Note: This page contains sample records for the topic zn-porphyrin tweezer host-guest from
While these samples are representative of the content of,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of
to obtain the most current and comprehensive results.
Last update: November 12, 2013.

Host-guest antenna materials.  


The focus of this review is on host-guest composites with photonic antenna properties. The material generally consists of cylindrical zeolite L crystals the channels of which are filled with dye molecules. The synthesis is based on the fact that molecules can diffuse into individual channels. This means that, under the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out by adding a closure molecule. Functionalization of the closure molecules allows tuning of, for example, wettability, refractive index, and chemical reactivity. The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within a certain volume of a dye-loaded nanocrystalline zeolite and radiationless transport to both ends of the cylinder or from the ends to the center. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device through a stopcock molecule. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation-energy-transfer phenomena, and challenges for developing new photonic devices. PMID:12923836

Calzaferri, Gion; Huber, Stefan; Maas, Huub; Minkowski, Claudia



Host-guest chemistry at the surface of gold nanoparticles  

Microsoft Academic Search

Host-guest chemistry plays an important role in modern supramolecular chemistry. Host-guest interactions have been used to construct novel nanoscale architectures in solution. The rapid advance of nanoparticle chemistry shows its strong potential in nanotechnology, which has been recognized as the technology for the next century. Surface modified nanoparticles have been successfully used in biological detection, catalysis, nanoelectronic and optical devices.

Jian Liu



Spectroscopic Study of Host-Guest Inclusion Complexes  

Microsoft Academic Search

A host-guest complex is formed by a host molecule encapsulating a guest molecule within it. The host materials in this study are basket-shaped structures, known as cyclodextrins, which can easily incorporate a variety of guests, such as drug molecules. These inclusion complexes made with cyclodextrins and drugs can be developed to have different release rates within the body. The cyclodextrin

Jenessa Lucas; Jennifer Holt



Thermodynamic integration to predict host-guest binding affinities.  


An alchemical free energy method with explicit solvent molecular dynamics simulations was applied as part of the blind prediction contest SAMPL3 to calculate binding free energies for seven guests to an acyclic cucurbit-[n]uril host. The predictions included determination of protonation states for both host and guests, docking pose generation, and binding free energy calculations using thermodynamic integration. We found a root mean square error (RMSE) of 3.6 kcal mol(-1) from the reference experimental results, with an R(2) correlation of 0.51. The agreement with experiment for the largest contributor to this error, guest 6, is improved by 1.7 kcal mol(-1) when a periodicity-induced free energy correction is applied. The corrections for the other ligands were significantly smaller, and altogether the RMSE was reduced by 0.4 kcal mol(-1). We link properties of the host-guest systems during simulation to errors in the computed free energies. Overall, we show that charged host-guest systems studied here, initialized in unconfirmed docking poses, present a challenge to accurate alchemical simulation methods. PMID:22350568

Lawrenz, Morgan; Wereszczynski, Jeff; Ortiz-Sánchez, Juan Manuel; Nichols, Sara E; McCammon, J Andrew



Molecular characterization of two host-guest associating hyaluronan derivatives.  


Molecular characteristics were determined of two high-molecular-weight water-soluble hyaluronan derivatives, namely beta-cyclodextrin (HA-beta-CD) and N-acylurea (EDC-HA). The weight-average molecular weight (M(w)) of HA-beta-CD and of EDC-HA, determined with a multi-angle light scattering detector connected on-line to a size exclusion chromatographic system, was respectively 185.3 and 86.8 kDa. However the M(w) value determined for the equimolar mixture of the two HA derivatives equaled 556.0 kDa. Similarly, the gyration radius of the above equimolar mixture, Rg = 80.6 nm, was significantly greater than the values found for the single HA derivative, i.e. 40.2 nm for HA-beta-CD and 23.8 nm for EDC-HA. These data indicate that the two kinds of substituents, bound to the polymeric chains, form host-guest/inclusion complexes resulting in polymacromolecular associates/aggregates. PMID:13680848

Soltés, L; Mendichi, R



Rational adjustment of multicolor emissions by cucurbiturils-based host-guest chemistry and photochemistry.  


The host-guest chemistry of cucurbiturils and the photochemistry of azastilbene derivatives are combined for the rationally adjusting multicolor emissions through forming different host-guest complexes and their corresponding photochemical products. Cucurbit[8]uril (CB[8]) can bind with azastilbene derivatives to form supramolecular polymers emitting orange light. The supramolecular polymers further facilitate the [2 + 2] cycloaddition of C?C bonds in azastilbenes by UV irradiation, emitting blue light. Different from CB[8], cucurbit[7]uril (CB[7]) encapsulates azastilbene derivatives to form a dumbbell-shaped host-guest complex, emitting dark-purple light. This dumbbell-shaped host-guest complex undergoes cis-isomerization after UV irradiation, thus emitting green light. Therefore, this strategy is promising for fabricating advanced stimuli-responsive fluorescent materials. PMID:23927076

Yang, Hui; Liu, Yiliu; Liu, Kai; Yang, Liulin; Wang, Zhiqiang; Zhang, Xi



Aquatic host-guest complex between a supramolecular G-quadruplex and the anticancer drug doxorubicin  

PubMed Central

We describe the synthesis of a fluorescent deoxyguanosine derivative that co-assembles (in water) with an unlabeled analogue into a heteromeric supramolecular G-quadruplex, which forms a host-guest complex with doxorubicin as evidenced by FRET experiments.

Martin-Hidalgo, Mariana; Rivera-Rios, Jean C.



Redox-responsive self-healing materials formed from host–guest polymers  

Microsoft Academic Search

Expanding the useful lifespan of materials is becoming highly desirable, and self-healing and self-repairing materials may become valuable commodities. The formation of supramolecular materials through host–guest interactions is a powerful method to create non-conventional materials. Here we report the formation of supramolecular hydrogels and their redox-responsive and self-healing properties due to host–guest interactions. We employ cyclodextrin (CD) as a host

Masaki Nakahata; Yoshinori Takashima; Hiroyasu Yamaguchi; Akira Harada



High effectiveness of oligothienylenevinylene as molecular wires in Zn-porphyrin and C60 connected systems.  


Photoinduced energy transfer and electron transfer processes have been found between the excited singlet state of Zn-porphyrin and C(60) via an oligothienylenevinylene bridge depending on the length of the oligothiophene and solvent polarity. PMID:17971968

Oswald, Frédéric; Islam, D-M Shafiqul; Araki, Yasuyuki; Troiani, Vincent; Caballero, Ruben; de la Cruz, Pilar; Ito, Osamu; Langa, Fernando



Mechanism of host-guest complexation by cucurbituril.  


The factors affecting host-guest complexation between the molecular container compound cucurbit[6]uril (CB6) and various guests in aqueous solution are studied, and a detailed complexation mechanism in the presence of cations is derived. The formation of the supramolecular complex is studied in detail for cyclohexylmethylammonium ion as guest. The kinetics and thermodynamics of complexation is monitored by NMR as a function of temperature, salt concentration, and cation size. The binding constants and the ingression rate constants decrease with increasing salt concentration and cation-binding constant, in agreement with a competitive binding of the ammonium site of the guest and the metal cation with the ureido carbonyl portals of CB6. Studies as a function of guest size indicate that the effective container volume of the CB6 cavity is approximately 105 A(3). It is suggested that larger guests are excluded for two reasons: a high activation barrier for ingression imposed by the tight CB6 portals and a destabilization of the complex due to steric repulsion inside. For example, in the case of the nearly spherical azoalkane homologues 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH, volume ca. 96 A(3)) and 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO, volume ca. 110 A(3)), the former forms the CB6 complex promptly with a sizable binding constant (1300 M(-1)), while the latter does not form a complex even after several months at optimized complexation conditions. Molecular mechanics calculations are performed for several CB6/guest complexes. A qualitative agreement is found between experimental and calculated activation energies for ingression as a function of both guest size and state of protonation. The potential role of constrictive binding by CB6 is discussed. PMID:15125673

Márquez, César; Hudgins, Robert R; Nau, Werner M



A semiconducting organic radical cationic host-guest complex.  


The self-assembly and solid-state semiconducting properties of single crystals of a trisradical tricationic complex composed of the diradical dicationic cyclobis(paraquat-p-phenylene) (CBPQT(2(•+))) ring and methyl viologen radical cation (MV(•+)) are reported. An organic field effect transistor incorporating single crystals of the CBPQT(2(•+))?MV(•+) complex was constructed using lithographic techniques on a silicon substrate and shown to exhibit p-type semiconductivity with a mobility of 0.05 cm(2) V(-1) s(-1). The morphology of the crystals on the silicon substrate was characterized using scanning electron microscopy which revealed that the complexes self-assemble into "molecular wires" observable by the naked-eye as millimeter long crystalline needles. The nature of the recognition processes driving this self-assembly, radical-radical interactions between bipyridinium radical cations (BIPY(•+)), was further investigated by resonance Raman spectroscopy in conjunction with theoretical investigations of the vibrational modes, and was supported by X-ray structural analyses of the complex and its free components in both their radical cationic and dicationic redox states. These spectroscopic investigations demonstrate that the bond order of the BIPY(•+) radical cationic units of host and guest components is not changed upon complexation, an observation which relates to its conductivity in the solid-state. We envision the modularity inherent in this kind of host-guest complexation could be harnessed to construct a library of custom-made electronic organic materials tailored to fit the specific needs of a given electronic application. PMID:23078281

Fahrenbach, Albert C; Sampath, Srinivasan; Late, Dattatray J; Barnes, Jonathan C; Kleinman, Samuel L; Valley, Nicholas; Hartlieb, Karel J; Liu, Zhichang; Dravid, Vinayak P; Schatz, George C; Van Duyne, Richard P; Stoddart, J Fraser



Determination of binding selectivities in host-guest complexation by electrospray\\/quadrupole ion trap mass spectrometry  

Microsoft Academic Search

The quantifiable relationship between the equilibrium solution composition and electrospray (ESI) mass spectral peak intensities\\u000a of simple host-guest complexes was investigated. Specifically, host-guest complexes of simple crown ethers or glymes with\\u000a alkali metals and ammonium ions were studied. Comparisons were made between the theoretical concentrations of host-guest complexes\\u000a derived in solution from known stability constants and the peak intensities for

Sheryl M. Blair; Esther C. Kempen; Jennifer S. Brodbelt



Supramolecular Chemistry: Induced Circular Dichroism to Study Host-Guest Geometry  

ERIC Educational Resources Information Center

|In this laboratory experiment, students obtain information about the structure of a host-guest complex from the interpretation of circular dichroism measurements. The value and sign of the induced circular dichroism (ICD) on an achiral chromophore guest when it complexes with a cyclodextrin can be related to the guest penetration and its…

Mendicuti, Francisco; Gonzalez-Alvarez, Maria Jose



Supramolecular Host-Guest Interaction for Labeling and Detection of Cellular Biomarkers**  

PubMed Central

Be my guest: A supramolecular host–guest interaction is utilized for highly efficient bioorthogonal labeling of cellular targets. Antibodies labeled with a cyclodextrin host molecule bind to adamantane-labeled magnetofluorescent nanoparticles (see picture) and provide an amplifiable strategy for biomarker detection that can be adapted to different diagnostic techniques such as molecular profiling or magnetic cell sorting.

Agasti, Sarit S.; Liong, Monty; Tassa, Carlos; Chung, Hyun Jung; Shaw, Stanley Y.



Redox-responsive self-healing materials formed from host-guest polymers  

PubMed Central

Expanding the useful lifespan of materials is becoming highly desirable, and self-healing and self-repairing materials may become valuable commodities. The formation of supramolecular materials through host–guest interactions is a powerful method to create non-conventional materials. Here we report the formation of supramolecular hydrogels and their redox-responsive and self-healing properties due to host–guest interactions. We employ cyclodextrin (CD) as a host molecule because it is environmentally benign and has diverse applications. A transparent supramolecular hydrogel quickly forms upon mixing poly(acrylic acid) (pAA) possessing ?-CD as a host polymer with pAA possessing ferrocene as a guest polymer. Redox stimuli induce a sol?gel phase transition in the supramolecular hydrogel and can control self-healing properties such as re-adhesion between cut surfaces.

Nakahata, Masaki; Takashima, Yoshinori; Yamaguchi, Hiroyasu; Harada, Akira



Redox-responsive self-healing materials formed from host-guest polymers.  


Expanding the useful lifespan of materials is becoming highly desirable, and self-healing and self-repairing materials may become valuable commodities. The formation of supramolecular materials through host-guest interactions is a powerful method to create non-conventional materials. Here we report the formation of supramolecular hydrogels and their redox-responsive and self-healing properties due to host-guest interactions. We employ cyclodextrin (CD) as a host molecule because it is environmentally benign and has diverse applications. A transparent supramolecular hydrogel quickly forms upon mixing poly(acrylic acid) (pAA) possessing ?-CD as a host polymer with pAA possessing ferrocene as a guest polymer. Redox stimuli induce a sol-gel phase transition in the supramolecular hydrogel and can control self-healing properties such as re-adhesion between cut surfaces. PMID:22027591

Nakahata, Masaki; Takashima, Yoshinori; Yamaguchi, Hiroyasu; Harada, Akira



Siderophore-redox active ionophore host-guest assemblies: A prototype for selective metal ion compartmentalization  

Microsoft Academic Search

The reduction potentials for two Wurster’s crowns, aza crown ethers which incorporate the redox active N,N,N?,N?-tetraalkyl-1,4-phenylenediamine into the structure of 18-crown-6, were studied in the presence of the siderophore ferrioxamine B, FeHDFB+. Addition of FeHDFB+ resulted in a positive shift in the host reduction potential for both aza crown ethers studied. This shift is explained in terms of host-guest supramolecular

Esther M. Tristani; Joseph I. Wirgau; George R. Dubay; John W. Sibert; Alvin L. Crumbliss



Probing Conformational Changes of Ubiquitin by Host-Guest Chemistry Using Electrospray Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

We report mechanistic studies of structural changes of ubiquitin (Ub) by host-guest chemistry with cucurbit[6]uril (CB[6]) using electrospray ionization mass spectrometry (ESI-MS) combined with circular dichroism spectroscopy and molecular dynamics (MD) simulation. CB[6] binds selectively to lysine (Lys) residues of proteins. Low energy collision-induced dissociation (CID) of the protein-CB[6] complex reveals CB[6] binding sites. We previously reported ( Anal. Chem. 2011, 83, 7916-7923) shifts in major charge states along with Ub-CB[6] complexes in the ESI-MS spectrum with addition of CB[6] to Ub from water. We also reported that CB[6] is present only at Lys6 or Lys11 in high charge state (+13) complex. In this study, we provide additional information to explain unique conformational change mechanisms of Ub by host-guest chemistry with CB[6] compared with solvent-driven conformational change of Ub. Additional CID study reveals that CB[6] is bound only to Lys48 and Lys63 in low charge state (+7) complex. MD simulation studies reveal that the high charge state complexes are attributed to the CB[6] bound to Lys11. The complexation prohibits salt bridge formation between Lys11 and Glu34 and induces conformational change of Ub. This results in formation of high charge state complexes in the gas phase. Then, by utilizing stronger host-guest chemistry of CB[6] with pentamethylenediamine, refolding of Ub via detaching CB[6] from the protein is performed. Overall, this study gives an insight into the mechanism of denatured Ub ion formation via host-guest interactions with CB[6]. Furthermore, this provides a direction for designing function-controllable supramolecular system comprising proteins and synthetic host molecules.

Lee, Jong Wha; Heo, Sung Woo; Lee, Shin Jung C.; Ko, Jae Yoon; Kim, Hyungjun; Kim, Hugh I.



Host-guest adaptability within oxothiomolybdenum wheels: structures, studies in solution and DFT calculations.  


The formation of host-guest cyclic architectures, built up through the self-condensation process of [Mo(2)O(2)S(2)](2+) oxothiocations around linear dicarboxylate ions such as adipate (Adip(2-)), suberate (Sub(2-)) and azelaate (Azel(2-)) anions is reported. The complexes [Mo(12)Adip](2-), [Mo(12)Sub](2-) and [Mo(14)Azel](2-) have been characterized in the solid state by X-ray diffraction and in solution by (1)H NMR in different solvents (D(2)O, DMF, DMSO and CD(3)CN). The host-guest dynamics appear to be dependent on the nature of the system and are mainly governed by mutual adaptability between the host and the guest. (1)H NMR DOSY experiments show systematic differences, either positive or negative between the experimental and calculated molecular weights which appear to be correlated with the charge of the anion. The relative stabilities of the twelve-membered rings containing the Adip(2-), Pim(2-) (pimelate) or Sub(2-) anions were determined experimentally and decrease according to the order [Mo(12)Adip](2-) > [Mo(12)Pim](2-) > [Mo(12)Sub](2-). The host-guest adaptability depends on the length of the carbon chain and gives rise to selective encapsulation processes. Finally, theoretical DFT investigations in the gas phase yielded conformations whose symmetry and geometrical parameters proved consistent with X-ray structures and (1)H NMR spectra recorded in DMSO or DMF. Energy calculation highlights the high flexibility of the ring showing that only 3.1 kJ mol(-1) accompanies the conformational change from circular to elliptical. The host-guest bond energy (Delta E) calculated for the Mo(12)-based clusters is consistent with the experimental stability scale, major variations being due to some constraints undergone by the central alkyl chain. PMID:17622422

Lemonnier, Jean-François; Floquet, Sébastien; Kachmar, Ali; Rohmer, Marie-Madeleine; Bénard, Marc; Marrot, Jerôme; Terazzi, Emmanuel; Piguet, Claude; Cadot, Emmanuel



Theranostic systems assembled in situ on demand by host-guest chemistry  

Microsoft Academic Search

Theranostic systems have been explored extensively for a diagnostic therapy in the forms of polymer conjugates, implantable devices, and inorganic nanoparticles. In this work, we report theranostic systems in situ assembled by host-guest chemistry responding to a request. As a model theranostic system on demand, cucurbit[6]uril-conjugated hyaluronate (CB[6]-HA) was synthesized and decorated with FITC-spermidine (spmd) and\\/or formyl peptide receptor like

Hyuntae Jung; Kyeng Min Park; Jeong-A. Yang; Eun Ju Oh; Don-Wook Lee; Sung Ho Ryu; Sei Kwang Hahn; Kimoon Kim



Host–guest complexes of docetaxel, an anti-cancer drug  

Microsoft Academic Search

Host–guest complexes of Docetaxel 1, an anti-cancer drug have been isolated and crystal structures are described. Docetaxel crystallized in the 1:1 molar ratio\\u000a with n-butanol, dimethylformamide (DMF) and acetonitrile (ACN) during crystallization from the respective solvents. In all the three\\u000a complexes (1 · n-butanol, 1 · DMF and 1 · ACN), docetaxel formed a host framework through hydrogen bonds and the guest solvent molecules occupied the

T. Lakshmi Kumar; Pooja Guleria; Peddy Vishweshwar; A. Sivalakshmidevi; J. Moses Babu; K. Vyas; Palle V. R. Acharyulu; N. M. Sekhar; B. Selva Kumar



ß-Cyclodextrin Host-Guest Complexes Probed under Thermodynamic Equilibrium: Thermodynamics and AFM Force Spectroscopy  

Microsoft Academic Search

The rupture forces of individual host-guest complexes between ß-cyclodextrin (ß-CD) heptathioether monolayers on Au(111) and several surface-confined guests were measured in aqueous medium by single molecule force spectroscopy using an atomic force microscope. Anilyl, toluidyl, tert-butylphenyl, and adamantylthiols (0.2-1%) were immobilized in mixed monolayers with 2-mercaptoethanol on gold-coated AFM tips. For all guests and for all surface coverages, the force-displacement

Tomasso Auletta; Jong de Menno R; Alart Mulder; Veggel van Frank C. J. M; Jurriaan Huskens; David N. Reinhoudt; Shan Zou; Szczepan Zapotoczny; Holger Schönherr; G. Julius Vancso; Laurens Kuipers



Theranostic systems assembled in situ on demand by host-guest chemistry.  


Theranostic systems have been explored extensively for a diagnostic therapy in the forms of polymer conjugates, implantable devices, and inorganic nanoparticles. In this work, we report theranostic systems in situ assembled by host-guest chemistry responding to a request. As a model theranostic system on demand, cucurbit[6]uril-conjugated hyaluronate (CB[6]-HA) was synthesized and decorated with FITC-spermidine (spmd) and/or formyl peptide receptor like 1 (FPRL1) specific peptide-spmd by simple mixing in aqueous solution. The resulting (FITC-spmd and/or peptide-spmd)@CB[6]-HA was successfully applied to the bioimaging of its target-specific delivery to B16F1 cells with HA receptors and its therapeutic signal transduction with elevated Ca(2+) and phosphor-extracellular signal-regulated kinase (pERK) levels in FPRL1-expressing human breast adenocarcinoma (FPRL1/MCF-7) cells. Finally, we could confirm in vitro and in vivo stability of the highly specific host-guest interaction. The on-demand theranostic platform technology using host-guest chemistry can be exploited for various bioimaging, biosensing, drug delivery, and tissue engineering applications. PMID:21788071

Jung, Hyuntae; Park, Kyeng Min; Yang, Jeong-A; Oh, Eun Ju; Lee, Don-Wook; Park, Kitae; Ryu, Sung Ho; Hahn, Sei Kwang; Kim, Kimoon



Highly emissive metal-organic framework composites by host-guest chemistry.  


The unique host-guest chemistry of metal-organic frameworks (MOFs) can be used to implement additional properties by loading the cavities with functional molecules or even nanoparticles. We describe the gas-phase loading of MOFs featuring either a three-dimensional (MOF-5, MOF-177 and UMCM-1) or one-dimensional channel system (MIL-53(Al)) with the highly emissive perylene derivative N,N-bis(2,6-dimethylphenyl)-3,4:9,10-perylene tetracarboxylic diimide (DXP) or an iridium complex, (2-carboxypyridyl)bis(3,5-difluoro-2-(2-pyridyl)phenyl)iridium(III) (FIrpic). The resulting host-guest composites show strong luminescence, with their optical properties being dominated by the guest species. DXP-loaded MOFs exhibit a high stability towards guest displacement by solvent molecules, while the interaction of FIrpic with the host is weaker. The emissive properties of intercalated DXP also indicate host-guest interactions such as caging effects, strong quenching of the MOF host emission, as well as aggregate formation. PMID:20473444

Müller, Maike; Devaux, André; Yang, Cheng-Han; De Cola, Luisa; Fischer, Roland A



Characterization of second coordination shell ionophore–siderophore host–guest assemblies and binding selectivities in binary and complex mixtures by electrospray ionization mass spectrometry  

Microsoft Academic Search

An ESI-MS method for the determination of host–guest association constants and binding selectivities for systems of binary\\u000a and complex mixtures, respectively, is presented in an effort to quantitatively study the strength of host–guest interactions,\\u000a while accounting for the different ESI-MS spray efficiencies of each component. Association constants were obtained for host–guest\\u000a complexes formed between a series of crown ether and

Esther M. Tristani; George R. Dubay; Alvin L. Crumbliss



Host-guest complexes between cucurbit[n]urils and acetanilides having aminopropyl units.  


2-(Propylamino)acetamide of aniline (1a), and bis-2-(propylamino)acetamide of ortho- (1b) and para-(1c) phenylenediamine form host-guest complexes with CB[6], CB[7] and CB[8] as evidenced by the variations in the (1)H NMR spectroscopy chemical shifts and observation in MALDI-TOF-MS and ESI-MS of ions at the corresponding mass. Binding constants for the 1:1 complexes were estimated from fluorescence titrations and were in the range 10(5)-10(6)M(-1). Models based on molecular mechanics for these supramolecular complexes are provided. In spite of the different geometries arising from the ortho- or para-substitution, phenylenediamides form complexes of similar strength in which the hydrophobic alkyl chains are accommodated inside the host cavity. Formation of these host-guest complexes in the solid state was also achieved by modifying an aminopropyl silica with chloroacetanilides and preparing three silica having analogues of compounds 1a-c anchored to the solid particles. Titrations showed, however, that these solids can adsorb a large percentage of CBs by unselective interactions that are not related to the formation of inclusion complexes. PMID:23541695

Buaki-Sogo, Mireia; Montes-Navajas, Pedro; Alvaro, Mercedes; Garcia, Hermenegildo



Calculation of Host-Guest Binding Affinities Using a Quantum-Mechanical Energy Model  

PubMed Central

The prediction of protein-ligand binding affinities is of central interest in computer-aided drug discovery, but it is still difficult to achieve a high degree of accuracy. Recent studies suggesting that available force fields may be a key source of error motivate the present study, which reports the first mining minima (M2) binding affinity calculations based on a quantum mechanical energy model, rather than an empirical force field. We apply a semi-empirical quantum-mechanical energy function, PM6-DH+, coupled with the COSMO solvation model, to 29 host-guest systems with a wide range of measured binding affinities. After correction for a systematic error, which appears to derive from the treatment of polar solvation, the computed absolute binding affinities agree well with experimental measurements, with a mean error 1.6 kcal/mol and a correlation coefficient of 0.91. These calculations also delineate the contributions of various energy components, including solute energy, configurational entropy, and solvation free energy, to the binding free energies of these host-guest complexes. Comparison with our previous calculations, which used empirical force fields, point to significant differences in both the energetic and entropic components of the binding free energy. The present study demonstrates successful combination of a quantum mechanical Hamiltonian with the M2 affinity method.

