co-precipitation reaction) stabilized by sodium oleate and MF modified by a biocompatible polymer, poly(ethylene glycol) (PEG), were considered. Regarding the bulk structure it was confirmed in the SANS experiment that comparatively small and compact (size 30 nm) aggregates of nanoparticle in the initial sample transfer to large and developed (size>130 nm, fractal dimension 2.7) associates in the PEG modified MF. This reorganization in the aggregates correlates with the changes in the neutron reflectivity that showed that a single adsorption layer of individual nanoparticles on the oxidized silicon surface for the initial MF disappears after the PEG modification. It is concluded that all particles in the modified fluid are in the aggregates that are not adsorbed by silicon.

Disaggregation of silver nanoparticle homoaggregates in a river water matrix.

PubMed

Metreveli, George; Philippe, Allan; Schaumann, Gabriele E

2015-12-01

Silver nanoparticles (Ag NPs) could be found in aquatic systems in the near future. Although the interplay between aggregate formation and disaggregation is an important factor for mobility, bioavailability and toxicity of Ag NPs in surface waters, the factors controlling disaggregation of Ag NP homoaggregates are still unknown. In this study, we investigated the reversibility of homoaggregation of citrate coated Ag NPs in a Rhine River water matrix. We characterized the disaggregation of Ag NP homoaggregates by ionic strength reduction and addition of Suwannee River humic acid (SRHA) in the presence of strong and weak shear forces. In order to understand the disaggregation processes, we also studied the nature of homoaggregates and their formation dynamics under the influence of SRHA, Ca(2+) concentration and nanoparticle concentration. Even in the presence of SRHA and at low particle concentrations (10 μg L(-1)), aggregates formed rapidly in filtered Rhine water. The critical coagulation concentration (CCC) of Ca(2+) in reconstituted Rhine water was 1.5 mmol L(-1) and was shifted towards higher values in the presence of SRHA. Analysis of the attachment efficiency as a function of Ca(2+) concentration showed that SRHA induces electrosteric stabilization at low Ca(2+) concentrations and cation-bridging flocculation at high Ca(2+) concentrations. Shear forces in the form of mechanical shaking or ultrasound were necessary for breaking the aggregates. Without ultrasound, SRHA also induced disaggregation, but it required several days to reach a stable size of dense aggregates still larger than the primary particles. Citrate stabilized Ag NPs may be in the form of reaction limited aggregates in aquatic systems similar to the Rhine River. The size and the structure of these aggregates will be dynamic and be determined by the solution conditions. Seasonal variations in the chemical composition of natural waters can result in a sedimentation-release cycle of engineered nanoparticles. Copyright © 2014 Elsevier B.V. All rights reserved.

The effect of coating on heat generation properties of Iron oxide nanoparticles

NASA Astrophysics Data System (ADS)

Yuan, Yuan

Magnetic nanoparticles have attracted more and more attention for their potential application as heating agents in cancer hyperthermia. The effectiveness of cancer hyperthermia can be increased by using particles that have a higher heat generation rate, quantified by specific absorption rate (SAR), at a smaller applied field. In order to optimize the functionality of nanoparticles as heating agents, it is essential to have a comprehensive understanding of factors that may influence SAR including coating and aggregation. In all biomedical applications, the magnetic particles are coated with surfactants and polymers to enhance biocompatibility, prevent agglomeration and add functionality. Coatings may profoundly influence particles' clustering behavior and magnetic properties. Yet its effect on the heat generation rate of the nanoparticles has been scarcely investigated. In this context, a systematic investigation was carried out in this dissertation in order to understand the impact of the surface coating of magnetic nanoparticles on their heat generation rate. The study also includes investigation of normal nerve cell viability in presence of biofunctionalized magnetic nanoparticles with and without exposure to magnetic heating. Commercially available suspensions of iron oxide nanoparticles with a diameter of approximately 10 nm and different coatings relevant to biomedical applications such as aminosilane, carboxymethyl-dextran, protein A, biotin were extensively characterized. First of all, magnetic phase reduction of magnetite nanoparticles was examined by studying the discrepancy between the volume fraction of magnetic phase calculated from magnetization curve and the magnetic core concentration obtained from Tiron chelation test. The findings indicated that coatings might interact with the surface atoms of the magnetic core and form a magnetically disordered layer reducing the total amount of the magnetic phase. Secondly, the impact of coating and aggregation on magnetic properties and heat generation rate of magnetic nanoparticles was investigated by comparing the experimental and predicted SAR. For this purpose, AC magnetic susceptibility of suspensions was measured and also calculated by Debye model. Both were used to predict SAR and then compare it to the measured SAR. Poor agreement was found when the predictions were based on the Debye model, which neglects dipolar interactions between nanoparticles within aggregations. For uncoated and amine-functionalized particles (with aggregations) experimental SAR was found to agree relatively well with predicted SAR using experimental susceptibility values, which is expected to capture magnetic losses. For biotin and protein A coated nanoparticles (both having large, asymmetric clusters), the experimental SAR of both samples was found to be higher than the SAR predicted with experimental susceptibility. This unexpected discrepancy was attributed in part to friction loss associated with the partial rotation of clusters. This hypothesis was confirmed by examining the temperature increasing rate of particles embeded in hydrogel with different stiffness. At last, the properties of magnetic nanoparticles dispersed in DI water, Neurobasal (NB), or astrocyte culture media were studied. The aminosilane coated nanoparticles that dispersed in astrocyte culture media presented highest susceptibility and SAR compared to that suspended in DI water or NB, which was attributed to its highest aggregation size and magnetization phase concentration. However, for starch coated nanoparticles, samples prepared in either media showed similar magnetic and heating properties. The cell studies started with investigation of the response of primary cortical neurons to magnetite nanoparticles with aminosilane, starch and polydimethylamine coatings. It was found that polydimethylamine functionalized nanoparticles induce cell death at all concentrations and complete removal of plasma membrane. Aminosilane and starch-coated particles affected metabolic activities only at higher concentrations while leaving the membrane intact. The iron oxide nanoparticle with aminosilane coating were then used to further study the response of neurons and astrocytes to local heat generated by magnetic nanoparticles. The culture results show that heating does not affect viability of neurons but influence the viability of astrocytes independent of final temperature.

Bovine Serum Albumin Nanoparticles Containing Amphotericin B: Characterization, Cytotoxicity and In Vitro Antifungal Evaluation.

PubMed

Casa, Diani Meza; Karam, Thaysa Ksiaskiewcz; Alves, Aline de Cristo Soares; Zgoda, Aline Aparecida; Khalil, Najeh Maissar; Mainardes, Rubiana Mara

2015-12-01

In this study, nanoparticles based on bovine serum albumin (BSA) containing amphotericin B (AmB) were obtained by the desolvation method and characterized with respect to size, size distribution, AmB encapsulation efficiency, AmB state of aggregation, and AmB in vitro release profile. After, the effect of nanoparticles on the cytotoxicity of human erythrocytes in vitro and efficacy over strains of Candida spp. were evaluated. The mean particle size was 156 nm and the AmB encapsulation efficiency was over 82%. The in vitro release profile revealed a sustained release of approximately 48% of AmB over 5 days. AmB is present in BSA nanoparticles as monomer. AmB-loaded nanoparticles showed very low index of hemolysis (less than 8%) in 72 h of assay compared to free AmB, which presented 100% of hemolysis in 2 h of incubation. The AmB-loaded BSA nanoparticles were as effective as free AmB against Candida albicans and Candida tropicalis, considering their sustained release profile. Thus, BSA nanoparticles are potential carriers for AmB, reducing its molecular aggregation and prolonging its release, resulting in lower cytotoxicity while maintaining its antifungal activity.

Study of the aggregation mechanism of polyglutamine peptides using replica exchange molecular dynamics simulations.

PubMed

Nakano, Miki; Ebina, Kuniyoshi; Tanaka, Shigenori

2013-04-01

Polyglutamine (polyQ, a peptide) with an abnormal repeat length is the causative agent of polyQ diseases, such as Huntington's disease. Although glutamine is a polar residue, polyQ peptides form insoluble aggregates in water, and the mechanism for this aggregation is still unclear. To elucidate the detailed mechanism for the nucleation and aggregation of polyQ peptides, replica exchange molecular dynamics simulations were performed for monomers and dimers of polyQ peptides with several chain lengths. Furthermore, to determine how the aggregation mechanism of polyQ differs from those of other peptides, we compared the results for polyQ with those of polyasparagine and polyleucine. The energy barrier between the monomeric and dimeric states of polyQ was found to be relatively low, and it was observed that polyQ dimers strongly favor the formation of antiparallel β-sheet structures. We also found a characteristic behavior of the monomeric polyQ peptide: a turn at the eighth residue is always present, even when the chain length is varied. We previously showed that a structure including more than two sets of β-turns is stable, so a long monomeric polyQ chain can act as an aggregation nucleus by forming several pairs of antiparallel β-sheet structures within a single chain. Since the aggregation of polyQ peptides has some features in common with an amyloid fibril, our results shed light on the mechanism for the aggregation of polyQ peptides as well as the mechanism for the formation of general amyloid fibrils, which cause the onset of amyloid diseases.

Insight on agglomerates of gold nanoparticles in glass based on surface plasmon resonance spectrum: study by multi-spheres T-matrix method

NASA Astrophysics Data System (ADS)

Avakyan, L. A.; Heinz, M.; Skidanenko, A. V.; Yablunovski, K. A.; Ihlemann, J.; Meinertz, J.; Patzig, C.; Dubiel, M.; Bugaev, L. A.

2018-01-01

The formation of a localized surface plasmon resonance (SPR) spectrum of randomly distributed gold nanoparticles in the surface layer of silicate float glass, generated and implanted by UV ArF-excimer laser irradiation of a thin gold layer sputter-coated on the glass surface, was studied by the T-matrix method, which enables particle agglomeration to be taken into account. The experimental technique used is promising for the production of submicron patterns of plasmonic nanoparticles (given by laser masks or gratings) without damage to the glass surface. Analysis of the applicability of the multi-spheres T-matrix (MSTM) method to the studied material was performed through calculations of SPR characteristics for differently arranged and structured gold nanoparticles (gold nanoparticles in solution, particles pairs, and core-shell silver-gold nanoparticles) for which either experimental data or results of the modeling by other methods are available. For the studied gold nanoparticles in glass, it was revealed that the theoretical description of their SPR spectrum requires consideration of the plasmon coupling between particles, which can be done effectively by MSTM calculations. The obtained statistical distributions over particle sizes and over interparticle distances demonstrated the saturation behavior with respect to the number of particles under consideration, which enabled us to determine the effective aggregate of particles, sufficient to form the SPR spectrum. The suggested technique for the fitting of an experimental SPR spectrum of gold nanoparticles in glass by varying the geometrical parameters of the particles aggregate in the recurring calculations of spectrum by MSTM method enabled us to determine statistical characteristics of the aggregate: the average distance between particles, average size, and size distribution of the particles. The fitting strategy of the SPR spectrum presented here can be applied to nanoparticles of any nature and in various substances, and, in principle, can be extended for particles with non-spherical shapes, like ellipsoids, rod-like and other T-matrix-solvable shapes.

Compositions and methods for direct capture of organic materials from process streams

DOEpatents

Lin, YuPo J.; Brotzman, Richard W.; Snyder, Seth W.

2016-08-09

A particulate magnetic nanostructured solid sorbent (MNSS) material is described herein. The particles of the MNSS comprise a plurality of tethered nanoparticles. The nanoparticles are tethered together by substantially linear hydrocarbon chains, a poly(alkylene oxide) chains, or a combination thereof connecting the nanoparticles in a three-dimensional elastic network with the nanoparticles as junctions of the network having junction functionality of about 2.1 to about 6. The surfaces of at least some of the nanoparticles comprise a polymerized siloxane bearing at least one sorption-aiding substituent selected from a hydrophilic group and a lipophilic group. The plurality of nanoparticles is made up of superparamagnetic nanoparticles or a combination of superparamagnetic and non-magnetic nanoparticles. The individual superparamagnetic nanoparticles comprise a passivating metal oxide coating around a core comprising at least one nanocrystalline metal or alloy having ferromagnetic or ferrimagnetic properties.

Sulfur Nanoparticles with Novel Morphologies Coupled with Brain-Targeting Peptides RVG as a New Type of Inhibitor Against Metal-Induced Aβ Aggregation.

PubMed

Sun, Jing; Xie, Wenjie; Zhu, Xufeng; Xu, Mengmeng; Liu, Jie

2018-04-18

Functionalized nanomaterials, which have been applied widely to inhibit amyloid-β protein (Aβ) aggregation, show enormous potential in the field of prevention and treatment of Alzheimer's disease (AD). A significant body of data has demonstrated that the morphology and size of nanomaterials have remarkable effects on their biological behaviors. In this work, we proposed and designed three kinds of brain-targeting sulfur nanoparticles (RVG@Met@SNPs) with novel morphologies (volute-like, tadpole-like, and sphere-like) and investigated the effect of different RVG@Met@SNPs on Aβ-Cu 2+ complex aggregation and their corresponding neurotoxicity. Among them, the sphere-like nanoparticles (RVG@Met@SS) exhibited the most effective inhibitory activity, due to their unique mini size effect, and they reduced 61.6% the Aβ-Cu 2+ complex aggregation and increased 92.4% SH-SY5Y cell viability in a dose of 10 μg/mL. In vitro and in vivo, the abilities of different morphologies of RVG@Met@SNPs to cross the blood-brain barrier (BBB) and target brain parenchymal cells were significantly different. Moreover, improvements in learning disability and cognitive loss were shown in the transgenic AD mice model using the Morris water maze test after multiple doses of RVG@Met@SNPs treatment. In general, the purpose of this research is to develop a biological application of sulfur nanoparticles and to provide a novel functionalized nanomaterial to treat AD.

Aggregation Kinetics of Diesel Soot Nanoparticles in Wet Environments.

PubMed

Chen, Chengyu; Huang, Weilin

2017-02-21

Soot produced during incomplete combustion consists mainly of carbonaceous nanoparticles (NPs) with severe adverse environmental and health effects, and its environmental fate and transport are largely controlled by aggregation. In this study, we examined the aggregation behavior for diesel soot NPs under aqueous condition in an effort to elucidate the fundamental processes that govern soot particle-particle interactions in wet environments such as rain droplets or surface aquatic systems. The influence of electrolytes and aqueous pH on colloidal stability of these NPs was investigated by measuring their aggregation kinetics in different aqueous solution chemistries. The results showed that the NPs had negatively charged surfaces and exhibited both reaction- and diffusion-limited aggregation regimes with rates depended upon solution chemistry. The aggregation kinetics data were in good agreement with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The critical coagulation concentrations (CCC) were quantified and the Hamaker constant was derived for the soot (1.4 × 10 -20 J) using the colloidal chemistry approach. The study indicated that, depending upon local aqueous chemistry, single soot NPs could remain stable against self-aggregation in typical freshwater environments and in neutral cloud droplets but are likely to aggregate under salty (e.g., estuaries) or acidic (e.g., acid rain droplets) aquatic conditions or both.

Chain-like nanostructures from anisotropic self-assembly of semiconducting metal oxide nanoparticles with a block copolymer.

PubMed

Wang, Junzheng; Winardi, Suminto; Sugawara-Narutaki, Ayae; Kumamoto, Akihito; Tohei, Tetsuya; Shimojima, Atsushi; Okubo, Tatsuya

2012-11-21

A facile method is reported for the preparation of chain-like nanostructures by anisotropic self-assembly of TiO(2) and SnO(2) nanoparticles with the aid of a block copolymer in an aqueous medium. Well-defined crystallographic orientations between neighbouring nanoparticles are observed in TiO(2) nanochains, which is important for tailoring the grain boundaries and thus enhancing charge transport.

Colorimetric detection of biothiols based on aggregation of chitosan-stabilized silver nanoparticles

NASA Astrophysics Data System (ADS)

Mohammadi, Somayeh; Khayatian, Gholamreza

2017-10-01

We have described a simple and reliable colorimetric method for the sensing of biothiols such as cysteine, homocysteine, and glutathione in biological samples. The selective binding of chitosan capped silver nanoparticles to biothiols induced aggregation of the chitosan-Ag NPs. But the other amino acids that do not have thiol group cannot aggregate the chitosan-Ag NPs. Aggregation of chitosan-Ag NPs has been confirmed with UV-vis absorption spectra, zeta potential and transmission electron microscopy images. Under optimum conditions, good linear relationships existed between the absorption ratios (at A500/A415) and the concentrations of cysteine, homocysteine, and glutathione in the range of 0.1-10.0 μM with detection limits of 15.0, 84.6 and 40.0 nM, respectively. This probe was successfully applied to detect these biothiols in biological samples (urine and plasma).

A Novel Magnetic Actuation Scheme to Disaggregate Nanoparticles and Enhance Passage across the Blood–Brain Barrier

PubMed Central

Le, Tuan-Anh; Amin, Faiz Ul; Kim, Myeong Ok

2017-01-01

The blood–brain barrier (BBB) hinders drug delivery to the brain. Despite various efforts to develop preprogramed actuation schemes for magnetic drug delivery, the unmodeled aggregation phenomenon limits drug delivery performance. This paper proposes a novel scheme with an aggregation model for a feed-forward magnetic actuation design. A simulation platform for aggregated particle delivery is developed and an actuation scheme is proposed to deliver aggregated magnetic nanoparticles (MNPs) using a discontinuous asymmetrical magnetic actuation. The experimental results with a Y-shaped channel indicated the success of the proposed scheme in steering and disaggregation. The delivery performance of the developed scheme was examined using a realistic, three-dimensional (3D) vessel simulation. Furthermore, the proposed scheme enhanced the transport and uptake of MNPs across the BBB in mice. The scheme presented here facilitates the passage of particles across the BBB to the brain using an electromagnetic actuation scheme. PMID:29271927

Aggregation control of quantum dots through ion-mediated hydrogen bonding shielding.

PubMed

Liu, Jianbo; Yang, Xiaohai; Wang, Kemin; He, Xiaoxiao; Wang, Qing; Huang, Jin; Liu, Yan

2012-06-26

Nanoparticle stabilization against detrimental aggregation is a critical parameter that needs to be well controlled. Herein, we present a facile and rapid ion-mediated dispersing technique that leads to hydrophilic aggregate-free quantum dots (QDs). Because of the shielding of the hydrogen bonds between cysteamine-capped QDs, the presence of F(-) ions disassembled the aggregates of QDs and afforded their high colloidal stability. The F(-) ions also greatly eliminated the nonspecific adsorption of the QDs on glass slides and cells. Unlike the conventional colloidal stabilized method that requires the use of any organic ligand and/or polymer for the passivation of the nanoparticle surface, the proposed approach adopts the small size and large diffusion coefficient of inorganic ions as dispersant, which offers the disaggregation a fast reaction dynamics and negligible influence on their intrinsic surface functional properties. Therefore, the ion-mediated dispersing strategy showed great potential in chemosensing and biomedical applications.

Magnetic fluid - a novel approach to treat amyloid-related diseases

NASA Astrophysics Data System (ADS)

Antosova, Andrea; Siposova, Katarina; Koneracka, Martina; Zavisova, Vlasta; Daxnerova, Zuzana; Vavra, Ivo; Fedunova, Diana; Bagelova, Jaroslava; Kopcansky, Peter; Gazova, Zuzana

Protein amyloid aggregates are associated with several human pathologies termed amyloid-related diseases. We have investigated effect of two magnetic fluids (MFs) - electrostatically stabilized Fe3O4 magnetic nanoparticles (MF1) and sterically stabilized Fe3O4 magnetic nanoparticles by sodium oleate with adsorbed BSA (MF2) on amyloid aggregation of two proteins - human insulin and hen egg lysozyme. We have found that both MF1 and MF2 are able to interact with amyloid fibrils in vitro resulting into decreasing of amyloid aggregates. The extent of fibril disruption depends on MF concentration with extensive reduction of amyloid aggregates, 90% for lysozyme and 70% for insulin (ratio protein: MF=1:5). The obtained results suggest that magnetite component of MF play significant role in the process of amyloid fibril depolymerisation. Our findings indicate that MF1 and MF2 have potential to be used for treatment of amyloid diseases.

A Novel Magnetic Actuation Scheme to Disaggregate Nanoparticles and Enhance Passage across the Blood-Brain Barrier.

PubMed

Hoshiar, Ali Kafash; Le, Tuan-Anh; Amin, Faiz Ul; Kim, Myeong Ok; Yoon, Jungwon

2017-12-22

The blood-brain barrier (BBB) hinders drug delivery to the brain. Despite various efforts to develop preprogramed actuation schemes for magnetic drug delivery, the unmodeled aggregation phenomenon limits drug delivery performance. This paper proposes a novel scheme with an aggregation model for a feed-forward magnetic actuation design. A simulation platform for aggregated particle delivery is developed and an actuation scheme is proposed to deliver aggregated magnetic nanoparticles (MNPs) using a discontinuous asymmetrical magnetic actuation. The experimental results with a Y-shaped channel indicated the success of the proposed scheme in steering and disaggregation. The delivery performance of the developed scheme was examined using a realistic, three-dimensional (3D) vessel simulation. Furthermore, the proposed scheme enhanced the transport and uptake of MNPs across the BBB in mice. The scheme presented here facilitates the passage of particles across the BBB to the brain using an electromagnetic actuation scheme.

Holographic Characterization of Colloidal Fractal Aggregates

NASA Astrophysics Data System (ADS)

Wang, Chen; Cheong, Fook Chiong; Ruffner, David B.; Zhong, Xiao; Ward, Michael D.; Grier, David G.

In-line holographic microscopy images of micrometer-scale fractal aggregates can be interpreted with the Lorenz-Mie theory of light scattering and an effective-sphere model to obtain each aggregate's size and the population-averaged fractal dimension. We demonstrate this technique experimentally using model fractal clusters of polystyrene nanoparticles and fractal protein aggregates composed of bovine serum albumin and bovine pancreas insulin. This technique can characterize several thousand aggregates in ten minutes and naturally distinguishes aggregates from contaminants such as silicone oil droplets. Work supported by the SBIR program of the NSF.

A Facile pH Controlled Citrate-Based Reduction Method for Gold Nanoparticle Synthesis at Room Temperature.

PubMed

Tyagi, Himanshu; Kushwaha, Ajay; Kumar, Anshuman; Aslam, Mohammed

2016-12-01

The synthesis of gold nanoparticles using citrate reduction process has been revisited. A simplified room temperature approach to standard Turkevich synthesis is employed to obtain fairly monodisperse gold nanoparticles. The role of initial pH alongside the concentration ratio of reactants is explored for the size control of Au nanoparticles. The particle size distribution has been investigated using UV-vis spectroscopy and transmission electron microscope (TEM). At optimal pH of 5, gold nanoparticles obtained are highly monodisperse and spherical in shape and have narrower size distribution (sharp surface plasmon at 520 nm). For other pH conditions, particles are non-uniform and polydisperse, showing a red-shift in plasmon peak due to aggregation and large particle size distribution. The room temperature approach results in highly stable "colloidal" suspension of gold nanoparticles. The stability test through absorption spectroscopy indicates no sign of aggregation for a month. The rate of reduction of auric ionic species by citrate ions is determined via UV absorbance studies. The size of nanoparticles under various conditions is thus predicted using a theoretical model that incorporates nucleation, growth, and aggregation processes. The faster rate of reduction yields better size distribution for optimized pH and reactant concentrations. The model involves solving population balance equation for continuously evolving particle size distribution by discretization techniques. The particle sizes estimated from the simulations (13 to 25 nm) are close to the experimental ones (10 to 32 nm) and corroborate the similarity of reaction processes at 300 and 373 K (classical Turkevich reaction). Thus, substitution of experimentally measured rate of disappearance of auric ionic species into theoretical model enables us to capture the unusual experimental observations.

Fe3O4 nanoparticles and nanocomposites with potential application in biomedicine and in communication technologies: Nanoparticle aggregation, interaction, and effective magnetic anisotropy

NASA Astrophysics Data System (ADS)

Allia, P.; Barrera, G.; Tiberto, P.; Nardi, T.; Leterrier, Y.; Sangermano, M.

2014-09-01

Magnetite nanoparticles with a size of 5-6 nm with potential impact on biomedicine and information/communication technologies were synthesized by thermal decomposition of Fe(acac)3 and subsequently coated with a silica shell exploiting a water-in-oil synthetic procedure. The as-produced powders (comprised of either Fe3O4 or Fe3O4@silica nanoparticles) were mixed with a photocurable resin obtaining two magnetic nanocomposites with the same nominal amount of magnetic material. The static magnetic properties of the two nanopowders and the corresponding nanocomposites were measured in the 10 K-300 K temperature range. Magnetic measurements are shown here to be able to give unambiguous information on single-particle properties such as particle size and magnetic anisotropy as well as on nanoparticle aggregation and interparticle interaction. A comparison between the size distribution functions obtained from magnetic measurements and from TEM images shows that figures estimated from properly analyzed magnetic measurements are very close to the actual values. In addition, the present analysis allows us to determine the value of the effective magnetic anisotropy and to estimate the anisotropy contribution from the surface. The Field-cooled/zero field cooled curves reveal a high degree of particle aggregation in the Fe3O4 nanopowder, which is partially reduced by silica coating and strongly decreased by dissolution in the host polymer. In all considered materials, the nanoparticles are magnetically interacting, the interaction strength being a function of nanoparticle environment and being the lowest in the nanocomposite containing bare, well-separate Fe3O4 particles. All samples behave as interacting superparamagnetic materials instead of ideal superparamagnets and follow the corresponding scaling law.