Muddana, Hari S.; Gilson, Michael K.



Characterizing and Understanding Self-Assembling, Nanocapsule Host-Guest Systems  

NASA Astrophysics Data System (ADS)

Supramolecular, self-assembled nanocapsules have been shown to be capable of entrapping fluorescent guests. Previous solid- and solution-state research, focusing on hydrogen-bonded C-alkylpyrogallol[4]arenes (PgC 6)nanocapsules, have shed light on the host-guest-relationship potential of these materials. Investigations of these nanocapsules with different fluorophores were undertaken to better understand the guest properties (e.g., size, shape, molecular volume, and functionality) needed to facilitate robust encapsulation. In addition, another relatively new nanocapsule containing metal ions in place of some of the hydrogen bonds was also examined. UV-Visible absorption and steady-state and dynamic fluorescence spectroscopic techniques were used to examine the host-guest interactions between the capsule interior and the fluorescent reporter molecule pyrene butanol that became encapsulated in the PgC 6 nanocapsule. Solution-state spectroscopic data was compared with solid-state, single-crystal, X-ray crystallographic results. This work supported the hypothesis that the tail functionality of the encapsulated guest is a critical feature for encapsulation and potentially ensures the robustness of that association. The research laid the foundation for understanding how to achieve successful encapsulation of future entities. The work advanced the understanding of the goodness-of-fit criterion between guest and host for these PgC6 supramolecular, self-assemblies.

Whetstine, Jena L.


Cytomimetic large-scale vesicle aggregation and fusion based on host-guest interaction.  


Herein, we have shown a large-scale cell-mimetic (cytomimetic) aggregation process by using cell-sized polymer vesicles as the building blocks and intervesicular host-guest molecular recognition interactions as the driving force. We first prepared the hyperbranched polymer vesicles named branched polymersomes (BPs) around 5-10 ?m through the aqueous self-assembly of a hyperbranched multiarm copolymer of HBPO-star-PEO [HBPO = hyperbranched poly(3-ethyl-3-oxetanemethanol); PEO = poly(ethylene oxide)]. Subsequently, adamantane-functionalized BPs (Ada-BPs) or ?-cyclodextrin-functionalized BPs (CD-BPs) were prepared through the coassembly of HBPO-star-PEO and Ada-modified HBPO-star-PEO (HBPO-star-PEO-Ada), or of HBPO-star-PEO and CD-modified HBPO-star-PEO (HBPO-star-PEO-CD), respectively. Macroscopic vesicle aggregates were obtained by mixing CD-BPs and Ada-BPs. The intervesicular host-guest recognition interactions between ?-CD units in CD-BPs and Ada units in Ada-BPs, which were proved by (1)H nuclear Overhauser effect spectroscopy (NOESY) spectrum and the fluorescence probe method, are responsible for the vesicle aggregation. Additionally, the vesicle fusion events happened frequently in the process of vesicle aggregation, which were certified by double-labeling fluorescent assay, real-time observation, content mixing assay, and component mixing assay. PMID:22129210

Jin, Haibao; Liu, Yong; Zheng, Yongli; Huang, Wei; Zhou, Yongfeng; Yan, Deyue



Strategies for Using Host-Guest Chemistry in the Extractive Separations of Ionic Guests  

SciTech Connect

Host-guest chemistry has led to a new paradigm in extractive separations, generating new possibilities for efficient separations of ionic species to meet the challenging needs of industry. This account describes the approach the authors have recently undertaken, recent results, and future directions toward highly selective separations of anions based on host?guest chemistry principles. The material presented deals mainly with the genesis and discovery of new extractive systems, illustrating the potential of particular chemical concepts with examples of practical application. Major questions of interest concern the role of anions in extractive processes and factors underlying the recognition and transport of anions. Theoretical efforts explore the technique of molecular-design itself as embodied in the evolving HostDesigner program. Design calculations are capable of generating ranked candidate multifunctional ion receptors based on hydrogen-bond-donor groups having O?H and N?H donor functionalities. Efforts to synthesize candidate receptors together with studies of molecular structure and the thermodynamics of binding and transport provide a complete picture for understanding structure-function relationships and feedback for further molecular modeling. Extraction data are evaluated in a thermochemical context in which the solvent matrix, including use of anion-solvating lipophilic alcohols, plays a pivotal role. Applications are envisioned for the solution of many types of separations needs, and examples are taken mainly from the authors' own research as applied to treatment of radioactive wastes for disposal.

Moyer, Bruce A.; Bonnesen, Peter V.; Custelcean, Radu; Delmau, Laetitia H.; Hay, Benjamin P.



A Stimuli-Responsive Nanopore Based on a Photoresponsive Host-Guest System  

NASA Astrophysics Data System (ADS)

The open-close states of the ion channels in a living system are regulated by multiple stimuli such as ligand, pH, potential and light. Functionalizing natural channels by using synthetic chemistry would provide biological nanopores with novel properties and applications. Here we use para-sulfonato-calix[4]arene-based host-guest supramolecular system to develop artificial gating mechanisms aiming at regulating wild-type ?-HL commanded by both ligand and light stimuli. Using the gating property of ?-hemolysin, we studied the host-guest interactions between para-sulfonato-calix[4]arene and 4, 4'-dipyridinium-azobenzene at the single-molecule level. Subsequently, we have extended the application of this gating system to the real-time study of light-induced molecular shuttle based on para-sulfonato-calix[4]arene and 4, 4'-dipyridinium-azobenzene at the single-molecule level. These experiments provide a more efficient method to develop a general tool to analyze the individual motions of supramolecular systems by using commercially available ?-HL nanopores.

Ying, Yi-Lun; Zhang, Junji; Meng, Fu-Na; Cao, Chan; Yao, Xuyang; Willner, Itamar; Tian, He; Long, Yi-Tao



A stimuli-responsive nanopore based on a photoresponsive host-guest system.  


The open-close states of the ion channels in a living system are regulated by multiple stimuli such as ligand, pH, potential and light. Functionalizing natural channels by using synthetic chemistry would provide biological nanopores with novel properties and applications. Here we use para-sulfonato-calix[4]arene-based host-guest supramolecular system to develop artificial gating mechanisms aiming at regulating wild-type ?-HL commanded by both ligand and light stimuli. Using the gating property of ?-hemolysin, we studied the host-guest interactions between para-sulfonato-calix[4]arene and 4, 4'-dipyridinium-azobenzene at the single-molecule level. Subsequently, we have extended the application of this gating system to the real-time study of light-induced molecular shuttle based on para-sulfonato-calix[4]arene and 4, 4'-dipyridinium-azobenzene at the single-molecule level. These experiments provide a more efficient method to develop a general tool to analyze the individual motions of supramolecular systems by using commercially available ?-HL nanopores. PMID:23588705

Ying, Yi-Lun; Zhang, Junji; Meng, Fu-Na; Cao, Chan; Yao, Xuyang; Willner, Itamar; Tian, He; Long, Yi-Tao



A host-guest-recognition-based electrochemical aptasensor for thrombin detection.  


A sensitive electrochemical aptasensor for thrombin detection is presented based on the host-guest recognition technique. In this sensing protocol, a 15 based thrombin aptamer (ab. TBA) was dually labeled with a thiol at its 3' end and a 4-((4-(dimethylamino)phenyl)azo) benzoic acid (dabcyl) at its 5' end, respectively, which was previously immobilized on one Au electrode surface by AuS bond and used as the thrombin probe during the protein sensing procedure. One special electrochemical marker was prepared by modifying CdS nanoparticle with ?-cyclodextrins (ab. CdS-CDs), which employed as electrochemical signal provider and would conjunct with the thrombin probe modified electrode through the host-guest recognition of CDs to dabcyl. In the absence of thrombin, the probe adopted linear structure to conjunct with CdS-CDs. In present of thrombin, the TBA bond with thrombin and transformed into its special G-quarter structure, which forced CdS-CDs into the solution. Therefore, the target-TBA binding event can be sensitively transduced via detecting the electrochemical oxidation current signal of Cd of CdS nanoparticles in the solution. Using this method, as low as 4.6 pM thrombin had been detected. PMID:22483358

Fan, Hao; Li, Hui; Wang, Qingjiang; He, Pingang; Fang, Yuzhi



Prediction of SAMPL3 Host-Guest Affinities with the Binding Energy Distribution Analysis Method (BEDAM)  

PubMed Central

BEDAM calculations are described to predict the free energies of binding of a series of anaesthetic drugs to a recently characterized acyclic cucurbituril host. The modeling predictions, conducted as part of the SAMPL3 host-guest affinity blind challenge, are generally in good quantitative agreement with the experimental measurements. The correlation coefficient between computed and measured binding free energies is 70% with high statistical significance. Multiple conformational stereoisomers and protonation states of the guests have been considered. Better agreement is obtained with high statistical confidence under acidic modeling conditions. It is shown that this level of quantitative agreement could have not been reached without taking into account reorganization energy and configurational entropy effects. Extensive conformational variability of the host, the guests and their complexes is observed in the simulations, affecting binding free energy estimates and structural predictions. A conformational reservoir technique is introduced as part of the parallel Hamiltonian replica exchange molecular dynamics BEDAM protocol to fully capture conformational variability. It is shown that these advanced computational strategies lead to converged free energy estimates for these systems, offering the prospect of utilizing host-guest binding free energy data for force field validation and development.

Gallicchio, Emilio; Levy, Ronald M.



Equilibrium isotope effects on noncovalent interactions in a supramolecular host-guest system.  


The self-assembled supramolecular complex [Ga(4)L(6)](12-) (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) can act as a molecular host in aqueous solution and bind cationic guest molecules to its highly charged exterior surface or within its hydrophobic interior cavity. The distinct internal cavity of host 1 modifies the physical properties and reactivity of bound guest molecules and can be used to catalyze a variety of chemical transformations. Noncovalent host-guest interactions in large part control guest binding, molecular recognition and the chemical reactivity of bound guests. Herein we examine equilibrium isotope effects (EIEs) on both exterior and interior guest binding to host 1 and use these effects to probe the details of noncovalent host-guest interactions. For both interior and exterior binding of a benzylphosphonium guest in aqueous solution, protiated guests are found to bind more strongly to host 1 (K(H)/K(D) > 1) and the preferred association of protiated guests is driven by enthalpy and opposed by entropy. Deuteration of guest methyl and benzyl C-H bonds results in a larger EIE than deuteration of guest aromatic C-H bonds. The observed EIEs can be well explained by considering changes in guest vibrational force constants and zero-point energies. DFT calculations further confirm the origins of these EIEs and suggest that changes in low-frequency guest C-H/D vibrational motions (bends, wags, etc.) are primarily responsible for the observed EIEs. PMID:22145944

Mugridge, Jeffrey S; Bergman, Robert G; Raymond, Kenneth N



Paramagnetic NMR investigation of dendrimer-based host-guest interactions.  


In this study, the host-guest behavior of poly(amidoamine) (PAMAM) dendrimers bearing amine, hydroxyl, or carboxylate surface functionalities were investigated by paramagnetic NMR studies. 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO) derivatives were used as paramagnetic guest molecules. The results showed that TEMPO-COOH significantly broaden the ¹H NMR peaks of amine- and hydroxyl-terminated PAMAM dendrimers. In comparison, no paramagnetic relaxation enhancement (PRE) was observed between TEMPO-NH?, TEMPO-OH and the three types of PAMAM dendrimers. The PRE phenomenon observed is correlated with the encapsulation of TEMPO-COOH within dendrimer pockets. Protonation of the tertiary amine groups within PAMAM dendrimers plays an important role during this process. Interestingly, the absence of TEMPO-COOH encapsulation within carboxylate-terminated PAMAM dendrimer is observed due to the repulsion of TEMPO-COO- anion and anionic dendrimer surface. The combination of paramagnetic probes and ¹H NMR linewidth analysis can be used as a powerful tool in the analysis of dendrimer-based host-guest systems. PMID:23762249

Wang, Fei; Shao, Naimin; Cheng, Yiyun



Encapsulation of a Rhodamine Dye within a Bile Acid Binding Protein: Toward Water Processable Functional Bio Host-Guest Materials.  


New strategies are requested for the preparation of bioinspired host-guest complexes to be employed in technologically relevant applications, as sensors and optoelectronic devices. We report here a new approach employing a single monomeric protein as host for the strongly fluorescent rhodamine dye. The selected protein, belonging to the intracellular lipid binding protein family, fully encapsulates one rhodamine molecule inside its cavity forming a host-guest complex stabilized by H and ?-hydrogen bonds, a salt bridge, and favorable hydrophobic contacts, as revealed by the NMR derived structural model. The protein-dye solutions are easily processable and form homogeneous thin films exhibiting excellent photophysical and morphological properties, as derived from photoluminescence and AFM data. The obtained results represent the proof of concept of the viability of this bio host-guest system for the development of bioinspired optoelectronic devices. PMID:24032431

Tomaselli, Simona; Giovanella, Umberto; Pagano, Katiuscia; Leone, Giuseppe; Zanzoni, Serena; Assfalg, Michael; Meinardi, Francesco; Molinari, Henriette; Botta, Chiara; Ragona, Laura



Energy transfer and phosphorescence-quenching dynamics in a phosphorescent host-guest system  

NASA Astrophysics Data System (ADS)

We investigated the energy transfer dynamics in a phosphorescent host-guest system. Two spirobifluorene derivatives, [2,7-bis(2,2-diphenylvinyl)-9,9'-spirobifluorene] (DPVSBF) and [2,7-bis(1,2,2-triphenylvinyl)-9,9'-spirobifluorene] (TPVSBF), were doped with the red phosphor complex [Os(bpftz)2(PPh2Me)2] (Os-R). The two hosts exhibit similar host-to-guest energy transfer efficiencies; however, the backward energy transfer from the Os-R complex to TPVSBF is slower than that from Os-R to DPVSBF. Quantum chemical calculations suggest that the backward energy transfer dynamics are related to the host's triplet-state energy level. The greater energy of the TPVSBF triplet state compared to that of DPVSBF plays a crucial role in its ability to confine triplet excitons in Os-R.

Chang, Chih-Wei; Lee, Rei-Yun; Diau, Eric Wei-Guang



Temperature-sensitive transitions below LCST in amphiphilic dendritic assemblies: host-guest implications.  


Oligo(ethylene glycol)-decorated supramolecular assemblies have been of great interest due to their charge-neutral character and thus their propensity to avoid nonspecific interactions. These systems are known to exhibit a macroscopic temperature-sensitive transition, where the assembly phase-separates from the aqueous phase at higher temperatures. While this so-called lower critical solution temperature (LCST) behavior has been well-studied, there have been no studies on the fate of these supramolecular assemblies below this transition temperature. The work here brings to light the presence of a second, sub-LCST transition, observed well below the LCST of oligo(ethylene glycol) (OEG)-based dendrons, where the host-guest properties of the assembly are significantly altered. This sub-LCST transition is accompanied by changes in the guest encapsulation stability and dynamics of host exchange. PMID:23692369

Fuller, Jack M; Raghupathi, Krishna R; Ramireddy, Rajasekhar R; Subrahmanyam, Ayyagari V; Yesilyurt, Volkan; Thayumanavan, S



Light-harvesting host-guest antenna materials for photonic devices  

NASA Astrophysics Data System (ADS)

Dye-loaded zeolite L host-guest materials were already successfully used in the realisation of efficient light-harvesting antenna systems. A new hierarchy of structural order is introduced by arranging the zeolite L crystals into densely packed, oriented monolayers on a substrate. In device engineering, a high degree of supramolecular organisation is a prerequisite for achieving desired macroscopic properties. The methods we developed to synthesise such monolayers, to fill them with dyes and to terminate them with a luminescent stopcock will be discussed as well as their influence on the design of novel materials. By subsequent insertion of two different types of dye molecules in a zeolite L monolayer, the first unidirectional antenna system was realised. UV-VIS absorption as well as NIR luminescence spectroscopy was carried out on dye-loaded zeolite L monolayers. We also report a novel concept for the preparation of thin layer, silicon based solar cells.

Calzaferri, Gion; Huber, Stefan; Devaux, André; Zabala Ruiz, Arantzazu; Li, Huanrong; Bossart, Olivia; Dieu, Le-Quyenh



Expansion-contraction of photoresponsive artificial muscle regulated by host-guest interactions  

PubMed Central

The development of stimulus-responsive polymeric materials is of great importance, especially for the development of remotely manipulated materials not in direct contact with an actuator. Here we design a photoresponsive supramolecular actuator by integrating host–guest interactions and photoswitching ability in a hydrogel. A photoresponsive supramolecular hydrogel with ?-cyclodextrin as a host molecule and an azobenzene derivative as a photoresponsive guest molecule exhibits reversible macroscopic deformations in both size and shape when irradiated by ultraviolet light at 365?nm or visible light at 430?nm. The deformation of the supramolecular hydrogel depends on the incident direction. The selectivity of the incident direction allows plate-shaped hydrogels to bend in water. Irradiating with visible light immediately restores the deformed hydrogel. A light-driven supramolecular actuator with ?-cyclodextrin and azobenzene stems from the formation and dissociation of an inclusion complex by ultraviolet or visible light irradiation.

Takashima, Yoshinori; Hatanaka, Shogo; Otsubo, Miyuki; Nakahata, Masaki; Kakuta, Takahiro; Hashidzume, Akihito; Yamaguchi, Hiroyasu; Harada, Akira



Kinetics of formation of the host-guest complex of a viologen with cucurbit[7]uril.  


Host-guest complexation between the dicationic viologen 1-tri(ethylene glycol)-1'-methyl-m-xylyl-4,4'-bipyridinium and cucurbit[7]uril (CB7) was studied at pH = 4.5 in water. The stability constants of the mono- and bis-CB7 adducts were determined at 25 °C by UV-vis spectroscopy. Stopped-flow kinetic experiments were performed to measure the formation and dissociation rate constants of the monoadduct: k(1) = (6.01 ± 0.03) × 10(6) M(-1)s(-1) and k(-1) = 52.7 ± 0.4 s(-1), respectively. Possible mechanisms of complexation are discussed in view of the kinetic results. PMID:22690827

Kalmár, József; Ellis, Shawna B; Ashby, Michael T; Halterman, Ronald L



1H NMR chemical shift calculations as a probe of supramolecular host-guest geometry.  


The self-assembled supramolecular host [Ga(4)L(6)](12-) (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) can encapsulate cationic guest molecules within its hydrophobic cavity and catalyze the chemical transformations of bound guests. The cavity of host 1 is lined with aromatic naphthalene groups, which create a magnetically shielded interior environment, resulting in upfield shifted (1-3 ppm) NMR resonances for encapsulated guest molecules. Using gauge independent atomic orbital (GIAO) DFT computations, we show that (1)H NMR chemical shifts for guests encapsulated in 1 can be efficiently and accurately calculated and that valuable structural information is obtained by comparing calculated and experimental chemical shifts. The (1)H NMR chemical shift calculations are used to map the magnetic environment of the interior of 1, discriminate between different host-guest geometries, and explain the unexpected downfield chemical shift observed for a particular guest molecule interacting with host 1. PMID:21714506

Mugridge, Jeffrey S; Bergman, Robert G; Raymond, Kenneth N



High-precision measurement of isotope effects on noncovalent host-guest interactions.  


The self-assembled supramolecular host [Ga(4)L(6)](12-) can bind cationic guest molecules to both the interior and exterior of the host assembly through noncovalent interactions. Very small equilibrium isotope effects (EIEs) have been precisely measured for the association of benzyltrimethylphosphonium isotopologues to the host exterior surface by adapting an NMR titration method originally developed by the Perrin group for measuring isotope effects on acidity constants. Deuteration of the phosphonium methyl groups was found to have a larger EIE than deuteration at the ring and benzyl positions, suggesting subtle differences in the noncovalent interactions between the host exterior and different guest C-H/D bonds. The application of this method to the measurement of EIEs on noncovalent host-guest interactions demonstrates the generality of this NMR technique in precisely measuring relative equilibrium constants. PMID:20050653

Mugridge, Jeffrey S; Bergman, Robert G; Raymond, Kenneth N



Host-guest inclusion complex of propafenone hydrochloride with ?- and ?-cyclodextrins: Spectral and molecular modeling studies  

NASA Astrophysics Data System (ADS)

Host-guest inclusion complexes of cyclodextrins (CDs) with a potential cardiovascular drug propafenone hydrochloride (PFO), were prepared and characterized using absorption, fluorescence, time-resolved fluorescence, SEM, FT-IR, DSC, 1H NMR, XRD and PM3 methods. The spectral studies suggested the phenyl ring along with carbonyl group is present inside of CD cavity. Solvent studies revealed that the normal Stokes shifted band originates from the locally excited state and the large Stokes shifted band occurs due to the emission from ICT. Nanosecond time-resolved studies indicated that PFO exhibits biexponential decay in water and triexponential decay in CD, indicating the formation of 1:1 inclusion complex. The results from solid state studies showed important modifications in the physicochemical properties of free PFO. The ?H, ?G and ?S of the complexation process were determined and it was found that the complexation processes were spontaneous. Investigations of thermodynamic and electronic properties confirmed the stability of the inclusion complex.

Siva, S.; Thulasidhasan, J.; Rajendiran, N.



The influence of host–guest inclusion complex formation on the biotransformation of cortisone acetate ? 1-dehydrogenation  

Microsoft Academic Search

An intensive and systematic investigation had been carried out on the ?1-dehydrogenation of cortisone acetate (CA) to prednisone acetate (PA) by Arthrobacter simplex TCCC 11037 in the presence of native and modified ?-cyclodextrins (?-CDs). The biotransformation was improved through the formation of the host–guest inclusion complex between CA and CDs in aqueous solution. The inclusion complexes of CDs with CA

Yin-Hu Ma; Min Wang; Zhi Fan; Yan-Bing Shen; Li-Ting Zhang



Gas/solvent-induced transformation and expansion of a nonporous solid to 1:1 host guest form  

SciTech Connect

Herein we report the gas (CO2, N2O and propane) and solvent (CS2 and acetone) induced transformation and expansion of guest free thermodynamic form of a p-tert-butylcalix [4]arene to 1:1 host guest form.

Thallapally, Praveen K.; McGrail, B. Peter; Dalgarno, Scott J.; Atwood, Jerry L.



Ionic galleries: a bilayered host-guest cocrystal of C-propyl pyrogallol[4]arene with an ionic liquid.  


We report on a cocrystal between C-propyl pyrogallol[4]arene and the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate exhibiting a remarkable bilayer topology comprising two unique host-guest complexes resulting from the ionic liquid cation binding in two distinctive orientations relative to the macrocycle. PMID:22531153

Fowler, Drew A; Teat, Simon J; Baker, Gary A; Atwood, Jerry L



Host-guest complexation of [60]fullerenes and porphyrins enabled by "click chemistry".  


Herein the synthesis, characterization, and organization of a first-generation dendritic fulleropyrrolidine bearing two pending porphyrins are reported. Both the dendron and the fullerene derivatives were synthesized by Cu(I) -catalyzed alkyne-azide cycloaddition (CuAAC). The electron-donor-acceptor conjugate possesses a shape that allows the formation of supramolecular complexes by encapsulation of C60 within the jaws of the two porphyrins of another molecule. The interactions between the two photoactive units (i.e., C60 and Zn-porphyrin) were confirmed by cyclic voltammetry as well as by steady-state and time-resolved spectroscopy. For example, a shift of about 85?mV was found for the first reduction of C60 in the electron-donor-acceptor conjugate compared with the parent molecules, which indicates that C60 is included in the jaws of the porphyrin. The fulleropyrrolidine compound exhibits a rich polymorphism, which was corroborated by AFM and SEM. In particular, it was found to form supramolecular fibrils when deposited on substrates. The morphology of the fibrils suggests that they are formed by several rows of fullerene-porphyrin complexes. PMID:23832804

Ho, Khanh-Hy Le; Hijazi, Ismail; Rivier, Lucie; Gautier, Christelle; Jousselme, Bruno; de Miguel, Gustavo; Romero-Nieto, Carlos; Guldi, Dirk M; Heinrich, Benoit; Donnio, Bertrand; Campidelli, Stéphane



High Precision Measurement of Isotope Effects on Noncovalent Host-Guest Interactions  

SciTech Connect

Isotope effects (IEs) are a powerful tool for examining the reactivity of, and interactions between, molecules. Recently, secondary IEs have been used to probe the nature of noncovalent interactions between guest and host molecules in supramolecular systems. While these studies can provide valuable insight into the specific interactions governing guest recognition and binding properties, IEs on noncovalent interactions are often very small and difficult to measure precisely. The Perrin group has developed an NMR titration method capable of determining ratios of equilibrium constants with remarkable precision. They have used this technique to study small, secondary equilibrium isotope effects (EIEs) on the acidity of carboxylic acids and phenols and on the basicity of amines, measuring differences down to thousandths of a pK{sub a} unit. It occurred to us that this titration method can in principle measure relative equilibrium constants for any process which is fast on the NMR timescale and for which the species under comparison are distinguishable by NMR. Here we report the application of this method to measure very small EIEs on noncovalent host-guest interactions in a supramolecular system.

Mugridge, Jeffrey S.; Bergman, Robert G.; Raymond, Kenneth N.



Host-guest complexes and pseudorotaxanes of cucurbit[7]uril with acetylcholinesterase inhibitors.  


Pseudorotaxanes may be assembled in aqueous solution using dicationic acetylcholinesterase inhibitors, such as succinylcholine, BW284c51, and alpha,omega-bis(trialkylammonium)alkane dications (or their phosphonium analogues), as bolaform axles and cucurbit[7]uril (CB[7]) as the wheel. With the exceptions of the shorter [(CH(3))(3)N(CH(2))(n)N(CH(3))(3)](2+) (n = 6, 8) dications, the addition of a second CB[7] results in the translocation of the first CB[7], such that the hydrophobic -NR(3)(+) and -PR(3)(+) end groups (R = Me or Et) are located in the cavities of the wheels, while the central portion of the axles extend through the CB[7] portals into the bulk solvent. In the case of the [Quin(CH(2))(10)Quin](2+) (Quin = quinuclidinium) dication, the CB[7] host(s) resides only on the quinuclidinium end group(s). The 1:1 host-guest stability constants range from 8 x 10(6) to 3 x 10(10) M(-1) and are dependent on both the nature of the end group as well as the length and hydrophobicity of the central linker. The magnitude of the stability constants for the 2:1 complexes closely follow the trend observed previously for CB[7] binding with the NR(4)(+) and PR(4)(+) cations. PMID:19799399

Wyman, Ian W; Macartney, Donal H



Laser spectroscopic study of cold host-guest complexes of crown ethers in the gas phase.  


A laser spectroscopic study on the structure and dynamics of cold host-guest inclusion complexes of crown ethers (CEs) with various neutral and ionic species in the gas phase is presented. The complexes with neutral guest species are formed by using supersonic free jets, and those with ionic species are generated with electrospray ionization combined with a cold 22-pole ion trap. For CEs, various sizes of 3n-crown-n ethers (n=4, 5, 6, and 8) and their benzene-substituted species are used. For the guest species, water, methanol, ammonia, acetylene, and phenol are employed as neutral guest species, and for charged guest species, alkali metal cations are chosen. The electronic and vibrational spectra of the complexes are measured by using various laser spectroscopic methods; electronic spectra for the neutral complexes are measured by laser-induced fluorescence. Discrimination of different species such as conformers is performed by ultraviolet-ultraviolet hole-burning spectroscopy. The vibrational spectra of selected species are observed by infrared-ultraviolet double-resonance (IR-UV DR) spectroscopy. For the ionic complexes, ultraviolet photodissociation and IR-UV DR spectroscopy are applied. The complex structures are determined by comparing the observed spectra with those of possible structures obtained by density functional theory calculations. How the host CEs change their conformation or which conformer prefers to form unique inclusion complexes are discussed. These results reveal the key interactions for forming special complexes leading to molecular recognition. PMID:23203940

Inokuchi, Yoshiya; Kusaka, Ryoji; Ebata, Takayuki; Boyarkin, Oleg V; Rizzo, Thomas R



Host-guest complexes between cryptophane-C and chloromethanes revisited  

PubMed Central

Cryptophane-C is composed of two nonequivalent cyclotribenzylene caps, one of which contains methoxy group substituents on the phenyl rings. The two caps are connected by three OCH2CH2O linkers in an anti arrangement. Host–guest complexes of cryptophane-C with dichloromethane and chloroform in solution were investigated in detail by nuclear magnetic resonance techniques and density functional theory (DFT) calculations. Variable temperature proton and carbon-13 spectra show a variety of dynamic processes, such as guest exchange and host conformational transitions. The guest exchange was studied quantitatively by exchange spectroscopy measurements or by line-shape analysis. The conformational preferences of the guest-containing host were interpreted through cross-relaxation measurements, providing evidence of the gauche+2 and gauche?2 conformations of the linkers. In addition, the mobility of the chloroform guest inside the cavity was studied by carbon-13 relaxation experiments. Combining different types of evidence led to a detailed picture of molecular recognition, interpreted in terms of conformational selection. Copyright © 2012 John Wiley & Sons, Ltd.

Takacs, Z; Soltesova, M; Kowalewski, J; Lang, J; Brotin, T; Dutasta, J-P



Host-guest chemistry of the (N,N'-diarylacetamidine)rhodium(III) complex in zeolite Y.  


The preparation of the (N,N'-diarylacetamidine)rhodium(III) complex in the cavities of zeolite Y is reported. The guest rhodium(III) complex was entrapped in the supercages of zeolite Y as a host by a two-step process in the liquid phase: (I) inclusion of rhodium(III) by ion-exchange in the structure and (II) introduction of N,N'-diarylacetamidine ligand followed by assembly of the complex inside the void space of the zeolite. The neat complex has also been prepared and characterized. The appropriate process selected for the in situ complex synthesis involved using an N,N'-diarylacetamidine ligand : rhodium(III) molar ratio of 4 : 1. Spectroscopic studies (Fourier transform infrared spectroscopy), chemical analyses, surface (X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction) and cyclic voltammetric studies were used to characterize the new host-guest materials. Analysis of the data of the neat and encapsulated complex show that the coordination of the rhodium(III) ion (as a guest in the host structure) by the nitrogen atoms of the N,N'-diarylacetamidine ligand occurred in a 2 : 1 stoichiometry. PMID:19606344

Fonseca, António M; Gonçalves, Sara; Parpot, Pier; Neves, Isabel C



Host-guest interaction of Hoechst 34580 and Cucurbit[7]uril.  


To track nuclear dynamic processes by fluorescence imaging, nuclear stains should be highly fluorescent, resistant to photobleaching, and inert to nuclear processes. The nuclear stains of the Hoechst family, such as Hoechst 34580, show bright fluorescence only on groove binding to DNA, and therefore may interfere with visualization of nuclear dynamic processes induced by other stimuli. We study host-guest interactions between Hoechst 34580 and Cucurbit[7]uril (CB7) in aqueous solutions. The formation of CB7-Hoechst 34580 inclusion complexes with stoichiometry of 2:1 in water and 1:1 in phosphate-buffered saline (PBS) solution (pH 7.0) is confirmed by (1)H NMR, absorption spectra, fluorescence spectra, MALDI-TOF MS, and molecular modeling. Compared to Hoechst 34580, the inclusion complex exhibits redshifted absorption, intensified fluorescence, improved photostability, weakened DNA binding affinity, comparable ability to penetrate cell nuclei, and better nuclear-staining capability, and thus a new avenue for the application of cucurbituril in fluorescence imaging is opened. PMID:21919182

Lei, Wanhua; Zhou, Qianxiong; Jiang, Guoyu; Hou, Yuanjun; Zhang, Baowen; Cheng, Xuexin; Wang, Xuesong



Cucurbit[7]uril: surfactant host-guest complexes in equilibrium with micellar aggregates.  


In order to compare the formation of host-guest complexes between ?-cyclodextrin (?-CD) or cucurbit[7]uril (CB7) and cationic surfactants we studied the hydrolysis of 4-methoxybenzenesulfonyl chloride (MBSC). The selected surfactants allowed the length of the hydrocarbon chain to be varied between 6 and 18 carbon atoms. Contrary to the expected behaviour, the values of the binding constants between CB7 and surfactants are independent of the alkyl chain length of the surfactant. In the case of ?-CD, however, a clear dependence of the binding constant on the hydrophobic character of the surfactant was observed. The values obtained with CB7 are significantly higher than those obtained with ?-CD and these differences are explained to be a consequence of electrostatic interactions of the surfactants with the portals of CB7. It was found that a small percentage of uncomplexed CB7 was in equilibrium with the cationic micelles and this percentage increased on increasing the hydrophobic character of the surfactant. PMID:21472839

Pessêgo, Marcia; Basilio, Nuno; Moreira, Jose A; García-Río, Luis



Unconventional electronic and magnetic functions of nanographene-based host-guest systems.  


Nanographene has a unique electronic structure which critically depends on the shape of its edge. A zigzag-edged nanographene sheet has a non-bonding pi-electron state (edge state), yielding a strong spin magnetism for edge-state localized spins, in spite of the absence of such a state in an armchair-edged nanographene sheet. Nanographite (stacked nanographene sheets)-network-based nanoporous carbon is employed as the host material to build unconventional magnetic systems based on the host-guest interaction. The physisorption of various guest materials can cause a reversible low-spin/high-spin magnetic switching phenomenon, whose feature varies depending on the type of guest species. The edge-state spins are utilized as a probe to detect a huge condensation of helium atoms in the nanopores. The giant magnetoresistance of the nanographite network is controlled by the physisorption of magnetic oxygen molecules. The confinement of potassium clusters in the nanopores surrounded by nanographite domains yields an interesting nanomagnetic state. Nanographene/nanographite is an intriguing pi-electron-based nanocarbon material with the potential of producing unconventional magnetic structures that cannot be obtained using bulk graphite. The processability of nanographene/nanographite is expected to give a variety of magnetic functions for spintronic applications. PMID:18629396

Enoki, Toshiaki; Takai, Kazuyuki



Enhanced host-guest electrochemical recognition of herbicide MCPA using a ?-cyclodextrin carbon nanotube sensor.  


An electrochemical sensor for the determination of the chlorophenoxy herbicide MCPA has been developed, based on a combination of multi-walled carbon nanotubes with incorporated ?-cyclodextrin and a polyaniline film modified glassy carbon electrode. The proposed molecular host-guest recognition based sensor has a high electrochemical sensitivity for the determination of MCPA. The electrochemical behaviour of MCPA at the chemically modified electrode was investigated in detail by cyclic voltammetry. The results indicate that the ?-CD/MWCNT modified glassy carbon electrode exhibits efficient electrocatalytic oxidation of MCPA with high sensitivity, stability and lifetime. The analytical characteristics of this film were used for the quantitative determination of MCPA in natural waters. Cyclic voltammetry in phosphate buffer solution at pH 6.0, allowed the development of a method to determine MCPA, without any previous steps of extraction, clean-up, or derivatization, in the range of 10-100 ?mol L(-1), with a detection limit of 0.99 ?mol L(-1) in water. The results were statistically compared with those obtained through an established high-performance liquid chromatography technique, no significant differences having been found between the two methods. PMID:22967554

Rahemi, V; Vandamme, J J; Garrido, J M P J; Borges, F; Brett, C M A; Garrido, E M P J



A versatile multicomponent assembly via ?-cyclodextrin host-guest chemistry on graphene for biomedical applications.  


A multi-component nanosystem based on graphene and comprising individual cyclodextrins at its surface is assembled, creating hybrid structures enabling new and important functionalities: optical imaging, drug storage, and cell targeting for medical diagnosis and treatment. These nanohybrids are part of a universal system of interchangeable units, capable of mutilple functionalities. The surface components, made of individual ?-cyclodextrin molecules, are the "hosts" for functional units, which may be used as imaging agents, for anti-cancer drug delivery, and as tumor-specific ligands. Specifically, individual ?-cyclodextrin (?-CD), with a known capability to host various molecules, is considered a module unit that is assembled onto graphene nanosheet (GNS). The cyclodextrin-functionalized graphene nanosheet (GNS/?-CD) enables "host-guest" chemistry between the nanohybrid and functional "payloads". The structure, composition, and morphology of the graphene nanosheet hybrid have been investigated. The nanohybrid, GNS/?-CD, is highly dispersive in various physiological solutions, reflecting the high biostability of cyclodextrin. Regarding the host capability, the nanohybrid is fully capable of selectively accommodating various biological and functional agents in a controlled fashion, including the antivirus drug amantadine, fluorescent dye [5(6)-carboxyfluorescein], and Arg-Gly-Asp (RGD) peptide-targeting ligands assisted by an adamantine linker. The loading ratio of 5(6)-carboxyfluorescein is as high as 110% with a drug concentration of 0.45 mg mL(-1). The cyclic RGD-functionalized nanohybrid exhibits remarkable targeting for HeLa cells. PMID:23047287

Dong, Haiqing; Li, Yongyong; Yu, Jinhai; Song, Yanyan; Cai, Xiaojun; Liu, Jiaqiang; Zhang, Jiaming; Ewing, Rodney C; Shi, Donglu



Host-guest complexations of local anaesthetics by cucurbit[7]uril in aqueous solution.  


The cucurbit[7]uril (CB[7]) host molecule forms very stable host-guest complexes with the local anaesthetics procaine (K(CB[7]) = (3.5 +/- 0.7) x 10(4) dm(3) mol(-1)), tetracaine (K(CB[7]) = (1.5 +/- 0.4) x 10(4) dm(3) mol(-1)), procainamide (K(CB[7]) = (7.8 +/- 1.6) x 10(4) dm(3) mol(-1)), dibucaine (K(CB[7]) = (1.8 +/- 0.4) x 10(5) dm(3) mol(-1)) and prilocaine (K(CB[7]) = (2.6 +/- 0.6) x 10(4) dm(3) mol(-1)) in aqueous solution (pD = 4.75). The stability constants are 2-3 orders of magnitude greater than the values reported for binding by the comparably sized beta-cyclodextrin host molecule. The inclusion by CB[7] raises the first pK(a) values of the anaesthetics by 0.5-1.9 pK units, as the protonated forms are bound more strongly in acidic solution. The complexation-induced chemical shift changes in the guest proton resonances provide an indication of the site(s) of binding and the effects of protonation on the location of the binding sites. PMID:20024155

Wyman, Ian W; Macartney, Donal H



Spectral and electrochemical study of host-guest inclusion complex between 2,4-dinitrophenol and ?-cyclodextrin  

NASA Astrophysics Data System (ADS)

The formation of host-guest inclusion complex of 2,4-dinitrophenol (2,4-DNP) with nano-hydrophobic cavity of ?-cyclodextrin (?-CD) in solution phase was studied by UV-visible spectrophotometer and electrochemical method (cyclic voltammetry, CV). The prototropic behaviors of 2,4-DNP with and without ?-CD and the ground state acidity constant (pKa) of host-guest inclusion complex (2,4-DNP-?-CD) were studied. The binding constant of inclusion complex at 303 K was calculated using Benesi-Hildebrand plot and thermodynamic parameter (?G) was also calculated. The solid inclusion complex formation between ?-CD and 2,4-DNP was confirmed by 1H NMR, FT-IR, XRD and SEM analysis. A schematic representation of this inclusion process is proposed by molecular docking studies using PatchDock server.

Srinivasan, K.; Stalin, T.; Sivakumar, K.


A Structural Model of Polyglutamine Determined from a Host-Guest Method Combining Experiments and Landscape Theory  

Microsoft Academic Search

Modeling the structure of natively disordered peptides has proved difficult due to the lack of structural information on these peptides. In this work, we use a novel application of the host-guest method, combining folding theory with experiments, to model the structure of natively disordered polyglutamine peptides. Initially, a minimalist molecular model (C?C?) of CI2 is developed with a structurally based

John M. Finke; Margaret S. Cheung; José N. Onuchic



On the Role of Dewetting Transitions in Host-Guest Binding Free Energy Calculations.  


We use thermodynamic integration (TI) and explicit solvent molecular dynamics (MD) simulation to estimate the absolute free energy of host-guest binding. In the unbound state, water molecules visit all of the internally accessible volume of the host, which is fully hydrated on all sides. Upon binding of an apolar guest, the toroidal host cavity is fully dehydrated; thus, during the intermediate ? stages along the integration, the hydration of the host fluctuates between hydrated and dehydrated states. Estimating free energies by TI can be especially challenging when there is a considerable difference in hydration between the two states of interest. We investigate these aspects using the popular TIP3P and TIP4P water models. TI free energy estimates through MD largely depend on water-related interactions, and water dynamics significantly affect the convergence of binding free energy calculations. Our results indicate that wetting/dewetting transitions play a major role in slowing the convergence of free energy estimation. We employ two alternative approaches-one analytical and the other empirically based on actual MD sampling-to correct for the standard state free energy. This correction is sizable (up to 4 kcal/mol), and the two approaches provide corrections that differ by about 1 kcal/mol. For the system considered here, the TIP4P water model combined with an analytical correction for the standard state free energy provides higher overall accuracy. This observation might be transferable to other systems in which water-related contributions dominate the binding process. PMID:23316123

Rogers, Kathleen E; Ortiz-Sánchez, Juan Manuel; Baron, Riccardo; Fajer, Mikolai; de Oliveira, César Augusto F; McCammon, J Andrew



Reduced activity of alkaline phosphatase due to host-guest interactions with humic superstructures.  


Nuclear Magnetic Resonance (NMR) spectroscopy was applied to directly study the interactions between the alkaline phosphatase enzyme (AP) and two different humic acids from a volcanic soil (HA-V) and a Lignite deposit (HA-L). Addition of humic matter to enzyme solutions caused signals broadening in (1)H-NMR spectra, and progressive decrease and increase of enzyme relaxation (T1 and T2) and correlation (?C) times, respectively. Spectroscopic changes were explained with formation of ever larger weakly-bound humic-enzyme complexes, whose translational and rotational motion was increasingly restricted. NMR diffusion experiments also showed that the AP diffusive properties were progressively reduced with formation of large humic-enzyme complexes. The more hydrophobic HA-L affected spectral changes more than the more hydrophilic HA-V. (1)H-NMR spectra also showed the effect of progressively greater humic-enzyme complexes on the hydrolysis of an enzyme substrate, the 4-nitrophenyl phosphate disodium salt hexahydrate (p-NPP). While AP catalysis concomitantly decreased NMR signals of p-NPP and increased those of nitrophenol, addition of humic matter progressively and significantly slowed down the rate of change for these signals. In agreement with the observed spectral changes, the AP catalytic activity was more largely inhibited by HA-L than by HA-V. Contrary to previous studies, in which humic-enzyme interactions were only indirectly assumed from changes in spectrophotometric behavior of enzyme substrates, the direct measurements of AP behavior by NMR spectroscopy indicated that humic materials formed weakly-bound host-guest complexes with alkaline phosphatase, and the enzyme catalytic activity was thereby significantly inhibited. These results suggest that the role of extracellular enzymes in soils may be considerably reduced when they come in contact with organic matter dissolved in the soil solution. PMID:23953249

Mazzei, Pierluigi; Oschkinat, Hartmut; Piccolo, Alessandro



Electronic and magnetic functions of nanographene-based host-guest system  

NASA Astrophysics Data System (ADS)

The electronic structure of nanographene having open edges crucially depends on its edge shape. According to theoretical predictions, nanographene has nonbonding ?-electron state (edge state) localized in zigzag edges. We investigated the electronic structure of graphene edges, the magnetism of the edge-state spins in nanographene and the effect of host-guest interaction on the magnetism. For magnetic investigations, we employed nanoporous activated carbon fiber (ACF) having a 3D disordered network of nanographite domains, each of which is a stack of 3-4 nanographene sheets. STM/STS investigations of hydrogen-terminated graphene edges confirm the presence of edge states around zigzag edges, in good agreement with theoretical works. The feature of the edge state depends on the detailed geometry of the edge structures. The magnetism of nanographene in ACF has a ferrimagnetism feature with a net magnetic moment, for which the cooperation of ferromagnetic intra-zigzag-edge and ferromagntic/antiferromagnetic inter-zigzag-edge interactions is responsible. Heat-treatment, which induces an insulator-metal transition, brings about spin glass state of the edge-state spins in the vicinity of the transition. Physisorption of guest species such as water, organic molecules, rare gas in the ACF nanopores generates a high-spin/low-spin magnetic switching phenomenon, in which a discontinuous reduction of the magnetic moment takes place. This is explained in terms of the strengthening of the inter-graphene-sheet antiferromagnetic interaction, which is induced by the mechanical compression of nanographite domains by the condensed guest molecules. The magnetic oxygen molecules physisorbed in the nanopores work seriously to decrease the magnetoresistance in ACF as a consequence of the interaction between the oxygen molecule spins and edge-state spins.

Enoki, Toshiaki



Prediction of SAMPL3 Host-Guest Binding Affinities: Evaluating the Accuracy of Generalized Force-Fields  

PubMed Central

We used the second-generation mining minima method (M2) to compute the binding affinities of the novel host-guest complexes in the SAMPL3 blind prediction challenge. The predictions were in poor agreement with experiment, and we conjectured that much of the error might derive from the force field, CHARMm with Vcharge charges. Repeating the calculations with other generalized force-fields led to no significant improvement, and we observed that the predicted affinities were highly sensitive to the choice of force-field. We therefore embarked on a systematic evaluation of a set of generalized force fields, based upon comparisons with PM6-DH2, a fast yet accurate semi-empirical quantum mechanics method. In particular, we compared gas-phase interaction energies and entropies for the host-guest complexes themselves, as well as for smaller chemical fragments derived from the same molecules. The mean deviations of the force field interaction energies from the quantum results were greater than 3 kcal/mol and 9 kcal/mol, for the fragments and host-guest systems respectively. We further evaluated the accuracy of force-fields for computing the vibrational entropies and found the mean errors to be greater than 4 kcal/mol. Given these errors in energy and entropy, it is not surprising in retrospect that the predicted binding affinities deviated from the experiment by several kcal/mol. These results emphasize the need for improvements in generalized force-fields and also highlight the importance of systematic evaluation of force-field parameters prior to evaluating different free-energy methods.

Muddana, Hari S.; Gilson, Michael K.



Optical Tweezers  

NSDL National Science Digital Library

Learn about the principles behind the optical tweezers or optical trapping experiment. Become familiar with the use of standard optics including optical alignment, and collection of data through the use of a camera-computer system. Examine the forces on a bead trapped by a laser.



Dynamic interplay between spin-crossover and host-guest function in a nanoporous metal-organic framework material.  

SciTech Connect

The nanoporous metal-organic framework [Fe(pz)Ni(CN){sub 4}], 1 (where pz is pyrazine), exhibits hysteretic spin-crossover at ambient conditions and is robust to the adsorption and desorption of a wide range of small molecular guests, both gases (N{sub 2}, O{sub 2}, CO{sub 2}) and vapors (methanol, ethanol, acetone, acetonitrile, and toluene). Through the comprehensive analysis of structure, host-guest properties, and spin-crossover behaviors, it is found that this pillared Hofmann system uniquely displays both guest-exchange-induced changes to spin-crossover and spin-crossover-induced changes to host-guest properties, with direct dynamic interplay between these two phenomena. Guest desorption and adsorption cause pronounced changes to the spin-crossover behavior according to a systematic trend in which larger guests stabilize the high-spin state and therefore depress the spin-crossover temperature of the host lattice. When stabilizing the alternate spin state of the host at any given temperature, these processes directly stimulate the spin-crossover process, providing a chemisensing function. Exploitation of the bistability of the host allows the modification of adsorption properties at a fixed temperature through control of the host spin state, with each state shown to display differing chemical affinities to guest sorption. Guest desorption then adsorption, and vice versa, can be used to switch between spin states in the bistable temperature region, adding a guest-dependent memory effect to this system.

Southon, P. D.; Liu, L.; Fellows, E. A.; Price, D. J.; Halder, G. J.; Chapman, K. W.; Moubaraki, B.; Murray, K. S.; Letard, J.F.; Kepert, C. J.; Univ. Sydney; Monash Univ.; Universite Bordeaux



Signal amplification for electrochemical immunosensing by in situ assembly of host-guest linked gold nanorod superstructure on immunocomplex.  