Modeling and self-assembly behavior of PEG-PLA-PEG triblock copolymers in aqueous solution

NASA Astrophysics Data System (ADS)

Wu, Xiaohan; Li, Suming; Coumes, Fanny; Darcos, Vincent; Lai Kee Him, Joséphine; Bron, Patrick

2013-09-01

A series of poly(ethylene glycol)-polylactide-poly(ethylene glycol) (PEG-PLA-PEG) triblock copolymers with symmetric or asymmetric chain structures were synthesized by combination of ring-opening polymerization and copper-catalyzed click chemistry. The resulting copolymers were used to prepare self-assembled aggregates by dialysis. Various architectures such as nanotubes, polymersomes and spherical micelles were observed from transmission electron microscopy (TEM), cryo-TEM and atomic force microscopy (AFM) measurements. The formation of diverse aggregates is explained by modeling from the angle of both geometry and thermodynamics. From the angle of geometry, a ``blob'' model based on the Daoud-Cotton model for star polymers is proposed to describe the aggregate structures and structural changes with copolymer composition and molar mass. In fact, the copolymer chains extend in aqueous medium to form single layer polymersomes to minimize the system's free energy if one of the two PEG blocks is short enough. The curvature of polymersomes is dependent on the chain structure of copolymers, especially on the length of PLA blocks. A constant branch number of aggregates (f) is thus required to preserve the morphology of polymersomes. Meanwhile, the aggregation number (Nagg) determined from the thermodynamics of self-assembly is roughly proportional to the total length of polymer chains. Comparing f to Nagg, the aggregates take the form of polymersomes if Nagg ~ f, and change to nanotubes if Nagg > f to conform to the limits from both curvature and aggregation number. The length of nanotubes is mainly determined by the difference between Nagg and f. However, the hollow structure becomes unstable when both PEG segments are too long, and the aggregates eventually collapse to yield spherical micelles. Therefore, this work gives new insights into the self-assembly behavior of PEG-PLA-PEG triblock copolymers in aqueous solution which present great interest for biomedical and pharmaceutical applications.A series of poly(ethylene glycol)-polylactide-poly(ethylene glycol) (PEG-PLA-PEG) triblock copolymers with symmetric or asymmetric chain structures were synthesized by combination of ring-opening polymerization and copper-catalyzed click chemistry. The resulting copolymers were used to prepare self-assembled aggregates by dialysis. Various architectures such as nanotubes, polymersomes and spherical micelles were observed from transmission electron microscopy (TEM), cryo-TEM and atomic force microscopy (AFM) measurements. The formation of diverse aggregates is explained by modeling from the angle of both geometry and thermodynamics. From the angle of geometry, a ``blob'' model based on the Daoud-Cotton model for star polymers is proposed to describe the aggregate structures and structural changes with copolymer composition and molar mass. In fact, the copolymer chains extend in aqueous medium to form single layer polymersomes to minimize the system's free energy if one of the two PEG blocks is short enough. The curvature of polymersomes is dependent on the chain structure of copolymers, especially on the length of PLA blocks. A constant branch number of aggregates (f) is thus required to preserve the morphology of polymersomes. Meanwhile, the aggregation number (Nagg) determined from the thermodynamics of self-assembly is roughly proportional to the total length of polymer chains. Comparing f to Nagg, the aggregates take the form of polymersomes if Nagg ~ f, and change to nanotubes if Nagg > f to conform to the limits from both curvature and aggregation number. The length of nanotubes is mainly determined by the difference between Nagg and f. However, the hollow structure becomes unstable when both PEG segments are too long, and the aggregates eventually collapse to yield spherical micelles. Therefore, this work gives new insights into the self-assembly behavior of PEG-PLA-PEG triblock copolymers in aqueous solution which present great interest for biomedical and pharmaceutical applications. Electronic supplementary information (ESI) available: 1H-NMR, DOSY, FTIR, and GPC measurements, methods and results of the copolymers in PEG-PLA-PEG synthesis. See DOI: 10.1039/c3nr02899b

Modeling thermionic emission from laser-heated nanoparticles

DOE PAGES

Mitrani, J. M.; Shneider, M. N.; Stratton, B. C.; ...

2016-02-01

An adjusted form of thermionic emission is applied to calculate emitted current from laser-heated nanoparticles and to interpret time-resolved laser-induced incandescence (TR-LII) signals. This adjusted form of thermionic emission predicts significantly lower values of emitted current compared to the commonly used Richardson-Dushman equation, since the buildup of positive charge in a laser-heated nanoparticle increases the energy barrier for further emission of electrons. Thermionic emission influences the particle's energy balance equation, which can influence TR-LII signals. Additionally, reports suggest that thermionic emission can induce disintegration of nanoparticle aggregates when the electrostatic Coulomb repulsion energy between two positively charged primary particles ismore » greater than the van der Waals bond energy. Furthermore, since the presence and size of aggregates strongly influences the particle's energy balance equation, using an appropriate form of thermionic emission to calculate emitted current may improve interpretation of TR-LII signals.« less

Incorporation of Active DNA/Cationic Polymer Polyplexes into Hydrogel Scaffolds

PubMed Central

Lei, Yuguo; Huang, Suxian; Sharif-Kashani, Pooria; Chen, Yong; Kavehpour, Pirouz; Segura, Tatiana

2010-01-01

The effective and sustained delivery of DNA and siRNAs locally would increase the applicability of gene therapy in tissue regeneration and cancer therapy. One promising approach is to use hydrogel scaffolds to encapsulate and deliver nucleotides in the form of nanoparticles to the disease sites. However, this approach is currently limited by the inability to load concentrated and active gene delivery nanoparticles into the hydrogels due to the severe nanoparticle aggregation during the loading process. Here, we present a process to load concentrated and un-aggregated non-viral gene delivery nanoparticles, using DNA/polyethylene imine (PEI) polyplexes as an example, into neutral polyethylene glycol (PEG), negatively charged hyaluronic acid (HA) and protein fibrin hydrogels crosslinked through various chemistries. The encapsulated polyplexes are highly active both in vitro and in vivo. We believe this process will significantly advance the applications of hydrogel scaffold mediated non-viral gene delivery in tissue regeneration and cancer therapy. PMID:20822811

Observation of Metal Nanoparticles for Acoustic Manipulation

PubMed Central

Chen, Mian; Cai, Feiyan; Wang, Chen; Wang, Zhiyong; Meng, Long; Li, Fei; Zhang, Pengfei; Liu, Xin

2017-01-01

Use of acoustic trapping for the manipulation of objects is invaluable to many applications from cellular subdivision to biological assays. Despite remarkable progress in a wide size range, the precise acoustic manipulation of 0D nanoparticles where all the structural dimensions are much smaller than the acoustic wavelength is still present challenges. This study reports on the observation of metal nanoparticles with different nanostructures for acoustic manipulation. Results for the first time exhibit that the hollow nanostructures play more important factor than size in the nanoscale acoustic manipulation. The acoustic levitation and swarm aggregations of the metal nanoparticles can be easily realized at low energy and clinically acceptable acoustic frequency by hollowing their nanostructures. In addition, the behaviors of swarm aggregations can be flexibly regulated by the applied voltage and frequency. This study anticipates that the strategy based on the unique properties of the metal hollow nanostructures and the manipulation method will be highly desirable for many applications. PMID:28546912

Observation of Metal Nanoparticles for Acoustic Manipulation.

PubMed

Chen, Mian; Cai, Feiyan; Wang, Chen; Wang, Zhiyong; Meng, Long; Li, Fei; Zhang, Pengfei; Liu, Xin; Zheng, Hairong

2017-05-01

Use of acoustic trapping for the manipulation of objects is invaluable to many applications from cellular subdivision to biological assays. Despite remarkable progress in a wide size range, the precise acoustic manipulation of 0D nanoparticles where all the structural dimensions are much smaller than the acoustic wavelength is still present challenges. This study reports on the observation of metal nanoparticles with different nanostructures for acoustic manipulation. Results for the first time exhibit that the hollow nanostructures play more important factor than size in the nanoscale acoustic manipulation. The acoustic levitation and swarm aggregations of the metal nanoparticles can be easily realized at low energy and clinically acceptable acoustic frequency by hollowing their nanostructures. In addition, the behaviors of swarm aggregations can be flexibly regulated by the applied voltage and frequency. This study anticipates that the strategy based on the unique properties of the metal hollow nanostructures and the manipulation method will be highly desirable for many applications.

Strain induced plasmon tuning in planar square-shaped aluminum nanoparticles array

NASA Astrophysics Data System (ADS)

Mokkath, Junais Habeeb

2018-06-01

Metal nanoparticle aggregate is an exciting platform for manipulating light-matter interactions at the nanoscale, thanks to the optically driven free electrons couple electrically across the inter-particle gap region. We use time dependent density functional theory calculations to investigate the optical response modulations in planar square-shaped aluminum nanoparticles array via morphology deformation (varying the inter-particle gap distance in the range of 2-20 Å) separately along one and two directions. We report the surprising observation that irrespective of the different morphology deformations, there exists a unique inter-particle gap distance of 12 Å for which, a maximum optical field enhancement can be achieved. We remark that plasmonic interaction between metal nanoparticles in an aggregate is controlled to a large extent by the size of the inter-particle gap distance. We believe that our quantum mechanical calculations will inspire and contribute to the design, control, and exploitation of aluminum based plasmonic devices.

Toxicity of Engineered Nickel Oxide and Cobalt Oxide Nanoparticles to Artemia salina in seawater

PubMed Central

Ates, Mehmet; Demir, Veysel; Arslan, Zikri; Camas, Mustafa; Celik, Fatih

2016-01-01

In this study, the effects of exposure to engineered nickel oxide (NiO 40–60 nm) and cobalt oxide (CoO <100 nm) nanoparticles (NP) were investigated on Artemia salina. Aggregation and stability of the aqueous NP suspensions were characterized by DLS and TEM. Acute exposure was conducted on nauplii (larvae) in seawater in a concentration range from 0.2 to 50 mg/L NPs for 24 h (short term) and 96 h (long term). The hydrodynamic diameters of NiO and CoO NPs in exposure medium were larger than those estimated by TEM. Accumulation rate of NiO NPs were found to be four times higher than that of CoO NPs under the same experimental conditions. Examinations under phase contrast microscope showed that the nanoparticles accumulated in the intestine of artemia, which increased with increasing exposure concentration. Differences were observed in the extent of dissolution of the NPs in the seawater. The CoO NPs dissolved significantly while NiO NPs were relatively more stable. Oxidative stress induced by the NP suspensions was measured by malondialdehyde assay. Suspensions of NiO NPs caused higher oxidative stress on nauplii than those of CoO NPs. The results imply that CoO and NiO NPs exhibit toxicity on artemia (e.g., zooplankton) that are an important source of food in aquatic food chain. PMID:27152058

A sensitive colorimetric assay system for nucleic acid detection based on isothermal signal amplification technology.

PubMed

Hu, Bo; Guo, Jing; Xu, Ying; Wei, Hua; Zhao, Guojie; Guan, Yifu

2017-08-01

Rapid and accurate detection of microRNAs in biological systems is of great importance. Here, we report the development of a visual colorimetric assay which possesses the high amplification capabilities and high selectivity of the rolling circle amplification (RCA) method and the simplicity and convenience of gold nanoparticles used as a signal indicator. The designed padlock probe recognizes the target miRNA and is circularized, and then acts as the template to extend the target miRNA into a long single-stranded nucleotide chain of many tandem repeats of nucleotide sequences. Next, the RCA product is hybridized with oligonucleotides tagged onto gold nanoparticles. This interaction leads to the aggregation of gold nanoparticles, and the color of the system changes from wine red to dark blue according to the abundance of miRNA. A linear correlation between fluorescence and target oligonucleotide content was obtained in the range 0.3-300 pM, along with a detection limit of 0.13 pM (n = 7) and a RSD of 3.9% (30 pM, n = 9). The present approach provides a simple, rapid, and accurate visual colorimetric assay that allows sensitive biodetection and bioanalysis of DNA and RNA nucleotides of interest in biologically important samples. Graphical abstract The colorimetric assay system for analyzing target oligonucleotides.

Fabrication, Light Emission, and Magnetism of Silica Nanoparticles Hybridized with AIE Luminogens and Inorganic Nanostructures

NASA Astrophysics Data System (ADS)

Faisal, Mahtab

Much research efforts have been devoted in developing new synthetic approaches for fluorescent silica nanoparticles (FSNPs) due to their potential high-technological applications. However, light emissions from most of the FSNPs prepared so far have been rather weak. This is due to the emission quenching caused by the aggregation of fluorophores in the solid state. We have observed a novel phenomenon of aggregation-induced emission (AIE): a series of propeller-shaped molecules such as tetraphenylethene (TPE) and silole are induced to emit efficiently by aggregate formation. Thus, they are ideal fluorophors for the construction of FSNPs and my thesis work focuses on the synthesis of silica nanoparticles containing these luminogens and magnetic nanostructures. Highly emissive FSNPs with core-shell structures are fabricated by surfactant-free sol-gel reactions of tetraphenylethene- (TPE) and silole-functionalized siloxanes followed by the reactions with tetraethoxysilane. The FSNPs are uniformly sized, surface-charged and colloidally stable. The diameters of the FSNPs are tunable in the range of 45--295 nm by changing the reaction conditions. Whereas their TPE and silole precursors are non-emissive, the FSNPs emit strong visible lights, thanks to the novel aggregation-induced emission characteristics of the TPE and silole aggregates in the hybrid nanoparticles. The FSNPs pose no toxicity to living cells and can be utilized to selectively image cytoplasm of HeLa cells. Applying the same tool in the presence of citrate-coated magnetite nanoparticles, uniform magnetic fluorescent silica nanoparticles (MFSNPs) with smooth surfaces are fabricated. These particles exhibit appreciable surface charges and hence good colloidal stability. They are superparamagnetic, exhibiting no hysteresis at room temperature. UV irradiation of a suspension of MFSNPs in ethanol gives strong blue and green emissions. The MFSNPs can selectively stain the cytoplasmic regions of the living cells. Sol-gel reaction in the presence of (3-aminopropyl)triethoxysilane has generated MFSNP-NH2 with numerous amino functionalities decorated on the surfaces, enabling them to immobilize bovine serum albumin efficiently. FSNPs with strong light emissions are facilely fabricated by thio-click chemistry, Cu(I)-catalyzed 1,3-dipolar cycloaddition, and sol-gel reaction. The FSNPs are characterized by SEM, TEM, IR, PL, and zeta potential analyses. They are uniformly sized with smooth surfaces. Upon photoexcitation, the FSNPs emit strong visible lights with fluorescence quantum yields up to 25.5%. Sugar-functionalized fluorescent silica nanoparticles are facilely fabricated by click reaction of azide-modified FSNPs with sugar- containing phenylacetylene catalyzed by Cu(PPh3)3Br in THF. The nanoparticles are uniformly sized and emit efficient light upon photoexcitation. They can function as fluorescent visualizers for intracellular imaging and can target specific cancer cells. Folic acid-functionalized fluorescent silica nanoparticles are facilely fabricated by surface functionalization of FSNPs with folic acid. The nanoparticles are spherical in shape. They possess high zeta potentials and hence exhibit excellent colloidal stability. UV irradiation of suspensions of the nanoparticles in ethanol gives strong blue and green emissions at 465 and 490 nm with absolute fluorescence quantum yields up to 47%. Carboxylic acid and thiol-functionalized fluorescent silica nanoparticles (FSNP-COOH and FSNP-SH) with uniform particle sizes, narrow size distributions, and smooth surface morphologies are fabricated. The nanoparticles possess high surface charges and exhibit strong light emissions upon photoexcitation. They can adsorb lysozyme strongly on their surfaces and for 5 mg of FSNP-COOH and FSNP-SH, they can take 209 and 86 mug of lysozyme. Thus, they are potential carriers for protein and fluorescent probes or biosensors for an array of biological applications.

Colloidal stability of superparamagnetic iron oxide nanoparticles in the central nervous system: a review.

PubMed

Champagne, Pierre-Olivier; Westwick, Harrison; Bouthillier, Alain; Sawan, Mohamad

2018-06-01

Superparamagnetic iron oxide nanoparticles (SPIONs) consist of nanosized metallic-based particles with unique magnetic properties. Their potential in both diagnostic and therapeutic applications in the CNS is at the source of an expanding body of the literature in recent years. Colloidal stability of nanoparticles represents their ability to resist aggregation and is a central aspect for the use of SPION in biological environment such as the CNS. This review gives a comprehensive update of the recent developments and knowledge on the determinants of colloidal stability of SPIONs in the CNS. Factors leading to aggregate formation and the repercussions of colloidal instability of SPION are reviewed in detail pertaining to their use in the CNS.

Ruthenium nanoparticles in ionic liquids: structural and stability effects of polar solutes.

PubMed

Salas, Gorka; Podgoršek, Ajda; Campbell, Paul S; Santini, Catherine C; Pádua, Agílio A H; Costa Gomes, Margarida F; Philippot, Karine; Chaudret, Bruno; Turmine, Mireille

2011-08-14

Ionic liquids are a stabilizing medium for the in situ synthesis of ruthenium nanoparticles. Herein we show that the addition of molecular polar solutes to the ionic liquid, even in low concentrations, eliminates the role of the ionic liquid 3D structure in controlling the size of ruthenium nanoparticles, and can induce their aggregation. We have performed the synthesis of ruthenium nanoparticles by decomposition of [Ru(COD)(COT)] in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(1)C(4)Im][NTf(2)], under H(2) in the presence of varying amounts of water or 1-octylamine. For water added during the synthesis of metallic nanoparticles, a decrease of the solubility in the ionic liquid was observed, showed by nanoparticles located at the interface between aqueous and ionic phases. When 1-octylamine is present during the synthesis, stable nanoparticles of a constant size are obtained. When 1-octylamine is added after the synthesis, aggregation of the ruthenium nanoparticles is observed. In order to explain these phenomena, we have explored the molecular interactions between the different species using (13)C-NMR and DOSY (Diffusional Order Spectroscopy) experiments, mixing calorimetry, surface tension measurements and molecular simulations. We conclude that the behaviour of the ruthenium nanoparticles in [C(1)C(4)Im][NTf(2)] in the presence of 1-octylamine depends on the interaction between the ligand and the nanoparticles in terms of the energetics but also of the structural arrangement of the amine at the nanoparticle's surface.

Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy.

PubMed

Jafri, S H M; Löfås, H; Fransson, J; Blom, T; Grigoriev, A; Wallner, A; Ahuja, R; Ottosson, H; Leifer, K

2013-06-07

Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.

Convergent mechanisms favor fast amyloid formation in two lambda 6a Ig light chain mutants.

PubMed

Valdés-García, Gilberto; Millán-Pacheco, César; Pastor, Nina

2017-08-01

Extracellular deposition as amyloids of immunoglobulin light chains causes light chain amyloidosis. Among the light chain families, lambda 6a is one of the most frequent in light chain amyloidosis patients. Its germline protein, 6aJL2, and point mutants, R24G and P7S, are good models to study fibrillogenesis, because their stability and fibril formation characteristics have been described. Both mutations make the germline protein unstable and speed up its ability to aggregate. To date, there is no molecular mechanism that explains how these differences in amyloidogenesis can arise from a single mutation. To look into the structural and dynamical differences in the native state of these proteins, we carried out molecular dynamics simulations at room temperature. Despite the structural similarity of the germline protein and the mutants, we found differences in their dynamical signatures that explain the mutants' increased tendency to form amyloids. The contact network alterations caused by the mutations, though different, converge in affecting two anti-aggregation motifs present in light chain variable domains, suggesting a different starting point for aggregation in lambda chains compared to kappa chains. © 2017 Wiley Periodicals, Inc.

Colorimetric detection of UV light-induced single-strand DNA breaks using gold nanoparticles.

PubMed

Kim, Joong Hyun; Chung, Chan Ho; Chung, Bong Hyun

2013-02-21

We developed a colorimetric method to specifically detect single-strand DNA breaks using gold nanoparticles. In our assay, broken DNA cannot stabilize gold nanoparticles to prevent salt-induced aggregation as good as intact DNA can, and this effect can be easily observed with the naked eye as a red-to-purple color change.

Stable, polymer-directed and SPION-nucleated magnetic amphiphilic block copolymer nanoprecipitates with readily reversible assembly in magnetic fields

NASA Astrophysics Data System (ADS)

Giardiello, Marco; Hatton, Fiona L.; Slater, Rebecca A.; Chambon, Pierre; North, Jocelyn; Peacock, Anita K.; He, Tao; McDonald, Tom O.; Owen, Andrew; Rannard, Steve P.

2016-03-01

The formation of inorganic-organic magnetic nanocomposites using reactive chemistry often leads to a loss of super-paramagnetisim when conducted in the presence of iron oxide nanoparticles. We present here a low energy and chemically-mild process of co-nanoprecipitation using SPIONs and homopolymers or amphiphilic block copolymers, of varying architecture and hydrophilic/hydrophobic balance, which efficiently generates near monodisperse SPION-containing polymer nanoparticles with complete retention of magnetism, and highly reversible aggregation and redispersion behaviour. When linear and branched block copolymers with inherent water-solubility are used, a SPION-directed nanoprecipitation mechanism appears to dominate the nanoparticle formation presenting new opportunities for tailoring and scaling highly functional systems for a range of applications.The formation of inorganic-organic magnetic nanocomposites using reactive chemistry often leads to a loss of super-paramagnetisim when conducted in the presence of iron oxide nanoparticles. We present here a low energy and chemically-mild process of co-nanoprecipitation using SPIONs and homopolymers or amphiphilic block copolymers, of varying architecture and hydrophilic/hydrophobic balance, which efficiently generates near monodisperse SPION-containing polymer nanoparticles with complete retention of magnetism, and highly reversible aggregation and redispersion behaviour. When linear and branched block copolymers with inherent water-solubility are used, a SPION-directed nanoprecipitation mechanism appears to dominate the nanoparticle formation presenting new opportunities for tailoring and scaling highly functional systems for a range of applications. Electronic supplementary information (ESI) available: Additional experimental details, NMR spectra, GPC chromatograms, kinetics experiments, graphs of nanopreciptate aggregation and cycling studies and SPION characterisation. See DOI: 10.1039/c6nr00788k

Precise control of polymer coated nanopores by nanoparticle additives: Insights from computational modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eskandari Nasrabad, Afshin; Coalson, Rob D.; Jasnow, David

Polymer-nanoparticle composites are a promising new class of materials for creation of controllable nano-patterned surfaces and nanopores. We use coarse-grained molecular dynamics simulations augmented with analytical theory to study the structural transitions of surface grafted polymer layers (brushes) induced by infiltration of nanoparticles that are attracted to the polymers in the layer. We systematically compare two different polymer brush geometries: one where the polymer chains are grafted to a planar surface and the other where the chains are grafted to the inside of a cylindrical nanochannel. We perform a comprehensive study of the effects of the material parameters such asmore » the polymer chain length, chain grafting density, nanoparticle size, strength of attraction between nanoparticles and polymer monomers, and, in the case of the cylindrically grafted brush, the radius of the cylinder. We find a very general behavioral motif for all geometries and parameter values: the height of the polymer brush is non-monotonic in the nanoparticle concentration in solution. As the nanoparticle concentration increases, the brush height first decreases and after passing through a minimum value begins to increase, resulting in the swelling of the nanoparticle infused brush. These morphological features may be useful for devising tunable “smart” nano-devices whose effective dimensions can be reversibly and precisely adjusted by changing the nanoparticle concentration in solution. The results of approximate Self-Consistent Field Theory (SCFT) calculations, applicable in the regime of strong brush stretching, are compared to the simulation results. The SCFT calculations are found to be qualitatively, even semi-quantitatively, accurate when applied within their intended regime of validity, and provide a useful and efficient tool for modeling such materials.« less

Design and preparation of bi-functionalized short-chain modified zwitterionic nanoparticles.

PubMed

Hu, Fenglin; Chen, Kaimin; Xu, Hong; Gu, Hongchen

2018-05-01

An ideal nanomaterial for use in the bio-medical field should have a distinctive surface capable of effectively preventing nonspecific protein adsorption and identifying target bio-molecules. Recently, the short-chain zwitterion strategy has been suggested as a simple and novel approach to create outstanding anti-fouling surfaces. In this paper, the carboxyl end group of short-chain zwitterion-coated silica nanoparticles (SiO 2 -ZWS) was found to be difficult to functionalize via a conventional EDC/NHS strategy due to its rapid hydrolysis side-reactions. Hence, a series of bi-functionalized silica nanoparticles (SiO 2 -ZWS/COOH) were designed and prepared by controlling the molar ratio of 3-aminopropyltriethoxysilane (APTES) to short-chain zwitterionic organosiloxane (ZWS) in order to achieve above goal. The synthesized SiO 2 -ZWS/COOH had similar excellent anti-fouling properties compared with SiO 2 -ZWS, even in 50% fetal bovine serum characterized by DLS and turbidimetric titration. Subsequently, SiO 2 -ZWS/COOH 5/1 was chosen as a representative and then demonstrated higher detection signal intensity and more superior signal-to-noise ratios compare with the pure SiO 2 -COOH when they were used as a bio-carrier for chemiluminescence enzyme immunoassay (CLEIA). These unique bi-functionalized silica nanoparticles have many potential applications in the diagnostic and therapeutic fields. Reducing nonspecific protein adsorption and enhancing the immobilized efficiency of specific bio-probes are two of the most important issues for bio-carriers, particularly for a nanoparticle based bio-carrier. Herein, we designed and prepared a bi-functional nanoparticle with anti-fouling property and bio conjugation capacity for further bioassay by improving the short-chain zwitterionic modification strategy we have proposed previously. The heterogeneous surface of this nanoparticle showed effective anti-fouling properties both in model protein solutions and fetal bovine serum (FBS). The modified nanoparticles can also be successfully functionalized with a specific antibody for CLEIA assay with a prominent bio-detection performance even in 50% FBS. In this paper, we also investigated an unexpectedly fast hydrolysis behavior of NHS-activated carboxylic groups within the pure short-chain zwitterionic molecule that led to no protein binding in the short-chain zwitterion modified nanoparticle. Our findings pave a new way for the designing of high performance bio-carriers, demonstrating their strong potential as a robust platform for diagnosis and therapy. Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Shape control of the magnetic iron oxide nanoparticles under different chain length of reducing agents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ngoi, Kuan Hoon; Chia, Chin-Hua, E-mail: chia@ukm.edu.my; Zakaria, Sarani

2015-09-25

We report on the effect of using reducing agents with different chain-length on the synthesis of iron oxide nanoparticles by thermal decomposition of iron (III) acetylacetonate in 1-octadecene. This modification allows us to control the shape of nanoparticles into spherical and cubic iron oxide nanoparticles. The highly monodisperse 14 nm spherical nanoparticles are obtained under 1,2-dodecanediol and average 14 nm edge-length cubic iron oxide nanoparticles are obtained under 1,2-tetradecanediol. The structural characterization such as transmission electron microscope (TEM) and X-ray diffraction (XRD) shows similar properties between two particles with different shapes. The vibrating sample magnetometer (VSM) shows no significant difference between sphericalmore » and cubic nanoparticles, which are 36 emu/g and 37 emu/g respectively and superparamagnetic in nature.« less

Tunable Pickering Emulsions with Environmentally Responsive Hairy Silica Nanoparticles.

PubMed

Liu, Min; Chen, Xiaoli; Yang, Zongpeng; Xu, Zhou; Hong, Liangzhi; Ngai, To

2016-11-30

Surface modification of the nanoparticles using surface anchoring of amphiphilic polymers offers considerable scope for the design of a wide range of brush-coated hybrid nanoparticles with tunable surface wettability that may serve as new class of efficient Pickering emulsifiers. In the present study, we prepared mixed polymer brush-coated nanoparticles by grafting ABC miktoarm star terpolymers consisting of poly(ethylene glycol), polystyrene, and poly[(3-triisopropyloxysilyl)propyl methacrylate] (μ-PEG-b-PS-b-PIPSMA) on the surface of silica nanoparticles. The wettability of the as-prepared nanoparticles can be precisely tuned by a change of solvent or host-guest complexation. 1 H NMR result confirmed that such wettability change is due to the reorganization of the polymer chain at the grafted layer. We show that this behavior can be used for stabilization and switching between water-in-oil (W/O) and oil-in-water (O/W) emulsions. For hairy particles initially dispersed in oil, W/O emulsions were always obtained with collapsed PEG chains and mobile PS chains at the grafted layer. However, initially dispersing the hairy particles in water resulted in O/W emulsions with collapsed PS chains and mobile PEG chains. When a good solvent for both PS and PEG blocks such as toluene was used, W/O emulsions were always obtained no matter where the hairy particles were dispersed. The wettability of the mixed polymer brush-coated silica particles can also be tuned by host-guest complexation between PEG block and α-CD. More importantly, our result showed that surprisingly the resultant mixed brush-coated hairy nanoparticles can be employed for the one-step production of O/W/O multiple emulsions that are not attainable from conventional Pickering emulsifiers. The functionalized hairy silica nanoparticles at the oil-water interface can be further linked together utilizing poly(acrylic acid) as the reversible linker to form supramolecular colloidosomes, which show pH-dependent release of cargo.

Epigallocatechin-3-gallate (EGCG)-stabilized selenium nanoparticles coated with Tet-1 peptide to reduce amyloid-β aggregation and cytotoxicity.

PubMed

Zhang, Jingnan; Zhou, Xianbo; Yu, Qianqian; Yang, Licong; Sun, Dongdong; Zhou, Yanhui; Liu, Jie

2014-06-11

Alzheimer's disease (AD), the most common neurodegenerative disease, is caused by an accumulation of amyloid-β (Aβ) plaque deposits in the brains. Evidence is increasingly showing that epigallocatechin-3-gallate (EGCG) can partly protect cells from Aβ-mediated neurotoxicity by inhibiting Aβ aggregation. In order to better understand the process of Aβ aggregation and amyloid fibril disaggregation and reduce the cytotoxicity of EGCG at high doses, we attached EGCG onto the surface of selenium nanoparticles (EGCG@Se). Given the low delivery efficiency of EGCG@Se to the targeted cells and the involvement of selenoprotein in antioxidation and neuroprotection, which are the key factors for preventing the onset and progression of AD, we synthesized EGCG-stabilized selenium nanoparticles coated with Tet-1 peptide (Tet-1-EGCG@Se, a synthetic selenoprotein analogue), considering the affinity of Tet-1 peptide to neurons. We revealed that Tet-1-EGCG@Se can effectively inhibit Aβ fibrillation and disaggregate preformed Aβ fibrils into nontoxic aggregates. In addition, we found that both EGCG@Se and Tet-1-EGCG@Se can label Aβ fibrils with a high affinity, and Tet-1 peptides can significantly enhance the cellular uptake of Tet-1-EGCG@Se in PC12 cells rather than in NIH/3T3 cells.

Effects of Complementary DNA and Salt on the Thermoresponsiveness of Poly(N-isopropylacrylamide)-b-DNA.

PubMed

Fujita, Masahiro; Hiramine, Hayato; Pan, Pengju; Hikima, Takaaki; Maeda, Mizuo

2016-02-02

The thermoresponsive structural transition of poly(N-isopropylacrylamide) (PNIPAAm)-b-DNA copolymers was explored. Molecular assembly of the block copolymers was facilitated by adding salt, and this assembly was not nucleated by the association between DNA strands but by the coil-globule transition of PNIPAAm blocks. Below the lower critical solution temperature (LCST) of PNIPAAm, the copolymer solution remained transparent even at high salt concentrations, regardless of whether DNA was hybridized with its complementary partner to form a double-strand (or single-strand) structure. At the LCST, the hybridized copolymer assembled in spherical nanoparticles, surrounded by double-stranded DNA; subsequently, the non-cross-linking aggregation occurred, while the nanoparticles were dispersed if the salt concentration was low or DNA blocks were unhybridized. When the DNA duplex was denatured to a single-stranded state by heating, the aggregated nanoparticles redispersed owing to the recovery of the steric repulsion of the DNA strands. The changes in the steric and electrostatic effects by hybridization and the addition of salt did not result in any specific attraction between DNA strands but merely decreased the repulsive interactions. The van der Waals attraction between the nanoparticles overcame such repulsive interactions so that the non-cross-linking aggregation of the micellar particles was mediated.

Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous sample-rotated small angle x-ray scattering and electrochemical methods approach [Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous grazing transmission small angle x-ray scattering and electrochemical methods approach

DOE PAGES

Hammons, Joshua A.; Ilavsky, Jan

2017-01-18

Nanoparticle electrodeposition is a simple and scalable approach to synthesizing supported nanoparticles. Used with a deep eutectic solvent (DES), surface nanoparticles can be assembled and exhibit unique surface charge separation when the DES is adsorbed on the nanoparticle surface. Key to understanding and controlling the assembly and the capacitance is a thorough understanding of surface particle mobility and charge screening, which requires an in-situ approach. In this study, Pb particle formation, size, shape and capacitance are resolved in a 1:2 choline Cl –: urea deep eutectic solvent whilst sweeping the cell potential in the range: 0.2 V to –1.2 Vmore » (vs. Ag/AgCl). These system parameters were resolved using a complementary suite of sample-rotated small angle X-ray scattering (SR-SAXS) and electrochemical impedance spectroscopy (EIS), which are presented and discussed in detail. This approach is able to show that both particle and ion transport are impeded in the DES, as aggregation occurs over the course of 6 minutes, and dissolved Pb ions accumulate and remain near the surface after a nucleation pulse is applied. The DES-Pb interactions strongly depend on the cell potential as evidenced by the specific differential capacitance of the Pb deposit, which has a maximum value of 2.5 +/– 0.5 F g –1 at –1.0 V vs. Ag/AgCl. Together, the SR-SAXS-EIS approach is able to characterize the unique nanoparticle capacitance, mobility and ion mobility in a DES and can be used to study a wide range of nanoparticle deposition systems in-situ.« less

Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous sample-rotated small angle x-ray scattering and electrochemical methods approach [Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous grazing transmission small angle x-ray scattering and electrochemical methods approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hammons, Joshua A.; Ilavsky, Jan

Nanoparticle electrodeposition is a simple and scalable approach to synthesizing supported nanoparticles. Used with a deep eutectic solvent (DES), surface nanoparticles can be assembled and exhibit unique surface charge separation when the DES is adsorbed on the nanoparticle surface. Key to understanding and controlling the assembly and the capacitance is a thorough understanding of surface particle mobility and charge screening, which requires an in-situ approach. In this study, Pb particle formation, size, shape and capacitance are resolved in a 1:2 choline Cl –: urea deep eutectic solvent whilst sweeping the cell potential in the range: 0.2 V to –1.2 Vmore » (vs. Ag/AgCl). These system parameters were resolved using a complementary suite of sample-rotated small angle X-ray scattering (SR-SAXS) and electrochemical impedance spectroscopy (EIS), which are presented and discussed in detail. This approach is able to show that both particle and ion transport are impeded in the DES, as aggregation occurs over the course of 6 minutes, and dissolved Pb ions accumulate and remain near the surface after a nucleation pulse is applied. The DES-Pb interactions strongly depend on the cell potential as evidenced by the specific differential capacitance of the Pb deposit, which has a maximum value of 2.5 +/– 0.5 F g –1 at –1.0 V vs. Ag/AgCl. Together, the SR-SAXS-EIS approach is able to characterize the unique nanoparticle capacitance, mobility and ion mobility in a DES and can be used to study a wide range of nanoparticle deposition systems in-situ.« less

Anomalous complete opaqueness in a sparse array of gold nanoparticle chains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai Benfeng; Tsinghua-Foxconn Nanotechnology Research Center, Tsinghua University, Beijing 100084; Department of Physics and Mathematics, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu

2011-08-22

We report on an anomalous polarization-switching extinction effect in a sparse array of gold nanoparticle chains: under normal incidence of light, the array is almost transparent for one polarization; whereas it is fully opaque (with nearly zero transmittance) for the orthogonal polarization within a narrow band, even though the nanoparticles cover only a tiny fraction (say, 3.5%) of the transparent substrate surface. We reveal that the strong polarization-dependent short-range dipolar coupling and long-range radiative coupling of gold nanoparticles in this highly asymmetric array is responsible for this extraordinary effect.

Quantification of the aggregation of magnetic nanoparticles with different polymeric coatings in cell culture medium

NASA Astrophysics Data System (ADS)

Eberbeck, D.; Kettering, M.; Bergemann, C.; Zirpel, P.; Hilger, I.; Trahms, L.

2010-10-01

The knowledge of the physico-chemical characteristics of magnetic nanoparticles (MNPs) is essential to enhance the efficacy of MNP-based therapeutic treatments (e.g. magnetic heating, magnetic drug targeting). According to the literature, the MNP uptake by cells may depend on the coating of MNPs, the surrounding medium as well as on the aggregation behaviour of the MNPs. Therefore, in this study, the aggregation behaviour of MNPs in various media was investigated. MNPs with different coatings were suspended in cell culture medium (CCM) containing fetal calf serum (FCS) and the distribution of the hydrodynamic sizes was measured by magnetorelaxometry (MRX). FCS as well as bovine serum albumin (BSA) buffer (phosphate buffered saline with 0.1% bovine serum albumin) may induce MNP aggregation. Its strength depends crucially on the type of coating. The degree of aggregation in CCM depends on its FCS content showing a clear, local maximum at FCS concentrations, where the IgG concentration (part of FCS) is of the order of the MNP number concentration. Thus, we attribute the observed aggregation behaviour to the mechanism of agglutination of MNPs by serum compartments as for example IgG. No aggregation was induced for MNPs coated with dextran, polyarabic acid or sodium phosphate, respectively, which were colloidally stable in CCM.

Water chemistry controlled aggregation and photo-transformation of silver nanoparticles in environmental waters.

PubMed

Yin, Yongguang; Yang, Xiaoya; Zhou, Xiaoxia; Wang, Weidong; Yu, Sujuan; Liu, Jingfu; Jiang, Guibin

2015-08-01

The inevitable release of engineered silver nanoparticles (AgNPs) into aquatic environments has drawn great concerns about its environmental toxicity and safety. Although aggregation and transformation play crucial roles in the transport and toxicity of AgNPs, how the water chemistry of environmental waters influences the aggregation and transformation of engineered AgNPs is still not well understood. In this study, the aggregation of polyvinylpyrrolidone (PVP) coated AgNPs was investigated in eight typical environmental water samples (with different ionic strengths, hardness, and dissolved organic matter (DOM) concentrations) by using UV-visible spectroscopy and dynamic light scattering. Raman spectroscopy was applied to probe the interaction of DOM with the surface of AgNPs. Further, the photo-transformation and morphology changes of AgNPs in environmental waters were studied by UV-visible spectroscopy, inductively coupled plasma mass spectrometry, and transmission electron microscopy. The results suggested that both electrolytes (especially Ca(2+) and Mg(2+)) and DOM in the surface waters are key parameters for AgNP aggregation, and sunlight could accelerate the morphology change, aggregation, and further sedimentation of AgNPs. This water chemistry controlled aggregation and photo-transformation should have significant environmental impacts on the transport and toxicity of AgNPs in the aquatic environments. Copyright © 2015. Published by Elsevier B.V.

Star Polymers Reduce Islet Amyloid Polypeptide Toxicity via Accelerated Amyloid Aggregation.

PubMed

Pilkington, Emily H; Lai, May; Ge, Xinwei; Stanley, William J; Wang, Bo; Wang, Miaoyi; Kakinen, Aleksandr; Sani, Marc-Antonie; Whittaker, Michael R; Gurzov, Esteban N; Ding, Feng; Quinn, John F; Davis, Thomas P; Ke, Pu Chun

2017-12-11

Protein aggregation into amyloid fibrils is a ubiquitous phenomenon across the spectrum of neurodegenerative disorders and type 2 diabetes. A common strategy against amyloidogenesis is to minimize the populations of toxic oligomers and protofibrils by inhibiting protein aggregation with small molecules or nanoparticles. However, melanin synthesis in nature is realized by accelerated protein fibrillation to circumvent accumulation of toxic intermediates. Accordingly, we designed and demonstrated the use of star-shaped poly(2-hydroxyethyl acrylate) (PHEA) nanostructures for promoting aggregation while ameliorating the toxicity of human islet amyloid polypeptide (IAPP), the peptide involved in glycemic control and the pathology of type 2 diabetes. The binding of PHEA elevated the β-sheet content in IAPP aggregates while rendering a new morphology of "stelliform" amyloids originating from the polymers. Atomistic molecular dynamics simulations revealed that the PHEA arms served as rodlike scaffolds for IAPP binding and subsequently accelerated IAPP aggregation by increased local peptide concentration. The tertiary structure of the star nanoparticles was found to be essential for driving the specific interactions required to impel the accelerated IAPP aggregation. This study sheds new light on the structure-toxicity relationship of IAPP and points to the potential of exploiting star polymers as a new class of therapeutic agents against amyloidogenesis.

A mobile system for a comprehensive online-characterization of nanoparticle aggregates based on wide-angle light scattering and laser-induced incandescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huber, Franz J. T.; Will, Stefan, E-mail: stefan.will@fau.de; Erlangen Graduate School in Advanced Optical Technologies

A mobile demonstrator for the comprehensive online-characterization of gas-borne nanoparticle aggregates is presented. Two optical measurement techniques are combined, both utilizing a pulsed Nd:YAG laser as light source. Aggregate size and fractal dimension are measured by Wide-Angle Light Scattering (WALS). An ellipsoidal mirror images elastically scattered light from scattering angles between 10° and 165° onto a CCD-camera chip resulting in an almost complete scattering diagram with high angular resolution. Primary particle size and volume fraction are measured by time-resolved Laser-Induced Incandescence (TiRe-LII). Here, particles are heated up to about 3000 K by the short laser pulse, the enhanced thermal radiationmore » signal is detected with gated photomultiplier tubes. Analysis of the signal decay time and maximum LII-signal allows for the determination of primary particle diameter and volume fraction. The performance of the system is demonstrated by combined measurements on soot nanoparticle aggregates from a soot aerosol generator. Particle and aggregate sizes are varied by using different equivalence ratios of the combustion in the generator. Soot volume fraction can be adjusted by different levels of dilution with air. Online-measurements were carried out demonstrating the favorable performance of the system and the potential for industrial applications such as process control and product development. The particle properties obtained are confirmed through transmission electron microscopy analysis on representative samples.« less

A mobile system for a comprehensive online-characterization of nanoparticle aggregates based on wide-angle light scattering and laser-induced incandescence.

PubMed

Huber, Franz J T; Altenhoff, Michael; Will, Stefan

2016-05-01

A mobile demonstrator for the comprehensive online-characterization of gas-borne nanoparticle aggregates is presented. Two optical measurement techniques are combined, both utilizing a pulsed Nd:YAG laser as light source. Aggregate size and fractal dimension are measured by Wide-Angle Light Scattering (WALS). An ellipsoidal mirror images elastically scattered light from scattering angles between 10° and 165° onto a CCD-camera chip resulting in an almost complete scattering diagram with high angular resolution. Primary particle size and volume fraction are measured by time-resolved Laser-Induced Incandescence (TiRe-LII). Here, particles are heated up to about 3000 K by the short laser pulse, the enhanced thermal radiation signal is detected with gated photomultiplier tubes. Analysis of the signal decay time and maximum LII-signal allows for the determination of primary particle diameter and volume fraction. The performance of the system is demonstrated by combined measurements on soot nanoparticle aggregates from a soot aerosol generator. Particle and aggregate sizes are varied by using different equivalence ratios of the combustion in the generator. Soot volume fraction can be adjusted by different levels of dilution with air. Online-measurements were carried out demonstrating the favorable performance of the system and the potential for industrial applications such as process control and product development. The particle properties obtained are confirmed through transmission electron microscopy analysis on representative samples.

A mobile system for a comprehensive online-characterization of nanoparticle aggregates based on wide-angle light scattering and laser-induced incandescence

NASA Astrophysics Data System (ADS)

Huber, Franz J. T.; Altenhoff, Michael; Will, Stefan

2016-05-01

A mobile demonstrator for the comprehensive online-characterization of gas-borne nanoparticle aggregates is presented. Two optical measurement techniques are combined, both utilizing a pulsed Nd:YAG laser as light source. Aggregate size and fractal dimension are measured by Wide-Angle Light Scattering (WALS). An ellipsoidal mirror images elastically scattered light from scattering angles between 10° and 165° onto a CCD-camera chip resulting in an almost complete scattering diagram with high angular resolution. Primary particle size and volume fraction are measured by time-resolved Laser-Induced Incandescence (TiRe-LII). Here, particles are heated up to about 3000 K by the short laser pulse, the enhanced thermal radiation signal is detected with gated photomultiplier tubes. Analysis of the signal decay time and maximum LII-signal allows for the determination of primary particle diameter and volume fraction. The performance of the system is demonstrated by combined measurements on soot nanoparticle aggregates from a soot aerosol generator. Particle and aggregate sizes are varied by using different equivalence ratios of the combustion in the generator. Soot volume fraction can be adjusted by different levels of dilution with air. Online-measurements were carried out demonstrating the favorable performance of the system and the potential for industrial applications such as process control and product development. The particle properties obtained are confirmed through transmission electron microscopy analysis on representative samples.

Does moving up a food chain increase aggregation in parasites?

PubMed Central

Lester, R. J. G.

2016-01-01

General laws in ecological parasitology are scarce. Here, we evaluate data on numbers of fish parasites published by over 200 authors to determine whether acquiring parasites via prey is associated with an increase in parasite aggregation. Parasite species were grouped taxonomically to produce 20 or more data points per group as far as possible. Most parasites that remained at one trophic level were less aggregated than those that had passed up a food chain. We use a stochastic model to show that high parasite aggregation in predators can be solely the result of the accumulation of parasites in their prey. The model is further developed to show that a change in the predators feeding behaviour with age may further increase parasite aggregation. PMID:27170651

Fluorimetric detection of Sn(2+) ion in aqueous medium using Salicylaldehyde based nanoparticles and application to natural samples analysis.

PubMed

Patil, Kishor S; Mahajan, Prasad G; Patil, Shivajirao R

2017-01-05

The fluorescent 2-[(E)-(2-phenylhydrazinylidene)methyl]phenol nanoparticles (PHPNPs) were prepared by a simple reprecipitation method. The prepared PHPNPs examined by Dynamic Light Scattering show narrower particle size distribution having an average particle size of 93.3nm. The Scanning Electron Microphotograph shows distinct spherical shaped morphology of nanoparticles. The blue shift in UV-absorption and fluorescence spectra of PHPNPs with respect to corresponding spectra of PHP in acetone solution indicates H- aggregates and Aggregation Induced Enhanced Emission (AIEE) for nanoparticles. The nanoparticles show selective tendency towards the recognition of Sn(2+) ions by enhancing the fluorescence intensity preference to Cu(2+), Fe(3+), Fe(2+), Ni(2+), NH4(+), Ca(2+), Pb(2+), Hg(2+) and Zn(2+) ions, which actually seem to quench the fluorescence of nanoparticles. The studies on Langmuir adsorption plot, fluorescence lifetime of PHPNPs, DLS-Zeta sizer, UV-visible and fluorescence titration with and without Sn(2+) helped to propose a suitable mechanism of fluorescence enhancement of nanoparticles by Sn(2+) and their binding ability during complexation. The fluorescence enhancement effect of PHPNPs induced by Sn(2+) is further used to develop an analytical method for detection of Sn(2+) from aqueous medium in environmental samples. Copyright © 2016 Elsevier B.V. All rights reserved.

Fluorimetric detection of Sn2 + ion in aqueous medium using Salicylaldehyde based nanoparticles and application to natural samples analysis

NASA Astrophysics Data System (ADS)

Patil, Kishor S.; Mahajan, Prasad G.; Patil, Shivajirao R.

2017-01-01

The fluorescent 2-[(E)-(2-phenylhydrazinylidene)methyl]phenol nanoparticles (PHPNPs) were prepared by a simple reprecipitation method. The prepared PHPNPs examined by Dynamic Light Scattering show narrower particle size distribution having an average particle size of 93.3 nm. The Scanning Electron Microphotograph shows distinct spherical shaped morphology of nanoparticles. The blue shift in UV-absorption and fluorescence spectra of PHPNPs with respect to corresponding spectra of PHP in acetone solution indicates H- aggregates and Aggregation Induced Enhanced Emission (AIEE) for nanoparticles. The nanoparticles show selective tendency towards the recognition of Sn2 + ions by enhancing the fluorescence intensity preference to Cu2 +, Fe3 +, Fe2 +, Ni2 +, NH4+, Ca2 +, Pb2 +, Hg2 + and Zn2 + ions, which actually seem to quench the fluorescence of nanoparticles. The studies on Langmuir adsorption plot, fluorescence lifetime of PHPNPs, DLS-Zeta sizer, UV-visible and fluorescence titration with and without Sn2 + helped to propose a suitable mechanism of fluorescence enhancement of nanoparticles by Sn2 + and their binding ability during complexation. The fluorescence enhancement effect of PHPNPs induced by Sn2 + is further used to develop an analytical method for detection of Sn2 + from aqueous medium in environmental samples.

Natural colloids are the dominant factor in the sedimentation of nanoparticles.

PubMed

Quik, Joris T K; Stuart, Martien Cohen; Wouterse, Marja; Peijnenburg, Willie; Hendriks, A Jan; van de Meent, Dik

2012-05-01

Estimating the environmental exposure to manufactured nanomaterials is part of risk assessment. Because nanoparticles aggregate with each other (homoaggregation) and with other particles (heteroaggregation), the main route of the removal of most nanoparticles from water is aggregation, followed by sedimentation. The authors used water samples from two rivers in Europe, the Rhine and the Meuse. To distinguish between small (mainly natural organic matter [NOM]) particles and the remainder of the natural colloids present, both filtered and unfiltered river water was used to prepare the particle suspensions. The results show that the removal of nanoparticles from natural river water follows first-order kinetics toward a residual concentration. This was measured in river water with less than 1 mg L(-1) CeO(2) nanoparticles. The authors inferred that the heteroaggregation with or deposition onto the solid fraction of natural colloids was the main mechanism causing sedimentation in relation to homoaggregation. In contrast, the NOM fraction in filtered river water stabilized the residual nanoparticles against further sedimentation for up to 12 d. In 10 mg L(-1) and 100 mg L(-1) CeO(2) nanoparticle suspensions, homoaggregation is likely the main mechanism leading to sedimentation. The proposed model could form the basis for improved exposure assessment for nanomaterials. Copyright © 2012 SETAC.

Directed deposition of inorganic oxide networks on patterned polymer templates

NASA Astrophysics Data System (ADS)

Ford, Thomas James Robert

Inspired by nature, we have successfully directed the deposition of inorganic oxide materials on polymer templates via a combination of top-down and bottom-up fabrication methods. We have functionally mimicked the hierarchical silica exoskeletons of diatoms, where specialized proteins chaperone the condensation of silicic acid into nanoscale silica networks confined by microscopic vesicle walls. We replaced the proteins with functionally analogous polyamines and vesicles with lithographically defined polymer templates. We grafted the polyamines either to the surface or throughout the template by changing the template chemistry and altering our grafting strategy. Exposure to an inorganic oxide precursor solution led to electrostatic aggregation at the polyamine chains, catalyzing hydrolysis and condensation to form long-range inorganic oxide nanoparticle networks. Grafted to epoxy surfaces, swelling effects and the hyperbranched brush morphology lead to the formation of nanofruit features that generated thin, conformal inorganic coatings. When the polyamines were grafted throughout hydrogel templates, we obtained composite networks that yielded faithful inorganic replicas of the original patterns. By varying the polyamine chain length and combustion parameters, we controlled the nanoparticle size, morphology, and crystalline phase. The polyamine morphology affected the resulting inorganic network in both fabrication schemes and we could control the depostion over multiple length scales. Because our methods were compatible with a variety of lithographic methods, we were able to generate inorganic replicas of 1D, 2D, and 3D polymer structures. These may be used for a wide range of applications, including sensing, catalysis, photonic, phononic, photovoltaic, and others that require well-defined inorganic structures.

Entropic depletion in colloidal suspensions and polymer liquids: Role of nanoparticle surface topography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banerjee, Debapriya; Yang, Jian; Schweizer, Kenneth S.

2015-01-01

Here, we employ a hybrid Monte Carlo plus integral equation theory approach to study how dense fluids of small nanoparticles or polymer chains mediate entropic depletion interactions between topographically rough particles where all interaction potentials are hard core repulsion. The corrugated particle surfaces are composed of densely packed beads which present variable degrees of controlled topographic roughness and free volume associated with their geometric crevices. This pure entropy problem is characterized by competing ideal translational and (favorable and unfavorable) excess entropic contributions. Surface roughness generically reduces particle depletion aggregation relative to the smooth hard sphere case. However, the competition betweenmore » ideal and excess packing entropy effects in the bulk, near the particle surface and in the crevices, results in a non-monotonic variation of the particle-monomer packing correlation function as a function of the two dimensionless length scale ratios that quantify the effective surface roughness. As a result, the inter-particle potential of mean force (PMF), second virial coefficient, and spinodal miscibility volume fraction vary non-monotonically with the surface bead to monomer diameter and particle core to surface bead diameter ratios. A miscibility window is predicted corresponding to an optimum degree of surface roughness that completely destroys depletion attraction resulting in a repulsive PMF. Variation of the (dense) matrix packing fraction can enhance or suppress particle miscibility depending upon the amount of surface roughness. Connecting the monomers into polymer chains destabilizes the system via enhanced contact depletion attraction, but the non-monotonic variations with surface roughness metrics persist.« less

The biomolecular corona of nanoparticles in circulating biological media

NASA Astrophysics Data System (ADS)

Pozzi, D.; Caracciolo, G.; Digiacomo, L.; Colapicchioni, V.; Palchetti, S.; Capriotti, A. L.; Cavaliere, C.; Zenezini Chiozzi, R.; Puglisi, A.; Laganà, A.

2015-08-01

When nanoparticles come into contact with biological media, they are covered by a biomolecular `corona', which confers a new identity to the particles. In all the studies reported so far nanoparticles are incubated with isolated plasma or serum that are used as a model for protein adsorption. Anyway, bodily fluids are dynamic in nature so the question arises on whether the incubation protocol, i.e. dynamic vs. static incubation, could affect the composition and structure of the biomolecular corona. Here we let multicomponent liposomes interact with fetal bovine serum (FBS) both statically and dynamically, i.e. in contact with circulating FBS (~40 cm s-1). The structure and composition of the liposome-protein corona, as determined by dynamic light scattering, electrophoretic light scattering and liquid chromatography tandem mass spectrometry, were found to be dependent on the incubation protocol. Specifically, following dynamic exposure to FBS, multicomponent liposomes were less enriched in complement proteins and appreciably more enriched in apolipoproteins and acute phase proteins (e.g. alpha-1-antitrypsin and inter-alpha-trypsin inhibitor heavy chain H3) that are involved in relevant interactions between nanoparticles and living systems. Supported by our results, we speculate that efficient predictive modeling of nanoparticle behavior in vivo will require accurate knowledge of nanoparticle-specific protein fingerprints in circulating biological media.When nanoparticles come into contact with biological media, they are covered by a biomolecular `corona', which confers a new identity to the particles. In all the studies reported so far nanoparticles are incubated with isolated plasma or serum that are used as a model for protein adsorption. Anyway, bodily fluids are dynamic in nature so the question arises on whether the incubation protocol, i.e. dynamic vs. static incubation, could affect the composition and structure of the biomolecular corona. Here we let multicomponent liposomes interact with fetal bovine serum (FBS) both statically and dynamically, i.e. in contact with circulating FBS (~40 cm s-1). The structure and composition of the liposome-protein corona, as determined by dynamic light scattering, electrophoretic light scattering and liquid chromatography tandem mass spectrometry, were found to be dependent on the incubation protocol. Specifically, following dynamic exposure to FBS, multicomponent liposomes were less enriched in complement proteins and appreciably more enriched in apolipoproteins and acute phase proteins (e.g. alpha-1-antitrypsin and inter-alpha-trypsin inhibitor heavy chain H3) that are involved in relevant interactions between nanoparticles and living systems. Supported by our results, we speculate that efficient predictive modeling of nanoparticle behavior in vivo will require accurate knowledge of nanoparticle-specific protein fingerprints in circulating biological media. Electronic supplementary information (ESI) available: Table S1: estimation of the corona thickness, sk, of elementary units (liposome-protein corona) clustered in k-fold equilibrium aggregates (t > 15 min). Tables S2 and S3: the full list of the most abundant corona proteins identified on the surface of multicomponent liposomes following dynamic and static incubation with fetal bovine serum. Table S4: the list of the unique proteins bound to MC liposomes following 90 min incubation with FBS under dynamic and static incubation. See DOI: 10.1039/c5nr03701h

Protein Aggregation and Its Impact on Product Quality

PubMed Central

Roberts, Christopher J.