An amplification strategy for signal tracing was developed by introducing a host-guest binding reaction into the assembly process of gold nanorods (AuNRs) superstructure. The amplification pathway firstly used a thio-?-cyclodextrin (SH-?-CD) functionalized gold nanoparticles to label signal antibody, and then in situ assembled multi-layer SH-?-CD end-functionalized AuNRs to sandwich immunocomplex on immunosensor surface by using 4,4,4,4-(21H, 23H-porphine-5,10,15,20-tetrayl) tetrakis (benzoic acid) as a bridge to achieve simple and convenient host-guest reaction. The built end-to-end AuNRs superstructure showed excellent performance for the signal amplification in connection with the electrochemical biosensing by preoxidation and then voltammetric analysis of gold element. Using ?-fetoprotein as an analyte, the immunosensor was constructed by covalently binding capture antibody to chitosan-carbon nanotubes-poly(diallyldimethylammonium chloride) modified electrode. The superstructure rich in AuNRs brought an enhanced detection sensitivity of protein, which could detect ?-fetoprotein in a linear range from 0.5 pg mL(-1) to 0.5 ng mL(-1) with a detection limit down to 0.032 pg mL(-1). The immunoassay exhibited good stability and acceptable reproducibility and accuracy. The in situ superstructure assembly could be extended to other labeled recognition systems, providing a promising novel avenue for signal amplification and potential applications in bioanalysis and clinical diagnostics. PMID:23500363

Lin, Dajie; Wu, Jie; Ju, Huangxian; Yan, Feng



NMR diffusion spectroscopy as a measure of host-guest complex association constants and as a probe of complex size.  


The complexes of cyclohexylacetic acid and cholic acid with beta-cyclodextrin were studied by NMR diffusion coefficient measurements. The diffusion coefficient of the 1:1 cyclohexylacetic acid/beta-cyclodextrin complex, K(a) = 1800 +/- 100 M(-1), is slightly slower (3.23 +/- 0.07 x 10(-6) cm(2) s(-1)) than that of beta-cyclodextrin (3.29 +/- 0.07 x 10(-6) cm(2) s(-1)). The diffusion coefficient of the 1:1 cholic acid/beta-cyclodextrin complex, K(a) = 5900 +/- 800 M(-1), is significantly slower (2.93 +/- 0.07 x 10(-6) cm(2) s(-1)) than that of beta-cyclodextrin. The results indicate that caution should be exercised when studying host-guest complexation by the so-called 'single point' technique. A novel data treatment is introduced which takes into account the diffusion behavior of all of the species when determining K(a). Experimentally determined diffusion coefficients of complexes are also a useful probe of the size of host-guest complexes. PMID:11597206

Cameron, K S; Fielding, L



Organic light-emitting diodes for lighting: High color quality by controlling energy transfer processes in host-guest-systems  

NASA Astrophysics Data System (ADS)

Exciton generation and transfer processes in a multilayer organic light-emitting diode (OLED) are studied in order to realize OLEDs with warm white color coordinates and high color-rendering index (CRI). We investigate a host-guest-system containing four phosphorescent emitters and two matrix materials with different transport properties. We show, by time-resolved spectroscopy, that an energy back-transfer from the blue emitter to the matrix materials occurs, which can be used to transport excitons to the other emitter molecules. Furthermore, we investigate the excitonic and electronic transfer processes by designing suitable emission layer stacks. As a result, we obtain an OLED with Commission Internationale de lÉclairage (CIE) coordinates of (0.444;0.409), a CRI of 82, and a spectrum independent of the applied current. The OLED shows an external quantum efficiency of 10% and a luminous efficacy of 17.4 lm/W at 1000 cd/m2.

Weichsel, Caroline; Reineke, Sebastian; Furno, Mauro; Lüssem, Björn; Leo, Karl



A host-guest supramolecular complex with photoregulated delivery of nitric oxide and fluorescence imaging capacity in cancer cells.  


Herein we report the design, preparation, and properties of a supramolecular system based on a tailored nitric oxide (NO) photodonor and a rhodamine-labeled ?-cyclodextrin conjugate. The combination of spectroscopic and photochemical experiments shows the absence of significant interchromophoric interactions between the host and the guest in the excited states. As a result, the complex is able to release NO under the exclusive control of visible light, as unambiguously demonstrated by direct detection of this transient species through an amperometric technique, and exhibits the typical red fluorescence of the rhodamine appendage. The supramolecular complex effectively internalizes in HeLa cancer cells as proven by fluorescence microscopy, shows a satisfactory biocompatibility in the dark, and induces about 50% of cell mortality upon irradiation with visible light. The convergence of all these properties in one single complex makes the present host-guest ensemble an appealing candidate for further delevopment of photoactivatable nanoscaled systems addressed to photostimulated NO-based therapy. PMID:23015376

Kandoth, Noufal; Malanga, Milo; Fraix, Aurore; Jicsinszky, László; Fenyvesi, Éva; Parisi, Tiziana; Colao, Ivana; Sciortino, Maria Teresa; Sortino, Salvatore



A synthetic host-guest system achieves avidin-biotin affinity by overcoming enthalpy-entropy compensation  

PubMed Central

The molecular host cucurbit[7]uril forms an extremely stable inclusion complex with the dicationic ferrocene derivative bis(trimethylammoniomethyl)ferrocene in aqueous solution. The equilibrium association constant for this host-guest pair is 3 × 1015 M?1 (Kd = 3 × 10?16 M), equivalent to that exhibited by the avidin–biotin pair. Although purely synthetic systems with larger association constants have been reported, the present one is unique because it does not rely on polyvalency. Instead, it achieves its extreme affinity by overcoming the compensatory enthalpy–entropy relationship usually observed in supramolecular complexes. Its disproportionately low entropic cost is traced to extensive host desolvation and to the rigidity of both the host and the guest.

Rekharsky, Mikhail V.; Mori, Tadashi; Yang, Cheng; Ko, Young Ho; Selvapalam, N.; Kim, Hyunuk; Sobransingh, David; Kaifer, Angel E.; Liu, Simin; Isaacs, Lyle; Chen, Wei; Moghaddam, Sarvin; Gilson, Michael K.; Kim, Kimoon; Inoue, Yoshihisa



The host-guest inclusion complex of p-chlorophenol inside [alpha]-cyclodextrin: An atoms in molecules study  

NASA Astrophysics Data System (ADS)

We report a study of the inclusion complex of p-chlorophenol inside [alpha]-cyclodextrin ([alpha]-CD) by the theory of atoms in molecules (AIM). We use a quantitative comparison of some AIM properties of isolated p-chlorophenol (PCP) and the inclusion complex (PCP-CD) and we characterize some weak interactions within the host-guest complex. Furthermore, we compare the electrophilic aromatic substitution on the p-chlorophenol in the isolated state and inside [alpha]-CD. The analysis of the bond critical points of PCP shows that there is no trend in the effect on the AIM properties of PCP due to inclusion in the [alpha]-CD.

Castillo, Norberto; Boyd, Russell J.



Cyclodextrin functionalized graphene nanosheets with high supramolecular recognition capability: synthesis and host-guest inclusion for enhanced electrochemical performance.  


Cyclodextrins (CDs) are oligosaccharides composed of six, seven, or eight glucose units (alpha-, beta-, or gamma-CD, respectively), which are toroidal in shape with a hydrophobic inner cavity and a hydrophilic exterior. These interesting characteristics can enable them to bind selectively various organic, inorganic and biological guest molecules into their cavities to form stable host-guest inclusion complexes or nanostructured supramolecular assemblies in their hydrophobic cavity. On the other hand graphene nanosheet (GN), a rising-star material, holds great promise for potential applications in many technological fields due to its high surface areas, low cost, and high conductivity. If GNs are modified with CDs, it is possible to obtain new materials simultaneously possessing unique properties of GNs and cyclodextrins through combining their individual obvious advantages. In this article, we demonstrate for the first time a simple wet-chemical strategy for the preparation of CD-graphene organic-inorganic hybrid nanosheets (CD-GNs), which exhibited high solubility and stability in polar solvent. The obtained CD-GNs were characterized by UV-vis spectroscopy, static contact angle measurement, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, atomic force microscopy, transmission electron microscopy, and electrochemical impedance spectroscopy, which confirmed that CD had been effectively functionalized on the surface of GNs. Furthermore, the formation mechanism of CD-GNs was also discussed. Interestingly, GNs here could load a number of CD molecules, which was very important for greatly enhancing the supramolecular function of CDs. Electrochemical results obviously reveal that CD-graphene organic-inorganic hybrid nanosheets could exhibit very high supramolecular recognition and enrichment capability and show much higher electrochemical response toward eight probe molecules (biomolecules and drugs) than unmodified GNs and carbon nanotubes, which is probably caused by the synergetic effects from GNs (high conductivity and high surface area) and CD molecules (host-guest recognition and enrichment). PMID:20583782

Guo, Yujing; Guo, Shaojun; Ren, Jiangtao; Zhai, Yueming; Dong, Shaojun; Wang, Erkang



Electrostatic docking of a supramolecular host-guest assembly to cytochrome c probed by bidirectional photoinduced electron transfer.  


A water-soluble octacarboxyhemicarcerand was used as a shuttle to transport redox-active substrates across the aqueous medium and deliver them to the target protein. The results show that weak multivalent interactions and conformational flexibility can be exploited to reversibly bind complex supramolecular assemblies to biological molecules. Hydrophobic electron donors and acceptors were encapsulated within the hemicarcerand, and photoinduced electron transfer (ET) between the Zn-substituted cytochrome c (MW = 12.3 kD) and the host-guest complexes (MW = 2.2 kD) was used to probe the association between the negatively charged hemicarceplex and the positively charged protein. The behavior of the resulting ternary protein-hemicarcerand-guest assembly was investigated in two binding limits: (1) when K(encaps) ? K(assoc), the hemicarcerand transports the ligand to the protein while protecting it from the aqueous medium; and (2) when K(assoc) > K(encaps), the hemicarcerand-protein complex is formed first, and the hemicarcerand acts as an artificial receptor site that intercepts ligands from solution and positions them close to the active site of the metalloenzyme. In both cases, ET mediated by the protein-bound hemicarcerand is much faster than that due to diffusional encounters with the respective free donor or acceptor in solution. The measured ET rates suggest that the dominant binding region of the host-guest complex on the surface of the protein is consistent with the docking area of the native redox partner of cytochrome c. The strong association with the protein is attributed to the flexible conformation and adaptable charge distribution of the hemicarcerand, which allow for surface-matching with the cytochrome. PMID:21038913

Jankowska, Katarzyna I; Pagba, Cynthia V; Piatnitski Chekler, Eugene L; Deshayes, Kurt; Piotrowiak, Piotr



High-pressure structural trends of Group 15 elements: simple packed structures versus complex host-guest arrangements.  


The Group 15 elements P, As, Sb, and Bi all have layered structures consisting of six-membered rings under ambient conditions and attain the body-centered cubic (bcc) structure at the highest pressures applied. In the intermediate pressure region, however, phosphorus and its heavier congeners behave profoundly differently. In this region P first attains the open packed simple cubic (sc) structure for a wide range of pressures and then transforms into the rarely observed simple hexagonal (sh) structure. For the heavier congeners complex, incommensurately modulated host-guest structures emerge as intermediate pressure structures. We investigated the high-pressure behavior of P and As by ab initio density functional calculations in which pseudopotentials and a plane wave basis set were employed. The incommensurately modulated high-pressure structure of As was approximated by a supercell. Our calculations reproduced the experimentally established pressure stability ranges of the sc and sh structures for P and the host-guest structure for As very well. We found that the sc and especially the sh structure are decisively stabilized by the admixture of d states in the occupied levels of the electronic structure. This admixture releases s-s antibonding states above the Fermi level (s-d mixing). With pressure, s-d mixing increases rapidly for P, whereas it remains at a low level for As. As a consequence, the band energy contribution to the total energy determines the structural stability for P in the intermediate pressure region, giving rise to simple packed structures. On the other hand, in the intermediate pressure region of the heavier Group 15 elements, a delicate interplay between the electrostatic Madelung energy and the band energy leads to the formation of complex structures. PMID:12658643

Häussermann, Ulrich



Very low amplified spontaneous emission threshold from a molecular host-guest energy transfer system and electroluminescence from light-emitting diode structure  

NASA Astrophysics Data System (ADS)

We report on the characteristics of a host-guest lasing system obtained by co-evaporation of an oligo(9,9-diarylfluorene) derivative named T3 with the red-emitter 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye (DCM). We demonstrate that the ambipolar semiconductor T3 can be implemented as active matrix in the realization of a host-guest system in which an efficient energy transfer takes place from T3 matrix to the lasing DCM molecules. We performed a spectroscopic study on the system by systematically varying the DCM concentration in the T3 matrix. Measurements of steady-state photoluminescence (PL), PL quantum yield (PLQY) and amplified spontaneous emission (ASE) threshold are used to optimize the acceptor concentration at which the ASE from DCM molecules takes place with the lowest threshold. Organic light-emitting diodes (OLEDs) implementing the DCM:T3 host-guest system as recombination layer are fabricated for verifying the optical properties of the optimised blend in real working devices. Indeed, the very low ASE threshold of T3:DCM makes the investigated blend an appealing system for use as active layer in lasing devices. In particular, the ambipolar charge transport properties of the T3 matrix and its field-effect characteristics make the host-guest system presented here an ideal candidate for the realization of electrically-pumped organic lasers.

Toffanin, Stefano; Capelli, Raffaella; Generali, Gianluca; Hwu, Tsyr-Yuan; Wong, Ken-Tsung; Zamboni, Roberto; Muccini, Michele



Copper based metal-organic molecular ring with inserted Keggin-type polyoxometalate: a stable photofunctional host-guest molecular system.  


Keggin polyphosphotungstate cluster was captured by a porous molecular ring with light sensitizing TPT molecules as connectors and copper ions as nodes. The self-assembly reaction gives a stable host-guest supramolecular system, demonstrating efficient heterogeneous photocatalytic behavior for the degradation of methyl orange in near-neutral conditions. PMID:22588148

Fu, Zhiyong; Zeng, Yu; Liu, Xiaoling; Song, Desheng; Liao, Shijun; Dai, Jingcao



Optical response of carbon nanotubes functionalized with (free-base, Zn) porphyrins, and phthalocyanines: A DFT study  

NASA Astrophysics Data System (ADS)

We use density-functional theory calculations to study the stability, electronic, and optical properties of free-base and Zn porphyrins and phthalocyanines (H2P, H2Pc, ZnP, and ZnPc) noncovalently attached onto a semiconducting carbon nanotube (CNT). The macrocycle physisorption is described by van der Waals density functional while optical response is obtained through the imaginary part of the dielectric function. Our results show a rather strong macrocycle binding energy, ranging from 1.0 to 1.5 eV, whereas the CNT geometry and electronic properties are weakly affected by the adsorbates. The optical spectrum shows that CNT-porphyrins and CNT-phthalocyanines assemblies would absorb at different energies of the visible solar radiation spectrum, which would increase the conversion energy efficiency in a photovoltaic device including both macrocycles.

Correa, J. D.; Orellana, W.



Cyclodextrin-modified micellar electrokinetic capillary chromatography separations of benzopyrene isomers. Correlation with computationally derived host-guest energies  

SciTech Connect

General adjustment of system retention is often inadequate to resolve structurally similar compounds in micellar electrokinetic capillary chromatography (MECC). The use of cyclodextrins (CDs) as mobile-phase additives is described for separations of structural isomers. CDs are shown to provide dramatic and selective effects on the retention of benzopyrene isomers. Efficient separations of six methyl-substituted and three 1-position-substituted benzopyrene isomers are presented. Derivatized [gamma]-CD discriminates between substitutional isomers less than native [gamma]-CD. A comparison of sodium dodecylsulfate (SDS) and sodium cholate (NaC) surfactant systems indicates that SDS-CD mobile phases are more favorable for separation of benzopyrene isomers. Possible separation mechanisms are discussed and evaluated based on results of these studies. The computational procedures of a commercial molecular modeling system are modified and used to determine interaction energies for various host-guest (i.e., [gamma]-CD-benzopyrene) combinations. By use of the average of the five best energy values from interaction energy matrices, correct elution order is predicted for the 1-position-substituted and most of the methyl-substituted benzopyrene isomers. Consideration of different possible CD-benzopyrene orientations must be made to correctly predict elution order. Inspection of the interaction energy matrices revealed no obvious energy barriers that would inhibit inclusion complex formation. 28 refs., 4 figs., 2 tabs.

Copper, C.L.; Sepaniak, M.J. (Univ. of Tennessee, Knoxville, TN (United States))



Enantioselective Host-Guest Complexation of Ru(II) trisdiimine complexes using neutral and anionic derivatized cyclodextrins  

PubMed Central

Enantioselective host-guest complexation between five racemic Ru(II) trisdiimine complexes and eight derivatized cyclodextrins (CDs) has been examined by NMR techniques. The appearance of non-equivalent complexation-induced shifts of between the ? and ?-enantionomers of the Ru(II) trisdiimine complexes and derivatized CDs is readily observed by NMR. In particular, sulfobutyl ether-?-cyclodextrin sodium salt (SBE-?-CD), R-naphtylethyl carbamate ?-cyclodextrin (RN-?-CD), and S-naphtylethyl carbamate ?-cyclodextrin (SN-?-CD) showed good enantiodiscrimination for all five Ru complexes examined, which indicates that aromatic and anionic derivatizing groups are beneficial for chiral recognition. The complexation stoichiometry between SBE-?-CD and [Ru(phen)3]2+ was found to be 1: 1 and binding constants reveal that ?-[Ru(phen)3]2+ binds more strongly to SBE-?-CD than the ?-enantiomer. Correlations between this NMR method and separative techniques based on CDs as chiral discriminating agents (i.e., selectors) are discussed in detail.

Sun, Ping; MacDonnell, Frederick M.; Armstrong, Daniel W.



Sulfonamide antibiotics embedded in high silica zeolite Y: a combined experimental and theoretical study of host-guest and guest-guest interactions.  


A combined experimental and computational study of the interactions of three sulfonamides--sulfadiazine, sulfamethazine, and sulfachloropyridazine--embedded into the cages of high silica zeolite Y is here proposed. For all host-guest systems, the close vicinity of aromatic rings with zeolite framework was evidenced by multidimensional and multinuclear ((1)H, (13)C, (29)Si) SS-NMR measurements. Host-guest and guest-guest interactions were also elucidated by in situ FTIR spectroscopy and confirmed by ab initio computational modeling. Single molecules of sulfamethazine and sulfachloropyridazine were stabilized inside the zeolite cage by the vicinity of methyl and amino groups, respectively. Sulfadiazine is present in both monomeric and dimeric forms. Multiple weak H-bonds and van der Waals type interactions between organic molecules and zeolite are responsible for the irreversible extraction from water of all the examined sulfa drugs. PMID:20184353

Braschi, Ilaria; Gatti, Giorgio; Paul, Geo; Gessa, Carlo E; Cossi, Maurizio; Marchese, Leonardo



Preorganized hydrogel: self-healing properties of supramolecular hydrogels formed by polymerization of host-guest-monomers that contain cyclodextrins and hydrophobic guest groups.  


Supramolecular hydrogels formed by a host-guest interaction show self-healing properties. The cube-shaped hydrogels with ?-cyclodextrin and adamantane guest molecules mend after being broken. The hydrogels sufficiently heal to form a single gel, and the initial strength is restored. Although contact between a freshly cut and uncut surface does not mend the gels, two freshly cut surfaces selectively mend. PMID:23423947

Kakuta, Takahiro; Takashima, Yoshinori; Nakahata, Masaki; Otsubo, Miyuki; Yamaguchi, Hiroyasu; Harada, Akira



Host-guest interaction of adamantine with a ?-cyclodextrin-functionalized AuPd bimetallic nanoprobe for ultrasensitive electrochemical immunoassay of small molecules.  


A modular labeling strategy was presented for electrochemical immunoassay via supramolecular host-guest interaction between ?-cyclodextrin (?-CD) and adamantine (ADA). An ADA-labeled antibody (ADA-Ab) was synthesized via amidation, and the number of ADA moieties loaded on a single antibody was calculated to be ~7. The ?-CD-functionalized gold-palladium bimetallic nanoparticles (AuPd-CD) were synthesized in aqueous solution via metal-S chemistry and characterized with transmission electron microscopy and X-ray photoelectron spectra. After the ADA-Ab was bound to the antigen-modified electrode surface with a competitive immunoreaction, AuPd-CD as a signal tag was immobilized onto the immunosensor by a host-guest interaction, leading to a large loading of AuPd nanoparticles. The highly efficient electrocatalysis by AuPd nanoparticles for NaBH4 oxidation produced an ultrasensitive response to chloramphenicol as a model of a small molecule antigen. The immunoassay method showed a wide linear range from 50 pg/mL to 50 ?g/mL and a detection limit of 4.6 pg/mL. The specific recognition of antigen by antibody resulted in good selectivity for the proposed method. The host-guest interaction strategy provided a universal labeling approach for the ultrasensitive detection of small molecule targets. PMID:23725199

Wang, Lisong; Lei, Jianping; Ma, Rongna; Ju, Huangxian



Experimental and theoretical charge density distribution in a host-guest system: synthetic terephthaloyl receptor complexed to adipic acid.  


The experimental charge density distributions in a host-guest complex have been determined. The host, 1,4-bis[[(6-methylpyrid-2-yl)amino]carbonyl]benzene (1) and guest, adipic acid (2). The molecular geometries of 1 and 2 are controlled by the presence in the complex of intermolecular hydrogen bonding interactions and the presence in the host 1 of intramolecular hydrogen bonding motifs. This system therefore serves as an excellent model for studying noncovalent interactions and their effects on structure and electron density, and the transferability of electron distribution properties between closely related molecules. For the complex, high resolution X-ray diffraction data created the basis for a charge density refinement using a pseudoatomic multipolar expansion (Hansen-Coppens formalism) against extensive low-temperature (T = 100 K) single-crystal X-ray diffraction data and compared with a selection of theoretical DFT calculations on the same complex. The molecules crystallize in the noncentrosymmetric space group P2(1)2(1)2(1) with two independent molecules in the asymmetric unit. A topological analysis of the resulting density distribution using the atoms in molecules methodology is presented along with multipole populations, showing that the host and guest structures are relatively unaltered by the geometry changes on complexation. Three separate refinement protocols were adopted to determine the effects of the inclusion of calculated hydrogen atom anisotropic displacement parameters on hydrogen bond strengths. For the isotropic model, the total hydrogen bond energy differs from the DFT calculated value by ca. 70 kJ mol(-1), whereas the inclusion of higher multipole expansion levels on anisotropic hydrogen atoms this difference is reduced to ca. 20 kJ mol(-l), highlighting the usefulness of this protocol when describing H-bond energetics. PMID:22548484

Nguyen, Thanh Ha; Howard, Sian T; Hanrahan, Jane R; Groundwater, Paul W; Platts, James A; Hibbs, David E



A Host-guest Relationship in Bone Morphogenetic Protein Receptor-II Defines Specificity in Ligand-Receptor Recognition  

PubMed Central

One of the most intriguing questions confronting the Bone Morphogenetic Protein family is the mechanism of ligand recognition, since there are more ligands than receptors. Crystal structures of two type II receptors ActR-II and BMPR-II are essentially identical, and a loop structure (A-loop) has been suggested to play a role in determining ligand specificity. Solution biophysical study showed mutations of several A-loop residues in these two receptors exert different ligand binding effects. Thus, the issues of mechanism of ligand recognition and specificity remain unresolved. We examined effects of mutations of residues Y40, G47, and S107 in BMPR-II receptor. These residues are not identified in contact with the ligand in the BMP-7-BMPR-II complex, but are found mutated in genetic diseases. They are likely to be useful in identifying their roles in differentiating the various BMP ligands. Spectroscopic probing revealed little mutation-induced structural change in BMPR-II. Ligand binding studies revealed that Y40 plays a significant role in differentiating three distinct ligands; G47 and S107 affect ligand binding to a lesser extent. The role of the A-loop in ActR-II or BMPR-II is dependent on the host sequence of the receptor extracellular domain (ECD) in which it is embedded, suggesting a host-guest relationship between the A-loop and the rest of the ECD. Computational analysis demonstrated a long-range connectivity between Y40, G47, and S107 and other locations in BMPR-II. An integration of these results on functional energetics and protein structures clearly demonstrate, for the first time, an intra-domain communication network within BMPR-II.

Yeh, Lee-Chuan C.; Falcon, Wilfredo E.; Garces, Andrea; Lee, J. Ching; Lee, John C.



Automation of an Optical Tweezers.  

National Technical Information Service (NTIS)

Optical tweezers is a newly developed instrument, which makes possible the manipulation of micro-optical particles under a microscope. In this paper, we present the automation of an optical tweezers which consists of a modified optical tweezers, equipped ...

B. Chang L. Hsu T. Hsieh



Fabrication of reversible poly(dimethylsiloxane) surfaces via host-guest chemistry and their repeated utilization in cardiac biomarker analysis.  


On the basis of the host-guest interactions between azobenzenes and cyclodextrins, a new strategy for the preparation of a dually functionalized poly(dimethylsiloxane) (PDMS) surface was investigated using surface-initiated atom-transfer radical polymerization (SI-ATRP) and click chemistry. The PDMS substrates were first oxidized in a H(2)SO(4)/H(2)O(2) solution to transform the surface Si-CH(3) groups into Si-OH groups. Then, the SI-ATRP initiator 3-(2-bromoisobutyramido)propyl(trime-thoxy)silane was grafted onto the substrates through a silanization reaction. Sequentially, the poly(ethylene glycol) (PEG) units were introduced onto the PDMS-Br surfaces via SI-ATRP reaction using oligo(ethylene glycol) methacrylate. Afterward, the bromide groups on the surface were converted to azido groups via nucleophilic substitution reaction with NaN(3). Finally, the azido-grafted PDMS surfaces were subjected to a click reaction with alkynyl and PEG-modified ?-cyclodextrins, resulting in the grafting of cyclodextrins onto the PDMS surfaces. The composition and chemical state of the modified surfaces were characterized via X-ray photoelectron spectroscopy, and the stability and dynamic characteristics of the cyclodextrin-modified PDMS substrates were investigated via attenuated total reflection-Fourier transform infrared spectroscopy and temporal contact angle experiments. The surface morphology of the modified PDMS surfaces was characterized through imaging using a multimode atomic force microscope. A protein adsorption assay using Alexa Fluor594-labeled bovine serum albumin, Alexa Fluor594-labeled chicken egg albumin, and FITC-labeled lysozyme shows that the prepared PDMS surfaces possess good protein-repelling properties. On-surface studies on the interactions between azobenzenes and the cyclodextrin-modified surfaces reveal that the reversible binding of azobenzene to the cyclodextrin-modified PDMS surfaces and its subsequent release can be reversibly controlled using UV irradiation. Sandwich fluoroimmunoassay of the cardiac markers myoglobin and fatty acid-binding protein demonstrates that the cyclodextrin-modified PDMS surfaces can be repeatedly utilized in disease biomarker analysis. PMID:22043937

Zhang, Yanrong; Ren, Li; Tu, Qin; Wang, Xueqin; Liu, Rui; Li, Li; Wang, Jian-Chun; Liu, Wenming; Xu, Juan; Wang, Jinyi



Hydrogen bonding interpolymer complex formation and study of its host-guest interaction with cyclodextrin and its application as an active delivery vehicle.  


Interpolymer complex formation through hydrogen bonding has been investigated between two polymers: poly(acrylamide) (PAAm) and poly(vinyl alcohol) (PVA). The differential properties of the interpolymer complex with varying molecular weights of PVA have been studied by taking three different molecular weights of PVA. Furthermore, the host-guest interaction between the interpolymer complexes prepared and ?-cyclodextrin (?-CD) has also been studied in detail. PAAm can form interpolymer complexes with PVA because of a cooperative hydrogen bonding interaction. The addition of ?-CD to a dilute aqueous solution of PAAm-PVA results in a competition between interpolymer hydrogen bonding and host-guest interactions. In this article, we have tried to decipher the complex chemistry that occurs in the microheterogeneous solution. The PAAm-PVA binary system and the PAAm-PVA-?-CD ternary systems have been well characterized by using a fluorescent probe, coumarin-102. Dynamic light scattering (DLS), Fourier transform infrared (FTIR), fluorescence microscopy, and time-resolved fluorescence studies have been performed to substantiate steady-state fluorescence experiments. The results indicate the occurrence of a competitive interaction between the hydrogen bonding of the interpolymer complexes and the host-guest interaction with ?-CD, whereby the later predominates. It is probable that the hydrophobic cavity of ?-CD is threaded with linear polymers, thus forming a macromolecular supraassembly. It has also been concluded that PAAm preferentially interacts with ?-CD by compromising its interaction with PVA. The enhanced deposition and retention of actives with this system was studied with a single species regrowth assay, antibacterial efficacy and the cell viability were studied using the live-dead staining protocol. This therefore opens new avenues in the targeted delivery of actives. PMID:23373846

Das, Somnath; Joseph, Maya T; Sarkar, Deboleena



?-cyclodextrin-ferrocene host-guest complex multifunctional labeling triple amplification strategy for electrochemical immunoassay of subgroup J of avian leukosis viruses.  


A novel sandwich-type electrochemical immunosensor was fabricated for ultrasensitive detection of subgroup J of avian leukosis virus (ALVs-J) by employing ?-cyclodextrin-ferrocene (CD-Fc) host-guest complex multifunctional Fe3O4 nanospheres as labels and ?-cyclodextrin functional graphene sheets (CD-GS) nanocomposite as sensor platform. The sensitivity was greatly improved based on the triple amplification strategy. Firstly, the CD-GS improved the electron transfer rate as well as increasing the surface area to capture a large amount of primary antibodies (Ab1). Secondly, the CD on the Fe3O4 surface with strong recognition capability could form stable CD-Fc host-guest inclusion complex and provided larger free room for the conjugation of secondary antibodies (Ab2) and glucose oxidase (GOD). Finally, the conjugated GOD exhibited extraordinary electrochemical biocatalysis towards the reduction reaction of Fc(+) by glucose. Under the optimized conditions, the electrochemical immunosensor exhibited a wide working range from 10(2.27)-10(3.50) TCID50/mL (TCID50: 50% tissue culture infective dose) with a low detection limit of 10(2.19) TCID50/mL (S/N=3). The selectivity, reproducibility, and stability are acceptable. The assay was evaluated for real avian serum sample, receiving satisfactory results. This new type of triple amplification strategy may provide potential applications for the clinic application. PMID:23454341

Shang, Kun; Wang, Xindong; Sun, Bing; Cheng, Ziqiang; Ai, Shiyun



Automation of optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers is a newly developed instrument, which makes possible the manipulation of micro-optical particles under a microscope. In this paper, we present the automation of an optical tweezers which consists of a modified optical tweezers, equipped with two motorized actuators to deflect a 1 W argon laser beam, and a computer control system including a joystick. The trapping of a single bead and a group of lactoacidofilus was shown, separately. With the aid of the joystick and two auxiliary cursers superimposed on the real-time image of a trapped bead, we demonstrated the simple and convenient operation of the automated optical tweezers. By steering the joystick and then pressing a button on it, we assign a new location for the trapped bead to move to. The increment of the motion 0.04 (mu) m for a 20X objective, is negligible. With a fast computer for image processing, the manipulation of the trapped bead is smooth and accurate. The automation of the optical tweezers is also programmable. This technique may be applied to accelerate the DNA hybridization in a gene chip. The combination of the modified optical tweezers with the computer control system provides a tool for precise manipulation of micro particles in many scientific fields.

Hsieh, Tseng-Ming; Chang, Bo-Jui; Hsu, Long



In vivo bioavailability and therapeutic assessment of host-guest inclusion phenomena for the hydrophobic molecule etodolac: pharmacodynamic and pharmacokinetic evaluation.  


The aim of present investigation was 1) to evaluate the in vivo bioavailability of an Etodolac (ETD)-Î-cyclodextrin (Î-CD) inclusion complex system prepared by kneading and spray drying techniques in rats, 2) to study the pharmacodynamic parameters in various animal models for analyzing the therapeutic response and, 3) to evaluate the pharmacokinetic profile of the drug administered. Inclusion complexation with Î-CD enhanced the solubility of the drug, improved bioavailability and reduced ulcerogenicity of ETD in rats. Pharmacodynamic studies were carried out in normal LACA mice and pharmacokinetic evaluation was done in male Wistar rats. Pharmacokinetic parameters evaluated for the inclusion complexes revealed good correlation. The minimum dose necessary to produce analgesic or anti-arthritic activity was also decreased, indicating that the host-guest strategy that uses Î-CD and ETD was very effective and could be successfully employed in the preparation of pharmaceutical formulations of anti-arthritics and analgesics. PMID:21179374

Sinha, Vivek Ranjan; Amita; Goel, Honey



Efficient singlet-singlet energy transfer in a novel host-guest assembly composed of an organic cavitand, aromatic molecules, and a clay nanosheet.  


A supramolecular host-guest assembly composed of a cationic organic cavitand (host), neutral aromatic molecules (guests), and an anionic clay nanosheet has been prepared and demonstrated that in this arrangement efficient singlet-singlet energy transfer could take place. The novelty of this system is the use of a cationic organic cavitand that enabled neutral organic molecules to be placed on an anionic saponite nanosheet. Efficient singlet-singlet energy transfer between neutral pyrene and 2-acetylanthracene enclosed within a cationic organic cavitand (octa amine) arranged on a saponite nanosheet was demonstrated through steady-state and time-resolved emission studies. The high efficiency was realized from the suppression of aggregation, segregation, and self-fluorescence quenching. We believe that the studies presented here using a novel supramolecular assembly have expanded the types of molecules that could serve as candidates for efficient energy-transfer systems, such as in an artificial light-harvesting system. PMID:23360204

Ishida, Yohei; Kulasekharan, Revathy; Shimada, Tetsuya; Takagi, Shinsuke; Ramamurthy, V



Chiral discrimination of the analgesic cizolirtine by using cyclodextrins: A (1)H NMR study on the solution structures of their host-guest complexes.  


The use of four cyclodextrins (three native and one beta-CD derivative) as NMR chiral solvating agents to resolve the enantiomers of (+/-)-cizolirtine, 1, and its chemical precursor (the carbinol, (+/-)-2), was investigated. The best enantiodiscrimination occurred when beta-cyclodextrin was used. ROESY experiments were performed to qualitatively ascertain the most probable host-guest structures in D(2)O solution, and the binding features found were explained in terms of spatial fitting of the guest molecules into the macrocyclic cavities. No geometrical differences were noted between the two diastereomeric complexes formed by a cyclodextrin and a racemic substrate, so the magnetic nonequivalence induced on guest protons by the enantioselective binding had to be explained as a result of subtle disparities in the orientation and/or the conformational state of the complexed enantiomers. PMID:10506430

Redondo, J; Blázquez, M A; Torrens, A



Optical Tweezers and Applications  

NSDL National Science Digital Library

Did you ever imagine that you can use light to move a microscopic plastic bead? Explore the forces on the bead or slow time to see the interaction with the laser's electric field. Use the optical tweezers to manipulate a single strand of DNA and explore the physics of tiny molecular motors. Can you get the DNA completely straight or stop the molecular motor?

Simulations, Phet I.; Adams, Wendy; Dubson, Michael; Malley, Chris; Perkins, Kathy; Perkins, Thomas



Optical tweezers computational toolbox  

Microsoft Academic Search

We describe a toolbox, implemented in Matlab, for the computational modelling of optical tweezers. The toolbox is designed for the calculation of optical forces and torques, and can be used for both spherical and nonspherical particles, in both Gaussian and other beams. The toolbox might also be useful for light scattering using either Lorenz–Mie theory or the T-matrix method.

Timo A. Nieminen; Vincent L. Y. Loke; Alexander B. Stilgoe; Agata M Bra?czyk; Norman R. Heckenberg; Halina Rubinsztein-Dunlop



Dynamic holographic optical tweezers  

Microsoft Academic Search

Optical trapping is an increasingly important technique for controlling and probing matter at length scales ranging from nanometers to millimeters. This paper describes methods for creating large numbers of high-quality optical traps in arbitrary three-dimensional configurations and for dynamically reconfiguring them under computer control. In addition to forming conventional optical tweezers, these methods also can sculpt the wavefront of each

Jennifer E. Curtis; Brian A. Koss; David G. Grier



Theory of optical tweezers  

Microsoft Academic Search

We derive an exact partial-wave (Mie) expansion of the axial force exerted on a transparent sphere by a laser beam focused through a high numerical aperture objective. The results hold throughout the range of interest for practical applications, as well as in the Rayleigh and geometrical optics limits. They allow, in principle, an absolute calibration of optical tweezers. Starting from

P. A. Maia Neto; H. M. Nussenzveig



Simple Host?Guest Chemistry To Modulate the Process of Concentration and Crystallization of Membrane Proteins by Detergent Capture in a Microfluidic Device  

SciTech Connect

This paper utilizes cyclodextrin-based host-guest chemistry in a microfluidic device to modulate the crystallization of membrane proteins and the process of concentration of membrane protein samples. Methyl-{beta}-cyclodextrin (MBCD) can efficiently capture a wide variety of detergents commonly used for the stabilization of membrane proteins by sequestering detergent monomers. Reaction Center (RC) from Blastochloris viridis was used here as a model system. In the process of concentrating membrane protein samples, MBCD was shown to break up free detergent micelles and prevent them from being concentrated. The addition of an optimal amount of MBCD to the RC sample captured loosely bound detergent from the protein-detergent complex and improved sample homogeneity, as characterized by dynamic light scattering. Using plug-based microfluidics, RC crystals were grown in the presence of MBCD, giving a different morphology and space group than crystals grown without MBCD. The crystal structure of RC crystallized in the presence of MBCD was consistent with the changes in packing and crystal contacts hypothesized for removal of loosely bound detergent. The incorporation of MBCD into a plug-based microfluidic crystallization method allows efficient use of limited membrane protein sample by reducing the amount of protein required and combining sparse matrix screening and optimization in one experiment. The use of MBCD for detergent capture can be expanded to develop cyclodextrin-derived molecules for fine-tuned detergent capture and thus modulate membrane protein crystallization in an even more controllable way.

Li, Liang; Nachtergaele, Sigrid; Seddon, Annela M.; Tereshko, Valentina; Ponomarenko, Nina; Ismagilov, Rustem F. (UC)



Study of host-guest interactions in benzodiazacoronands by means of solid state NMR spectroscopy, X-ray diffraction and quantum mechanical computations.  


In this work we present solid state data for five host-guest complexes formed by N-(4,19-dioxo-2,8,15,21-tetraoxa-5,18-diazatricyclohexacosa-1(25),9(14),10,12,22(26),23-hexaen-26-yl)-benzamide (1) belonging to the group of benzodiazacoronands, achiral compounds for which chiral crystals were found (J. Kalisiak and J. Jurczak, Cryst. Growth Des., 2006, 6, 20). The X-ray structure was resolved for four of them. It was found that 1 crystallizes in P2(1)/c, P1 and P2(1)/n achiral space groups. Differentiation of molecular packing and the presence of guest molecules within the crystal lattice were analyzed with solid state NMR. An attempt was made to correlate changes in (13)C ?(ii) and (15)N ?(ii) chemical shift tensor values, obtained from analysis of spinning sidebands of 1D and 2D (2D PASS) NMR spectra, with changes in the strength of hydrogen bonding. Quantum mechanical DFT GIAO calculations of NMR shielding parameters carried out on structures with coordinates taken from XRD were employed for signals assignment and verification of structural constraints. PMID:21384038

Nowicka, Katarzyna; Bujacz, Anna; Paluch, Piotr; Sobczuk, Adam; Jeziorna, Agata; Ciesielski, W?odzimierz; Bujacz, Grzegorz D; Jurczak, Janusz; Potrzebowski, Marek J



Nanoscale Molecular Tweezers  

NSDL National Science Digital Library

The featured molecules for this month are drawn from the "Research Advances" column by Angela G. King, and represent some of the structures from the research on molecular tweezers (published in J. Am. Chem. Soc. 2004, 126, 8124). The structures below are based on the figure on page 1690 showing two types of receptors that switch between U and W shapes upon coordination of soft metal cations, acting in the manner of mechanical tweezers. When viewing these molecules in Chime you must render in ball and stick or space filling modes in order to see the incorporated metal ions. In several cases the torsion angles connecting the anthracene substituents to the rest of the molecule are not well defined and have been drawn as either coplanar or orthogonal to the central ring system. At a moderate level of theory, the torsion angle in those instances where it has been set to 90° displays a broad minimum ranging for 50?130°.


Physics in Action: Optical Tweezers  

NSDL National Science Digital Library

This website introduces the concept of an optical tweezer, a laser trap used to manipulate objects as small as single molecules. This site lists several applications of optical tweezers and explains their application in molecular biology. Diagrams and links provide further information.



Interferometer Control of Optical Tweezers.  

National Technical Information Service (NTIS)

This paper discusses progress in using spatial light modulators and interferometry to control the beam profile of an optical tweezers. The approach being developed is to use a spatial light modulator (SLM) to control the phase profile of the tweezers beam...

A. J. Decker



Recent Advances in Optical Tweezers  

Microsoft Academic Search

It has been over 20 years since the pioneering work of Arthur Ashkin, and in the intervening years, the field of optical tweezers has grown tremendously. Optical tweezers are now being used in the inves- tigation of an increasing number of biochemical and biophysical processes, from the basic mechanical properties of biological poly- mers to the multitude of molecular machines

Jeffrey R. Moffitt; Yann R. Chemla; Steven B. Smith; Carlos Bustamante



On chip shapeable optical tweezers  

NASA Astrophysics Data System (ADS)

Particles manipulation with optical forces is known as optical tweezing. While tweezing in free space with laser beams was established in the 1980s, integrating the optical tweezers on a chip is a challenging task. Recent experiments with plasmonic nanoantennas, microring resonators, and photonic crystal nanocavities have demonstrated optical trapping. However, the optical field of a tweezer made of a single microscopic resonator cannot be shaped. So far, this prevents from optically driven micromanipulations. Here we propose an alternative approach where the shape of the optical trap can be tuned by the wavelength in coupled nanobeam cavities. Using these shapeable tweezers, we present micromanipulation of polystyrene microspheres trapped on a silicon chip. These results show that coupled nanobeam cavities are versatile building blocks for optical near-field engineering. They open the way to much complex integrated tweezers using networks of coupled nanobeam cavities for particles or bio-objects manipulation at a larger scale.

Renaut, C.; Cluzel, B.; Dellinger, J.; Lalouat, L.; Picard, E.; Peyrade, D.; Hadji, E.; de Fornel, F.



Optical tweezers for medical diagnostics.  


Laser trapping by optical tweezers makes possible the spectroscopic analysis of single cells. Use of optical tweezers in conjunction with Raman spectroscopy has allowed cells to be identified as either healthy or cancerous. This combined technique is known as laser tweezers Raman spectroscopy (LTRS), or Raman tweezers. The Raman spectra of cells are complex, since the technique probes nucleic acids, proteins, and lipids; but statistical analysis of these spectra makes possible differentiation of different classes of cells. In this article the recent development of LTRS is described along with two illustrative examples for potential application in cancer diagnostics. Techniques to expand the uses of LTRS and to improve the speed of LTRS are also suggested. PMID:23559336

LaFratta, Christopher N



Optofluidic tweezer on a chip  

PubMed Central

A novel method to realize an optical tweezer involving optofluidic operation in a microchannel is proposed. To manipulate the optical tweezer, light from an optical fiber is passed through both PDMS (polydimethylsiloxane)-air surface lenses and an optofluidic region, which is located in a control channel. Two liquids with different refractive indices (RIs) are introduced into the control channel to form two different flow patterns (i.e., laminar and segmented flows), depending on the liquid compositions, the channel geometry, and the flow rates. By altering the shapes of the interface of the two liquids in the optofluidic region, we can continuously or intermittently control the optical paths of the light. To demonstrate the functionality of the proposed method, optical tweezer operations on a chip are performed. Changing the flow pattern of two liquids with different RIs in the optofluidic region results in successful trapping of a 25 ?m diameter microsphere and its displacement by 15 ?m.

Ono, K.; Kaneda, S.; Shiraishi, T.; Fujii, T.



Optical doughnut for optical tweezers.  


We describe novel optical doughnuts for optical tweezers. With new phase functions, the proposed doughnut beams have dark cores in specified shapes. The technique can offer a simple method for creating a variety of beam shapes to match the trapped objects. One can rotate the beams directly by revolving their phase structures about their axes on the initial plane. The technique for generating the traditional Laguerre-Gaussian beam can be used to create these novel beams. PMID:12747724

Zhang, D W; Yuan, X C



Nanometric optical tweezers based on nanostructured substrates  

Microsoft Academic Search

The ability to control the position of a mesoscopic object with nanometric precision is important for the rapid progress of nanoscience. One of the most promising tools to achieve such control is optical tweezers, which trap objects near the focus of a laser beam. However, the drawbacks of conventional tweezers include a trapping volume that is diffraction-limited and significant brownian

N. W. Roberts; M. R. Dickinson; Y. Zhang; A. N. Grigorenko



Computer-generated holographic optical tweezer arrays  

Microsoft Academic Search

Holographic techniques significantly extend the capabilities of laser tweezing, making possible extended trapping patterns for manipulating large numbers of particles and volumes of soft matter. We describe practical methods for creating arbitrary configurations of optical tweezers using computer-generated diffractive optical elements. While the discussion focuses on ways to create planar arrays of identical tweezers, the approach can be generalized to

Eric R. Dufresne; Gabriel C. Spalding; Matthew T. Dearing; Steven A. Sheets; David G. Griera



Absolute calibration of optical tweezers  

SciTech Connect

As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB ('geometrical optics') approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and 'jump' effects are also confirmed.

Viana, N.B.; Mazolli, A.; Maia Neto, P.A.; Nussenzveig, H.M.; Rocha, M.S.; Mesquita, O.N. [LPO-COPEA and Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-590 (Brazil); Departamento de Fisica, Instituto de Ciencias ExatasUniversidade Federal de Minas Gerais, Belo Horizonte, MG, 30123-970 (Brazil)



Artificial neural networks for determination of enantiomeric composition of alpha-phenylglycine using UV spectra of cyclodextrin host-guest complexes: comparison of feed-forward and radial basis function networks.  


In this work feed-forward neural networks and radial basis function networks were used for the determination of enantiomeric composition of alpha-phenylglycine using UV spectra of cyclodextrin host-guest complexes and the data provided by two techniques were compared. Wavelet transformation (WT) and principal component analysis (PCA) were used for data compression prior to neural network construction and their efficiencies were compared. The structures of the wavelet transformation-radial basis function networks (WT-RBFNs) and wavelet transformation-feed-forward neural networks (WT-FFNNs), were simplified by using the corresponding wavelet coefficients of three mother wavelets (Mexican hat, daubechies and symlets). Dilation parameters, number of inputs, hidden nodes, learning rate, transfer functions, number of epochs and SPREAD values were optimized. Performances of the proposed methods were tested with regard to root mean square errors of prediction (RMSE%), using synthetic solutions containing a fixed concentration of beta-cyclodextrin (beta-CD) and fixed concentration of alpha-phenylglycine (alpha-Gly) with different enantiomeric compositions. Although satisfactory results with regard to some statistical parameters were obtained for all the investigated methods but the best results were achieved by WT-RBFNs. PMID:18371852

Afkhami, Abbas; Abbasi-Tarighat, Maryam; Bahram, Morteza



Microcrystal manipulation with laser tweezers.  


X-ray crystallography is the method of choice to deduce atomic resolution structural information from macromolecules. In recent years, significant investments in structural genomics initiatives have been undertaken to automate all steps in X-ray crystallography from protein expression to structure solution. Robotic systems are widely used to prepare crystallization screens and change samples on synchrotron beamlines for macromolecular crystallography. The only remaining manual handling step is the transfer of the crystal from the mother liquor onto the crystal holder. Manual mounting is relatively straightforward for crystals with dimensions of >25?µm; however, this step is nontrivial for smaller crystals. The mounting of microcrystals is becoming increasingly important as advances in microfocus synchrotron beamlines now allow data collection from crystals with dimensions of only a few micrometres. To make optimal usage of these beamlines, new approaches have to be taken to facilitate and automate this last manual handling step. Optical tweezers, which are routinely used for the manipulation of micrometre-sized objects, have successfully been applied to sort and mount macromolecular crystals on newly designed crystal holders. Diffraction data from CPV type 1 polyhedrin microcrystals mounted with laser tweezers are presented. PMID:23793156

Wagner, Armin; Duman, Ramona; Stevens, Bob; Ward, Andy



Quantum limited particle sensing in optical tweezers  

SciTech Connect

Particle sensing in optical tweezers systems provides information on the position, velocity, and force of the specimen particles. The conventional quadrant detection scheme is applied ubiquitously in optical tweezers experiments to quantify these parameters. In this paper, we show that quadrant detection is nonoptimal for particle sensing in optical tweezers and propose an alternative optimal particle sensing scheme based on spatial homodyne detection. A formalism for particle sensing in terms of transverse spatial modes is developed and numerical simulations of the efficacies of both quadrant and spatial homodyne detection are shown. We demonstrate that 1 order of magnitude improvement in particle sensing sensitivity can be achieved using spatial homodyne over quadrant detection.