2014-01-01

Protein pharmaceutical products are typically active as folded monomers that are composed of one or more protein chains, such as the heavy and light chains in monoclonal antibodies that are a mainstay of current drug pipelines. There are numerous possible aggregated states for a given protein, some of which are potentially useful, while most of which are considered deleterious from the perspective of pharmaceutical product quality and performance. This review provides an overview of how and why different aggregated states of proteins occur, how this potentially impacts product quality and performance, fundamental approaches to control aggregate formation, and the practical approaches that are currently used in the pharmaceutical industry. PMID:25173826

Thermoswitchable catalysis controlled by reversible dispersion/aggregation change of nanoreactors in the presence of α-CD polymers

NASA Astrophysics Data System (ADS)

Li, Yinfeng; Hu, Jie; Niu, Chengrong; Leng, Jinghang; Li, Songjun

2018-06-01

The present work was aimed at preparing a thermosensitive nanoreactor system which could adjust its dispersion/aggregation status according to external temperature change to achieve the switchable catalysis. The mesoporous silica nanoparticle (MSNP) was selected as the framework material of the nanoreactor, and Ag nanoparticles were encapsulated in the mesoporous silica by an in situ reaction. Dodecyl groups were introduced onto MSNP surface, which could transform reversibly between complexation and disassociation with α-cyclodextrin (CD) cavity upon temperature change. It was found that the nanoreactors aggregated and the catalysis was effectively switched ‘off’ in the presence of CD polymers at low temperature (20 °C). However, when the temperature increased to 50 °C, the nanoreactors redispersed and catalysis successfully switched ‘on’.

Thermoswitchable catalysis controlled by reversible dispersion/aggregation change of nanoreactors in the presence of α-CD polymers.

PubMed

Li, Yinfeng; Hu, Jie; Niu, Chengrong; Leng, Jinghang; Li, Songjun

2018-06-01

The present work was aimed at preparing a thermosensitive nanoreactor system which could adjust its dispersion/aggregation status according to external temperature change to achieve the switchable catalysis. The mesoporous silica nanoparticle (MSNP) was selected as the framework material of the nanoreactor, and Ag nanoparticles were encapsulated in the mesoporous silica by an in situ reaction. Dodecyl groups were introduced onto MSNP surface, which could transform reversibly between complexation and disassociation with α-cyclodextrin (CD) cavity upon temperature change. It was found that the nanoreactors aggregated and the catalysis was effectively switched 'off' in the presence of CD polymers at low temperature (20 °C). However, when the temperature increased to 50 °C, the nanoreactors redispersed and catalysis successfully switched 'on'.

Determination of pyrophosphate and sulfate using polyhexamethylene guanidine hydrochloride-stabilized silver nanoparticles.

PubMed

Terenteva, E A; Apyari, V V; Dmitrienko, S G; Garshev, A V; Volkov, P A; Zolotov, Yu A

2018-04-01

Positively charged polyhexamethylene guanidine hydrochloride-stabilized silver nanoparticles (PHMG-AgNPs) were prepared and applied as a colorimetric probe for single-step determination of pyrophosphate and sulfate. The approach is based on the nanoparticles aggregation leading to change in their absorption spectra and color of the solution. Due to both electrostatic and steric stabilization these nanoparticles show decreased sensitivity relatively to many common anions, which allows for simple and rapid direct single-step determination of pyrophosphate and sulfate. Effects of different factors (time of interaction, pH, concentrations of anions and the nanoparticles) on aggregation of PHMG-AgNPs and analytical performance of the procedure were investigated. The method allows for the determination of pyrophosphate and sulfate in the range of 0.16-2μgmL -1 and 20-80μgmL -1 with RSD of 2-5%, respectively. The analysis can be performed using either spectrophotometry or naked-eye detection. Practical application of the method was shown by the example of pyrophosphate determination in baking powder sample. Copyright © 2017 Elsevier B.V. All rights reserved.

Protonation of epigallocatechin-3-gallate (EGCG) results in massive aggregation and reduced oral bioavailability of EGCG-dispersed selenium nanoparticles.

PubMed

Wu, Shanshan; Sun, Kang; Wang, Xin; Wang, Dongxu; Wan, Xiaochun; Zhang, Jinsong

2013-07-31

The current results show that epigallocatechin-3-gallate (EGCG), in the form of phenolic anions at pH 8.0, can effectively disperse selenium nanoparticles. However, at gastric juice pH (1.0), the EGCG-dispersed selenium nanoparticles (referred to as E-Se) extensively aggregated, so that nano features largely disappeared. This demonstrates that deprotonated phenolic anions of EGCG play an important role in maintaining E-Se stability and suggests that E-Se would suffer from reduced oral bioavailability. To validate this conjecture, size-equivalent E-Se and bovine serum albumin (BSA)-dispersed selenium nanoparticles (B-Se), whose physicochemical properties were not altered at pH 1.0, were orally administered to selenium-deficient mice. In comparison to B-Se, the bioavailabilities of E-Se as indicated with hepatic and renal glutathione peroxidase activity and hepatic selenium levels were significantly (p < 0.01) reduced by 39, 32, and 31%, respectively. Therefore, the present study reveals that size-equivalent selenium nanoparticles prepared by different dispersers do not necessarily guarantee equivalent oral bioavailability.

In vivo tumor-targeted dual-modal fluorescence/CT imaging using a nanoprobe co-loaded with an aggregation-induced emission dye and gold nanoparticles.

PubMed

Zhang, Jimei; Li, Chan; Zhang, Xu; Huo, Shuaidong; Jin, Shubin; An, Fei-Fei; Wang, Xiaodan; Xue, Xiangdong; Okeke, C I; Duan, Guiyun; Guo, Fengguang; Zhang, Xiaohong; Hao, Jifu; Wang, Paul C; Zhang, Jinchao; Liang, Xing-Jie

2015-02-01

As an intensely studied computed tomography (CT) contrast agent, gold nanoparticle has been suggested to be combined with fluorescence imaging modality to offset the low sensitivity of CT. However, the strong quenching of gold nanoparticle on fluorescent dyes requires complicated design and shielding to overcome. Herein, we report a unique nanoprobe (M-NPAPF-Au) co-loading an aggregation-induced emission (AIE) red dye and gold nanoparticles into DSPE-PEG(2000) micelles for dual-modal fluorescence/CT imaging. The nanoprobe was prepared based on a facile method of "one-pot ultrasonic emulsification". Surprisingly, in the micelles system, fluorescence dye (NPAPF) efficiently overcame the strong fluorescence quenching of shielding-free gold nanoparticles and retained the crucial AIE feature. In vivo studies demonstrated the nanoprobe had superior tumor-targeting ability, excellent fluorescence and CT imaging effects. The totality of present studies clearly indicates the significant potential application of M-NPAPF-Au as a dual-modal non-invasive fluorescence/X-ray CT nanoprobe for in vivo tumor-targeted imaging and diagnosis. Copyright © 2014 Elsevier Ltd. All rights reserved.

A universal approach to the synthesis of nanodendrites of noble metals.

PubMed

Feng, Yan; Ma, Xiaohong; Han, Lin; Peng, Zhijian; Yang, Jun

2014-06-07

Nanomaterials usually exhibit structure-dependent catalytic activity, selectivity, and stability. Herein, we report a universal approach for the synthesis of noble metal nanoparticles with a dendritic structure, which is based on the reduction of metal acetylacetonate precursors in oleylamine at a temperature of 160 °C. In this strategy, the metal acetylacetonate precursors are reduced into metal atoms by oleylamine and grow into metal nanoparticles, while oleylamine is simultaneously converted into oleylamide to protect the nanoparticles. The competition between particle aggregation and oleylamide passivation is essential to the formation of a large number of particle aggregates, which eventually grow into nanodendrites via Ostwald ripening process. In particular, in comparison with commercial PtRu/C catalysts, the alloy PtRuOs nanodendrites exhibited superior catalytic activity toward methanol oxidation.

Optical devices and methods employing nanoparticles, microcavities, and semicontinuous metal films

NASA Technical Reports Server (NTRS)

Shalaev, Vladimir M. (Inventor); Sarychev, Andrey K. (Inventor); Armstrong, Robert L. (Inventor); Smith, Harold V. (Inventor); Ying, Z. Charles (Inventor)

2006-01-01

An optical sensing enhancing material (and corresponding method of making) comprising: a medium, the medium comprising a plurality of aggregated nanoparticles comprising fractals; and a microcavity, wherein the medium is located in a vicinity of the microcavity. Also an optical sensor and sensing method comprising: providing a doped medium, the medium comprising a plurality of aggregated nanoparticles comprising fractals, with the material; locating the doped medium in the vicinity of a microcavity; exciting the doped medium with a light source; and detecting light reflected from the doped medium. Also an optical sensing enhancing material comprising a medium, the medium comprising a semicontinuous metal film of randomly distributed metal particles and their clusters at approximately their percolation threshold. The medium preferably additionally comprises a microcavity/microresonator. Also devices and methods employing such material.

Facile, one-pot synthesis, and antibacterial activity of mesoporous silica nanoparticles decorated with well-dispersed silver nanoparticles.

PubMed

Tian, Yue; Qi, Juanjuan; Zhang, Wei; Cai, Qiang; Jiang, Xingyu

2014-08-13

In this study, we exploit a facile, one-pot method to prepare MCM-41 type mesoporous silica nanoparticles decorated with silver nanoparticles (Ag-MSNs). Silver nanoparticles with diameter of 2-10 nm are highly dispersed in the framework of mesoporous silica nanoparticles. These Ag-MSNs possess an enhanced antibacterial effect against both Gram-positive and Gram-negative bacteria by preventing the aggregation of silver nanoparticles and continuously releasing silver ions for one month. The cytotoxicity assay indicates that the effective antibacterial concentration of Ag-MSNs shows little effect on human cells. This report describes an efficient and economical route to synthesize mesoporous silica nanoparticles with uniform silver nanoparticles, and these nanoparticles show promising applications as antibiotics.

Magnetic filtration of phase separating ferrofluids: From basic concepts to microfluidic device

NASA Astrophysics Data System (ADS)

Kuzhir, P.; Magnet, C.; Ezzaier, H.; Zubarev, A.; Bossis, G.

2017-06-01

In this work, we briefly review magnetic separation of ferrofluids composed of large magnetic particles (60 nm of the average size) possessing an induced dipole moment. Such ferrofluids exhibit field-induced phase separation at relatively low particle concentrations (∼0.8 vol%) and magnetic fields (∼10 kA/m). Particle aggregates appearing during the phase separation are extracted from the suspending fluid by magnetic field gradients much easier than individual nanoparticles in the absence of phase separation. Nanoparticle capture by a single magnetized microbead and by multi-collector systems (packed bed of spheres and micro-pillar array) has been studied both experimentally and theoretically. Under flow and magnetic fields, the particle capture efficiency Λ decreases with an increasing Mason number for all considered geometries. This decrease may become stronger for aggregated magnetic particles (Λ ∝Ma-1.7) than for individual ones (Λ ∝Ma-1) if the shear fields are strong enough to provoke aggregate rupture. These results can be useful for development of new magneto-microfluidic immunoassays based on magnetic nanoparticles offering a much better sensitivity as compared to presently used magnetic microbeads.

Synthesis and characterization of superparamagnetic iron oxide nanoparticles as calcium-responsive MRI contrast agents

NASA Astrophysics Data System (ADS)

Xu, Pengfei; Shen, Zhiwei; Zhang, Baolin; Wang, Jun; Wu, Renhua

2016-12-01

Superparamagnetic iron oxide nanoparticles (SPIONs) as T2 contrast agents have great potential to sense calcium ion (Ca2+) using magnetic resonance imaging (MRI). Here we prepared calcium-responsive SPIONs for MRI, formed by combining poly(ethylene glycol) (PEG) and polyethylenimine (PEI) coated iron oxide nanoparticle (PEI/PEG-SPIONs) contrast agents with the straightforward calcium-sensing compound EGTA (ethylene glycol tetraacetic acid). EGTA was conjugated onto PEI/PEG-SPIONs using EDC/sulfo-NHS method. EGTA-SPIONs were characterized using TEM, XPS, DSL, TGA and SQUIID. DSL results show that the SPIONs aggregate in the presence of Ca2+. MRI analyses indicate that the water proton T2 relaxation rates in HEPES suspensions of the EGTA-SPIONs significantly increase with the calcium concentration because the SPIONs aggregate in the presence of Ca2+. The T2 values decreased 25% when Ca2+ concentration decreased from 1.2 to 0.8 mM. The aggregation of EGTA-SPIONs could be reversed by EDTA. EGTA-SPIONs have potential as smart contrast agents for Ca2+-sensitive MRI.

Superhydrophobic Surfaces with Very Low Hysteresis Prepared by Aggregation of Silica Nanoparticles During In Situ Urea-Formaldehyde Polymerization.

PubMed

Diwan, Anubhav; Jensen, David S; Gupta, Vipul; Johnson, Brian I; Evans, Delwyn; Telford, Clive; Linford, Matthew R

2015-12-01

We present a new method for the preparation of superhydrophobic materials by in situ aggregation of silica nanoparticles on a surface during a urea-formaldehyde (UF) polymerization. This is a one-step process in which a two-tier topography is obtained. The polymerization is carried out for 30, 60, 120, 180, and 240 min on silicon shards. Silicon surfaces are sintered to remove the polymer. SEM and AFM show both an increase in the area covered by the nanoparticles and their aggregation with increasing polymerization time. Chemical vapor deposition of a fluorinated silane in the presence of a basic catalyst gives these surfaces hydrophobicity. Deposition of this low surface energy silane is confirmed by the F 1s signal in XPS. The surfaces show advancing water contact angles in excess of 160 degrees with very low hysteresis (< 7) after 120 min and 60 min polymerization times for 7 nm and 14 nm silica, respectively. Depositions are successfully demonstrated on glass substrates after they are primed with a UF polymer layer. Superhydrophobic surfaces can also be prepared on unsintered substrates.

Dispersed synthesis of uniform Fe3O4 magnetic nanoparticles via in situ decomposition of iron precursor along cotton fibre for Sudan dyes analysis in food samples.

PubMed

Bentahir, Yassine; Elmarhoum, Said; Salghi, Rachid; Algarra, Manuel; Ríos, Angel; Zougagh, Mohammed

2017-11-01

Fe 3 O 4 magnetic nanoparticles, with a negative charge surface, are known to have efficient adsorbent properties, but they tend to be agglomerated into larger aggregates or flocs, which can cause loss of specific area. The addition of cotton fibre, as a stabiliser in preparation of the Fe 3 O 4 nanoparticles, is able to efficiently reduce particle aggregation, and thus, effective particle size, resulting in much greater specific surface area and adsorption sites. Fe 3 O 4 nanoparticles synthesis was accomplished by in situ high-temperature decomposition of the precursor ferric ion in the presence of cotton fibre and ethylene glycol solvent. The morphology of Fe 3 O 4 nanoparticles was characterised by field emission scanning electron microscopy and X-ray diffraction, which confirmed that the magnetic nanoparticles are highly dispersed. These Fe 3 O 4 nanoparticles were used for clean-up and pre-concentration of Sudan dyes in chilli and hot red sauces, prior to their determination by capillary liquid chromatography diode array detection. A comparative study of analyte pre-concentration was conducted with magnetic nanoparticles prepared with and without cotton fibre showing that both solid phases adsorb the analytes, but higher recoveries were obtained when using cotton fibre which therefore was selected for extraction of Sudan dyes.

Synthesis of noble metal nanoparticles

NASA Astrophysics Data System (ADS)

Bahadory, Mozhgan

Improved methods were developed for the synthesis of noble metal nanoparticles. Laboratory experiments were designed for introducing of nanotechnology into the undergraduate curriculum. An optimal set of conditions for the synthesis of clear yellow colloidal silver was investigated. Silver nanoparticles were obtained by borohydride reduction of silver nitrate, a method which produces particles with average size of 12+/-2 nm, determined by Transmission Electron Microscopy (TEM). The plasmon absorbance is at 397 nm and the peak width at half maximum (PWHM) is 70-75 nm. The relationship between aggregation and optical properties was determined along with a method to protect the particles using polyvinylpyrrolidone (PVP). A laboratory experiment was designed in which students synthesize yellow colloidal silver, estimate particle size using visible spectroscopy, and study aggregation effects. The synthesis of the less stable copper nanoparticles is more difficult because copper nanopaticles are easily oxidized. Four methods were used for the synthesis of copper nanoparticles, including chemical reduction with sodium borohydride, sodium borohydride with potassium iodide, isopropyl alcohol with cetyltrimethylammonium bormide (CTAB) and reducing sugars. The latter method was also the basis for an undergraduate laboratory experiment. For each reaction, the dependence of stability of the copper nanoparticles on reagent concentrations, additives, relative amounts of reactants, and temperature is explored. Atomic force microscopy (AFM), TEM and UV-Visible Spectroscopy were used to characterize the copper nanoparticles. A laboratory experiment to produce copper nanoparticles from household chemicals was developed.

Anti-Adhesive Behaviors between Solid Hydrate and Liquid Aqueous Phase Induced by Hydrophobic Silica Nanoparticles.

PubMed

Min, Juwon; Baek, Seungjun; Somasundaran, P; Lee, Jae W

2016-09-20

This study introduces an "anti-adhesive force" at the interface of solid hydrate and liquid solution phases. The force was induced by the presence of hydrophobic silica nanoparticles or one of the common anti-agglomerants (AAs), sorbitan monolaurate (Span 20), at the interface. The anti-adhesive force, which is defined as the maximum pushing force that does not induce the formation of a capillary bridge between the cyclopentane (CP) hydrate particle and the aqueous solution, was measured using a microbalance. Both hydrophobic silica nanoparticles and Span 20 can inhibit adhesion between the CP hydrate probe and the aqueous phase because silica nanoparticles have an aggregative property at the interface, and Span 20 enables the hydrate surface to be wetted with oil. Adding water-soluble sodium dodecyl sulfate (SDS) to the nanoparticle system cannot affect the aggregative property or the distribution of silica nanoparticles at the interface and, thus, cannot change the anti-adhesive effect. However, the combined system of Span 20 and SDS dramatically reduces the interfacial tension: emulsion drops were formed at the interface without any energy input and were adsorbed on the CP hydrate surface, which can cause the growth of hydrate particles. Silica nanoparticles have a good anti-adhesive performance with a relatively smaller dosage and are less influenced by the presence of molecular surfactants; consequently, these nanoparticles may have a good potential for hydrate inhibition as AAs.

Alterations in Physical State of Silver Nanoparticles Exposed to Synthetic Human Stomach Fluid

EPA Science Inventory

The bioavailability of ingested silver nanoparticles (AgNPs) depends in large part on initial particle size, shape and surface coating, properties which will influence aggregation, solubility and chemical composition during transit of the gastrointestinal tract. Citrate-stabilize...

Phase stability and dynamics of entangled polymer-nanoparticle composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mangal, Rahul; Srivastava, Samanvaya; Archer, Lynden A.

Nanoparticle–polymer composites, or polymer–nanoparticle composites (PNCs), exhibit unusual mechanical and dynamical features when the particle size approaches the random coil dimensions of the host polymer. Here, we harness favourable enthalpic interactions between particle-tethered and free, host polymer chains to create model PNCs, in which spherical nanoparticles are uniformly dispersed in high molecular weight entangled polymers. Investigation of the mechanical properties of these model PNCs reveals that the nanoparticles have profound effects on the host polymer motions on all timescales. On short timescales, nanoparticles slow-down local dynamics of the host polymer segments and lower the glass transition temperature. On intermediate timescales,more » where polymer chain motion is typically constrained by entanglements with surrounding molecules, nanoparticles provide additional constraints, which lead to an early onset of entangled polymer dynamics. Finally, on long timescales, nanoparticles produce an apparent speeding up of relaxation of their polymer host.« less

Regime of aggregate structures and magneto-rheological characteristics of a magnetic rod-like particle suspension: Monte Carlo and Brownian dynamics simulations

NASA Astrophysics Data System (ADS)

Okada, Kazuya; Satoh, Akira

2017-09-01

In the present study, we address a suspension composed ferromagnetic rod-like particles to elucidate a regime change in the aggregate structures and the magneto-rheological characteristics. Monte Carlo simulations have been employed for investigating the aggregate structures in thermodynamic equilibrium, and Brownian dynamics simulations for magneto-rheological features in a simple shear flow. The main results obtained here are summarized as follows. For the case of thermodynamic equilibrium, the rod-like particles aggregate to form thick chain-like clusters and the neighboring clusters incline in opposite directions. If the external magnetic field is increased, the thick chain-like clusters in the magnetic field direction grow thicker by adsorbing the neighboring clusters that incline in the opposite direction. Hence, a significant phase change in the particle aggregates is not induced by an increase in the magnetic field strength. For the case of a simple shear flow, even a weak shear flow induces a significant regime change from the thick chain-like clusters of thermodynamic equilibrium into wall-like aggregates composed of short raft-like clusters. A strong external magnetic field drastically changes these aggregates into wall-like aggregates composed of thick chain-like clusters rather than the short raft-like clusters. The internal structure of these aggregates is not strongly influenced by a shear flow, and the formation of the short raft-like clusters is maintained inside the aggregates. The main contribution to the net viscosity is the viscosity component due to magnetic particle-particle interaction forces in relation to the present volumetric fraction. Hence, a larger magnetic interaction strength and also a stronger external magnetic field give rise to a larger magneto-rheological effect. However, the dependence of the viscosity on these factors is governed in a complex manner by whether or not the wall-like aggregates are composed mainly of short raft-like clusters. An increase in the shear rate functions to simply decrease the effect of the magnetic particle-particle and the particle-field interactions.

Alpha-helix to beta-sheet transition in long-chain poly-l-lysine: Formation of alpha-helical fibrils by poly-l-lysine.

PubMed

Cieślik-Boczula, Katarzyna

2017-06-01

The temperature-induced α-helix to β-sheet transition in long-chain poly-l-lysine (PLL), accompanied by the gauche-to-trans isomerization of CH 2 groups in the hydrocarbon side chains of Lys amino acid residues, and formation of β-sheet as well as α-helix fibrillar aggregates of PLL have been studied using Fourier-transform infrared (FT-IR) and vibrational circular dichroism (VCD) spectroscopy, and transmission electron microscopy (TEM). In a low-temperature alkaline water solution or in a methanol-rich water mixture, the secondary structure of PLL is represented by α-helical conformations with unordered and gauche-rich hydrocarbon side chains. Under these conditions, PLL molecules aggregate into α-helical fibrils. PLLs dominated by extended antiparallel β-sheet structures with highly ordered trans-rich hydrocarbon side chains are formed in a high-temperature range at alkaline pD and aggregate into fibrillar, protofibrillar, and spherical forms. Presented data support the idea that fibrillar aggregation is a varied phenomenon possible in repetitive structural elements with not only a β-sheet-rich conformation, but also an α-helical-rich conformation. Copyright © 2017 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.

Gold nanoparticles as a platform for creating a multivalent poly-SUMO chain inhibitor that also augments ionizing radiation.

PubMed

Li, Yi-Jia; Perkins, Angela L; Su, Yang; Ma, Yuelong; Colson, Loren; Horne, David A; Chen, Yuan

2012-03-13

Protein-protein interactions mediated by ubiquitin-like (Ubl) modifications occur as mono-Ubl or poly-Ubl chains. Proteins that regulate poly-SUMO (small ubiquitin-like modifier) chain conjugates play important roles in cellular response to DNA damage, such as those caused by cancer radiation therapy. Additionally, high atomic number metals, such as gold, preferentially absorb much more X-ray energy than soft tissues, and thus augment the effect of ionizing radiation when delivered to cells. In this study, we demonstrate that conjugation of a weak SUMO-2/3 ligand to gold nanoparticles facilitated selective multivalent interactions with poly-SUMO-2/3 chains leading to efficient inhibition of poly-SUMO-chain-mediated protein-protein interactions. The ligand-gold particle conjugate significantly sensitized cancer cells to radiation but was not toxic to normal cells. This study demonstrates a viable approach for selective targeting of poly-Ubl chains through multivalent interactions created by nanoparticles that can be chosen based on their properties, such as abilities to augment radiation effects.

Gold nanoparticles as a platform for creating a multivalent poly-SUMO chain inhibitor that also augments ionizing radiation

PubMed Central

Li, Yi-Jia; Perkins, Angela L.; Su, Yang; Ma, Yuelong; Colson, Loren; Horne, David A.; Chen, Yuan

2012-01-01

Protein-protein interactions mediated by ubiquitin-like (Ubl) modifications occur as mono-Ubl or poly-Ubl chains. Proteins that regulate poly-SUMO (small ubiquitin-like modifier) chain conjugates play important roles in cellular response to DNA damage, such as those caused by cancer radiation therapy. Additionally, high atomic number metals, such as gold, preferentially absorb much more X-ray energy than soft tissues, and thus augment the effect of ionizing radiation when delivered to cells. In this study, we demonstrate that conjugation of a weak SUMO-2/3 ligand to gold nanoparticles facilitated selective multivalent interactions with poly-SUMO-2/3 chains leading to efficient inhibition of poly-SUMO-chain-mediated protein-protein interactions. The ligand-gold particle conjugate significantly sensitized cancer cells to radiation but was not toxic to normal cells. This study demonstrates a viable approach for selective targeting of poly-Ubl chains through multivalent interactions created by nanoparticles that can be chosen based on their properties, such as abilities to augment radiation effects. PMID:22388745

Formation of hollow silica nanospheres by reverse microemulsion

NASA Astrophysics Data System (ADS)

Lin, Cheng-Han; Chang, Jen-Hsuan; Yeh, Yi-Qi; Wu, Si-Han; Liu, Yi-Hsin; Mou, Chung-Yuan

2015-05-01

Uniform hollow silica nanospheres (HSNs) synthesized with reverse microemulsion have great application potential as nanoreactors because enzymes or nanocatalysts can be easily encapsulated de novo in synthesis. Water-in-oil (w/o) reverse microemulsions comprising the polymeric surfactant polyoxyethylene (5) isooctylphenyl ether (Igepal CA-520), ammonia and water in a continuous oil phase (alkanes) coalesce into size-tunable silica nanoparticles via diffusion aggregation after the introduction of silica precursors. Here, we elucidate in detail the growth mechanism for silica nanoparticles via nucleation of ammonium-catalyzed silica oligomers from tetraethylorthosilicate (TEOS) and nanoporous aminopropyltrimethoxy silane (APTS) in the reverse microemulsion system. The formation pathway was studied in situ with small-angle X-ray scattering (SAXS). We find a four-stage process showing a sigmoidal growth behavior in time with a crossover from the induction period, early nucleation stage, coalescence growth and a final slowing down of growth. Various characterizations (TEM, N2 isotherm, dynamic light scattering, zeta potential, NMR, elemental analysis) reveal the diameters, scattering length density (SLD), mesoporosity, surface potentials and chemical compositions of the HSNs. Oil phases of alkanes with different alkyl chains are systematically employed to tune the sizes of HSNs by varying oil molar volumes, co-solvent amounts or surfactant mixture ratios. Silica condensation is incomplete in the core region, with the silica source of TEOS and APTS leading to the hollow silica nanosphere after etching with warm water.Uniform hollow silica nanospheres (HSNs) synthesized with reverse microemulsion have great application potential as nanoreactors because enzymes or nanocatalysts can be easily encapsulated de novo in synthesis. Water-in-oil (w/o) reverse microemulsions comprising the polymeric surfactant polyoxyethylene (5) isooctylphenyl ether (Igepal CA-520), ammonia and water in a continuous oil phase (alkanes) coalesce into size-tunable silica nanoparticles via diffusion aggregation after the introduction of silica precursors. Here, we elucidate in detail the growth mechanism for silica nanoparticles via nucleation of ammonium-catalyzed silica oligomers from tetraethylorthosilicate (TEOS) and nanoporous aminopropyltrimethoxy silane (APTS) in the reverse microemulsion system. The formation pathway was studied in situ with small-angle X-ray scattering (SAXS). We find a four-stage process showing a sigmoidal growth behavior in time with a crossover from the induction period, early nucleation stage, coalescence growth and a final slowing down of growth. Various characterizations (TEM, N2 isotherm, dynamic light scattering, zeta potential, NMR, elemental analysis) reveal the diameters, scattering length density (SLD), mesoporosity, surface potentials and chemical compositions of the HSNs. Oil phases of alkanes with different alkyl chains are systematically employed to tune the sizes of HSNs by varying oil molar volumes, co-solvent amounts or surfactant mixture ratios. Silica condensation is incomplete in the core region, with the silica source of TEOS and APTS leading to the hollow silica nanosphere after etching with warm water. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01395j

Synthesis of silver nanoparticles in melts of amphiphilic polyesters

NASA Astrophysics Data System (ADS)

Vasylyev, S.; Damm, C.; Segets, D.; Hanisch, M.; Taccardi, N.; Wasserscheid, P.; Peukert, W.

2013-03-01

The current work presents a one-step procedure for the synthesis of amphiphilic silver nanoparticles suitable for production of silver-filled polymeric materials. This solvent free synthesis via reduction of Tollens’ reagent as silver precursor in melts of amphiphilic polyesters consisting of hydrophilic poly(ethylene glycol) blocks and hydrophobic alkyl chains allows the production of silver nanoparticles without any by-product formation. This makes them especially interesting for the production of medical devices with antimicrobial properties. In this article the influences of the chain length of the hydrophobic block in the amphiphilic polyesters and the process temperature on the particle size distribution (PSD) and the stability of the particles against agglomeration are discussed. According to the results of spectroscopic and viscosimetric investigations the silver precursor is reduced to elemental silver nanoparticles by a single electron transfer process from the poly(ethylene glycol) chain to the silver ion.

Chain dynamics and nanoparticle motion in attractive polymer nanocomposites subjected to large deformations.

PubMed

Senses, Erkan; Tyagi, Madhusudan; Natarajan, Bharath; Narayanan, Suresh; Faraone, Antonio

2017-11-08

The effect of large deformation on the chain dynamics in attractive polymer nanocomposites was investigated using neutron scattering techniques. Quasi-elastic neutron backscattering measurements reveal a substantial reduction of polymer mobility in the presence of attractive, well-dispersed nanoparticles. In addition, large deformations are observed to cause a further slowing down of the Rouse rates at high particle loadings, where the interparticle spacings are slightly smaller than the chain dimensions, i.e. in the strongly confined state. No noticeable change, however, was observed for a lightly confined system. The reptation tube diameter, measured by neutron spin echo, remained unchanged after shear, suggesting that the level of chain-chain entanglements is not significantly affected. The shear-induced changes in the interparticle bridging reflect the slow nanoparticle motion measured by X-ray photon correlation spectroscopy. These results provide a first step for understanding how large shear can significantly affect the segmental motion in nanocomposites and open up new opportunities for designing mechanically responsive soft materials.

Chain dynamics and nanoparticle motion in attractive polymer nanocomposites subjected to large deformations

DOE PAGES

Senses, Erkan; Tyagi, Madhusudan; Natarajan, Bharath; ...

2017-09-28

The effect of large deformation on the chain dynamics in attractive polymer nanocomposites was investigated using neutron scattering techniques. Quasielastic neutron backscattering measurements reveal a substantial reduction of polymer mobility in the presence of attractive, well-dispersed nanoparticles. Additionally, large deformations are observed to cause a further slowing down of the Rouse rates at high particle loadings, where the interparticle spacings are slightly smaller than the chain dimensions, i.e. in the strongly confined state. No noticeable change, however, was observed for a lightly confined system. The reptation tube diameter, measured by neutron spin echo, remained unchanged after shear, suggesting that themore » level of chain-chain entanglements is not significantly affected. The shearinduced changes in the interparticle bridging reflects on the slow nanoparticle motion measured by X-ray photon correlation spectroscopy. These results provide a first step for understanding how large shear can significantly affect the segmental motion in nanocomposites and open up new opportunities for designing mechanically responsive soft materials.« less

Chain dynamics and nanoparticle motion in attractive polymer nanocomposites subjected to large deformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senses, Erkan; Tyagi, Madhusudan; Natarajan, Bharath

The effect of large deformation on the chain dynamics in attractive polymer nanocomposites was investigated using neutron scattering techniques. Quasielastic neutron backscattering measurements reveal a substantial reduction of polymer mobility in the presence of attractive, well-dispersed nanoparticles. Additionally, large deformations are observed to cause a further slowing down of the Rouse rates at high particle loadings, where the interparticle spacings are slightly smaller than the chain dimensions, i.e. in the strongly confined state. No noticeable change, however, was observed for a lightly confined system. The reptation tube diameter, measured by neutron spin echo, remained unchanged after shear, suggesting that themore » level of chain-chain entanglements is not significantly affected. The shearinduced changes in the interparticle bridging reflects on the slow nanoparticle motion measured by X-ray photon correlation spectroscopy. These results provide a first step for understanding how large shear can significantly affect the segmental motion in nanocomposites and open up new opportunities for designing mechanically responsive soft materials.« less

Biodistribution of a High Dose of Diamond, Graphite, and Graphene Oxide Nanoparticles After Multiple Intraperitoneal Injections in Rats.

PubMed

Kurantowicz, Natalia; Strojny, Barbara; Sawosz, Ewa; Jaworski, Sławomir; Kutwin, Marta; Grodzik, Marta; Wierzbicki, Mateusz; Lipińska, Ludwika; Mitura, Katarzyna; Chwalibog, André

2015-12-01

Carbon nanoparticles have recently drawn intense attention in biomedical applications. Hence, there is a need for further in vivo investigations of their biocompatibility and biodistribution via various exposure routes. We hypothesized that intraperitoneally injected diamond, graphite, and graphene oxide nanoparticles may have different biodistribution and exert different effects on the intact organism. Forty Wistar rats were divided into four groups: the control and treated with nanoparticles by intraperitoneal injection (4 mg of nanoparticles/kg body weight) eight times during the 4-week period. Blood was collected for evaluation of blood morphology and biochemistry parameters. Photographs of the general appearance of each rat's interior were taken immediately after sacrifice. The organs were excised and their macroscopic structure was visualized using a stereomicroscope. The nanoparticles were retained in the body, mostly as agglomerates. The largest agglomerates (up to 10 mm in diameter) were seen in the proximity of the injection place in the stomach serous membrane, between the connective tissues of the abdominal skin, muscles, and peritoneum. Numerous smaller, spherical-shaped aggregates (diameter around 2 mm) were lodged among the mesentery. Moreover, in the connective and lipid tissue in the proximity of the liver and spleen serosa, small aggregates of graphite and graphene oxide nanoparticles were observed. However, all tested nanoparticles did not affect health and growth of rats. The nanoparticles had no toxic effects on blood parameters and growth of rats, suggesting their potential applicability as remedies or in drug delivery systems.

Exchange of TiO2 nanoparticles between streams and streambeds.

PubMed

Boncagni, Natalia Ticiana; Otaegui, Justo Manuel; Warner, Evelyn; Curran, Trisha; Ren, Jianhong; de Cortalezzi, Maria Marta Fidalgo

2009-10-15

The expanding use of manufactured nanoparticles has increased the potential for their release into the natural environment. Particularly, TiO2 nanoparticles pose significant exposure risk to humans and other living species due to their extensive use in a wide range of fields. To better understand the environmental and health risks associated with the release of TiO2 nanoparticles, knowledge on their fate and transport is needed. This study evaluates the transport of two different TiO2 nanoparticles: one commercially available (P25 TiO2 and the other synthesized at a lab scale (synthesized TiO2). Laboratory flume, column, and batch experiments were conducted to investigate the processes dominating the transport of TiO2 nanoparticles between streams and streambeds and to characterize the properties of these nanoparticles under different physicochemical conditions. Results show that the synthesized TiO2 was more stable compared to the P25 TiO2, which underwent significant aggregation under the same experimental conditions. As a result, P25 TiO2 deposited at a faster rate than the synthesized TiO2 in the streambed. Both types of TiO2 nanoparticles deposited in the streambed were easily released when the stream velocity was increased. The aggregation and deposition of P25 TiO2 were highly dependent on pH. A process-based colloid exchange model was applied to interpret the observed transport behavior of the TiO2 nanoparticles.

Two-Way Gold Nanoparticle Label-Free Sensing of Specific Sequence and Small Molecule Targets Using Switchable Concatemers.

PubMed

Zhu, Longjiao; Shao, Xiangli; Luo, Yunbo; Huang, Kunlung; Xu, Wentao

2017-05-19

A two-way colorimetric biosensor based on unmodified gold nanoparticles (GNPs) and a switchable double-stranded DNA (dsDNA) concatemer have been demonstrated. Two hairpin probes (H1 and H2) were first designed that provided the fuels to assemble the dsDNA concatemers via hybridization chain reaction (HCR). A functional hairpin (FH) was rationally designed to recognize the target sequences. All the hairpins contained a single-stranded DNA (ssDNA) loop and sticky end to prevent GNPs from salt-induced aggregation. In the presence of target sequence, the capture probe blocked in the FH recognizes the target to form a duplex DNA, which causes the release of the initiator probe by FH conformational change. This process then starts the alternate-opening of H1 and H2 through HCR, and dsDNA concatemers grow from the target sequence. As a result, unmodified GNPs undergo salt-induced aggregation because the formed dsDNA concatemers are stiffer and provide less stabilization. A light purple-to-blue color variation was observed in the bulk solution, termed the light-off sensing way. Furthermore, H1 ingeniously inserted an aptamer sequence to generate dsDNA concatemers with multiple small molecule binding sites. In the presence of small molecule targets, concatemers can be disassembled into mixtures with ssDNA sticky ends. A blue-to-purple reverse color variation was observed due to the regeneration of the ssDNA, termed the light-on way. The two-way biosensor can detect both nucleic acids and small molecule targets with one sensing device. This switchable sensing element is label-free, enzyme-free, and sophisticated-instrumentation-free. The detection limits of both targets were below nanomolar.

Dielectric Anistropy, Elastic Constants, and Threshold Voltage Measurements of Gold-nanoparticle Colloids in Nematic 5CB

NASA Astrophysics Data System (ADS)

Visco, Angelo; Foust, Jon; Belobradich, Joseph; Mahmood, Rizwan; Zapien, Donald

We have explored electro-optical and thermal properties of gold nanoparticles (GNPs) colloids in 4-cyano- 4'-pentylbiphenyl (5CB) liquid crystals (LCs). GNP's do not readily disperse in a LC host and, so, have been treated with either, 1-Hexane-thiol, 1-Dodecane-thiol, or 1-Octadecyl-thiol. This treatment suppresses the aggregation of GNPs within the 5CB host to a threshold of approximately 0.7% GNP by weight. Our measurements on dodecanethiol and hexanethiol treated GNPs showed an unusual, steep trough in the dielectric anisotropy and elastic constants at a critical concentration of 0.0862 wt. % GNPs in 5CB. Due to the order parameter, we have observed a peak in the transition temperature at the same critical concentration. Above the critical concentration the transition temperatures, dielectric anisotropy, and elastic constants level off to within experimental uncertainty. Measurements of dodecanethiol treated GNPs in 5CB reveal distinctions in the rate of change in dielectric anisotropy as compared to hexanethiol treated GNPs in 5CB. This effect is possibly due to the increased carbon concentration in dodeccanethiol compared to hexanethiol. Attempts to mix the Smectic A (SmA), 8CB liquid crystal using our hexanethiol and dodecanethiol GNPs were unsuccessful for particle sizes of 100nm and 28nm. We suspect that this is due to an insufficient length of the carbon-chain and U.V. spectroscopy measurements may prove useful in characterizing the resulting aggregation. We hope the system will be helpful in modifying the properties of mesophases that may ultimately results in developing new electro-optical devices. Acknowledgements: The funding for the project was provided by Slippery Rock University (2015-2016).

Effect of Areal Density of Polymer Chains on Gold Nanoparticles on Nanoparticle Location in a Block Copolymer Template

NASA Astrophysics Data System (ADS)

Kim, B. J.; Bang, J.; Hawker, C. J.; Kramer, E. J.

2006-03-01

It is well established that one block of a copolymer can interact preferentially with an inorganic substrate to produce wetting and domain orientation. We take advantage of this preferential interaction to control the location of 2.5 nm diameter Au nanoparticles coated with short thiol-terminated polystyrene (Mn=3.4 kg/mol) chains (PS-SH) in a symmetric poly(styrene-b-2 vinyl-pyridine) (PS-b-P2VP) diblock copolymer (Mn=196 kg/mol) by changing the areal density σ of the PS-SH on the Au. If σ >= 1.6 chains/nm^2, the preferential interaction between the P2VP of the PS-b-P2VP and the Au surface is screened and the Au localizes in the center of the PS domains. If σ <= 1.4 chains/nm^2 , the Au particles are localized at the PS-P2VP interface. Au nanoparticles coated with thiol terminated P2VP (Mn=3 kg/mol) localize in the center of the P2VP domain of the PS-P2VP over the entire range of σ, demonstrating the localization of the PS coated Au nanoparticles at the interface at low values of σ is due to the unscreened Au-P2VP interaction.

Magnetic Fluids Have Ability to Decrease Amyloid Aggregation Associated with Amyloid-Related Diseases

NASA Astrophysics Data System (ADS)

Antosova, Andrea; Koneracka, Martina; Siposova, Katarina; Zavisova, Vlasta; Daxnerova, Zuzana; Vavra, Ivo; Fabian, Martin; Kopcansky, Peter; Gazova, Zuzana

2010-12-01

At least twenty human proteins can fold abnormally to form pathological deposits that are associated with several amyloid-related diseases. We have investigated the effect of four magnetic fluids (MFs)—electrostatically stabilized Fe3O4 magnetic nanoparticles (MF1) and sterically stabilized Fe3O4 magnetic nanoparticles by sodium oleate (MF2, MF3 and MF4) with adsorbed BSA (MF2) or dextran (MF4)—on amyloid aggregation of two proteins, human insulin and chicken egg lysozyme. The morphology, particle size and size distribution of the prepared magnetic fluids were characterized. We have found that MFs are able to decrease amyloid aggregation of both studied proteins and the extent of depolymerization depended on the MF properties. The most effective reduction was observed for MF4 as 90% decrease of amyloids was detected for insulin and lysozyme amyloid aggregates. Our findings indicate that MFs have potential to be used for treatment of amyloid diseases.

Rewritable and pH-Sensitive Micropatterns Based on Nanoparticle "Inks"

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, D. W.; Lagzi, Istvan; Wesson, Paul J.

2010-08-16

Rewritable micropatterns based on nanoparticle “inks” are created in gel substrates by wet stamping. The colors of the patterns depend on pH, reflect the degree of nanoparticle aggregation, and can be written using acids and erased using bases. Micropatterns imprinted with salts are “permanent” but can change color upon pH changes; these patterns act as multiple-use pH sensors.

A close collaboration of chitosan with lipid colloidal carriers for drug delivery applications.

PubMed

Bugnicourt, Loïc; Ladavière, Catherine

2017-06-28

Chitosan and lipid colloids have separately shown a growing interest in the field of drug delivery applications. Their success is mainly due to their interesting physicochemical behaviors, as well as their biological properties such as bioactivity and biocompatibility. While chitosan is a well-known cationic polysaccharide with the ability to strongly interact with drugs and biological matrices through mainly electrostatic interactions, lipid colloids are carriers particularly recognized for the drug vectorization. In recent years, the combination of both entities has been considered because it offers new systems which gather the advantages of each of them to efficiently deliver various types of bioactive species. The purpose of this review is to describe these associations between chemically-unmodified chitosan chains (solubilized or dispersed) and lipid colloids (as nanoparticles or organized in lipid layers), as well as their potential in the drug delivery area so far. Three assemblies have mainly been reported in the literature: i) lipid nanoparticles (solid lipid nanoparticles or nanostructured lipid carriers) coated with chitosan chains, ii) lipid vesicles covered with chitosan chains, and iii) chitosan chains structured in nanoparticles with a lipid coating. Their elaboration processes, their physicochemical characterization, and their biological studies are detailed and discussed herein. The different bioactive species (drugs and bio(macro)molecules) incorporated in these assemblies, their maximal incorporation efficiency, and their loading capacity are also presented. This review reveals the versatility of these assemblies. Depending on the organization of lipids (i.e., nanoparticles or vesicles) and the state of polymer chains (i.e., solubilized or dispersed under the form of nanoparticles), a large variety of drugs can be successfully incorporated, and various routes of administration can be considered. Copyright © 2017 Elsevier B.V. All rights reserved.

Interaction of Nanoparticles with Biofilms

EPA Science Inventory

In this work we have studied the interaction and adsorption of engineered nanoparticles such as TiO2, ZnO, CeO2 , and carbon nanotubes with biofilms. Biofilm is an extracellular polymeric substance coating comprised of living material and it is an aggregation of bacteria, algae, ...

Does moving up a food chain increase aggregation in parasites?

PubMed

Lester, R J G; McVinish, R

2016-05-01

General laws in ecological parasitology are scarce. Here, we evaluate data on numbers of fish parasites published by over 200 authors to determine whether acquiring parasites via prey is associated with an increase in parasite aggregation. Parasite species were grouped taxonomically to produce 20 or more data points per group as far as possible. Most parasites that remained at one trophic level were less aggregated than those that had passed up a food chain. We use a stochastic model to show that high parasite aggregation in predators can be solely the result of the accumulation of parasites in their prey. The model is further developed to show that a change in the predators feeding behaviour with age may further increase parasite aggregation. © 2016 The Author(s).

Direct Visualization of the Hydration Layer on Alumina Nanoparticles with the Fluid Cell STEM in situ

PubMed Central

Firlar, Emre; Çınar, Simge; Kashyap, Sanjay; Akinc, Mufit; Prozorov, Tanya

2015-01-01

Rheological behavior of aqueous suspensions containing nanometer-sized powders is of relevance to many branches of industry. Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models. Formation of so-called hydration layer on alumina nanoparticles in water was hypothesized, but never observed experimentally. We report here on the direct visualization of aqueous suspensions of alumina with the fluid cell in situ. We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions. We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions. Our findings elucidate the source of high viscosity observed for nanoparticle suspensions and are of direct relevance to many industrial sectors including materials, food, cosmetics, pharmaceutical among others employing colloidal slurries with nanometer-scale particles. PMID:25996055

Preparation and characterization of chondroitin-sulfate-A-coated magnetite nanoparticles for biomedical applications

NASA Astrophysics Data System (ADS)

Tóth, Ildikó Y.; Illés, Erzsébet; Szekeres, Márta; Tombácz, Etelka

2015-04-01

Polysaccharides are promising candidates for manufacturing biocompatible core-shell nanoparticles with potential in vivo use. Superparamagnetic magnetite nanoparticles (MNPs) have prospective application in both diagnosis and therapy, and so developing a novel polysaccharide shell on MNP core is of great challenge. MNPs were prepared by co-precipitation, then the surface of purified MNPs was coated with chondroitin-sulfate-A (CSA) to obtain core-shell structured magnetite nanoparticles (CSA@MNP). The effect of the added amount of CSA on the surface charging and the aggregation state of MNPs at various pHs and 10 mM NaCl was measured by electrophoresis and dynamic light scattering. The amphoteric behavior of MNPs was fundamentally modified by adsorption of CSA polyanions. A very low CSA-loading induces the aggregation of MNPs, while four times more stabilizes the dispersions over the whole pH-range studied. The coagulation kinetics experiments measured at pH=6.3±0.3 showed that salt tolerance of CSA@MNPs rises up to ~150 mM NaCl.

Direct Visualization of the Hydration Layer on Alumina Nanoparticles with the Fluid Cell STEM in situ.

PubMed

Firlar, Emre; Çınar, Simge; Kashyap, Sanjay; Akinc, Mufit; Prozorov, Tanya

2015-05-21

Rheological behavior of aqueous suspensions containing nanometer-sized powders is of relevance to many branches of industry. Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models. Formation of so-called hydration layer on alumina nanoparticles in water was hypothesized, but never observed experimentally. We report here on the direct visualization of aqueous suspensions of alumina with the fluid cell in situ. We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions. We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions. Our findings elucidate the source of high viscosity observed for nanoparticle suspensions and are of direct relevance to many industrial sectors including materials, food, cosmetics, pharmaceutical among others employing colloidal slurries with nanometer-scale particles.

Direct visualization of the hydration layer on alumina nanoparticles with the fluid cell STEM in situ

DOE PAGES

Firlar, Emre; Çınar, Simge; Kashyap, Sanjay; ...

2015-05-21

Rheological behavior of aqueous suspensions containing nanometer-sized powders is of relevance to many branches of industry. Unusually high viscosities observed for suspensions of nanoparticles compared to those of micron size powders cannot be explained by current viscosity models. Formation of so-called hydration layer on alumina nanoparticles in water was hypothesized, but never observed experimentally. We report here on the direct visualization of aqueous suspensions of alumina with the fluid cell in situ. We observe the hydration layer formed over the particle aggregates and show that such hydrated aggregates constitute new particle assemblies and affect the flow behavior of the suspensions.more » We discuss how these hydrated nanoclusters alter the effective solid content and the viscosity of nanostructured suspensions. As a result, our findings elucidate the source of high viscosity observed for nanoparticle suspensions and are of direct relevance to many industrial sectors including materials, food, cosmetics, pharmaceutical among others employing colloidal slurries with nanometer-scale particles.« less

Microemulsion synthesis and magnetic properties of FexNi(1-x) alloy nanoparticles

NASA Astrophysics Data System (ADS)

Beygi, H.; Babakhani, A.

2017-01-01

This paper investigates synthesis of FexNi(1-x) bimetallic nanoparticles by microemulsion method. Through studying the mechanism of nanoparticles formation, it is indicated that synthesis of nanoparticles took placed by simultaneous reduction of metal ions and so nanoparticles structure is homogeneous alloy. FexNi(1-x) nanoparticles with different sizes, morphologies and compositions were synthesized by changing the microemulsion parameters such as water/surfactant/oil ratio, presence of co-surfactant and NiCl2·6H2O to FeCl2·4H2O molar ratio. Synthesized nanoparticles were characterized by transmission electron microscopy, particle size analysis, X-ray diffraction, atomic absorption and thermogravimetric analyses. The results indicated that, presence of butanol as co-surfactant led to chain-like arrangement of nanoparticles. Also, finer nanoparticles were synthesized by decreasing the amount of oil and water and increasing the amount of CTAB. The results of vibrating sample magnetometer suggested that magnetic properties of FexNi(1-x) alloy nanoparticles were affected by composition, size and morphology of the particles. Spherical and chain-like FexNi(1-x) alloy nanoparticles were superparamagnetic and ferromagnetic, respectively. Furthermore, higher iron in the composition of nanoparticles increases the magnetic properties.

Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy

NASA Astrophysics Data System (ADS)

Jafri, S. H. M.; Löfås, H.; Fransson, J.; Blom, T.; Grigoriev, A.; Wallner, A.; Ahuja, R.; Ottosson, H.; Leifer, K.

2013-05-01

Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra. Electronic supplementary information (ESI) available: Methods and materials. Details of the ab initio calculation of molecular vibrations and inelastic spectra of ODT between two Au electrodes. A model of carrier transport through the molecular junctions. See DOI: 10.1039/c3nr00505d

Edge states and topological phase transitions in chains of dielectric nanoparticles

DOE PAGES

Kruk, Sergey; Slobozhanyuk, Alexey; Denkova, Denitza; ...

2017-01-12

Recently introduced field of topological photonics aims to explore the concepts of topological insulators for novel phenomena in optics. Here polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain. Here, it is observed experimentally and described how theoretically topological phase transitions at the nanoscale define a change from trivial to nontrivial topological states when the edge mode is excited.

Edge states and topological phase transitions in chains of dielectric nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruk, Sergey; Slobozhanyuk, Alexey; Denkova, Denitza

Recently introduced field of topological photonics aims to explore the concepts of topological insulators for novel phenomena in optics. Here polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain. Here, it is observed experimentally and described how theoretically topological phase transitions at the nanoscale define a change from trivial to nontrivial topological states when the edge mode is excited.

Fabrication of coated bovine serum albumin (BSA)-epigallocatechin gallate (EGCG) nanoparticles and their transport across monolayers of human intestinal epithelial Caco-2 cells.

PubMed

Li, Zheng; Ha, Jungheun; Zou, Tao; Gu, Liwei

2014-06-01

The bovine serum albumin (BSA)-epigallocatechin gallate (EGCG) nanoparticles were fabricated using a desolvation method, and coated with poly-ε-lysine or chitosan. BSA-EGCG nanoparticles (BEN), poly-ε-lysine coated BSA-EGCG nanoparticles (PBEN), and chitosan coated BSA-EGCG nanoparticles (CBEN) had a spherical morphology and a size of 186, 259, and 300 nm, respectively. The loading efficiency of EGCG in these nanoparticles was 32.3%, 35.4%, and 32.7%, whereas the loading capacity was 18.9%, 17.0%, and 16.0% (w/w), respectively. Poly-ε-lysine or chitosan coating prevented the aggregation of nanoparticles at pH 4.5-5.0. However, they caused particle aggregation at pH 6.5-7.0. BEN had negative zeta-potentials between pH 4.5 and 6.0. Poly-ε-lysine or chitosan coating changed the zeta-potentials to positive. The release study of EGCG from the nanoparticles in the simulated gastric or intestinal fluid with or without digestive enzymes showed that poly-ε-lysine and chitosan coatings delayed EGCG release from the nanoparticles. Poly-ε-lysine or chitosan coating improved the stability of EGCG during storage at 60 °C compared with EGCG in the uncoated particles. EGCG in BEN, PBEN, and CBEN had a decreasing apparent permeability coefficient (Papp) on Caco-2 monolayers, whereas pure EGCG showed relatively stable Papp during the incubation over time. EGCG in CBEN showed significantly higher Papp, suggesting that chitosan coated BSA-EGCG nanoparticles may improve the absorption of EGCG.