Tay, J.W. [Jack Dodd Centre for Photonics and Ultracold Atoms, Department of Physics, University of Otago, Dunedin (New Zealand); Hsu, Magnus T. L. [School of Mathematics and Physics, University of Queensland, St. Lucia, Queensland 4072 (Australia); Bowen, Warwick P. [Jack Dodd Centre for Photonics and Ultracold Atoms, Department of Physics, University of Otago, Dunedin (New Zealand); School of Mathematics and Physics, University of Queensland, St. Lucia, Queensland 4072 (Australia)



Optical tweezers based on polarization interferometer  

NASA Astrophysics Data System (ADS)

In this paper, we propose optical tweezers based on a biaxial crystal. To control the movement of opaque particles, we use the shift polarization interferometer. The results of experimental study of laser tweezers are shown. We demonstrates movement of a microparticle of toner using singular-optical trap, rotate a particle due to orbital momentum, conversion of two traps when changing the plane of polarizer transmission and converging of two traps.

Angelsky, Oleg V.; Maksimyak, Andrew P.; Maksimyak, Peter P.; Dominikov, Mykola M.



Manipulation of Microobjects by Optical Tweezers  

Microsoft Academic Search

Radiation pressure from a tightly focused laser beam can be used as optical tweezers to confine, position, and transport microparticles.\\u000a Ashkin’s group first demonstrated this technique in 1986 [1]. Optical tweezers provide unique features such as remote manipulation\\u000a of micro\\/nano particles in unique features such as remote manipulation of micro\\/nano particles in liquid, noninvasive manipulation\\u000a of biological samples, precise manipulation

Shoji Maruo


Characterization of microparticles with driven optical tweezers.  


We discuss how actively-driven optical tweezers may be used to characterize Brownian microparticles. Two experiments are described in detail. We follow the thermal fluctuations of a charged particle in an oscillatory electric field and demonstrate that charges as low as a few elementary charges can be measured accurately and reproducibly. Secondly, we measure the orientational dynamics of a trapped rotating droplet and use circular polarimetry within optical tweezers to determine in situ birefringence. PMID:18214111

Wood, Tiffany A; Roberts, G Seth; Eaimkhong, Sarayoot; Bartlett, Paul



Optical Tweezer as a Viscometer  

NASA Astrophysics Data System (ADS)

An optical tweezer (OT) has been widely used to study the mechanical properties of microscopic living biological systems like red blood cells. These studies are based on measurement of deformations caused by a force exerted directly or indirectly by an optical trap. The trap is usually pre-calibrated using Stokes viscous force of the suspension fluids for the biological system which is directly proportional to the viscosity of the fluids. Therefore, calibration of the trap depends on the viscosity of the fluid which depends on temperature. In this work, we have demonstrated that OT can be used to precisely measure the viscosity of biological fluids affected by temperature. Using a an infrared laser trap which is calibrated using silica sphere suspended in a distilled deionized water and measuring the power as function of escape velocity, we have measured the viscosities of a newborn and unborn bovine serum with a different concentration of antibodies.

Erenso, Daniel; Elrod, Samuel; Barns, Taylor; Farone, Anthony; Farone, Mary



Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy  

Microsoft Academic Search

Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. Here we describe these techniques and illustrate them with examples highlighting current capabilities and limitations.

Attila Nagy; Keir C Neuman



Lipid Bilayer-Integrated Optoelectronic Tweezers for Nanoparticle Manipulations.  

National Technical Information Service (NTIS)

Remotely manipulating a large number of microscopic objects is important to soft-condensed matter physics, biophysics, and nanotechnology. Optical tweezers and optoelectronic tweezers have been widely used for this purpose but face critical challenges whe...

S. Ota S. Wang X. Yin X. Zhang Y. Wang



Micro Magnetic Tweezers for Nanomanipulation Inside Live Cells  

Microsoft Academic Search

This study reports the design, realization, and characterization of a multi-pole magnetic tweezers that enables us to maneuver small magnetic probes inside living cells. So far, magnetic tweezers can be divided into two categories: I), tweezers that allow the exertion of high forces but consist of only one or two poles and therefore are capable of only exerting forces in

Anthony H. B. de Vries; Bea E. Krenn; Roel van Driel; Johannes S. Kanger



Particles sorting in micro-channel system utilizing magnetic tweezers and optical tweezers  

NASA Astrophysics Data System (ADS)

This study evaluates a method for separating magnetic microparticles in a micro channel by using embedded inverted-laser tweezers, a microflow pump, and a micro magnet. Various particles were separated using optical and/or magnetic tweezers, and were identified and counted to determine the dependence of the sorting rate on the channel flow velocity. The particle sorting experiment showed good separation results when the designed channel and magnetic tweezers were used. For magnetic particles, lower flow velocities corresponded to larger separating rates with a maximum separating rate of 81%. When the designed channel and optical tweezers were used, the polystyrene particle separating rate was as high as 94%. When both the optical tweezers and the magnetic tweezers were used, the optical tweezers were more effective in trapping polystyrene particles with flow velocities between 0.09 and 0.25 ?m/s. For flow velocities between 0.09 and 0.17 ?m/s, the separating rate for polystyrene particles reached 95% and the separating rate for magnetic particles reached 85%. This hybrid system can be applied to the separation of various particles in unknown mixtures.

Chung, Yung-Chiang; Chen, Po-Wen; Fu, Chao-Ming; Wu, Jian-Min



Quantum computation architecture using optical tweezers  

SciTech Connect

We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few 100 {mu}s, while keeping the error probability due to vibrational excitations and spontaneous scattering below 10{sup -3}. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing.

Weitenberg, Christof [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); Kuhr, Stefan [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); University of Strathclyde, Department of Physics, SUPA, Glasgow G4 0NG (United Kingdom); Moelmer, Klaus; Sherson, Jacob F. [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)



Micro-objective manipulated with optical tweezers  

SciTech Connect

A microscope is described that uses a {mu}m-sized ball lens, which is here termed micro-objective, manipulated with optical tweezers to image the side view of the arbitrary region of a sample. Since this micro-objective is small in size, it can go into a concave region to produce a local image of the inside which the conventional microscope cannot observe. Preliminary results show good lens performance from the micro-objective when combined with optical tweezers. {copyright} {ital 1997 American Institute of Physics.}

Sasaki, M.; Kurosawa, T.; Hane, K. [Department of Mechatronics and Precision Engineering, Tohoku University, Sendai 980-77 (Japan)



The Computer Generation of Holographic Optical Tweezers  

NASA Astrophysics Data System (ADS)

Due to their ability to apply forces on a small scale, optical tweezers are useful for a variety of biological and physical applications. The utility of optical tweezers can be extended by producing multiple traps with different characteristics from a single beam. One method for achieving this is to manipulate the phase of a trapping laser's wave front with a computer generated kinoform displayed on a spatial light modulator. We compare the performance of two algorithms for kinoform calculation, a Gerchberg-Saxton algorithm and a direct search algorithm, and discuss how they address problems inherent to computer generated holographic optical tweezing.

Deceglie, Michael; Pribik, Rodd; Lyon, Jeremy; Browne, Kerry



Optical Tweezers Array and Nimble Tweezers Probe Generated by Spatial- Light Modulator.  

National Technical Information Service (NTIS)

An optical tweezers is being developed at the NASA Glenn Research Center as a visiblelight interface between ubiquitous laser technologies and the interrogation, visualization, manufacture, control, and energization of nanostructures such as silicon carbi...

A. J. Decker B. Jassemnejad R. E. Seibel K. E. Weiland



Computational models for new fiber optic tweezers  

NASA Astrophysics Data System (ADS)

This paper discusses the calculation of the trapping forces in optical tweezers using a combination of the finite differences time domain (FDTD) method and the Lorentz force on electric dipoles. The results of 2D simulations of the trapping of a circular particle by a waveguide with a circular tip are presented and discussed.

Rodrigues Ribeiro, R. S.; Jorge, P. A. S.; Guerreiro, A.



Tying a molecular knot with optical tweezers  

Microsoft Academic Search

, but the analysis of the buckled shape was complicated. Here we report the continuous control of the radius of curvature of a molecular strand by tying a knot in it, using optical tweezers to manipulate the strand's ends. We find that actin filaments break at the knot when the knot diameter falls below 0.4 mm. The pulling force at

Yasuharu Arai; Ryohei Yasuda; Ken-ichirou Akashi; Yoshie Harada; Hidetake Miyata; Kazuhiko Kinosita Jr; Hiroyasu Itoh



Micromanipulation of Retinal Neurons by Optical Tweezers  

Microsoft Academic Search

Micromanipulation by optical tweezers has been tested in cultures of mature isolated retinal cells to determine its potential for use in creating synaptic circuits in vitro. Rod and cone photoreceptors as well as other retinal nerve cell types could be optically trapped with a 980 nm diode laser mounted on an inverted light microscope using a 40x oil immersion objective

E. Townes-Anderson; R. S. St. Jules; D. M. Sherry; J. Lichtenberger; M. Hassanain



Twin-core fiber optical tweezers.  


We present an abruptly tapered twin-core fiber optical tweezers, which is fabricated by fusing and drawing the twin-core fiber. In the twin-core fiber, the two beams are guided by the tapered fiber. At the end of the fiber tip, a larger converge angle between the two beams are made due to the abrupt tapered shape, which is formed a fast divergent optical field. The microscopic particle trapping performance of this special designed tapered twin-core fiber tip is investigated. The functionality of the proposed novel twin-core fiber optical tweezers is extended since an in-fiber integrated Mach-Zehnder interferometer has been used to control orientation of the trapped particle. The distribution of the optical field emerging from the tapered fiber tip is simulated based on the beam propagation method (BPM). By using this two-beam combination technique, a strong enough gradient forces well is obtained for microscopic particles trapping in three dimensions. The abruptly tapered twin-core fiber optical tweezers is rigid and easy to handle, especially useful for building up a multi-tweezers system for trapping and manipulating micro-scale particles. PMID:18542553

Yuan, Libo; Liu, Zhihai; Yang, Jun; Guan, Chunying



Quantum-noise quenching in atomic tweezers  

SciTech Connect

The efficiency of extracting single atoms or molecules from an ultracold bosonic reservoir is theoretically investigated for a protocol based on lasers, coupling the hyperfine state in which the atoms form a condensate to another stable state, in which the atom experiences a tight potential in the regime of collisional blockade, the quantum tweezers. The transfer efficiency into the single-atom ground state of the tight trap is fundamentally limited by the collective modes of the condensate, which are thermally and dynamically excited. The noise due to these excitations can be quenched for sufficiently long laser pulses, thereby achieving high efficiencies. These results show that this protocol can be applied to initializing a quantum register based on tweezer traps for neutral atoms.

Zippilli, Stefano [Departament de Fisica, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain); Theoretische Physik, Universitaet des Saarlandes, D-66041 Saarbruecken (Germany); Fachbereich Physik and Research Center OPTIMAS, Technische Universitaet Kaiserslautern, D-67663 Kaiserslautern (Germany); Mohring, Bernd; Schleich, Wolfgang [Institut fuer Quantenphysik, Universitaet Ulm, D-89081 Ulm (Germany); Lutz, Eric [Department of Physics, University of Augsburg, D-86135 Augsburg (Germany); Morigi, Giovanna [Departament de Fisica, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain); Theoretische Physik, Universitaet des Saarlandes, D-66041 Saarbruecken (Germany)



The Smallest Tweezers in the World  

ERIC Educational Resources Information Center

|A pair of fine tweezers and a steady hand may well be enough to pick up a grain of sand, but what would you use to hold something hundreds of times smaller still, the size of only one micron? The answer is to use a device that is not mechanical in nature but that relies instead on the tiny forces that light exerts on small particles: "optical…

Lewalle, Alexandre



Interactive approach to optical tweezers control  

SciTech Connect

We have developed software with an interactive user interface that can be used to generate phase holograms for use with spatial light modulators. The program utilizes different hologram design techniques, allowing the user to select an appropriate algorithm. The program can be used to generate multiple beams and can be used for beam steering. We see a major application of the program to be in optical tweezers to control the position, number, and type of optical traps.

Leach, Jonathan; Wulff, Kurt; Sinclair, Gavin; Jordan, Pamela; Courtial, Johannes; Thomson, Laura; Gibson, Graham; Karunwi, Kayode; Cooper, Jon; Laczik, Zsolt John; Padgett, Miles



Processing carbon nanotubes with holographic optical tweezers  

Microsoft Academic Search

We report the first demonstration that carbon nanotubes can be trapped and\\u000amanipulated by optical tweezers. This observation is surprising because\\u000aindividual nanotubes are substantially smaller than the wavelength of light,\\u000aand thus should not be amenable to optical trapping. Even so, nanotube bundles,\\u000aand perhaps even individual nanotubes, can be transported at high speeds,\\u000adeposited onto substrates, untangled, and

Joseph Plewa; Evan Tanner; Daniel M. Mueth; David G. Grier



Pi-dimer formation in an oligothiophene tweezer molecule.  


An oligothiophene tweezer molecule, which has two quaterthiophene moieties connected to create an electrochemically activated hinge, has been synthesized. Two-electron oxidation of the tweezer molecule produces an intramolecular pi-dimer between the two oligothiophene moieties at room temperature as confirmed by UV-vis absorption, electrochemistry, and EPR experiments. PMID:18839962

Takita, Ryo; Song, Changsik; Swager, Timothy M



Raman-tweezers spectroscopy of single biological cells and organelles  

NASA Astrophysics Data System (ADS)

Raman tweezers, also called laser tweezers Raman spectroscopy (LTRS), is an instrument that combines optical tweezers and confocal Raman microscopy for simultaneous manipulation and analysis of single biological cells or organelles in a physiological solution without the need of introducing biochemical tags. The optical tweezers part of the LTRS system uses a tightly focused near-infrared beam to capture and immobilize a biological particle in a liquid medium by the gradient force. The Raman spectroscopy part can generate vibrational spectra of the trapped particle to provide composition and conformation information of molecules based on measuring molecular vibrations from the scattered light. In this talk, we will present the physical principle and instrumentation of optical tweezers and micro-Raman spectroscopy system. Applications in rapid detection and identification of microorganisms, sorting of living cells, and real-time measurement of the dynamical changes in biochemical properties of macromolecules within living cells, and detection of recombinant proteins in transgenic cells will be presented.

Li, Yongqing



Optical capsule and tweezer array for molecular motor use.  


A generation of optical capsules and tweezers within a modified optical add-drop filter known as PANDA ring resonator with a new concept is proposed. By using dark and bright solitons, the orthogonal tweezers can be formed within the system and observed simultaneously at the output ports. Under the resonant condition, the optical capsules and tweezers generated by dark and bright soliton pair corresponding to the left-hand and right-hand rotating solitons (tweezers) can be generated. When a soliton is interacted by an object, an angular momentum of either bright or dark tweezers is imparted to the object, in which two possible spin states known as tweezer spins are exhibited. Furthermore, an array of molecular capsules and spins, i.e., trapped molecules can be generated and detected by using the proposed system, which can be used to form large scale tweezer or capsule spins. In application, the trapped molecules can be moved and rotated securely to the required destinations, which can be useful for many applications, especially, in medical diagnosis, therapy and surgery. PMID:23955778

Yupapin, Preecha P; Kulsirirat, Kathawut; Techithdeera, Wicharn



21 CFR 878.5360 - Tweezer-type epilator.  

Code of Federal Regulations, 2010 CFR provided at the tip of the tweezer used to remove hair may be radio frequency, galvanic (direct current), or a combination of radio frequency and galvanic energy. (b) Classification. Class I (general controls). The device...



21 CFR 878.5360 - Tweezer-type epilator.  

Code of Federal Regulations, 2013 CFR




Using molecular tweezers to move and image nanoparticles  

NASA Astrophysics Data System (ADS)

The ability to manipulate nanoparticles is significant in nanoscale science and technology. As sizes of the objects scale down to the sub-10 nm regime, it imposes a great challenge for the conventional optical tweezers. There has been much effort to explore alternative manipulation methods including using nanostructures, electron beams, scanning probes, etc. In this paper, an overview of the latest advances in trapping and manipulation of nanoparticles with a focus on the emergent electron tweezers is provided.

Zheng, Haimei



Investigation of mechanical property of a cell by optical tweezers  

NASA Astrophysics Data System (ADS)

Mechanical property of a cell is investigated from reaction force generated on a particle fixed on a cell by moving with optical tweezers. This system is called as cell palpation system. By using of this system we can measure mechanical property at a desired location on a cell surface just by locating the probe particle with optical tweezers. We have investigated focal adhesion formation through mechanical property measurement after initiation of touching by the probe particle.

Sugiura, T.



Using molecular tweezers to move and image nanoparticles.  


The ability to manipulate nanoparticles is significant in nanoscale science and technology. As sizes of the objects scale down to the sub-10 nm regime, it imposes a great challenge for the conventional optical tweezers. There has been much effort to explore alternative manipulation methods including using nanostructures, electron beams, scanning probes, etc. In this paper, an overview of the latest advances in trapping and manipulation of nanoparticles with a focus on the emergent electron tweezers is provided. PMID:23592008

Zheng, Haimei



Single-pair FRET characterization of DNA tweezers.  


The self-assembly properties of DNA make it an ideal choice for the construction of nanomachines such as DNA tweezers. Because nanomachines function as individual units, they need to be studied on the single-molecule level. From single-pair FRET investigations, we show that "open" tweezers exist in a single conformation with minimal FRET efficiency, whereas upon addition of a "closing strand", three conformations are observed, which are averaged out in ensemble measurements. PMID:17163711

Müller, Barbara K; Reuter, Andreas; Simmel, Friedrich C; Lamb, Don C



Bead movement by single kinesin molecules studied with optical tweezers  

Microsoft Academic Search

KINESIN, a mechanoenzyme that couples ATP hydrolysis to movement along microtubules, is thought to power vesicle transport and other forms of microtubule-based motility1-6. Here, microscopic silica beads7 were precoated with carrier protein8,9, exposed to low concentrations of kinesin, and individually manipulated with a single-beam gradient-force optical particle trap10-12 ('optical tweezers') directly onto microtubules. Optical tweezers greatly improved the efficiency of

Steven M. Block; Lawrence S. B. Goldstein; Bruce J. Schnapp



Metal nanoparticle-functionalized DNA tweezers: from mechanically programmed nanostructures to switchable fluorescence properties.  


DNA tweezers are modified with two 10-nm sized Au NPs and one 5-nm sized Au NP. Upon treatment of the tweezers with fuel and antifuel nucleic acid strands, the switchable closure and opening of the tweezers proceed, leading to the control of programmed nanostructures of the tethered NPs. The tweezers are further modified with a single 10-nm sized nanoparticle, and a fluorophore unit (Cy3), positioned at different distinct sites of the tweezers. The reversible and cyclic fluorescence quenching or fluorescence enhancement phenomena, upon the dynamic opening/closure of the different tweezers, are demonstrated. PMID:23815358

Shimron, Simcha; Cecconello, Alessandro; Lu, Chun-Hua; Willner, Itamar



Characterization of objective transmittance for optical tweezers  

SciTech Connect

We have measured the overall transmittance of a laser beam through an oil immersion objective as a function of the transverse size of the laser beam, using the dual-objective method. Our results show that the objective transmittance is not uniform and that its dependence on the radial beam's position can be modeled by a Gaussian function. This property affects the intensity distribution pattern in the sample region and should be taken into account in theoretical descriptions of optical tweezers. Moreover, one must consider this position dependence to determine the local laser power delivered at the sample region by the dual-objective method, especially when the beam overfills the objective's back entrance. If the transmittance is assumed to be uniform, the local power is overestimated.

Viana, N. B.; Rocha, M. S.; Mesquita, O. N.; Mazolli, A.; Neto, P. A. Maia



Characterization of microorganisms using Raman tweezers  

NASA Astrophysics Data System (ADS)

The ability to identify and characterize microorganisms (algae, bacteria, eukaryotic cells) from minute sample volumes in a rapid and reliable way is the crucial first step in their classification and characterization. In the light of this challenge related to microorganisms exploitation Raman spectroscopy can be used as a powerful tool for chemical analysis. Raman spectroscopy can elucidate fundamental questions about the metabolic processes and intercellular variability on a single cell level. Moreover, Raman spectroscopy can be combined with optical tweezers and with microfluidic chips to measure nutrient dynamics and metabolism in vivo, in real-time, and label free. We demonstrate the feasibility to employ Raman spectroscopy-based sensor to sort microorganisms (bacteria, algae) according to the Raman spectra. It is now quite feasible to sort algal cells according to the degree of unsaturation (iodine value) in lipid storage bodies.

Samek, Ota; Pilát, Zdenek; Jonás, Alexandr; Zemánek, Pavel; Sery, Mojmir; Jezek, Jan; Bernatová, Silvie; Nedbal, Ladislav; Trtílek, Martin



High-resolution laser-based detection for magnetic tweezers  

NASA Astrophysics Data System (ADS)

Magnetic tweezers are a versatile and powerful single-molecule manipulation technique capable of applying force and torque on single bio-molecules. They afford several unique advantages over other single-molecule manipulation techniques such as optical tweezers or atomic force microscopy. The hallmark of magnetic tweezers is the ability to twist bio-molecules without the need for complex optical instrumentation. Perhaps less known but of equal significance, magnetic tweezers rely on a slowly decaying magnetic field gradient (1 mm) to impose force so they are intrinsically configured in a passive force clamp mode. These features make magnetic tweezers particularly well suited for the study of nucleic acid structure, DNA topology, and protein-nucleic acid interactions. The one downside to most magnetic tweezers to date is that they rely on video tracking methods to determine the position of the particle. Despite recent progress, the spatial and temporal resolution and accuracy are fundamentally limited by image tracking techniques. I will describe recent improvements utilizing laser-based detection to overcome these limitations. We implemented back-scattered laser-based detection combined with video image tracking to achieve high-resolution, high-bandwidth, three-dimensional position tracking.

Neuman, Keir



Eukaryotic membrane tethers revisited using magnetic tweezers  

NASA Astrophysics Data System (ADS)

Membrane nanotubes, under physiological conditions, typically form en masse. We employed magnetic tweezers (MTW) to extract tethers from human brain tumor cells and compared their biophysical properties with tethers extracted after disruption of the cytoskeleton and from a strongly differing cell type, Chinese hamster ovary cells. In this method, the constant force produced with the MTW is transduced to cells through super-paramagnetic beads attached to the cell membrane. Multiple sudden jumps in bead velocity were manifest in the recorded bead displacement-time profiles. These discrete events were interpreted as successive ruptures of individual tethers. Observation with scanning electron microscopy supported the simultaneous existence of multiple tethers. The physical characteristics, in particular, the number and viscoelastic properties of the extracted tethers were determined from the analytic fit to bead trajectories, provided by a standard model of viscoelasticity. Comparison of tethers formed with MTW and atomic force microscopy (AFM), a technique where the cantilever-force transducer is moved at constant velocity, revealed significant differences in the two methods of tether formation. Our findings imply that extreme care must be used to interpret the outcome of tether pulling experiments performed with single molecular techniques (MTW, AFM, optical tweezers, etc). First, the different methods may be testing distinct membrane structures with distinct properties. Second, as soon as a true cell membrane (as opposed to that of a vesicle) can attach to a substrate, upon pulling on it, multiple nonspecific membrane tethers may be generated. Therefore, under physiological conditions, distinguishing between tethers formed through specific and nonspecific interactions is highly nontrivial if at all possible.