Hydrodynamic radius fluctuations in model DNA-grafted nanoparticles

NASA Astrophysics Data System (ADS)

Vargas-Lara, Fernando; Starr, Francis W.; Douglas, Jack F.

2016-05-01

We utilize molecular dynamics simulations (MD) and the path-integration program ZENO to quantify hydrodynamic radius (Rh) fluctuations of spherical symmetric gold nanoparticles (NPs) decorated with single-stranded DNA chains (ssDNA). These results are relevant to understanding fluctuation-induced interactions among these NPs and macromolecules such as proteins. In particular, we explore the effect of varying the ssDNA-grafted NPs structural parameters, such as the chain length (L), chain persistence length (lp), NP core size (R), and the number of chains (N) attached to the nanoparticle core. We determine Rh fluctuations by calculating its standard deviation (σRh) of an ensemble of ssDNA-grafted NPs configurations generated by MD. For the parameter space explored in this manuscript, σR h shows a peak value as a function of N, the amplitude of which depends on L, lp and R, while the broadness depends on R.

Polymer-Particle Nanocomposites: Size and Dispersion Effects

NASA Astrophysics Data System (ADS)

Moll, Joseph

Polymer-particle nanocomposites are used in industrial processes to enhance a broad range of material properties (e.g. mechanical, optical, electrical and gas permeability properties). This dissertation will focus on explanation and quantification of mechanical property improvements upon the addition of nanoparticles to polymeric materials. Nanoparticles, as enhancers of mechanical properties, are ubiquitous in synthetic and natural materials (e.g. automobile tires, packaging, bone), however, to date, there is no thorough understanding of the mechanism of their action. In this dissertation, silica (SiO2) nanoparticles, both bare and grafted with polystyrene (PS), are studied in polymeric matrices. Several variables of interest are considered, including particle dispersion state, particle size, length and density of grafted polymer chains, and volume fraction of SiO2. Polymer grafted nanoparticles behave akin to block copolymers, and this is critically leveraged to systematically vary nanoparticle dispersion and examine its role on the mechanical reinforcement in polymer based nanocomposites in the melt state. Rheology unequivocally shows that reinforcement is maximized by the formation of a transient, but long-lived, percolating polymer-particle network with the particles serving as the network junctions. The effects of dispersion and weight fraction of filler on nanocomposite mechanical properties are also studied in a bare particle system. Due to the interest in directional properties for many different materials, different means of inducing directional ordering of particle structures are also studied. Using a combination of electron microscopy and x-ray scattering, it is shown that shearing anisotropic NP assemblies (sheets or strings) causes them to orient, one in front of the other, into macroscopic two-dimensional structures along the flow direction. In contrast, no such flow-induced ordering occurs for well dispersed NPs or spherical NP aggregates! This work also addresses the interfacial, rigid polymer layer, or 'bound layer' which has long been of interest in polymer nanocomposites and polymer thin films. The divergent properties of the 'bound layer' as compared to the bulk material can have very important effects on properties, including mechanical properties. This is especially true in polymer nanocomposites, where at high weight fractions, 'bound layer' polymer can easily make up 20% or more of total material! Here we quantify this layer of bound polymer as a function of particle size, polymer molecular weight and other variables, primarily using thermogravimetric analysis but also dynamic light scattering and differential scanning calorimetry. We find that as nanoparticles become smaller, the 'bound layer' systematically decreases in thickness. This result is quite relevant to explanations of many polymer nanocomposite properties that depend on size, including mechanical and barrier properties. Many additional important and new results are reported herein. These include the importance of dispersion state in the resulting mechanical properties of polymer-particle nanocomposites, where a systematic study showed an optimal dispersion state of a connected particle network. An additional and unexpected finding in this system was the critical dependence of composite properties on grafted chain length of particles. As the grafted chain length is increased, the strain which leads to yielding in a steady shear experiment is increased in a linear relationship. At very high rates, this yielding process completely switches mechanisms, from yielding of the particle network to yielding of the entangled polymer network! A surprising correlation between the amount of bound polymer in solution and in the bulk was also found and is interpreted herein. Self-assembly was further explored in a range of different systems and it was found that grafted particles and there mimics have vast potential in the creation of a wide array of particle superstructures. In concert, these experiments provide a comprehensive picture of mechanical reinforcement in polymer-particle nanocomposites. Not only is the dispersion state of the particles crucial, but the presence of grafted chains is also so for proper reinforcement. Here many routes to ideal dispersion are detailed and the important role of grafted chains is also resolved.

Sorting process of nanoparticles and applications of same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tyler, Timothy P.; Henry, Anne-Isabelle; Van Duyne, Richard P.

In one aspect of the present invention, a method for sorting nanoparticles includes preparing a high-viscosity density gradient medium filled in a container, dispersing nanoparticles into an aqueous solution to form a suspension of the nanoparticles, each nanoparticle having one or more cores and a shell encapsulating the one or more cores, layering the suspension of the nanoparticles on the top of the high-viscosity density gradient medium in the container, and centrifugating the layered suspension of the nanoparticles on the top of the high-viscosity density gradient medium in the container at a predetermined speed for a predetermined period of timemore » to form a gradient of fractions of the nanoparticles along the container, where each fraction comprises nanoparticles in a respective one of aggregation states of the nanoparticles.« less

Human serum albumin (HSA) nanoparticles: reproducibility of preparation process and kinetics of enzymatic degradation.

PubMed

Langer, K; Anhorn, M G; Steinhauser, I; Dreis, S; Celebi, D; Schrickel, N; Faust, S; Vogel, V

2008-01-22

Nanoparticles prepared from human serum albumin (HSA) are versatile carrier systems for drug delivery and can be prepared by an established desolvation process. A reproducible process with a low batch-to-batch variability is required for transfer from the lab to an industrial production. In the present study the batch-to-batch variability of the starting material HSA on the preparation of nanoparticles was investigated. HSA can build dimers and higher aggregates because of a free thiol group present in the molecule. Therefore, the quality of different HSA batches was analysed by size exclusion chromatography (SEC) and analytical ultracentrifugation (AUC). The amount of dimerised HSA detected by SEC did not affect particle preparation. Higher aggregates of the protein detected in two batches by AUC disturbed nanoparticle formation at pH values below 8.0. At pH 8.0 and above monodisperse particles between 200 and 300 nm could be prepared with all batches, with higher pH values leading to smaller particles. Besides human derived albumin a particle preparation was also feasible based on recombinant human serum albumin (rHSA). Under comparable preparation conditions monodisperse nanoparticles could be achieved and the same effects of protein aggregates on particle formation were observed. For nanoparticulate drug delivery systems the enzymatic degradation is a crucial parameter for the release of an embedded drug. For this reason, besides the particle preparation process, particle degradation in the presence of different enzymes was studied. Under acidic conditions HSA as well as rHSA nanoparticles could be digested by pepsin and cathepsin B. At neutral pH trypsin, proteinase K, and protease were suitable for particle degradation. It could be shown that the kinetics of particle degradation was dependent on the degree of particle stabilisation. Therefore, the degree of particle stabilisation will influence drug release after cellular accumulation of HSA nanoparticles.

Heterogeneous chain dynamics and aggregate lifetimes in precise acid-containing polyethylenes: Experiments and simulations

DOE PAGES

Middleton, L. Robert; Tarver, Jacob D.; Cordaro, Joseph; ...

2016-11-10

Melt state dynamics for a series of strictly linear polyethylenes with precisely spaced associating functional groups were investigated. The periodic pendant acrylic acid groups form hydrogen-bonded acid aggregates within the polyethylene (PE) matrix. The dynamics of these nanoscale heterogeneous morphologies were investigated from picosecond to nanosecond timescales by both quasi-elastic neutron scattering (QENS) measurements and fully atomistic molecular dynamics (MD) simulations. Two dynamic processes were observed. The faster dynamic processes which occur at the picosecond timescales are compositionally insensitive and indicative of spatially restricted local motions. The slower dynamic processes are highly composition dependent and indicate the structural relaxation ofmore » the polymer backbone. Higher acid contents, or shorter PE spacers between pendant acid groups, slow the structural relaxation timescale and increase the stretching parameter (β) of the structural relaxation. Additionally, the dynamics of specific hydrogen atom positions along the backbone correlate structural heterogeneity imposed by the associating acid groups with a mobility gradient along the polymer backbone. At time intervals (<2 ns), the mean-squared displacements for the four methylene groups closest to the acid groups are up to 10 times smaller than those of methylene groups further from the acid groups. At longer timescales acid aggregates rearrange and the chain dynamics of the slow, near-aggregate regions and the faster bridge regions converge, implying a characteristic timescale for the passage of chains between aggregates. As a result, the characterization of the nanoscale chain dynamics in these associating polymer systems both provides validation of simulation force fields and provides understanding of heterogeneous chain dynamics in associating polymers.« less

Amyloid fibril formation by the chain B subunit of monellin occurs by a nucleation-dependent polymerization mechanism.

PubMed

Sabareesan, A T; Udgaonkar, Jayant B

2014-02-25

Proteins possessing very different structures, or even no structure, form amyloid fibrils that are very similar in internal structure. This suggests that the mechanisms by which amyloid fibrils form might be very similar, irrespective of whether the fibrils are associated with disease or with normal cellular function, or even if they have no physiological importance. In this context, it is important to have a model protein system whose amyloid fibril formation is robust in its reproducibility, which can reveal the fundamentals of the amyloid fibril reaction that may be applicable to all proteins. In this study, the aggregation mechanism of amyloid fibril formation by chain B of the heterodimeric protein monellin has been elucidated in detail. It is shown that the aggregation reaction meets all the stringent kinetic criteria of a homogeneous nucleation-dependent polymerization mechanism, which is valid over a wide range of protein concentrations. Quantitative analyses of the kinetic data using one approach based on features of the entire kinetic curve, and another based on only the initial rate of aggregation, indicate that the thermodynamic nucleus is a dimer. Spherical oligomers are observed by atomic force microscopy to form transiently early during fibril formation but are off-pathway to the direct fibril formation pathway. It is shown that amyloid fibril formation can be prevented by the addition of chain A of monellin at early stages of chain B aggregation: the two free chains combine to form native monellin, which leads to the dissociation of early aggregates.

Surface properties and aggregate morphology of partially fluorinated carboxylate-type anionic gemini surfactants.

PubMed

Yoshimura, Tomokazu; Bong, Miri; Matsuoka, Keisuke; Honda, Chikako; Endo, Kazutoyo

2009-11-01

Three anionic homologues of a novel partially fluorinated carboxylate-type anionic gemini surfactant, N,N'-di(3-perfluoroalkyl-2-hydroxypropyl)-N,N'-diacetic acid ethylenediamine (2C(n)(F) edda, where n represents the number of carbon atoms in the fluorocarbon chain (4, 6, and 8)) were synthesized. In these present gemini surfactants, the relatively small carboxylic acid moieties form hydrophilic head groups. The surface properties or structures of the aggregates of these surfactants are strongly influenced by the nonflexible fluorocarbons and small head groups; this is because these surfactants have a closely packed molecular structure. The equilibrium surface tension properties of these surfactants were measured at 298.2K for various fluorocarbon chain lengths. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain lengths for 2C(n)(F) edda (n=4, 6, and 8) showed a minimum for n=6. Furthermore, the lowest surface tension of 2C(6)(F) edda at the cmc was 16.4mNm(-1). Such unique behavior has not been observed even in the other fluorinated surfactants. Changes in the shapes and sizes of these surfactant aggregate with concentration were investigated by dynamic light scattering and transmission electron microscopy (TEM). The TEM micrographs showed that in an aqueous alkali solution, 2C(n)(F) edda mainly formed aggregates with stringlike (n=4), cagelike (n=6), and distorted bilayer structures (n=8). The morphological changes in the aggregates were affected by the molecular structure composed of nonflexible fluorocarbon chains and flexible hydrocarbon chains.

Tuning aggregation of microemulsion droplets and silica nanoparticles using solvent mixtures.

PubMed

Salabat, Alireza; Eastoe, Julian; Mutch, Kevin J; Tabor, Rico F

2008-02-15

The effect of solvent on stability of water-in-oil microemulsions has been studied with AOT (sodium bis(2-ethylhexyl)sulfosuccinate) and different solvent mixtures of n-heptane, toluene and dodecane. Dynamic light scattering DLS was used to monitor the apparent diffusion coefficient D(A) and effective microemulsion droplet diameter on changing composition of the solvent. Interdroplet attractive interactions, as indicated by variations in D(A), can be tuned by formulation of appropriate solvent mixtures using heptane, toluene, and dodecane. In extreme cases, solvent mixtures can be used to induce phase transitions in the microemulsions. Aggregation and stability of model AOT-stabilized silica nanoparticles in different solvents were also investigated to explore further these solvent effects. For both systems the state of aggregation can be correlated with the effective molecular volume of the solvent V(mol)(eff) mixture.

Surface Changes and Impurity Release Kinetics of Titanium Dioxide Nanoparticles in Aqueous Environment

EPA Science Inventory

Previous studies have found the significant role of impurities (i.e., silicon, phosphorus) in the aggregation and sedimentation of TiO2 nanoparticles in water environment. However, it is not understood whether dissolution of the impurities potentially impacts the environment or t...

Electrokinetic Properties of Fullerene nC60 Nanoparticles: Role of Co-ions and pH

EPA Science Inventory

Environmental exposure, bioavailability, and mobility of nanoparticles (NPs) in part depend on their aggregated state and their surface charge. These fundamental characteristics are functions of the aqueous media in which the particles are suspended. For example, inorganic ions p...

Effect of UV irradiation on the aggregation of TiO2 in an aquatic environment: Influence of humic acid and pH.

PubMed

Wang, Peifang; Qi, Ning; Ao, Yanhui; Hou, Jun; Wang, Chao; Qian, Jin

2016-05-01

The behavior of photoactive TiO2 nanoparticles in an aquatic environment under UV irradiation was investigated. When there was no UV light irradiation, the attachment of humic acid (HA) onto the TiO2 nanoparticles improved their stability due to an increase in the electrostatic and steric repulsions between the particles. However, our study demonstrated that UV light clearly influenced the aggregation of TiO2 nanoparticles. Half an hour of UV irradiation caused the particles to aggregate from 331.0 nm to 1505.0 nm at a pH of 3.0. Similarly, the particles aggregated from 533.2 nm to 1037.0 nm at a pH of 6.5 and from 319.0 nm to 930.0 nm at a pH of 9.0. The aggregation continued with increased irradiation time, except for the condition at pH 3.0, which demonstrated disaggregation. Furthermore, we determined that the photocatalytic degradation of the HA dominated the behavior of TiO2 in our study. From the results of HA removal and 3DEEM fluorescence spectra data for the solution, a change in the HA was in accordance with the size change of the TiO2. The results illustrated that the UV irradiation affected the behavior of light-active nanomaterial (such as TiO2) in an aquatic system, thus influencing their bioavailability and reactivity. Copyright © 2016 Elsevier Ltd. All rights reserved.

In situ imaging of ultra-fast loss of nanostructure in nanoparticle aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egan, Garth C.; Sullivan, Kyle T.; LaGrange, Thomas

2014-02-28

The word “nanoparticle” nominally elicits a vision of an isolated sphere; however, the vast bulk of nanoparticulate material exists in an aggregated state. This can have significant implications for applications such as combustion, catalysis, and optical excitation, where particles are exposed to high temperature and rapid heating conditions. In such environments, particles become susceptible to morphological changes which can reduce surface area, often to the detriment of functionality. Here, we report on thermally-induced coalescence which can occur in aluminum nanoparticle aggregates subjected to rapid heating (10{sup 6}–10{sup 11} K/s). Using dynamic transmission electron microscopy, we observed morphological changes in nanoparticle aggregatesmore » occurring in as little as a few nanoseconds after the onset of heating. The time-resolved probes reveal that the morphological changes initiate within 15 ns and are completed in less than 50 ns. The morphological changes were found to have a threshold temperature of about 1300 ± 50 K, as determined by millisecond-scale experiments with a calibrated heating stage. The temperature distribution of aggregates during laser heating was modeled with various simulation approaches. The results indicate that, under rapid heating conditions, coalescence occurs at an intermediate temperature between the melting points of aluminum and the aluminum oxide shell, and proceeds rapidly once this threshold temperature is reached.« less

Simple preparation of magnetic field-responsive structural colored Janus particles.

PubMed

Teshima, Midori; Seki, Takahiro; Takeoka, Yukikazu

2018-03-08

We established a simple method for preparing Janus particles displaying different structural colors using submicron-sized fine silica particles and magnetic nanoparticles composed of Fe 3 O 4 . A w/o emulsion is prepared by vortex-stirring a mixed aqueous solution of suspended fine silica particles and magnetic nanoparticles and of hexadecane containing an emulsifier. Subsequent drying of the emulsion on a hot plate using a magnetic stirrer provides a polydisperse particle aggregate displaying two different structural colors according to the ratio of the amount of fine silica particles to the amount of magnetic nanoparticles. This polydisperse particle aggregate can be converted into monodisperse particles simply by using a sieve made of stainless steel. In the presence of a magnet, the monodisperse Janus particles can change their orientation and can switch between two different structural colors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Min; Mikecz, Anna von

Despite of their exponentially growing use, little is known about cell biological effects of nanoparticles. Here, we report uptake of silica (SiO{sub 2}) nanoparticles to the cell nucleus where they induce aberrant clusters of topoisomerase I (topo I) in the nucleoplasm that additionally contain signature proteins of nuclear domains, and protein aggregation such as ubiquitin, proteasomes, cellular glutamine repeat (polyQ) proteins, and huntingtin. Formation of intranuclear protein aggregates (1) inhibits replication, transcription, and cell proliferation; (2) does not significantly alter proteasomal activity or cell viability; and (3) is reversible by Congo red and trehalose. Since SiO{sub 2} nanoparticles trigger amore » subnuclear pathology resembling the one occurring in expanded polyglutamine neurodegenerative disorders, we suggest that integrity of the functional architecture of the cell nucleus should be used as a read out for cytotoxicity and considered in the development of safe nanotechnology.« less

Biosynthesis and computational analysis of amine-ended dual thiol ligand functionalized gold nanoparticles for conventional spectroscopy detection of melamine.

PubMed

Anand, K; Singh, Thishana; Madhumitha, G; Phulukdaree, A; Gengan, Robert M; Chuturgoon, A A

2017-04-01

The bio-synthesized DTAuNPs have an average size of 21nm. The aggregation extent depends on the concentration of melamine, which was validated by UV-vis spectra and visual method of melamine detection was developed. The major observation in this method was the color change of DTAuNPs from red to purple due to the aggregation of ligand capped gold nanoparticles instigated by melamine. The reaction of color changes were processed due to the shifting of bonding in hydrogen in between nanoparticles and melamine. The aggregation extent depends on the concentration of melamine, which can be validated UV-vis spectra and visual method of detecting melamine is developed. The electron density and conventional UV-vis, FTIR spectroscopy and DFT studies on the ligand was performed using computational methods. The theoretical and experimental data for the energy transitions and the molar extinction coefficients of the ligands studied has been obtained. Further, the ligand capped gold nanoparticles was assessed for cytotoxicity against A549 cells which resulted in significant decrease in cell viability was noted in 50μg/mL DTAu, 4-ATP and AXT treated cells at 2h (85% and 66%) and 6h (83% and 36%) respectively, (p<0.01) were studied and reported in this manuscript. Copyright © 2017 Elsevier B.V. All rights reserved.

Formation of wormlike aggregates of fluorocarbon-hydrocarbon hybrid surfactant by Langmuir-Blodgett transfer and alignment of gold nanoparticles.

PubMed

Kondo, Yukishige; Fukuoka, Hiroshi; Nakano, Shuichi; Hayashi, Kohei; Tsukagoshi, Tatsuya; Matsumoto, Mutsuyoshi; Yoshino, Norio

2007-05-22

A novel anionic fluorocarbon-hydrocarbon hybrid surfactant (SS-Hyb-Na+) with a disulfide group has been synthesized from 11-bromo-1-undecanal and perfluorohexylethyl iodide via three steps. The Langmuir-Blodgett (LB) transfer of the 1:100 (mol/mol) mixed monolayer of SS-Hyb-Na+ and stearyl alcohol (C18OH) formed on an aqueous solution containing a cationic polymer, poly(diallyldimethylammonium chloride) (PDDA+Cl-) onto a hydrophobic silicon wafer yields the formation of wormlike aggregates consisting of SS-Hyb-/PDDA+ polyion complexes. It is found that the aggregates align along the withdrawal direction of the wafer substrate. When the wafer on which the wormlike aggregates exist is immersed into the dispersion of gold nanoparticles (Au NPs) prepared by the citrate reduction method, Au NPs align along the wormlike structures. Even though the surface of the wafer is placed either vertical or parallel to the monolayer compression direction during the LB transfer, the one-dimensional (1D) array of Au NPs is observed along the withdrawal direction of the wafer. This indicates that the wormlike aggregates of SS-Hyb-/PDDA+ complexes are aligned during the LB transfer, and the aligned aggregates behave as a scaffold in the 1D array of Au NPs.

Formation and decay of charge carriers in aggregate nanofibers consisting of poly(3-hexylthiophene)-coated gold nanoparticles.

PubMed

Lee, Dongki; Lee, Jaewon; Song, Ki-Hee; Rhee, Hanju; Jang, Du-Jeon

2016-01-21

Thin nanofibers (NFs) of J-dominant aggregates with a thickness of 15 nm and thick NFs of H-dominant aggregates with a thickness of 25 nm were fabricated by the self-assembly of poly(3-hexylthiophene)-coated gold nanoparticles. The formation and decay dynamics of the charge carriers, which are dependent on the aggregate types of NFs, was investigated by time-resolved emission and transient-absorption spectroscopy. With increasing excitation energy, the fraction of the fast emission decay component decreased, suggesting that the fast formation of polaron pairs (PP), localized (LP), and delocalized polarons (DP) results from higher singlet exciton states produced by the singlet fusion. The faster decay dynamics of DP and LP in the thick NFs than in thin NFs is due to the increased delocalization of DP and LP. As the interchain aggregation is weaker than intrachain aggregation, PP decays faster in thin NFs than in thick NFs. In both thin and thick NFs, although triplet (T1) excitons were barely observed with excitation at 532 nm on a nanosecond time scale, they were observed with excitation at 355 nm, showing that T1 excitons within NFs are generated mainly through the singlet fission from a higher singlet exciton state rather than through intersystem crossing.

Sorption of organic phosphates and its effects on aggregation of hematite nanoparticles in monovalent and bivalent solutions.

PubMed

Xu, Chen-Yang; Li, Jiu-Yu; Xu, Ren-Kou; Hong, Zhi-Neng

2017-03-01

Sorption of organic phosphates-myo-inositol hexakisphosphate (IHP) and glycerol phosphate (GP) and its effects on the early stage of hematite aggregation kinetics were investigated at different pH and electrolyte composition. KH 2 PO 4 (KP) was taken as an inorganic P source for comparison. Results indicated that for all types of P, the sorption amounts decreased with increasing solution pH. Sorption amount of IHP was almost two times that of KP, while those of GP and KP were close. Both organic P and inorganic P interacted with hematite via ligand exchange through their phosphate groups, which conveyed negative charges to mineral surface and significantly decreased the zeta potential of hematite. In Na + solution, critical coagulation concentrations (CCCs) of hematite suspensions increased with increasing P concentration and followed the order of KP < GP < IHP at pH 5.5. Compared with KP, the organic P could more effectively stabilize the hematite suspension not only through increasing the negative charges and electrostatic repulsive force, but also through steric repulsion between P-sorbed hematite nanoparticles. When the pH was increased from 5.5 to 10.0, the CCCs of the hematite suspensions with GP and IHP decreased mainly because of the great reductions in organic P sorption amounts and consequent decreases in electrostatic and steric repulsive forces. However, enhanced aggregation was observed in the presence of IHP at pH 4.5 and above in low Ca 2+ solutions. The precipitation of calcium phytate formed net-like structure, which served as bridges to bind hematite nanoparticles and resulted in enhanced aggregation. These results have important implications for assessing the fate and transport of organic P and hematite nanoparticles in soil and aquatic environments.

Fluorescent nanoparticles based on AIE fluorogens for bioimaging.

PubMed

Yan, Lulin; Zhang, Yan; Xu, Bin; Tian, Wenjing

2016-02-07

Fluorescent nanoparticles (FNPs) have recently attracted increasing attention in the biomedical field because of their unique optical properties, easy fabrication and outstanding performance in imaging. Compared with conventional molecular probes including small organic dyes and fluorescent proteins, FNPs based on aggregation-induced emission (AIE) fluorogens have shown significant advantages in tunable emission and brightness, good biocompatibility, superb photo- and physical stability, potential biodegradability and facile surface functionalization. In this review, we summarize the latest advances in the development of fluorescent nanoparticles based on AIE fluorogens including polymer nanoparticles and silica nanoparticles over the past few years, and the various biomedical applications based on these fluorescent nanoparticles are also elaborated.

Size-dependent interaction of silica nanoparticles with lysozyme and bovine serum albumin proteins

NASA Astrophysics Data System (ADS)

Yadav, Indresh; Aswal, Vinod K.; Kohlbrecher, Joachim

2016-05-01

The interaction of three different sized (diameter 10, 18, and 28 nm) anionic silica nanoparticles with two model proteins—cationic lysozyme [molecular weight (MW) 14.7 kDa)] and anionic bovine serum albumin (BSA) (MW 66.4 kDa) has been studied by UV-vis spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The adsorption behavior of proteins on the nanoparticles, measured by UV-vis spectroscopy, is found to be very different for lysozyme and BSA. Lysozyme adsorbs strongly on the nanoparticles and shows exponential behavior as a function of lysozyme concentration irrespective of the nanoparticle size. The total amount of adsorbed lysozyme, as governed by the surface-to-volume ratio, increases on lowering the size of the nanoparticles for a fixed volume fraction of the nanoparticles. On the other hand, BSA does not show any adsorption for all the different sizes of the nanoparticles. Despite having different interactions, both proteins induce similar phase behavior where the nanoparticle-protein system transforms from one phase (clear) to two phase (turbid) as a function of protein concentration. The phase behavior is modified towards the lower concentrations for both proteins with increasing the nanoparticle size. DLS suggests that the phase behavior arises as a result of the nanoparticles' aggregation on the addition of proteins. The size-dependent modifications in the interaction potential, responsible for the phase behavior, have been determined by SANS data as modeled using the two-Yukawa potential accounting for the repulsive and attractive interactions in the systems. The protein-induced interaction between the nanoparticles is found to be short-range attraction for lysozyme and long-range attraction for BSA. The magnitude of attractive interaction irrespective of protein type is enhanced with increase in the size of the nanoparticles. The total (attractive+repulsive) potential leading to two-phase formation is found to be more attractive for larger sized nanoparticles. The nanoparticle aggregates are characterized by mass fractal.

Two-Dimensional Self-Assembly and Chemical Synthesis of Charged Gold Nanoparticles in Non-Polar Solvents

NASA Astrophysics Data System (ADS)

Martin, Matthew Nichols

Gold nanoparticles between 1 and 10 nm in diameter exhibit size-dependent electronic and optical properties that cannot be explained by molecular science and which deviate significantly from their bulk counterparts. For example, the melting temperature of gold nanoparticles less than 5 nm in diameter is around 300 °C [1], whereas bulk gold melts at over 1000 °C [2]. Gold nanoparticles require precise control over particle diameter in order to exploit and tailor their unique properties; however, tuning the size reproducibly and predictably has proved to be a challenge. One of the most difficult obstacles to overcome is nanoparticle aggregation, since nanoparticles flocculate at room temperature quite readily. In 1994, Brust et al. solved the aggregation problem by introducing monolayer protection coatings on gold nanoparticles, in which organic ligand molecules are attached to the nanoparticle surface and create a physical barrier between the gold core and solvent. This was a definitive solution to size stability, since nanoparticles never aggregate, however the synthesis method does not generate monodisperse nanoparticles and has poor size-tuning capabilities. We developed a synthesis method for gold nanoparticles that improves greatly upon the Brust method. Starting from scratch, we discovered a "sweet zone" for aqueous gold nanoparticles, revealing how to make "naked" (stabilizer-free) gold nanoparticles which are continuously and precisely controlled between 3.2 and 5.2 nm in diameter, both reproducibly and predictably. Naked nanoparticles are then coated with organic 1-dodecanethiol ligand molecules, and transferred to hexane. Since all reaction byproducts remain in the water-phase, no postsynthesis cleaning or size-filtering is necessary, reducing the total synthesis time from ~24 hours in the Brust method, to less than 10 minutes. Surprisingly, our nanoparticles are highly negatively charged in nonpolar solvents. This unexpectedly caused nanoparticles to be unstable in toluene but stable in hexane. Consequently, nanoparticles float to the air-toluene interface, and after evaporation of toluene, form large 2D monolayer films of nanoparticle that are uniform at nanometer, micrometer, and millimeter length scales. This facile 2D self-assembly method also displays extremely size-dependent features in the 3.2 -- 5.2 nm range. Additionally, we managed to expand our synthesis method to include smaller gold nanoparticles. Since small gold clusters less than 2 nm in diameter are exponentially more efficient than other conventional catalysts, we labored to synthesize nanoclusters with diameters less than 2 nm, and fortunately, reduced the synthesis time to 2 minutes. With complete size control of gold nanoparticles between 1 and 5 nm, we have developed a truly novel synthesis method that forms a strong basis for many interesting studies. We have also discovered a novel method for place exchange reactions of organic molecular coatings. Ligand exchange of water-soluble thiols for alkylamines was performed at room temperature and occurred in less than 10 seconds, and allowed for the phase-transfer of nanoparticles from nonpolar solvents back to water. This method is extremely useful for the biological nanoparticle community as they are already using nanoparticles for drug delivery, DNA sensing, and molecular recognition.

A new measure of molecular attractions between nanoparticles near kT adhesion energy

NASA Astrophysics Data System (ADS)

Kendall, Kevin; Dhir, Aman; Du, Shangfeng

2009-07-01

The weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e.g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

Evolution of Microstructure and Mechanical Properties of Oxide Dispersion Strengthened Steels Made from Water-Atomized Ferritic Powder

NASA Astrophysics Data System (ADS)

Arkhurst, Barton Mensah; Kim, Jeoung Han

2018-05-01

Nano-structured oxide dispersion strengthened (ODS) steels produced from a 410L stainless steel powder prepared by water-atomization was studied. The influences of Ti content and milling time on the microstructure and the mechanical properties were analysed. It was found that the ODS steels made from the Si bearing 410L powder contained Y-Ti-O, Y-Ti-Si-O, Y-Si-O, and TiO2 oxides. Most nanoparticles produced after 80 h of milling were aggregated nanoparticles; however, after 160 h of milling, most aggregated nanoparticles dissociated into smaller individual nanoparticles. Perfect mixing of Y and Ti was not achieved even after the longer milling time of 160 h; instead, the longer hours of milling rather resulted in Si incorporation into the Y-Ti-O rich nanoparticles and a change in the matrix morphology from an equiaxed microstructure to a tempered martensite-like microstructure. The overall micro-hardness of the ODS steel increased with the increase of milling time. After 80 and 160 h, the microhardnesses were over 400 HV, which primarily resulted from the finer dispersed nanoparticles and in part to the formation of martensitic phases. Tensile strength of the 410L ODS steels was comparable with that of ODS steel produced from gas-atomized powder.

Exciton–exciton annihilation as a probe of interchain interactions in PPV–oligomer aggregates

DOE PAGES

Peteanu, Linda A.; Chowdhury, Sanchari; Wildeman, Jurjen; ...

2017-01-20

One measure of exciton mobility in an aggregate is the efficiency of exciton–exciton annihilation (EEA). Both exciton mobilities and EEA are enhanced for aggregate morphologies in which the distances between chromophores and their relative orientations are favorable for Förster energy transfer. Here this principle is applied to gauge the strength of interchain interactions in aggregates of two substituted PPV oligomers of 7 (OPPV7) and 13 (OPPV13) phenylene rings. These are models of the semiconducting conjugated polymer MEH–PPV. The aggregates were formed by adding a poor solvent (methanol or water) to the oligomers dissolved in a good solvent. Aggregates formed frommore » the longer-chain oligomer and/or by addition of the more polar solvent showed the largest contribution of EEA in their emission decay dynamics. This was found to correlate with the degree to which the steady-state emission spectrum of the monomer is altered by aggregation. Furthermore, the wavelength dependence of the EEA signal was also shown to be useful in differentiating emission features due to monomeric and aggregated chains when their spectra overlap significantly.« less

Exciton-Exciton Annihilation as a Probe of Interchain Interactions in PPV-Oligomer Aggregates.

PubMed

Peteanu, Linda A; Chowdhury, Sanchari; Wildeman, Jurjen; Sfeir, Matthew Y

2017-02-23

One measure of exciton mobility in an aggregate is the efficiency of exciton-exciton annihilation (EEA). Both exciton mobilities and EEA are enhanced for aggregate morphologies in which the distances between chromophores and their relative orientations are favorable for Förster energy transfer. Here this principle is applied to gauge the strength of interchain interactions in aggregates of two substituted PPV oligomers of 7 (OPPV7) and 13 (OPPV13) phenylene rings. These are models of the semiconducting conjugated polymer MEH-PPV. The aggregates were formed by adding a poor solvent (methanol or water) to the oligomers dissolved in a good solvent. Aggregates formed from the longer-chain oligomer and/or by addition of the more polar solvent showed the largest contribution of EEA in their emission decay dynamics. This was found to correlate with the degree to which the steady-state emission spectrum of the monomer is altered by aggregation. The wavelength dependence of the EEA signal was also shown to be useful in differentiating emission features due to monomeric and aggregated chains when their spectra overlap significantly.

Dynamics of polymer nanoparticles and chains.

NASA Astrophysics Data System (ADS)

Streletzky, Kiril; McKenna, John; Hillier, Gerry

2006-10-01

We present a Dynamic Light Scattering study of transport properties of the polymer chains and nanoparticles made out of the same starting solution. The spectra of both systems are highly non-exponential requiring a spectral time moment analysis. Our findings indicate the existence of several modes of relaxation in both systems. The comparison of the mean relaxation rates and diffusion coefficients of the different modes in two systems under good solvent conditions will be reported. Temperature sensitivity of the polymer nanoparticles and its possible applications in pharmaceutical, coatings, and petroleum industries will also be discussed.

Using multivalency to tailor the superselective binding of polymers on substrates

NASA Astrophysics Data System (ADS)

Tito, Nicholas; Frenkel, Daan

2014-03-01

Multivalency is a microscopic design concept in which a single nanoscopic entity contains multiple ligands, each of which may bind to multiple receptors on another entity. A useful property of many multivalent systems is ``superselectivity,'' where the fraction of the multivalent species bound to their complementary receptors grows sharply with the total number of receptors available. For example in the past two decades, multivalency has been exploited to develop DNA-coated nanoparticles that self-assemble into aggregates over an extremely narrow temperature window. In this talk, we use analytic and self-consistent field theories to explore the binding of multivalent polymers to receptors on a flat substrate. Discussion will focus on how the sequence, number, and binding strength of ligands along the polymer chain can be used to tune the superselectivity of the system. Comparison with recent experiments on model systems will be presented as time permits. We wish to thank ERC Advanced Grant 227758.

Thermally induced hydrosilylation at deuterium-terminated silicon nanoparticles: an investigation of the radical chain propagation mechanism.

PubMed

Holm, Jason; Roberts, Jeffrey T

2009-06-16

Isotopic labeling techniques were employed to study alkene addition to hydrogen- and deuterium-terminated silicon nanoparticles. Deuterium-terminated silicon nanoparticle synthesis is described, as is the characterization of fresh deuterium-terminated particles by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and in situ Fourier transform infrared spectroscopy (FTIR). Particles were refluxed in pure 1-dodecene and subsequently characterized by FTIR and nuclear magnetic resonance (NMR) spectroscopy. (1)H NMR results showed features consistent with dodecyl-terminated nanoparticles. Infrared absorption spectra of refluxed particles showed strong evidence of new C-D bond formation, which is consistent with a radical chain mechanism for alkene addition by hydrosilylation.

Thermal conductivity enhancements and viscosity properties of water based Nanofluid containing carbon nanotubes decorated with ag nanoparticles

NASA Astrophysics Data System (ADS)

Gu, Yanni; Xu, Sheng; Wu, Xiaoshan

2018-01-01

The water based nanofluid containing carbon nanotube (CNT) decorated with Ag nanoparticles (Ag/CNT) is prepared. Its thermal conductivity (k) enhancement increases with the thermal filler loading and the decoration quantity of Ag nanoparticles. The low absolute CNT content will decrease the tangles or aggregations among the CNTs, and it will be good at the Brownian motion of CNTs in the water. It has positive effects on the thermal conductivity of nanofluid. With the increase of Ag loading, the average size of Ag nanoparticles increased, and further results in the decrease of dispersing amount of Ag/CNT as the weight of Ag/CNT is fixed. Little dispersing quantity of Ag/CNT makes it possible that the Ag/CNT particles disperse well in the fluid. So it is not easy for CNTs to form aggregation. The high intrinsic k of CNT and the effective thermal conductive networks forming by CNTs and Ag nanoparticles are good at the k enhancement. With temperature increase the k of Ag/CNT nanofluid appears improvement. The study results make it possible to develop high-efficiency nanofluid for advanced thermal management regions.

Precisely controlled fabrication, manipulation and in-situ analysis of Cu based nanoparticles.

PubMed

Martínez, L; Lauwaet, K; Santoro, G; Sobrado, J M; Peláez, R J; Herrero, V J; Tanarro, I; Ellis, G J; Cernicharo, J; Joblin, C; Huttel, Y; Martín-Gago, J A

2018-05-08

The increasing demand for nanostructured materials is mainly motivated by their key role in a wide variety of technologically relevant fields such as biomedicine, green sustainable energy or catalysis. We have succeeded to scale-up a type of gas aggregation source, called a multiple ion cluster source, for the generation of complex, ultra-pure nanoparticles made of different materials. The high production rates achieved (tens of g/day) for this kind of gas aggregation sources, and the inherent ability to control the structure of the nanoparticles in a controlled environment, make this equipment appealing for industrial purposes, a highly coveted aspect since the introduction of this type of sources. Furthermore, our innovative UHV experimental station also includes in-flight manipulation and processing capabilities by annealing, acceleration, or interaction with background gases along with in-situ characterization of the clusters and nanoparticles fabricated. As an example to demonstrate some of the capabilities of this new equipment, herein we present the fabrication of copper nanoparticles and their processing, including the controlled oxidation (from Cu 0 to CuO through Cu 2 O, and their mixtures) at different stages in the machine.

TiO2 Nanoparticle Uptake by the Water Flea Daphnia magna via Different Routes is Calcium-Dependent.

PubMed

Tan, Ling-Yan; Huang, Bin; Xu, Shen; Wei, Zhong-Bo; Yang, Liu-Yan; Miao, Ai-Jun

2016-07-19

Calcium plays versatile roles in aquatic ecosystems. In this study, we investigated its effects on the uptake of polyacrylate-coated TiO2 nanoparticles (PAA-TiO2-NPs) by the water flea (cladoceran) Daphnia magna. Particle distribution in these daphnids was also visualized using synchrotron radiation-based micro X-ray fluorescence spectroscopy, transmission electron microscopy, and scanning electron microscopy. At low ambient Ca concentrations in the experimental medium ([Ca]dis), PAA-TiO2-NPs were well dispersed and distributed throughout the daphnid; the particle concentration was highest in the abdominal zone and the gut, as a result of endocytosis and passive drinking of the nanoparticles, respectively. Further, Ca induced PAA-TiO2-NP uptake as a result of the increased Ca influx. At a high [Ca]dis, the PAA-TiO2-NPs formed micrometer-sized aggregates that were ingested by D. magna and concentrated only in its gut, independent of the Ca influx. Our results demonstrated the multiple effects of Ca on nanoparticle bioaccumulation. Specifically, well-dispersed nanoparticles were taken up by D. magna through endocytosis and passive drinking whereas the uptake of micrometer-sized aggregates relied on active ingestion.

Thermal conductivity enhancements and viscosity properties of water based Nanofluid containing carbon nanotubes decorated with ag nanoparticles

NASA Astrophysics Data System (ADS)

Gu, Yanni; Xu, Sheng; Wu, Xiaoshan

2018-06-01

The water based nanofluid containing carbon nanotube (CNT) decorated with Ag nanoparticles (Ag/CNT) is prepared. Its thermal conductivity ( k) enhancement increases with the thermal filler loading and the decoration quantity of Ag nanoparticles. The low absolute CNT content will decrease the tangles or aggregations among the CNTs, and it will be good at the Brownian motion of CNTs in the water. It has positive effects on the thermal conductivity of nanofluid. With the increase of Ag loading, the average size of Ag nanoparticles increased, and further results in the decrease of dispersing amount of Ag/CNT as the weight of Ag/CNT is fixed. Little dispersing quantity of Ag/CNT makes it possible that the Ag/CNT particles disperse well in the fluid. So it is not easy for CNTs to form aggregation. The high intrinsic k of CNT and the effective thermal conductive networks forming by CNTs and Ag nanoparticles are good at the k enhancement. With temperature increase the k of Ag/CNT nanofluid appears improvement. The study results make it possible to develop high-efficiency nanofluid for advanced thermal management regions.

Enhanced Delivery of Chemotherapy to Tumors Using a Multi-Component Nanochain with Radiofrequency-Tunable Drug Release

PubMed Central

Peiris, Pubudu M.; Bauer, Lisa; Toy, Randall; Tran, Emily; Pansky, Jenna; Doolittle, Elizabeth; Schmidt, Erik; Hayden, Elliott; Mayer, Aaron; Keri, Ruth A.; Griswold, Mark A.; Karathanasis, Efstathios

2012-01-01

While nanoparticles maximize the amount of chemotherapeutic drug in tumors relative to normal tissues, nanoparticle-based drugs are not accessible to the majority of cancer cells because nanoparticles display patchy, near-perivascular accumulation in tumors. To overcome the limitations of current drugs in their molecular or nanoparticle form, we developed a nanoparticle based on multi-component nanochains to deliver drug to the majority of cancer cells throughout a tumor while reducing off-target delivery. The nanoparticle is composed of three magnetic nanospheres and one doxorubicin-loaded liposome assembled in a 100-nm-long chain. These nanoparticles display prolonged blood circulation and significant intratumoral deposition in tumor models in rodents. Furthermore, the magnetic particles of the chains serve as a mechanical transducer to transfer radiofrequency energy to the drug-loaded liposome. The defects on the liposomal walls trigger the release of free drug capable of spreading throughout the entire tumor, which results in a wide-spread anticancer effect. PMID:22486623

Plasmonic nanoparticle chain in a light field: a resonant optical sail.

PubMed

Albaladejo, Silvia; Sáenz, Juan José; Marqués, Manuel I

2011-11-09

Optical trapping and driving of small objects has become a topic of increasing interest in multidisciplinary sciences. We propose to use a chain made of metallic nanoparticles as a resonant light sail, attached by one end point to a transparent object and propelling it by the use of electromagnetic radiation. Driving forces exerted on the chain are theoretically studied as a function of radiation's wavelength and chain's alignments with respect to the direction of radiation. Interestingly, there is a window in the frequency spectrum in which null-torque equilibrium configuration, with minimum geometric cross section, corresponds to a maximum in the driving force.

Surface water retardation around single-chain polymeric nanoparticles: critical for catalytic function?

PubMed

Stals, Patrick J M; Cheng, Chi-Yuan; van Beek, Lotte; Wauters, Annelies C; Palmans, Anja R A; Han, Songi; Meijer, E W

2016-03-01

A library of water-soluble dynamic single-chain polymeric nanoparticles (SCPN) was prepared using a controlled radical polymerisation technique followed by the introduction of functional groups, including probes at targeted positions. The combined tools of electron paramagnetic resonance (EPR) and Overhauser dynamic nuclear polarization (ODNP) reveal that these SCPNs have structural and surface hydration properties resembling that of enzymes.

Dielectric relaxation behavior of colloidal suspensions of palladium nanoparticle chains dispersed in PVP/EG solution.

PubMed

Chen, Zhen; Zhao, Kong-Shuang; Guo, Lin; Feng, Cai-Hong

2007-04-28

Dielectric measurements were carried out on colloidal suspensions of palladium nanoparticle chains dispersed in poly(vinyl pyrrolidone)/ethylene glycol (PVP/EG) solution with different particle volume fractions, and dielectric relaxation with relaxation time distribution and small relaxation amplitude was observed in the frequency range from 10(5) to 10(7) Hz. By means of the method based on logarithmic derivative of the dielectric constant and a numerical Kramers-Kronig transform method, two dielectric relaxations were confirmed and dielectric parameters were determined from the dielectric spectra. The dielectric parameters showed a strong dependence on the volume fraction of palladium nanoparticle chain. Through analyzing limiting conductivity at low frequency, the authors found the conductance percolation phenomenon of the suspensions, and the threshold volume fraction is about 0.18. It was concluded from analyzing the dielectric parameters that the high frequency dielectric relaxation results from interfacial polarization and the low frequency dielectric relaxation is a consequence of counterion polarization. They also found that the dispersion state of the palladium nanoparticle chain in PVP/EG solution is dependent on the particle volume fraction, and this may shed some light on a better application of this kind of materials.

Crazing of nanocomposites with polymer-tethered nanoparticles

DOE PAGES

Meng, Dong; Kumar, Sanat K.; Ge, Ting; ...

2016-09-07

The crazing behavior of polymer nanocomposites formed by blending polymer grafted nanoparticles with an entangled polymer melt is studied by molecular dynamics simulations. We focus on the three key differences in the crazing behavior of a composite relative to the pure homopolymer matrix, namely, a lower yield stress, a smaller extension ratio, and a grafted chain length dependent failure stress. The yield behavior is found to be mostly controlled by the local nanoparticle-grafted polymer interfacial energy, with the grafted polymer-polymer matrix interfacial structure being of little to no relevance. Increasing the attraction between nanoparticle core and the grafted polymer inhibitsmore » void nucleation and leads to a higher yield stress. In the craze growth regime, the presence of “grafted chain” sections of ≈100 monomers alters the mechanical response of composite samples, giving rise to smaller extension ratios and higher drawing stresses than for the homopolymer matrix. As a result, the dominant failure mechanism of composite samples depends strongly on the length of the grafted chains, with disentanglement being the dominant mechanism for short chains, while bond breaking is the failure mode for chain lengths >10N e, where N e is the entanglement length.« less

Structure of rigid polymers confined to nanoparticles: Molecular dynamics simulations insight

DOE PAGES

Maskey, Sabina; Lane, J. Matthew D.; Perahia, Dvora; ...

2016-02-04

Nanoparticles (NPs) grafted with organic layers form hybrids able to retain their unique properties through integration into the mesoscopic scale. The organic layer structure and response often determine the functionality of the hybrids on the mesoscopic length scale. Using molecular dynamics (MD) simulations, we probe the conformation of luminescent rigid polymers, dialkyl poly(p-phenylene ethynylene)s (PPE), end-grafted onto a silica nanoparticle in different solvents as the molecular weights and polymer coverages are varied. We find that, in contrast to NP-grafted flexible polymers, the chains are fully extended independent of the solvent. In toluene and decane, which are good solvents, the graftedmore » PPEs chains assume a similar conformation to that observed in dilute solutions. In water, which is a poor solvent for the PPEs, the polymer chains form one large cluster but remain extended. The radial distribution of the chains around the core of the nanoparticle is homogeneous in good solvents, whereas in poor solvents clusters are formed independent of molecular weights and coverages. As a result, the clustering is distinctively different from the response of grafted flexible and semiflexible polymers.« less

Dielectrophoresis-magnetophoresis force driven magnetic nanoparticle movement in transformer oil based magnetic fluids.

PubMed

Lee, Jong-Chul; Lee, Sangyoup

2013-09-01

Magnetic fluid is a stable colloidal mixture contained magnetic nanoparticles coated with a surfactant. Recently, it was found that the fluid has properties to increase heat transfer and dielectric characteristics due to the added magnetic nanoparticles in transformer oils. The magnetic nanoparticles in the fluid experience an electrical force directed toward the place of maximum electric field strength when the electric field is applied. And when the external magnetic field is applied, the magnetic nanoparticles form long chains oriented along the direction of the field. The behaviors of magnetic nanoparticles in both the fields must play an important role in changing the heat transfer and dielectric characteristics of the fluids. In this study, we visualized the movement of magnetic nanoparticles influenced by both the fields applied in-situ. It was found that the magnetic nanoparticles travel in the region near the electrode by the electric field and form long chains along the field direction by the magnetic field. It can be inferred that the movement of magnetic nanoparticles appears by both the fields, and the breakdown voltage of transformer oil based magnetic fluids might be influenced according to the dispersion of magnetic nanoparticles.

A Highly Efficient and Photostable Photosensitizer with Near-Infrared Aggregation-Induced Emission for Image-Guided Photodynamic Anticancer Therapy.

PubMed

Wu, Wenbo; Mao, Duo; Hu, Fang; Xu, Shidang; Chen, Chao; Zhang, Chong-Jing; Cheng, Xiamin; Yuan, Youyong; Ding, Dan; Kong, Deling; Liu, Bin

2017-09-01

Photodynamic therapy (PDT), which relies on photosensitizers (PS) and light to generate reactive oxygen species to kill cancer cells or bacteria, has attracted much attention in recent years. PSs with both bright emission and efficient singlet oxygen generation have also been used for image-guided PDT. However, simultaneously achieving effective 1 O 2 generation, long wavelength absorption, and stable near-infrared (NIR) emission with low dark toxicity in a single PS remains challenging. In addition, it is well known that when traditional PSs are made into nanoparticles, they encounter quenched fluorescence and reduced 1 O 2 production. In this contribution, these challenging issues have been successfully addressed through designing the first photostable photosensitizer with aggregation-induced NIR emission and very effective 1 O 2 generation in aggregate state. The yielded nanoparticles show very effective 1 O 2 generation, bright NIR fluorescence centered at 820 nm, excellent photostability, good biocompatibility, and negligible dark in vivo toxicity. Both in vitro and in vivo experiments prove that the nanoparticles are excellent candidates for image-guided photodynamic anticancer therapy. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanoparticle Encapsulation in Diblock Copolymer/Homopolymer Blend Thin Film Mixtures

NASA Astrophysics Data System (ADS)

Zhao, Junnan; Chen, Xi; Green, Peter

2014-03-01

We investigated the organization of low concentrations of poly (2-vinylpyridine) (P2VP) grafted gold nanoparticles within a diblock copolymer polystyrene-b-poly (2-vinylpyridine) (PS-b-P2VP)/homopolymer polystyrene (PS) blend thin film. The PS-b-P2VP copolymers formed micelles, composed of inner cores of P2VP block and outer coronae of PS blocks, throughout the homopolymer PS. All nanoparticles were encapsulated within micelle cores and each micelle contained one or no nanoparticle, on average. When the host PS chains are much longer than corona chains, micelles tended to self-organize at the interfaces. Otherwise, they were dispersed throughout the PS host. In comparison to the neat PS-b-P2VP/PS blend, the nanoparticles/PS-b-P2VP/PS system had a higher density of smaller micelles, influenced largely by the number of nanoparticles in the system. The behavior of this system is understood in terms of the maximization of the nanoparticle/micelle core interactions and of the translational entropies of the micelles and the nanoparticles.

Simple and Sensitive Colorimetric Assay for Pb2+ Based on Glutathione Protected Ag Nanoparticles by Salt Amplification.

PubMed

Chen, Zhang; Li, Huidong; Chu, Lin; Liu, Chenbin; Luo, Shenglian

2015-02-01

A simple and sensitive colorimetric assay for Pb2+ detection has been reported using glutathione protected silver nanoparticles (AgNPs) by salt amplification. The naked AgNPs aggregate under the influence of salt. Glutathione (GSH) can bind to AgNPs via Ag-S bond, helping AgNPs to against salt-induced aggregation. However, GSH binding to AgNPs can be compromised by the interaction between Pb2+ and GSH. As a result, Pb2+-mediated aggregation of AgNPs under the influence of salt is reflected by the UV-Visible spectrum, and the qualitative and quantitative detection for Pb2+ is accomplished, with the detection range 0.5-4 µM and a detection limit of 0.5 µM. At the same time, Pb2+ in real water sample is detected. Furthermore, the high selectivity and low cost of the assay means it is promising for enviromental applications.

Space charge effects on the dielectric response of polymer nanocomposites

NASA Astrophysics Data System (ADS)

Shen, Zhong-Hui; Wang, Jian-Jun; Zhang, Xin; Lin, Yuanhua; Nan, Ce-Wen; Chen, Long-Qing; Shen, Yang

2017-08-01

Adding high-κ ceramic nanoparticles into polymers is a general strategy to improve the performances in energy storage. Classic effective medium theories may fail to predict the effective permittivity in polymer nanocomposites wherein the space charge effects are important. In this work, a computational model is developed to understand the space charge effects on the frequency-dependent dielectric properties including the real permittivity and the loss for polymer nanocomposites with both randomly distributed and aggregated nanoparticle fillers. It is found that the real permittivity of the SrTiO3/polyethylene (12% SrTiO3 in volume fraction) nanocomposite can be increased to as high as 60 when there is nanoparticle aggregation and the ion concentration in the bulk polymer is around 1016 cm-3. This model can be employed to quantitatively predict the frequency-dependent dielectric properties for polymer nanocomposites with arbitrary microstructures.

Determination of anionic surface active agents using silica coated magnetite nanoparticles modified with cationic surfactant aggregates.

PubMed

Pena-Pereira, Francisco; Duarte, Regina M B O; Trindade, Tito; Duarte, Armando C

2013-07-19

The development of a novel methodology for extraction and preconcentration of the most commonly used anionic surface active agents (SAAs), linear alkylbenzene sulfonates (LAS), is presented herein. The present method, based on the use of silica-magnetite nanoparticles modified with cationic surfactant aggregates, was developed for determination of C10-C13 LAS homologues. The proposed methodology allowed quantitative recoveries of C10-C13 LAS homologues by using a reduced amount of magnetic nanoparticles. Limits of detection were in the range 0.8-1.9μgL(-1) for C10-C13 LAS homologues, while the repeatability, expressed as relative standard deviation (RSD), ranged from 2.0 to 3.9% (N=6). Finally, the proposed method was successfully applied to the analysis of a variety of natural water samples. Copyright © 2013 Elsevier B.V. All rights reserved.