Hosu, Basarab G.; Sun, Mingzhai; Marga, Françoise; Grandbois, Michel; Forgacs, Gabor



Laser tweezers Raman spectroscopy of single cells  

NASA Astrophysics Data System (ADS)

Raman scattering is an inelastic collision between the vibrating molecules inside the sample and the incident photons. During this process, energy exchange takes place between the photon and the scattering molecule. By measuring the energy change of the photon, the molecular vibration mode can be probed. The vibrational spectrum contains valuable information about the disposition of atomic nuclei and chemical bonds within a molecule, the chemical compositions and the interactions between the molecule and its surroundings. In this dissertation, laser tweezers Raman spectroscopy (LTRS) technique is applied for the analysis of biological cells and human cells at single cell level. In LTRS, an individual cell is trapped in aqueous medium with laser tweezers, and Raman scattering spectra from the trapped cell are recorded in real-time. The Raman spectra of these cells can be used to reveal the dynamical processes of cell growth, cell response to environment changes, and can be used as the finger print for the identification of a bacterial cell species. Several biophysical experiments were carried out using LTRS: (1) the dynamic germination process of individual spores of Bacillus thuringiensis was detected via Ca-DPA, a spore-specific biomarker molecule; (2) inactivation and killing of Bacillus subtilis spores by microwave irradiation and wet heat were studied at single cell level; (3) the heat shock activation process of single B. subtilis spores were analyzed, in which the reversible transition from glass-like state at low temperature to liquid-like state at high temperature in spore was revealed at the molecular level; (4) the kinetic processes of bacterial cell lysis of E. coli by lysozyme and by temperature induction of lambda phage were detected real-time; (5) the fixation and rehydration of human platelets were quantitatively evaluated and characterized with Raman spectroscopy method, which provided a rapid way to quantify the quality of freeze-dried therapeutic platelet products for long term preservation; (6) LTRS based depolarized Raman spectroscopy was developed and used to do bacterial cell identification of similar species. From these experiments, several new findings and conclusions have been obtained. (1) single spore dynamic germination was measured for the first time. The result showed the time-to-germinate of a single spore was stochastic and could be discrete. (2) the thermal nature of spore killing in solution by microwaves was identified, Spores killed directly by microwaves showed death marker in Raman spectrum; (3) The Ca-DPA inside the spore core of a spore would undergo a structure modification during heat shock, which was related to the spores' state transition from a glass-like to a rubbery-like state, this structure modification during heat shock was reversible; (4) the kinetic molecular processes of E. coli cell lysis by lysozyme and by temperature induction of bacterial phage were recorded for the first time. The different cellular processes of the lysis were revealed based on the two different mechanisms; (5) LTRS technique was successfully applied to characterize human platelet fixation; a major procedure for long term preservation of therapeutic human platelet products; (6) A depolarization laser tweezers Raman spectroscopy (DLTRS) technique was developed to enhance the ability to discriminate similar bacterial species.

Chen, De


Sterically controlled recognition of macromolecular sequence information by molecular tweezers.  


Sequence-specific binding is demonstrated between pyrene-based tweezer molecules and soluble, high molar mass copolyimides. The binding involves complementary pi-pi stacking interactions, polymer chain-folding, and hydrogen bonding and is extremely sensitive to the steric environment around the pyromellitimide binding-site. A detailed picture of the intermolecular interactions involved has been obtained through single-crystal X-ray studies of tweezer complexes with model diimides. Ring-current magnetic shielding of polyimide protons by the pyrene "arms" of the tweezer molecule induces large complexation shifts of the corresponding 1H NMR resonances, enabling specific triplet sequences to be identified by their complexation shifts. Extended comonomer sequences (triplets of triplets in which the monomer residues differ only by the presence or absence of a methyl group) can be "read" by a mechanism which involves multiple binding of tweezer molecules to adjacent diimide residues within the copolymer chain. The adjacent-binding model for sequence recognition has been validated by two conceptually different sets of tweezer binding experiments. One approach compares sequence-recognition events for copolyimides having either restricted or unrestricted triple-triplet sequences, and the other makes use of copolymers containing both strongly binding and completely nonbinding diimide residues. In all cases the nature and relative proportions of triple-triplet sequences predicted by the adjacent-binding model are fully consistent with the observed 1H NMR data. PMID:18047339

Colquhoun, Howard M; Zhu, Zhixue; Cardin, Christine J; Gan, Yu; Drew, Michael G B



High-Resolution Optical Tweezers for Single-Molecule Manipulation  

PubMed Central

Forces hold everything together and determine its structure and dynamics. In particular, tiny forces of 1-100 piconewtons govern the structures and dynamics of biomacromolecules. These forces enable folding, assembly, conformational fluctuations, or directional movements of biomacromolecules over sub-nanometer to micron distances. Optical tweezers have become a revolutionary tool to probe the forces, structures, and dynamics associated with biomacromolecules at a single-molecule level with unprecedented resolution. In this review, we introduce the basic principles of optical tweezers and their latest applications in studies of protein folding and molecular motors. We describe the folding dynamics of two strong coiled coil proteins, the GCN4-derived protein pIL and the SNARE complex. Both complexes show multiple folding intermediates and pathways. ATP-dependent chromatin remodeling complexes translocate DNA to remodel chromatin structures. The detailed DNA translocation properties of such molecular motors have recently been characterized by optical tweezers, which are reviewed here. Finally, several future developments and applications of optical tweezers are discussed. These past and future applications demonstrate the unique advantages of high-resolution optical tweezers in quantitatively characterizing complex multi-scale dynamics of biomacromolecules.

Zhang, Xinming; Ma, Lu; Zhang, Yongli



Surface imaging using holographic optical tweezers.  


We present an imaging technique using an optically trapped cigar-shaped probe controlled using holographic optical tweezers. The probe is raster scanned over a surface, allowing an image to be taken in a manner analogous to scanning probe microscopy (SPM), with automatic closed loop feedback control provided by analysis of the probe position recorded using a high speed CMOS camera. The probe is held using two optical traps centred at least 10 µm from the ends, minimizing laser illumination of the tip, so reducing the chance of optical damage to delicate samples. The technique imparts less force on samples than contact SPM techniques, and allows highly curved and strongly scattering samples to be imaged, which present difficulties for imaging using photonic force microscopy. To calibrate our technique, we first image a known sample--the interface between two 8 µm polystyrene beads. We then demonstrate the advantages of this technique by imaging the surface of the soft alga Pseudopediastrum. The scattering force of our laser applied directly onto this sample is enough to remove it from the surface, but we can use our technique to image the algal surface with minimal disruption while it is alive, not adhered and in physiological conditions. The resolution is currently equivalent to confocal microscopy, but as our technique is not diffraction limited, there is scope for significant improvement by reducing the tip diameter and limiting the thermal motion of the probe. PMID:21646693

Phillips, D B; Grieve, J A; Olof, S N; Kocher, S J; Bowman, R; Padgett, M J; Miles, M J; Carberry, D M



Systematical study of the trapping forces of optical tweezers formed by different types of optical ring beams  

Microsoft Academic Search

The technique of optical tweezers has been improved a lot since its invention, which extends the application fields of optical tweezers. Besides the conventionally used Gaussian beams, different types of ring beams have also been used to form optical tweezers for different purposes. The two typical kinds of ring beams used in optical tweezers are the hollow Gaussian beam and

Sheng-Hua Xu; Yin-Mei Li; Li-Ren Lou



Optical tweezers based on near infrared diode laser  

NASA Astrophysics Data System (ADS)

Emission from a single-mode 100 mW diode laser at 840 nm is used to create optical tweezers: the trapping laser beam is introduced into a microscope and focused by the objective. The microscope also allows monitoring of the motion of the trapped particles. The optical tweezers were monitored with objectives having different numerical apertures between 0.65 and 1.3. The optical trapping of polystyrene spheres with a radius between 0.11 and 7.45 micrometers and of biological objects, the flagellated alga Tetraselmis, with typical dimensions of 8 X 8 X 13 micrometers 3 were studied. The efficiency of the optical tweezers has been characterized through a parameter Q and compared with theoretical models.

Grego, S.; Arimondo, Ennio; Frediani, Carlo



Mechanical manipulation of bone and cartilage cells with 'optical tweezers'.  


The single beam optical gradient trap (optical tweezers) uses a single beam of laser light to non-invasively manipulate microscopic particles. Optical tweezers exerting a force of approximately 7 pN were applied to single bone and cartilage derived cells in culture and changes in intracellular calcium levels were observed using Fluo-3 labelling. Human derived osteoblasts responded to optical tweezers with an immediate increase in [Ca2+]i that was inhibited by the addition of a calcium channel blocker nifedipine. Force applied to different regions of cells resulted in a variable response. [Ca2+]i elevation in response to load was lower in rat femur derived osteoblasts, and not apparent in primary chondrocytes and the osteocytic cell line (MLO Y4). PMID:10508913

Walker, L M; Holm, A; Cooling, L; Maxwell, L; Oberg, A; Sundqvist, T; El Haj, A J



Cellular viscoelasticity probed by active rheology in optical tweezers  

NASA Astrophysics Data System (ADS)

A novel approach to probe viscoelastic properties of cells based on double trap optical tweezers is reported. Frequency dependence of the tangent of phase difference in the movement of the opposite erythrocyte edges while one of the edges is forced to oscillate by optical tweezers appeared to be highly dependent on the rigidity of the cellular membrane. Effective viscoelastic parameters characterizing red blood cells with different stiffnesses (normal and glutaraldehyde-fixed) are determined. It is shown that the photo-induced effects caused by laser trapping at the power level used in the experiments are negligible giving the possibility to use the offered technique for dynamic monitoring of soft materials viscoelastic properties.

Lyubin, Evgeny V.; Khokhlova, Maria D.; Skryabina, Maria N.; Fedyanin, Andrey A.



Highly reduced iron-doped lithium niobate for optoelectronic tweezers  

NASA Astrophysics Data System (ADS)

We investigate the applicability of highly reduced lithium niobate samples doped with iron for the use as optoelectronic tweezers. Increasing the reduction degree of Fe-doped lithium niobate is well known to increase the photoconductivity and reduce the writing time of internal space-charge fields. Based on our measurements of the photorefractive properties, we determine the optimal conditions for dielectrophoretic trapping and present the application of Fe-doped lithium niobate as optoelectronic tweezers. For higher reduction degrees, an unexpected decrease in the photovoltaic current density and the saturation space-charge field is reported.

Esseling, Michael; Zaltron, Annamaria; Argiolas, Nicola; Nava, Giovanni; Imbrock, Jörg; Cristiani, Ilaria; Sada, Cinzia; Denz, Cornelia



Magneto-optical tweezers built around an inverted microscope  

SciTech Connect

We present a simple experimental setup of magneto-optical tweezers built around an inverted microscope. Two pairs of coils placed around the focal point of the objective generate a planar-rotating magnetic field that is perpendicular to the stretching direction. This configuration allows us to control the rotary movement of a paramagnetic bead trapped in the optical tweezers. The mechanical design is universal and can be simply adapted to any inverted microscope and objective. The mechanical configuration permits the use of a rather large experimental cell and the simple assembly and disassembly of the magnetic attachment.

Claudet, Cyril; Bednar, Jan



Fundamental constraints on particle tracking with optical tweezers  

NASA Astrophysics Data System (ADS)

A general quantum limit to the sensitivity of particle position measurements is derived following the simple principle of the Heisenberg microscope. The value of this limit is calculated for particles in the Rayleigh and Mie scattering regimes, and with parameters which are relevant to optical tweezers experiments. The minimum power required to observe the zero-point motion of a levitating bead is also calculated, with the optimal particle diameter always smaller than the wavelength. We show that recent optical tweezers experiments are within two orders of magnitude of quantum limited sensitivity, suggesting that quantum optical resources may soon play an important role in high sensitivity tracking applications.

Taylor, Michael A.; Knittel, Joachim; Bowen, Warwick P.



Marker-free cell discrimination by holographic optical tweezers  

NASA Astrophysics Data System (ADS)

We introduce a method for marker-free cell discrimination based on optical tweezers. Cancerous, non-cancerous, and drug-treated cells could be distinguished by measuring the trapping forces using holographic optical tweezers. We present trapping force measurements on different cell lines: normal pre-B lymphocyte cells (BaF3; "normal cells"), their Bcr-Abl transformed counterparts (BaF3-p185; "cancer cells") as a model for chronic myeloid leukaemia (CML) and Imatinib treated BaF3-p185 cells. The results are compared with reference measurements obtained by a commercial flow cytometry system.

Schaal, F.; Warber, M.; Zwick, S.; van der Kuip, H.; Haist, T.; Osten, W.



Tunable optical tweezers for wavelength-dependent measurements  

PubMed Central

Optical trapping forces depend on the difference between the trap wavelength and the extinction resonances of trapped particles. This leads to a wavelength-dependent trapping force, which should allow for the optimization of optical tweezers systems, simply by choosing the best trapping wavelength for a given application. Here we present an optical tweezer system with wavelength tunability, for the study of resonance effects. With this system, the optical trap stiffness is measured for single trapped particles that exhibit either single or multiple extinction resonances. We include discussions of wavelength-dependent effects, such as changes in temperature, and how to measure them.

Hester, Brooke; Campbell, Gretchen K.; Lopez-Mariscal, Carlos; Filgueira, Carly Levin; Huschka, Ryan; Halas, Naomi J.; Helmerson, Kristian



Ultrahigh frequency lensless ultrasonic transducers for acoustic tweezers application.  


Similar to optical tweezers, a tightly focused ultrasound microbeam is needed to manipulate microparticles in acoustic tweezers. The development of highly sensitive ultrahigh frequency ultrasonic transducers is crucial for trapping particles or cells with a size of a few microns. As an extra lens would cause excessive attenuation at ultrahigh frequencies, two types of 200-MHz lensless transducer design were developed as an ultrasound microbeam device for acoustic tweezers application. Lithium niobate single crystal press-focused (PF) transducer and zinc oxide self-focused transducer were designed, fabricated and characterized. Tightly focused acoustic beams produced by these transducers were shown to be capable of manipulating single microspheres as small as 5 µm two-dimensionally within a range of hundreds of micrometers in distilled water. The size of the trapped microspheres is the smallest ever reported in the literature of acoustic PF devices. These results suggest that these lensless ultrahigh frequency ultrasonic transducers are capable of manipulating particles at the cellular level and that acoustic tweezers may be a useful tool to manipulate a single cell or molecule for a wide range of biomedical applications. PMID:23042219

Lam, Kwok Ho; Hsu, Hsiu-Sheng; Li, Ying; Lee, Changyang; Lin, Anderson; Zhou, Qifa; Kim, Eun Sok; Shung, Kirk Koping



Dynamic array generation and pattern formation for optical tweezers  

Microsoft Academic Search

The generalised phase contrast approach is used for the generation of optical arrays of arbitrary beam shape, suitable for applications in optical tweezers for the manipulation of biological specimens. This approach offers numerous advantages over current techniques involving the use of computer-generated holograms or diffractive optical elements. We demonstrate a low-loss system for generating intensity patterns suitable for the trapping

Paul C Mogensen; Jesper Glückstad



Multifunctional optical tweezers using computer-generated holograms  

Microsoft Academic Search

Optical tweezers are capable of trapping microscopic particles by photon momentum transfer. The use of dynamic computer-generated holograms for beam shaping allows a high flexibility in terms of trap characteristics and features. We use a liquid crystal display (LCD) to display the holograms. Efficiency losses caused by the periodic electrode structure of the LCD have been clearly reduced by use

J. Liesener; M. Reicherter; T. Haist; H. J. Tiziani



Assembly of 3-dimensional structures using programmable holographic optical tweezers  

Microsoft Academic Search

The micromanipulation of objects into 3-dimensional geometries within holographic optical tweezers is carried out using modified Gerchberg-Saxton (GS) and direct binary search (DBS) algorithms to produce the hologram designs. The algorithms calculate sequences of phase holograms, which are implemented using a spatial light modulator, to reconfigure the geometries of optical traps in many planes simultaneously. The GS algorithm is able

Gavin Sinclair; Pamela Jordan; Johannes Courtial; Miles Padgett; Jon Cooper; Zsolt John Laczik



Automated trapping, assembly, and sorting with holographic optical tweezers  

PubMed Central

We combine real-time feature recognition with holographic optical tweezers to automatically trap, assemble, and sort micron-sized colloidal particles. Closed loop control will enable new applications of optical micromanipulation in biology, medicine, materials science, and possibly quantum computation.

Chapin, Stephen C.; Germain, Vincent; Dufresne, Eric R.



Investigating the thermodynamics of small biosystems with optical tweezers  

NASA Astrophysics Data System (ADS)

We present two examples of how single-molecule experimental techniques applied to biological systems can give insight into problems within the scope of equilibrium and nonequilibrium mesoscopic thermodynamics. The first example is the mapping of the free energy landscape of a macromolecule, the second the experimental verification of Crooks’ fluctuation theorem. In both cases the experimental setup comprises optical tweezers and DNA molecules.

Mossa, Alessandro; Huguet, Josep Maria; Ritort, Felix



Long lifetime of single atom in optical tweezer with laser cooling  

NASA Astrophysics Data System (ADS)

Single cesium atom prepared in a large-magnetic-gradient magneto-optical trap (MOT) has been efficiently loaded into a microscopic far-off-resonance optical trap (FORT, or optical tweezer), and the atom can be transferred back and forth between two traps with high efficiency. The intensity noise spectra of tweezer laser are measured and the heating mechanisms in optical tweezer are analyzed. To prolong the lifetime of single atom trapped in optical tweezer, laser cooling technique is utilized to decrease atom's kinetic energy, and the effective temperature of single atom in tweezer is estimated by the release-and-recapture (R&R) method. Thanks to laser cooling, typical lifetime of ~ 130.6 +/- 1.8 s for single atom in tweezer is obtained. These works provides a good starting point for coherent manipulation of single atom.

Wang, Junmin; He, Jun; Yang, Baodong; Zhang, Tiancai; Peng, Kunchi



Reversible Guest Exchange Mechanisms in Supramolecular Host-GuestAssemblies  

SciTech Connect

Synthetic chemists have provided a wide array of supramolecular assemblies able to encapsulate guest molecules. The scope of this tutorial review focuses on supramolecular host molecules capable of reversibly encapsulating polyatomic guests. Much work has been done to determine the mechanism of guest encapsulation and guest release. This review covers common methods of monitoring and characterizing guest exchange such as NMR, UV-VIS, mass spectroscopy, electrochemistry, and calorimetry and also presents representative examples of guest exchange mechanisms. The guest exchange mechanisms of hemicarcerands, cucurbiturils, hydrogen-bonded assemblies, and metal-ligand assemblies are discussed. Special attention is given to systems which exhibit constrictive binding, a motif common in supramolecular guest exchange systems.

Pluth, Michael D.; Raymond, Kenneth N.



Influence of gold nanoparticles' size on the trapping performance of optical tweezers  

NASA Astrophysics Data System (ADS)

Gold nanoparticles are considered to be better probes than the traditional polystyrene nanobeads in nanomaterials and nanobiotechnology. Meanwhile, optical tweezers are very popular tool for manipulation and force measurement in these fields. Gold nanoparticles with different size will receive radiation forces with different scale in optical tweezers. This paper theoretically studies the trapping performance of the optical tweezers for the gold nanoparticle with different size, and finally gives the relation curves between the radiation forces and the radius of the of the particle.

Liu, Xiaoyu; Lu, Guang



Sensing interactions in the microworld with optical tweezers  

NASA Astrophysics Data System (ADS)

Optical Tweezers have become a widespread tool in Cell Biology, microengineering and other fields requiring delicate micromanipulation. But for those sensitive tasks, it remains difficult to handle objects without damaging them. As the precision in position and force measurement increase, the richness of information cannot be fully exploited with simple interfaces such as a mouse or a common joystick. For this reason, we propose a haptic force-feedback optical tweezer command and a force-feedback system controlled by one hand. The system combines accurate force measurement using a fast camera and the coupling of these measured forces with a human operator. The overall transparency allows even the feeling of the Brownian motion.

Pacoret, Cécile; Bowman, Richard; Gibson, Graham; Sinan, Haliyo D.; Bergander, Arvid; Carberry, David; Régnier, Stéphane; Padgett, Miles



Measurements of trapping efficiency and stiffness in optical tweezers  

Microsoft Academic Search

We report an experimental study concerning the radial forces of an optical tweezers acting on spherical polystyrene particles diluted in water solution. The radius of the trapped beads varied between 0.5 and 7.5 ?m, i.e., in an intermediate range between Rayleigh and geometric optics regime. As a force calibration method we used the viscous drag exerted by a fluid flow.

N. Malagnino; G. Pesce; A. Sasso; E. Arimondo



Evidence for localized cell heating induced by infrared optical tweezers  

Microsoft Academic Search

The confinement of liposomes and Chinese hamster ovary (CHO) cells by infrared (IR) optical tweezers is shown to result in sample heating and temperature increases by several degrees centigrade, as measured by a noninvasive, spatially resolved fluorescence detection technique. For micron-sized spherical liposome vesicles having bilayer membranes composed of the phospholipid 1,2-diacyl-pentadecanoyl-glycero-phosphocholine (15-OPC), a temperature rise of â¼1.45±0.15 °C\\/100 mW

Y. Liu; D. K. Cheng; G. J. Sonek; M. W. Berns; C. F. Chapman; B. J. Tromberg



Membrane Tether Formation from Outer Hair Cells with Optical Tweezers  

Microsoft Academic Search

Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-?m polystyrene beads. Tether formation force and tether force were measured in static and dynamic conditions. A greater force was required for tether formations from OHC lateral wall (499±152 pN) than from OHC basal end (142±49 pN). The difference

Zhiwei Li; Bahman Anvari; Masayoshi Takashima; Peter Brecht; Jorge H. Torres; William E. Brownell



Detection and Characterization of Individual Intermolecular Bonds Using Optical Tweezers  

Microsoft Academic Search

The development of scanning probe techniques has made it possible to examine protein-protein interactions at the level of individual molecular pairs. A calibrated optical tweezers, along with immunoglobulin G (IgG)-coated polystyrene microspheres, has been used to detect individual surface-linked Staphylococcus protein A (SpA) molecules and to characterize the strength of the noncovalent IgG-SpA bond. Microspheres containing, on average, less than

Andrea L. Stout



Modified Hybrid Plasmonic Waveguides as Tunable Optical Tweezers  

NASA Astrophysics Data System (ADS)

We propose a series of modified hybrid plasmonic waveguide systems. It is found that their propagation distances and mode areas depend on their shapes notably. The optical trapping forces exerting on the dielectric nanoparticles are calculated, and the strength and range of the forces can be adjusted by altering the shapes of the waveguides. These features demonstrate the possibility of using the modified hybrid waveguide systems to design tunable nanoscale optical tweezers.

Zhang, Lu; Yang, Shu



Spatially resolved magnetometry using cold atoms in dark optical tweezers.  


We use Faraday spectroscopy of atoms confined to crossed hollow beam tweezers to map magnetic fields over 3 millimeters with 200 micron resolution in a single trap loading cycle. The hollow beams are formed using spatial light modulation, and the trap location is scanned using acousto-optic deflectors. We demonstrate the technique by mapping a linear quadrupole magnetic field with 10 nT sensitivity. PMID:20174047

Fatemi, Fredrik K; Bashkansky, Mark



Superresolution imaging in optical tweezers using high-speed cameras  

Microsoft Academic Search

High-speed cameras are reliable alternatives for the direct characterization of optical trap force and particle motion in optical tweezers setups, replacing indirect motion measurements often performed by quadrant detectors. In the present approach, subpixel motion data of the trapped particle is retrieved from a high-speed low-resolution video sequence. Due to the richness structure of motion diversity of microscopic trapped particles,

Juan Pablo Staforelli; Esteban Vera; Jos'e Manuel Brito; Pablo Solano; Sergio Torres; Carlos Saavedra



Multispectral optical tweezers for molecular diagnostics of single biological cells  

NASA Astrophysics Data System (ADS)

Optical trapping of single biological cells has become an established technique for controlling and studying fundamental behavior of single cells with their environment without having "many-body" interference. The development of such an instrument for optical diagnostics (including Raman and fluorescence for molecular diagnostics) via laser spectroscopy with either the "trapping" beam or secondary beams is still in progress. This paper shows the development of modular multi-spectral imaging optical tweezers combining Raman and Fluorescence diagnostics of biological cells.

Butler, Corey; Fardad, Shima; Sincore, Alex; Vangheluwe, Marie; Baudelet, Matthieu; Richardson, Martin



Robotic cell manipulation with optical tweezers for biomechanical characterization  

Microsoft Academic Search

In this paper, we demonstrate the effectiveness of robotic cell stretching with optical tweezers for biomechanical characterization. Optical traps serve as end-effectors to manipulate micro-beads attached to the cell surface. The dynamics of the cell-bead mixture during cell stretching is investigated for the first time. Based on our previous work, cell stiffness is extracted and biomechanical properties of cells can

Youhua Tan; Dong Sun; Shuk Han Cheng; Ronald A. Li



Cluster formation in ferrofluids induced by holographic optical tweezers.  


Holographic optical tweezers were used to show the interaction between a strongly focused laser beam and magnetic nanoparticles in ferrofluid. When the light intensity was high enough, magnetic nanoparticles were removed from the beam center and formed a dark ring. The same behavior was observed when focusing vortex or Bessel beams. The interactions between two or more separated rings of magnetic nanoparticles created by independent optical traps were also observed. PMID:24081086

Masajada, Jan; Bacia, Marcin; Drobczy?ski, S?awomir



The effect of Mie resonances on trapping in optical tweezers.  