Body-on-a-chip simulation with gastrointestinal tract and liver tissues suggests that ingested nanoparticles have the potential to cause liver injury.

PubMed

Esch, Mandy B; Mahler, Gretchen J; Stokol, Tracy; Shuler, Michael L

2014-08-21

The use of nanoparticles in medical applications is highly anticipated, and at the same time little is known about how these nanoparticles affect human tissues. Here we have simulated the oral uptake of 50 nm carboxylated polystyrene nanoparticles with a microscale body-on-a-chip system (also referred to as multi-tissue microphysiological system or micro Cell Culture Analog). Using the 'GI tract-liver-other tissues' system allowed us to observe compounding effects and detect liver tissue injury at lower nanoparticle concentrations than was expected from experiments with single tissues. To construct this system, we combined in vitro models of the human intestinal epithelium, represented by a co-culture of enterocytes (Caco-2) and mucin-producing cells (TH29-MTX), and the liver, represented by HepG2/C3A cells, within one microfluidic device. The device also contained chambers that together represented the liquid portions of all other organs of the human body. Measuring the transport of 50 nm carboxylated polystyrene nanoparticles across the Caco-2/HT29-MTX co-culture, we found that this multi-cell layer presents an effective barrier to 90.5 ± 2.9% of the nanoparticles. Further, our simulation suggests that a larger fraction of the 9.5 ± 2.9% nanoparticles that travelled across the Caco-2/HT29-MTX cell layer were not large nanoparticle aggregates, but primarily single nanoparticles and small aggregates. After crossing the GI tract epithelium, nanoparticles that were administered in high doses estimated in terms of possible daily human consumption (240 and 480 × 10(11) nanoparticles mL(-1)) induced the release of aspartate aminotransferase (AST), an intracellular enzyme of the liver that indicates liver cell injury. Our results indicate that body-on-a-chip devices are highly relevant in vitro models for evaluating nanoparticle interactions with human tissues.

Synthesis and characterization of a poly(lactic-co-glycolic acid) core + poly(N-isopropylacrylamide) shell nanoparticle system

PubMed Central

Kosinski, Aaron M.; Brugnano, Jamie L.; Seal, Brandon L.; Knight, Frances C.; Panitch, Alyssa

2012-01-01

Poly(lactic-co-glycolic acid) (PLGA) is a popular material used to prepare nanoparticles for drug delivery. However, PLGA nanoparticles lack desirable attributes including active targeting abilities, resistance to aggregation during lyophilization, and the ability to respond to dynamic environmental stimuli. To overcome these issues, we fabricated a nanoparticle consisting of a PLGA core encapsulated within a shell of poly(N-isopropylacrylamide). Dynamic light scattering and transmission electron microscope imaging were used to characterize the nanoparticles, while an MTT assay and ELISA suggested biocompatibility in THP1 cells. Finally, a collagen type II binding assay showed successful modification of these nanoparticles with an active targeting moiety. PMID:23507885

Surface plasmon resonances of protein-conjugated gold nanoparticles on graphitic substrates

NASA Astrophysics Data System (ADS)

Phan, Anh D.; Hoang, Trinh X.; Nghiem, Thi H. L.; Woods, Lilia M.

2013-10-01

We present theoretical calculations for the absorption properties of protein-coated gold nanoparticles on graphene and graphite substrates. As the substrate is far away from nanoparticles, numerical results show that the number of protein bovine serum molecules aggregating on gold surfaces can be quantitatively determined for gold nanoparticles with arbitrary size by means of the Mie theory and the absorption spectra. The presence of a graphene substrate near the protein-conjugated gold nanoparticles results in a red shift of the surface plasmon resonances of the nanoparticles. This effect can be modulated upon changing the graphene chemical potential. Our findings show that the graphene and graphite affect the absorption spectra in a similar way.

NMR study on the network structure of a mixed gel of kappa and iota carrageenans.

PubMed

Hu, Bingjie; Du, Lei; Matsukawa, Shingo

2016-10-05

The temperature dependencies of the (1)H T2 and diffusion coefficient (D) of a mixed solution of kappa-carrageenan and iota-carrageenan were measured by NMR. Rheological and NMR measurements suggested an exponential formation of rigid aggregates of kappa-carrageenan and a gradual formation of fine aggregates of iota-carrageenan during two step increases of G'. The results also suggested that longer carrageenan chains are preferentially involved in aggregation, thus resulting in a decrease in the average Mw of solute carrageenans. The results of diffusion measurements for poly(ethylene oxide) (PEO) suggested that kappa-carrageenan formed thick aggregates that decreased hindrance to PEO diffusion by decreasing the solute kappa-carrageenan concentration in the voids of the aggregated chains, and that iota-carrageenan formed fine aggregates that decreased the solute iota-carrageenan concentration less. DPEO in a mixed solution of kappa-carrageenan and iota-carrageenan suggested two possibilities for the microscopic network structure: an interpenetrating network structure, or micro-phase separation. Copyright © 2016. Published by Elsevier Ltd.

Probing amyloid fibril formation of the NFGAIL peptide by computer simulations

NASA Astrophysics Data System (ADS)

Melquiond, Adrien; Gelly, Jean-Christophe; Mousseau, Normand; Derreumaux, Philippe

2007-02-01

Amyloid fibril formation, as observed in Alzheimer's disease and type II diabetes, is currently described by a nucleation-condensation mechanism, but the details of the process preceding the formation of the nucleus are still lacking. In this study, using an activation-relaxation technique coupled to a generic energy model, we explore the aggregation pathways of 12 chains of the hexapeptide NFGAIL. The simulations show, starting from a preformed parallel dimer and ten disordered chains, that the peptides form essentially amorphous oligomers or more rarely ordered β-sheet structures where the peptides adopt a parallel orientation within the sheets. Comparison between the simulations indicates that a dimer is not a sufficient seed for avoiding amorphous aggregates and that there is a critical threshold in the number of connections between the chains above which exploration of amorphous aggregates is preferred.

Epoxy and Silicone Optical Nanocomposites Filled with Grafted Nanoparticles

NASA Astrophysics Data System (ADS)

Tao, Peng

Polymer nanocomposites, as a technologically important class of materials, exhibit diverse functional properties, and are used for applications ranging from structural and biomedical to electronic and optical. The properties of polymer nanocomposites are determined, in part, by the chemical composition of the polymer matrix and the nanofillers. Their properties are also sensitive to the geometry and size of the nanofillers, and to spatial distribution of the fillers. Control of the nanoparticle size and dispersion within a given polymer provides opportunities to tailor and optimize the properties of nanocomposites for specific application. For optical applications such as encapsulation of light emitting diodes (LEDs), polymer nanocomposites filled with homogeneously dispersed nanoparticles would endow the polymer encapsulant with new functionality without sacrificing optical transparency. To this end, this thesis focuses on developing a simple and versatile approach towards the fabrication of epoxy and silicone transparent nanocomposites using matrix compatible chain-grafted nanoparticles as fillers, and studying the optical properties of the nanocomposites. The surface chemistry and grafted polymer chain design have been shown to play an important role in determining the dispersion state of the grafted nanoparticles and hence the final optical properties of the nanocomposites. To prepare transparent epoxy nanocomposites, poly (glycidyl methacrylate) (PGMA) chains were grafted onto the optical nanoparticle surfaces via a combined phosphate ligand exchange process and azide-alkyne "click" chemistry. The dispersion behavior of PGMA-grafted nanoparticles within the epoxy matrix was investigated by systematically varying the grafting density and grafted chain length. It was found that within the small molecular weight epoxy resins, the dispersion states are more sensitive to the grafting density than the molecular weight of grafted chains. With high grafting densities, the grafted PGMA brushes effectively screen the van der Waals attraction between the particles, and homogenous nanoparticle dispersions of grafted nanoparticles were obtained. Transparent high refractive index TiO2/epoxy thin film and bulk nancomposites were obtained by dispersing PGMA brushes-grafted TiO2 nanoparticles into a commercial epoxy matrix. The refractive index of the nanocomposites showed a linear dependence on the volume fraction of TiO2 nanoparticles and the optical transparency could be generally described by the Rayleigh scattering model. This powerful dispersing technique was further employed to make visibly transparent, UV/IR blocking ITO/epoxy nanocomposites which can be easily applied onto glass and plastic substrates as energy saving optical coating materials. To produce transparent silicone nanocomposites, we directly coupled phosphate-terminated PDMS chains onto the optical nanoparticle surface. It was observed that the mono-modal PDMS-grafted particles usually formed agglomerates within silicone matrices, whereas the bimodal PDMS-grafted particles were able to be individually dispersed even within high molecular weight matrices. Transparent high refractive index bulk TiO2/silicone nanocomposites were successfully prepared by filling with bimodal PDMS-grafted TiO2 nanoparticles. Furthermore, we used the PDMS-grafted TiO2/silicone nanocomposite as a model system to create a methodology to predict and control the dispersion behavior of grafted nanoparticles. The good agreement between experimental observation of dispersion of mono-modal and bimodal grafted particles and theoretical prediction would better guide future experiments and lead to predictability in polymer composite design. Finally, the bimodal grafted chain design was implemented in the preparation of transparent and luminescent CdSe/silicone nanocomposites with potential application as non-scattering light conversion materials for LEDs. The homogeneous dispersion of bimodal PDMS-grafted CdSe quantum dots not only minimizes the transparency loss due to scattering, but also benefits the uniformity and long-term stability of photoluminescence of the nanocomposites.

Online Coupling of Flow-Field Flow Fractionation and Single Particle Inductively Coupled Plasma-Mass Spectrometry: Characterization of Nanoparticle Surface Coating Thickness and Aggregation State

EPA Science Inventory

Surface coating thickness and aggregation state have strong influence on the environmental fate, transport, and toxicity of engineered nanomaterials. In this study, flow-field flow fractionation coupled on-line with single particle inductively coupled plasma-mass spectrometry i...

Characterization of core/shell Cu/Ag nanopowders synthesized by electrochemistry and assessment of their impact on hemolysis, platelet aggregation, and coagulation on human blood for potential wound dressing use

NASA Astrophysics Data System (ADS)

Laloy, Julie; Haguet, Hélène; Alpan, Lutfiye; Mancier, Valérie; Mejia, Jorge; Levi, Samuel; Dogné, Jean-Michel; Lucas, Stéphane; Rousse, Céline; Fricoteaux, Patrick

2017-08-01

Copper/silver core/shell nanopowders with different metal ratio have been elaborated by electrochemistry (ultrasound-assisted electrolysis followed by a displacement reaction). Characterization was performed by several methods (X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, centrifugal liquid sedimentation, and zeta potential measurements). The mean diameter of all nanoparticles is around 10 nm. The impact of each nanopowder on hemolysis, platelet aggregation, and coagulation has been studied on whole human blood. Hemolysis assays were performed with spectrophotometric measurement and platelet aggregation, with light transmission aggregometry and was compared to Cu/Pt core/shell nanoparticles with similar size as negative control. Calibrated thrombin generation test has been used for a coagulation study. They neither impact platelet aggregation nor hemolysis and have a procoagulant effect whatever their composition (i.e., metal ratio). These results highlight that such nanopowders have a potential use in medical applications (e.g., wound dressing).

Effects of aqueous suspensions of titanium dioxide nanoparticles on Artemia salina: assessment of nanoparticle aggregation, accumulation and toxicity

PubMed Central

Ates, Mehmet; Daniels, James; Arslan, Zikri; Farah, Ibrahim O.

2012-01-01

Aquatic stability and impact of titanium dioxide nanoparticles (TiO2 NPs, 10-30 nm) was investigated using Artemia salina. Acute exposure was conducted on nauplii (larvae) and adults in seawater in a concentration range from 10 to 100 mg/L TiO2 NPs for 24 h and 96 h. Rapid aggregation occurred in all suspensions of TiO2 NPs to form micrometer size particles. Yet, both nauplii and adults accumulated the aggregates significantly. Average TiO2 content in nauplii ranged from 0.47 to 3.19 mg/g and from 1.29 to 4.43 mg/g in 24 h and 96 h, respectively. Accumulation in adults was higher ranging from 2.30 to 4.19 mg/g and from 4.38 to 6.20 mg/g in 24 h and 96 h, respectively. Phase contrast microscopy images revealed that Artemia were unable to excrete the particles. Thus, the TiO2 aggregates filled inside the guts. No significant mortality or toxicity occurred within 24 h at any dose. Lipid peroxidation levels characterized with malondialdehyde (MDA) concentrations were not statistically different from those of the controls (p>0.05). These results suggested that suspensions of the TiO2 NPs were nontoxic to Artemia, most likely due to the formation of benign TiO2 aggregates in water. In contrast, both mortality and lipid peroxidation increased in extended exposure to 96 h. Highest mortality occurred in 100 mg/L TiO2 NP suspensions; 18% for nauplii and 14% for adults (LC50 > 100 mg/L). These effects were attributed to the particle loading inside the guts leading to oxidative stress as a result of impaired food uptake for a long period of time. PMID:22810381

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peteanu, Linda A.; Chowdhury, Sanchari; Wildeman, Jurjen

One measure of exciton mobility in an aggregate is the efficiency of exciton–exciton annihilation (EEA). Both exciton mobilities and EEA are enhanced for aggregate morphologies in which the distances between chromophores and their relative orientations are favorable for Förster energy transfer. Here this principle is applied to gauge the strength of interchain interactions in aggregates of two substituted PPV oligomers of 7 (OPPV7) and 13 (OPPV13) phenylene rings. These are models of the semiconducting conjugated polymer MEH–PPV. The aggregates were formed by adding a poor solvent (methanol or water) to the oligomers dissolved in a good solvent. Aggregates formed frommore » the longer-chain oligomer and/or by addition of the more polar solvent showed the largest contribution of EEA in their emission decay dynamics. This was found to correlate with the degree to which the steady-state emission spectrum of the monomer is altered by aggregation. Furthermore, the wavelength dependence of the EEA signal was also shown to be useful in differentiating emission features due to monomeric and aggregated chains when their spectra overlap significantly.« less

Intracellular Nanoparticle Aggregation as a Mechanism for Inducing Apoptosis in Breast Cancer Cells

DTIC Science & Technology

2010-09-01

Viral nanoparticles as tools for intravital vascular imaging. Nature Medicine, 2006. 12(3): p. 354-360. 16. Speelmans, G., et al., Transport Studies of...999. 22. Lee, C.C., et al., A single dose of doxorubicin-functionalized bow-tie dendrimer cures mice bearing C-26 colon carcinomas. Proceedings of

Rapid and selective lead (II) colorimetric sensor based on azacrown ether-functionalized gold nanoparticles

NASA Astrophysics Data System (ADS)

Alizadeh, A.; Khodaei, M. M.; Karami, Ch; Workentin, M. S.; Shamsipur, M.; Sadeghi, M.

2010-08-01

A gold nanoparticle (AuNPs)-based simple and fast colorimetric sensor for selective detecting of Pb(II) in aqueous solution has been developed. Monodisperse AuNPs (approx. 2.0 nm diameter) has been prepared facilely and further modified with an alkanethiol-bearing monoazacrown ether terminus. These AuNPs are shown to selectively sense Pb2 + through color change, which is visually discernible by an appearance of the surface plasmon band (SPB) at 520 nm. The recognition mechanism is attributed to the unique structure of the monoazacrown ether attached to AuNPs and metal sandwich coordination between two azacrown ether moieties that are attached to separate nanoparticles. This inter-particle cross-linking results in an aggregation and apparent color change from brown to purple. Additionally, TEM experiments support the optical absorption data proving the aggregation between azacrown ether-capped gold nanoparticles. This AuNP-based colorimetric assay is a facile and robust method and allows fast detection of Pb2 + at ambient temperatures. More importantly, the developed technique does not utilize enzymatic reactions, light-sensitive dye molecules, lengthy protocols or sophisticated instrumentation.

Aggregation and network formation in self-assembly of protein (H3.1) by a coarse-grained Monte Carlo simulation.

PubMed

Pandey, R B; Farmer, B L

2014-11-07

Multi-scale aggregation to network formation of interacting proteins (H3.1) are examined by a knowledge-based coarse-grained Monte Carlo simulation as a function of temperature and the number of protein chains, i.e., the concentration of the protein. Self-assembly of corresponding homo-polymers of constitutive residues (Cys, Thr, and Glu) with extreme residue-residue interactions, i.e., attractive (Cys-Cys), neutral (Thr-Thr), and repulsive (Glu-Glu), are also studied for comparison with the native protein. Visual inspections show contrast and similarity in morphological evolutions of protein assembly, aggregation of small aggregates to a ramified network from low to high temperature with the aggregation of a Cys-polymer, and an entangled network of Glu and Thr polymers. Variations in mobility profiles of residues with the concentration of the protein suggest that the segmental characteristic of proteins is altered considerably by the self-assembly from that in its isolated state. The global motion of proteins and Cys polymer chains is enhanced by their interacting network at the low temperature where isolated chains remain quasi-static. Transition from globular to random coil transition, evidenced by the sharp variation in the radius of gyration, of an isolated protein is smeared due to self-assembly of interacting networks of many proteins. Scaling of the structure factor S(q) with the wave vector q provides estimates of effective dimension D of the mass distribution at multiple length scales in self-assembly. Crossover from solid aggregates (D ∼ 3) at low temperature to a ramified fibrous network (D ∼ 2) at high temperature is observed for the protein H3.1 and Cys polymers in contrast to little changes in mass distribution (D ∼ 1.6) of fibrous Glu- and Thr-chain configurations.

Aggregation and network formation in self-assembly of protein (H3.1) by a coarse-grained Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Pandey, R. B.; Farmer, B. L.

2014-11-01

Multi-scale aggregation to network formation of interacting proteins (H3.1) are examined by a knowledge-based coarse-grained Monte Carlo simulation as a function of temperature and the number of protein chains, i.e., the concentration of the protein. Self-assembly of corresponding homo-polymers of constitutive residues (Cys, Thr, and Glu) with extreme residue-residue interactions, i.e., attractive (Cys-Cys), neutral (Thr-Thr), and repulsive (Glu-Glu), are also studied for comparison with the native protein. Visual inspections show contrast and similarity in morphological evolutions of protein assembly, aggregation of small aggregates to a ramified network from low to high temperature with the aggregation of a Cys-polymer, and an entangled network of Glu and Thr polymers. Variations in mobility profiles of residues with the concentration of the protein suggest that the segmental characteristic of proteins is altered considerably by the self-assembly from that in its isolated state. The global motion of proteins and Cys polymer chains is enhanced by their interacting network at the low temperature where isolated chains remain quasi-static. Transition from globular to random coil transition, evidenced by the sharp variation in the radius of gyration, of an isolated protein is smeared due to self-assembly of interacting networks of many proteins. Scaling of the structure factor S(q) with the wave vector q provides estimates of effective dimension D of the mass distribution at multiple length scales in self-assembly. Crossover from solid aggregates (D ˜ 3) at low temperature to a ramified fibrous network (D ˜ 2) at high temperature is observed for the protein H3.1 and Cys polymers in contrast to little changes in mass distribution (D ˜ 1.6) of fibrous Glu- and Thr-chain configurations.

Effect of magnetic dipolar interactions on nanoparticle heating efficiency: Implications for cancer hyperthermia

PubMed Central

Branquinho, Luis C.; Carrião, Marcus S.; Costa, Anderson S.; Zufelato, Nicholas; Sousa, Marcelo H.; Miotto, Ronei; Ivkov, Robert; Bakuzis, Andris F.

2013-01-01

Nanostructured magnetic systems have many applications, including potential use in cancer therapy deriving from their ability to heat in alternating magnetic fields. In this work we explore the influence of particle chain formation on the normalized heating properties, or specific loss power (SLP) of both low- (spherical) and high- (parallelepiped) anisotropy ferrite-based magnetic fluids. Analysis of ferromagnetic resonance (FMR) data shows that high particle concentrations correlate with increasing chain length producing decreasing SLP. Monte Carlo simulations corroborate the FMR results. We propose a theoretical model describing dipole interactions valid for the linear response regime to explain the observed trends. This model predicts optimum particle sizes for hyperthermia to about 30% smaller than those previously predicted, depending on the nanoparticle parameters and chain size. Also, optimum chain lengths depended on nanoparticle surface-to-surface distance. Our results might have important implications to cancer treatment and could motivate new strategies to optimize magnetic hyperthermia. PMID:24096272

Quantifying the brush structure and assembly of mixed brush nanoparticles in solution

NASA Astrophysics Data System (ADS)

Koski, Jason; Frischknecht, Amalie

The arrangement of nanoparticles in a polymer melt or solution is critical to the resulting material properties. A common strategy to control the distribution of nanoparticles is to graft polymer chains onto the surface of the nanoparticles. An emerging strategy to further control the arrangement of nanoparticles is to graft polymer chains of different types and/or different lengths onto the surface of the nanoparticle, though this considerably increases the parameter space needed to describe the system. Theoretical models that are capable of predicting the assembly of nanoparticles in a melt or solution are thus desirable to guide experiments. In this talk, I will describe a recently developed non-equilibrium method that is appealing in its ability to tractably account for fluctuations and that can directly relate to experiments. To showcase the utility of this method, I apply it to mixed brush grafted nanoparticles in solution where fluctuations are prominent. Specifically, I investigate the role of experimentally relevant parameters on the structure of the brush and the corresponding effects on the assembly of the nanoparticles in solution. These results can be directly linked to experiments to help narrow the relevant parameter space for optimizing these materials.

Nontemplated Approach to Tuning the Spectral Propertiesof Cyanine-Based Fluorescent NanoGUMBOS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Susmita; Bwambok, David; El-Zahab, Bilal

2010-01-01

Template-free controlled aggregation and spectral properties in fluorescent organic nanoparticles (FONs) is highly desirable for various applications.Herein, we report a nontemplated method for controlling the aggregation in near-infrared (NIR) cyanine-based nanoparticles derived from a group of uniformmaterials based on organic salts (GUMBOS). Cationic heptamethine cyanine dye 1,10,3,3,30,30-hexamethylindotricarbocyanine (HMT) was coupled with five different anions, viz., [NTf2 -], [BETI-], [TFPB-], [AOT-], and [TFP4B-], by an ion-exchange method to obtain the respective GUMBOS. The nanoGUMBOS obtained via a reprecipitation method were primarily amorphous and spherical (30-100 nm) as suggested by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). The formationmore » of tunable self-assemblies within the nanoGUMBOS was characterized using absorption and fluorescence spectroscopy in conjunction with molecular dynamics simulations. Counterion-controlled spectral properties observed in the nanoGUMBOS were attributed to variations in J/H ratios with different anions. Association with the [AOT-] anion afforded predominant J aggregation enabling the highest fluorescence intensity, whereas [TFP4B-] disabled the fluorescence due to predominantHaggregation in the nanoparticles. Analyses of the stacking angle of the cations based on molecular dynamic simulation results in [HMT][NTf2], [HMT][BETI], and [HMT][AOT] dispersed in water and a visual analysis of the representative simulation snapshots also imply that the type of aggregation was controlled through the counterion associated with the dye cation.« less

Versatile theranostics agents designed by coating ferrite nanoparticles with biocompatible polymers

NASA Astrophysics Data System (ADS)

Zahraei, M.; Marciello, M.; Lazaro-Carrillo, A.; Villanueva, A.; Herranz, F.; Talelli, M.; Costo, R.; Monshi, A.; Shahbazi-Gahrouei, D.; Amirnasr, M.; Behdadfar, B.; Morales, M. P.

2016-06-01

Three biocompatible polymers, polyethylene glycol (PEG), dextran and chitosan, have been used in this work to control the colloidal stability of magnetic nanoparticles (14 ± 5 nm in diameter) and to vary the aggregation state in order to study their effect on relaxometric and heating properties. Two different coating strategies have been deeply developed; one based on the formation of an amide bond between citric acid coated nanoparticles (NPs) and amine groups present on the polymer surface and the other based on the NP encapsulation. Relaxometric properties revealed that proton relaxation rates strongly depend on the coating layer hydrophilicity and the aggregation state of the particles due to the presence of magnetic interactions. Thus, while PEG coating reduces particle aggregation by increasing inter-particle spacing leading to reduction of both T1 and T2 relaxation, dextran and chitosan lead to an increase mainly in T2 values due to the aggregation of particles in bigger clusters where they are in close contact. Dextran and chitosan coated NPs have also shown a remarkable heating effect during the application of an alternating magnetic field. They have proved to be potential candidates as theranostic agents for cancer diagnosis and treatment. Finally, cytotoxicity of PEG conjugated NPs, which seem to be ideal for intravenous administration because of their small hydrodynamic size, was investigated resulting in high cell viability even at 0.2 mg Fe ml-1 after 24 h of incubation. This suspension can be used as drug/biomolecule carrier for in vivo applications.

Synthesis and fabrication of sized-controlled nanoparticles: Using surface self-assemblies as building blocks for developing supralattices on nanocomposite materials

NASA Astrophysics Data System (ADS)

Yee, Chanel Kitmon

2001-10-01

A general one-phase synthesis for self-assembling thiols onto gold, platinum, palladium and iridium nanoparticles using tetrahydrofuran (THF) as the solvent, and lithium triethylborohydride (superhydride) as the reducing agent, is presented. Using the same synthetic procedure gold nanoparticles functionalized with 11-hydroxyundecane-1-thiol and 4'-bromo-4-mercaptobiphenyl were prepared to show that the availability and reflexibility of this method could lead to surface fabrication with various type of facial moieties. Alkyl selenide- and alkyl thiolate-functionalized gold nanoparticles were also prepared by the same method at 6°C. The properties were compared to their counterparts made at 25°C. The formation of the Se-Au bond and S-Au bonds was investigated by transmission Fourier transform infrared spectroscopy (FTIR), while the bond nature in each case was examined by x-ray photoelectron spectroscopy (XPS). Particle size was determined by Transmission Electron Microscopy (TEM), and further confirmed by ultraviolet spectroscopy (UV). Superparamagnetic Fe and Fe2O3 nanoparticles were synthesized by ultrasound irradiation and post-fabricated with alkyl sulfonic acids of various chain lengths and octadecyl phosphonic acid. TEM reveals nanoparticles of 5--10 mn in diameter. FTIR spectra suggest that the alkyl chains are packed in a solid-like assembly with packing disorder increasing with the decreasing chain length. The octadecyl sulfonic acid coating displays the lowest magnetization within the sulfonic acid series, which may be explained by the high packing and ordering of the alkyl chains on the particle surface. The smallest value of magnetization in the OPA case suggests that the spin-state of surface Fe3+ ions is affected by the bonded surfactant, and that the phosphonate empty d-orbitals increase magnetic interactions between neighboring Fe3+ spins. To build superstructures beyond the monolayer level, a general route for the attachment of amino-terminated biomolecules to nanoparticles was proposed. Thiophene thiolate-functionalized platinum nanoparticles were prepared and reacted with nitrosonium tetrafluoroborate to provide the nitroso-functionalized nanoparticles. The reaction of the nitroso group with primary amines to yield strong N=N bonds might provide a general route for the attachment of amino-terminated biomolecules to nanoparticles. The attachment of two cytidine molecules to platinum nanoparticles was accomplished, and experimental data were provided to demonstrate the intended grafting reaction.