We calculate trapping forces, trap stiffness and interference effects for spherical particles in optical tweezers using electromagnetic theory. We show the dependence of these on relative refractive index and particle size. We investigate resonance effects, especially in high refractive index particles where interference effects are expected to be strongest. We also show how these simulations can be used to assist in the optimal design of traps. PMID:18795041

Stilgoe, Alexander B; Nieminen, Timo A; Knöener, Gregor; Heckenberg, Norman R; Rubinsztein-Dunlop, Halina



Lipid bilayer-integrated optoelectronic tweezers for nanoparticle manipulations.  


Remotely manipulating a large number of microscopic objects is important to soft-condensed matter physics, biophysics, and nanotechnology. Optical tweezers and optoelectronic tweezers have been widely used for this purpose but face critical challenges when applied to nanoscale objects, including severe photoinduced damages, undesired ionic convections, or irreversible particle immobilization on surfaces. We report here the first demonstration of a lipid bilayer-integrated optoelectronic tweezers system for simultaneous manipulation of hundreds of 60 nm gold nanoparticles in an arbitrary pattern. We use a fluid lipid bilayer membrane with a ~5 nm thickness supported by a photoconductive electrode to confine the diffusion of chemically tethered nanoparticles in a two-dimensional space. Application of an external a.c. voltage together with patterned light selectively activates the photoconducting electrode that creates strong electric field localized near the surface. The field strength changes most significantly at the activated electrode surface where the particles tethered to the membrane thus experience the strongest dielectrophoretic forces. This design allows us to efficiently achieve dynamic, reversible, and parallel manipulation of many nanoparticles. Our approach to integrate biomolecular structures with optoelectronic devices offers a new platform enabling the study of thermodynamics in many particle systems and the selective transport of nanoscale objects for broad applications in biosensing and cellular mechanotransductions. PMID:23659726

Ota, Sadao; Wang, Sheng; Wang, Yuan; Yin, Xiaobo; Zhang, Xiang



Precession mechanism of nematic liquid crystal droplet under optical tweezers  

NASA Astrophysics Data System (ADS)

Optical Tweezers are well known for manipulating and tracking microscopic particles used in many biological and microfluidic applications. Trapping birefringent particles, e.g. liquid crystal droplets, gives insight into the aspect of light polarization in optical tweezers. The outstanding properties of liquid crystal droplets are their high refractive index and birefringent property suitable for light angular momentum transfer. Under the microscope, the Maltese cross of radial nematic liquid crystal droplet was observed. Trapped under 1064 nm Optical Tweezers with power lower than 80 mW, the droplet precession around the focal point of the laser beam was observed due to circular polarization of laser. In this study we show that the precession behavior of radial nematic droplet depends on the degree of ellipticity of polarization state of light, power of the laser source and size of the radial nematic droplet, affecting the induced electrical polarization and internal reordering of the droplets. The theoretical explanation and the model of this behavior have also been determined and discussed.

Phanphak, S.; Pattanaporkratana, A.; Limtrakul, J.; Chattham, N.



Magnetic tweezers: micromanipulation and force measurement at the molecular level.  

PubMed Central

Cantilevers and optical tweezers are widely used for micromanipulating cells or biomolecules for measuring their mechanical properties. However, they do not allow easy rotary motion and can sometimes damage the handled material. We present here a system of magnetic tweezers that overcomes those drawbacks while retaining most of the previous dynamometers properties. Electromagnets are coupled to a microscope-based particle tracking system through a digital feedback loop. Magnetic beads are first trapped in a potential well of stiffness approximately 10(-7) N/m. Thus, they can be manipulated in three dimensions at a speed of approximately 10 microm/s and rotated along the optical axis at a frequency of 10 Hz. In addition, our apparatus can work as a dynamometer relying on either usual calibration against the viscous drag or complete calibration using Brownian fluctuations. By stretching a DNA molecule between a magnetic particle and a glass surface, we applied and measured vertical forces ranging from 50 fN to 20 pN. Similarly, nearly horizontal forces up to 5 pN were obtained. From those experiments, we conclude that magnetic tweezers represent a low-cost and biocompatible setup that could become a suitable alternative to the other available micromanipulators.

Gosse, Charlie; Croquette, Vincent



High-speed holographic optical tweezers using a ferroelectric liquid crystal microdisplay.  


We demonstrate the advantages of a ferroelectric liquid crystal spatial light modulator for optical tweezer array applications. The fast switching speeds of the ferroelectric device (compared to conventional nematic systems) is shown to enable very rapid reconfiguration of trap geometries, controlled, high speed particle movement, and tweezer array multiplexing. PMID:19466092

Hossack, William; Theofanidou, Eirini; Crain, Jason; Heggarty, Kevin; Birch, Martin



High-speed holographic optical tweezers using a ferroelectric liquid crystal microdisplay  

NASA Astrophysics Data System (ADS)

We demonstrate the advantages of a ferroelectric liquid crystal spatial light modulator for optical tweezer array applications. The fast switching speeds of the ferroelectric device (compared to conventional nematic systems) is shown to enable very rapid reconfiguration of trap geometries, controlled, high speed particle movement, and tweezer array multiplexing.

Hossack, William J.; Theofanidou, Eirini; Crain, Jason; Heggarty, Kevin; Birch, Martin



Applications of Optical Tweezers and an Integrated Force Measurement Module for Biomedical Research.  

National Technical Information Service (NTIS)

Optical tweezers are useiul for manipulating biological samples and measuring biological forces. in the present study, we have integrated a ward atter analysis (FORSA) module into the 'single-beam gradient force optical tweezers'. The entire set-up was th...

B. Liao C. Huang D. Wang J. Tsai W. L. Hwang



Advanced optical tweezers for the study of cellular and molecular biomechanics  

Microsoft Academic Search

Optical tweezers are an important tool for studying cellular and molecular biomechanics. We present a robust optical tweezers device with advanced features including: multiple optical traps, acousto-optic trap steering, and back focal plane interferometry position detection. We integrate these features into an upright microscope, with no compromise to its capabilities (differential interference contrast microscopy (DIC), fluorescence microscopy, etc.). Acousto-optic deflectors

Gary J. Brouhard; Henry T. Schek; Alan J. Hunt



Raman sorting and identification of single living micro-organisms with optical tweezers  

Microsoft Academic Search

We report on a novel technique for sorting and identification of single biological cells and food-borne bacteria based on laser tweezers and Raman spectroscopy (LTRS). With this technique, biological cells of different physiological states in a sample chamber were identified by their Raman spectral signatures and then they were selectively manipulated into a clean collection chamber with optical tweezers through

Changan Xie; De Chen; Yong-Qing Li



Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers  

Microsoft Academic Search

A cell of the bacterium Escherichia coli was tethered covalently to a glass coverslip by a single f lagellum, and its rotation was stopped by using optical tweezers. The tweezers acted directly on the cell body or indirectly, via a trapped polystyrene bead. The torque generated by the f lagel- lar motor was determined by measuring the displacement of the




High-speed holographic optical tweezers using a ferroelectric liquid crystal microdisplay  

Microsoft Academic Search

We demonstrate the advantages of a ferroelectric liquid crystal spatial light modulator for optical tweezer array applications. The fast switching speeds of the ferroelectric device (compared to conventional nematic systems) is shown to enable very rapid reconfiguration of trap geometries, controlled, high speed particle movement, and tweezer array multiplexing.

William J. Hossack; Eirini Theofanidou; Jason Crain; Kevin Heggarty; Martin Birch



Photonic Force Microscope Based on Optical Tweezers and Two-Photon Excitation for Biological Applications  

Microsoft Academic Search

A new scanning probe microscope, the photonic force microscope (PFM), based on optical tweezers and two-photon absorption processes for biological applications is described. Optical tweezers are used to trap a fluorescent latex bead with a diameter of 200 nm in an aqueous solution in all three dimensions. The fluorescent dye is chosen to fulfill the two-photon absorption criterion for the

Ernst-Ludwig Florin; Arnd Pralle; J. K. Heinrich Hörber; Ernst H. K. Stelzer



Stress Response in Caenorhabditis elegans Caused by Optical Tweezers: Wavelength, Power, and Time Dependence  

Microsoft Academic Search

Optical tweezers have emerged as a powerful technique for micromanipulation of living cells. Although the technique often has been claimed to be nonintrusive, evidence has appeared that this is not always the case. This work presents evidence that near-infrared continuous-wave laser light from optical tweezers can produce stress in Caenorhabditis elegans. A transgenic strain of C. elegans, carrying an integrated

Guenther Leitz; Erik Fällman; Simon Tuck; Ove Axner



Differential Detection of Dual Traps Improves the Spatial Resolution of Optical Tweezers  

Microsoft Academic Search

The drive toward more sensitive single-molecule manipulation techniques has led to the recent development of optical tweezers capable of resolving the motions of biological systems at the subnanometer level, approaching the fundamental limit set by Brownian fluctuations. One successful approach has been the dual-trap optical tweezers, in which the system of study is held at both ends by microspheres in

Jeffrey R. Moffitt; Yann R. Chemla; David Izhaky; Carlos Bustamante



Single DNA molecule grafting and manipulation using a combined atomic force microscope and an optical tweezer  

Microsoft Academic Search

In this letter, we report on spatially selecting and grafting a DNA-tethered bead to an atomic force microscope (AFM) cantilever, using an optical tweezer. To quantify this technique, we measure force versus extension of a single DNA molecule using AFM. For such studies, we have developed a micromanipulation approach by combining an AFM, an optical tweezer, and visualization setup. The

G. V. Shivashankar; A. Libchaber



Efficient extension of the trapping lifetime of single atoms in an optical tweezer by laser cooling  

NASA Astrophysics Data System (ADS)

Optical tweezers have become powerful tools for the confinement and manipulation of neutral atoms, molecules, mesoscopic biological molecules and living cells. In our experiment, a single caesium atom was prepared in a large-magnetic-gradient magneto-optical trap (MOT). It was then efficiently transferred back and forth between the MOT and a 1064 nm microscopic optical tweezer. The atomic transfer between the MOT and the tweezer can be employed to measure the trapping lifetime and the energy distribution of the single atom in the tweezer. In order to extend the trapping lifetime, laser cooling is used to decrease the atom's kinetic energy. The trapping lifetime was extended from ~75 to ~130 s by applying a 10 ms laser cooling phase just after the single atom is transferred into the tweezer.

He, Jun; Yang, Baodong; Zhang, Tiancai; Wang, Junmin



MatLab program for precision calibration of optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are used as force transducers in many types of experiments. The force they exert in a given experiment is known only after a calibration. Computer codes that calibrate optical tweezers with high precision and reliability in the (x,y)-plane orthogonal to the laser beam axis were written in MatLab (MathWorks Inc.) and are presented here. The calibration is based on the power spectrum of the Brownian motion of a dielectric bead trapped in the tweezers. Precision is achieved by accounting for a number of factors that affect this power spectrum. First, cross-talk between channels in 2D position measurements is tested for, and eliminated if detected. Then, the Lorentzian power spectrum that results from the Einstein-Ornstein-Uhlenbeck theory, is fitted to the low-frequency part of the experimental spectrum in order to obtain an initial guess for parameters to be fitted. Finally, a more complete theory is fitted, a theory that optionally accounts for the frequency dependence of the hydrodynamic drag force and hydrodynamic interaction with a nearby cover slip, for effects of finite sampling frequency (aliasing), for effects of anti-aliasing filters in the data acquisition electronics, and for unintended ``virtual'' filtering caused by the position detection system. Each of these effects can be left out or included as the user prefers, with user-defined parameters. Several tests are applied to the experimental data during calibration to ensure that the data comply with the theory used for their interpretation: Independence of x- and y-coordinates, Hooke's law, exponential distribution of power spectral values, uncorrelated Gaussian scatter of residual values. Results are given with statistical errors and covariance matrix. Program summary Title of program: tweezercalib Catalogue identifier: ADTV Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland. Program Summary URL: Computer for which the program is designed and others on which it has been tested: General computer running MatLab (MathWorks Inc.). Programming language used: MatLab (MathWorks Inc.). Uses ``Optimization Toolbox'' and ``Statistics Toolbox''. Memory required to execute with typical data: Of order 4 times the size of the data file. High speed storage required: None No. of lines in distributed program, including test data, etc.: 133183 No. of bytes in distributed program, including test data, etc.: 1043674 Distribution format: tar gzip file Nature of physical problem: Calibrate optical tweezers with precision by fitting theory to experimental power spectrum of position of bead doing Brownian motion in incompressible fluid, possibly near microscope cover slip, while trapped in optical tweezers. Thereby determine spring constant of optical trap and conversion factor for arbitrary-units-to-nanometers for detection system. Method of solution: Elimination of cross-talk between quadrant photo-diode's output channels for positions (optional). Check that distribution of recorded positions agrees with Boltzmann distribution of bead in harmonic trap. Data compression and noise reduction by blocking method applied to power spectrum. Full accounting for hydrodynamic effects: Frequency-dependent drag force and interaction with nearby cover slip (optional). Full accounting for electronic filters (optional), for ``virtual filtering'' caused by detection system (optional). Full accounting for aliasing caused by finite sampling rate (optional). Standard non-linear least-squares fitting. Statistical support for fit is given, with several plots suitable for inspection of consistency and quality of data and fit. Restrictions on the complexity of the problem: Data should be positions of bead doing Brownian motion while held by optical tweezers. For high precision in final results, data should be time series measured over a long time, with sufficiently high experimental sampling rate: The sampling rate should be well above the characteristic frequency of the trap, the so-called corner frequency. Thu

Toli?-Nørrelykke, Iva Marija; Berg-Sørensen, Kirstine; Flyvbjerg, Henrik



Evidence for localized cell heating induced by infrared optical tweezers  

SciTech Connect

The confinement of liposomes and Chinese hamster ovary (CHO) cells by infrared (IR) optical tweezers is shown to result in sample heating and temperature increases by several degrees centigrade, as measured by a noninvasive, spatially resolved fluorescence detection technique. For micron-sized spherical liposome vesicles having bilayer membranes composed of the phospholipid 1,2-diacyl-pentadecanoyl-glycero-phosphocholine (15-OPC), a temperature rise of {similar_to}1.45{plus_minus}0.15 {degree}C/100 mW is observed when the vesicles are held stationary with a 1.064 {mu}m optical tweezers having a power density of {similar_to}10{sup 7} W/cm{sup 2} and a focused spot size of {similar_to}0.8 {mu}m. The increase in sample temperature is found to scale linearly with applied optical power in the 40 to 250 mW range. Under the same trapping conditions, CHO cells exhibit an average temperature rise of nearly 1.15{plus_minus}0.25 {degree}C/100 mW. The extent of cell heating induced by infrared tweezers confinement can be described by a heat conduction model that accounts for the absorption of infrared (IR) laser radiation in the aqueous cell core and membrane regions, respectively. The observed results are relevant to the assessment of the noninvasive nature of infrared trapping beams in micromanipulation applications and cell physiological studies. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Liu, Y.; Cheng, D.K.; Sonek, G.J. [Department of Electrical and Computer Engineering and Beckman Laser Institute and Medical Clinic, University of California, Irvine, California 92717 (United States); Berns, M.W.; Chapman, C.F.; Tromberg, B.J. [Department of Biophysics, and Beckman Laser Institute and Medical Clinic, University of California, Irvine, California 92717 (United States)



Single atoms in optical tweezers for quantum computing  

NASA Astrophysics Data System (ADS)

Our group is interested in neutral atom quantum computing. With this goal in mind, we have recently shown how a single rubidium atom trapped in an optical tweezer can be used to store, manipulate and measure a qubit. I will detail in this talk how we trap and observe a single atom in an optical tweezer created by focusing a far-off resonant laser down to a sub-micron waist. Our qubit is encoded on the |0>=|F =1, M=0> and |1>=|F =2, M=0> hyperfine sublevels of a rubidium 87 atom. We initialize the qubit by optical pumping. We read the state of the qubit using a state selective measurement limited by the quantum projection noise. We perform single qubit operation by driving a two-photon Raman transition. We have measured the coherence time of our qubit by Ramsey interferometry. After applying a spin-echo sequence, we have found an irreversible dephasing time of about 40 ms. To perform a computation, a feature is the ability to perform a gate between two arbitrary qubits of the register. As a first step, we have demonstrated a scheme where the qubit is transfered between two tweezers with no loss of coherence and no change in the external degrees of freedom of the atom. We have then moved the atom over distances typical of the separation between atoms in an array of dipole traps, and shown that this transport does not affect the coherence of the qubit. Finally, I will present our progress towards entangling two atoms, a key ingredient towards building a two-qubit gate.

Browaeys, Antoine



Continuous cell lysis in microfluidics through acoustic and optoelectronic tweezers  

NASA Astrophysics Data System (ADS)

A versatile platform for efficient cell lysis using a combination of acoustic and electric fields in a microchannel is presented. Cell membrane disruption is triggered by electric fields inducing electroporation and then lysis. The principle of optoelectronic tweezers (OET) is applied to control the electric field strength and a surface acoustic wave transducer is attached to an OET chip to implement acoustic tweezing (AT). The system is characterized in terms of spatial control of electric fields, single cell precision and lysis times. Under continuous operation, a combination of AT and OET improves cell lysis significantly achieving for sample concentrations of 106 cell/ml lysis efficiencies of > 99%.

Witte, Christian; Kremer, Clemens; Cooper, Jonathan M.; Neale, Steven L.



Frequency-dependent cell death by optical tweezers manipulation.  


Optical tweezers were used to scan individual Chronic Myelogenous Leukemia cells to determine if the cell death depends on the scanning conditions. Although increasing the scanning frequency or amplitude means greater force applied to the cells, their effects on cell death are not a simple increasing trend, as observed in the optical microscopy. Indeed, cell death sharply increased at particular screening frequencies and amplitudes, whereas other frequencies or amplitudes were less detrimental. These results suggest that cell damage was more sensitive to certain scanning conditions, rather than simply high-applied forces. PMID:23553530

Ng, K S; Zhou, Z L; Ngan, A H W



Optical Tweezers for Sample Fixing in Micro-Diffraction Experiments  

SciTech Connect

In order to manipulate, characterize and measure the micro-diffraction of individual structural elements down to single phospholipid liposomes we have been using optical tweezers (OT) combined with an imaging microscope. We were able to install the OT system at the microfocus beamline ID13 at the ESRF and trap clusters of about 50 multi-lamellar liposomes (< 10 {mu}m large cluster). Further we have performed a scanning diffraction experiment with a 1 micrometer beam to demonstrate the fixing capabilities and to confirm the size of the liposome cluster by X-ray diffraction.

Amenitsch, H.; Rappolt, M.; Sartori, B.; Laggner, P. [Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz (Austria); Cojoc, D.; Ferrari, E.; Garbin, V.; Di Fabrizio, E. [CNR-INFM, Lab TASC, Area di Ricerca, 34012 Basovizza (Italy); Burghammer, M.; Riekel, Ch. [ESRF, 6 rue Jules Horowitz, BP220, 38043 Grenoble Cedex (France)



Optical lock-in particle tracking in optical tweezers  

NASA Astrophysics Data System (ADS)

We demonstrate a lock-in particle tracking scheme in optical tweezers based on stroboscopic modulation of an illuminating optical field. This scheme is found to evade low frequency noise sources while otherwise producing an equivalent position measurement to continuous measurement. This was demonstrated, and found to yield on average 20dB of noise suppression in the frequency range 10-5000 Hz, where low frequency laser noise and electronic noise was significant, and 35 dB of noise suppression in the range 550-710 kHz where laser relaxation oscillations introduced laser noise. The setup is simple, and compatible with any trapping optics.

Taylor, Michael A.; Knittel, Joachim; Bowen, Warwick P.



Multiplexed force measurements on live cells with holographic optical tweezers.  


We describe open-loop and closed-loop multiplexed force measurements using holographic optical tweezers. We quantify the performance of our novel video-based control system in a driven suspension of colloidal particles. We demonstrate our system's abilities with the measurement of the mechanical coupling between Aplysia bag cell growth cones and beads functionalized with the neuronal cell adhesion molecule, apCAM. We show that cells form linkages which couple beads to the underlying cytoskeleton. These linkages are intermittent, stochastic and heterogeneous across beads distributed near the leading edge of a single growth cone. PMID:19365444

Mejean, Cecile O; Schaefer, Andrew W; Millman, Eleanor A; Forscher, Paul; Dufresne, Eric R



Multiplexed force measurements on live cells with holographic optical tweezers  

PubMed Central

We describe open-loop and closed-loop multiplexed force measurements using holographic optical tweezers. We quantify the performance of our novel video-based control system in a driven suspension of colloidal particles. We demonstrate our system's abilities with the measurement of the mechanical coupling between Aplysia bag cell growth cones and beads functionalized with the neuronal cell adhesion molecule, apCAM. We show that cells form linkages which couple beads to the underlying cytoskeleton. These linkages are intermittent, stochastic and heterogeneous across beads distributed near the leading edge of a single growth cone.

Mejean, Cecile O.; Schaefer, Andrew W.; Millman, Eleanor A.; Forscher, Paul; Dufresne, Eric R.



Near-field single tractor-beam acoustical tweezers  

NASA Astrophysics Data System (ADS)

The possibility to trap a sphere in the near-field of a single-beam piston transducer is theoretically demonstrated. Conditions are found where a rigid, fluid, elastic, and viscoelastic sphere with arbitrary radius placed in the near-field and centered on the axis of a circular piezoelectric transducer vibrating uniformly, experiences a pulling force, so the acoustical waves act as a ``tractor'' beam. Numerical predictions illustrate the theory with particular emphasis on the distance from the source, the size of the transducer, and the elastic properties of the sphere. Those results can potentially suggest a simple and reliable method in designing acoustical tweezers.

Mitri, F. G.



Patterning of microspheres and microbubbles in an acoustic tweezers.  


We describe the construction of an ultrasonic device capable of micro-patterning a range of microscopic particles for bioengineering applications such as targeted drug delivery. The device is formed from seven ultrasonic transducers positioned around a heptagonal cavity. By exciting two or three transducers simultaneously, lines or hexagonal shapes can be formed with microspheres, emulsions and microbubbles. Furthermore, phase control of the transducers allows patterning at any desired position in a controlled manner. The paper discusses in detail direct positioning of functionalised microspheres, emulsions and microbubbles. With the advantages of miniaturization, rapid and simple fabrication, ultrasonic tweezers is a potentially useful tool in many biomedical applications. PMID:23225102

Bernassau, A L; Macpherson, P G A; Beeley, J; Drinkwater, B W; Cumming, D R S



Mechanical properties of a giant liposome studied using optical tweezers  

NASA Astrophysics Data System (ADS)

The mechanical properties of a micrometer-sized giant liposome are studied by deforming it from the inside using dual-beam optical tweezers. As the liposome is extended, its shape changes from a sphere to a lemon shape, and finally, a tubular part is generated. The surface tension ? and the bending rigidity ? of the lipid membrane are obtained from the measured force-extension curve. In a one-phase liposome, it was found that ? increases as the charged component increases but ? remains approximately constant. In a two-phase liposome, the characteristic deformation and the force-extension curve differ from those observed for the one-phase liposome.

Shitamichi, Yoko; Ichikawa, Masatoshi; Kimura, Yasuyuki



Hybrid optical tweezers for dynamic micro-bead arrays  

NASA Astrophysics Data System (ADS)

Dynamic micro-bead arrays offer great flexibility and potential as sensing tools in various scientific fields. Two optical trapping techniques, the GPC method using a spatial light modulator and a mechanical scanning method using galvano mirrors, are combined in a hybrid optical tweezers system to handle dynamic micro-bead arrays. This system provides greater versatility while the GPC method creates massive micro-bead arrays in a 2D space, where the trapped beads can be manipulated smoothly and very quickly in a 3D space using the mechanical scanning method. Four typical examples are demonstrated in real time.

Tanaka, Yoshio; Tsutsui, Shogo; Ishikawa, Mitsuru; Kitajima, Hiroyuki



Optical tweezers: Characterization and systems approach to high bandwidth force estimation  

NASA Astrophysics Data System (ADS)

In recent times, the hard boundaries between classical fields of sciences have almost disappeared. There is a cross-pollination of ideas between sciences, engineering and mathematics. This work investigates a modern tool of micro-manipulation of microscopic particles that is used primarily by bio-physicists and bio-chemists for single cell, single molecule studies. This tool called the Optical Tweezers can trap microscopic dielectric particles using radiation pressure of light. Optical tweezers is increasingly being used in bio-assays as it provides a means to observe bio-molecules non invasively and offers a spatial resolution in nanometers and force resolution in femto-Newtons at millisecond timescales. In this work, physics governing the operating principle behind optical tweezers is presented, followed by a step by step procedure to build an optical tweezers system having measurement and actuation capability along with a controller logic for feedback implementation. The working of optical tweezers system is presented using a spring mass damper model and the traditional methods of optical tweezers characterization are discussed. A comprehensive view of Optical tweezers is then presented from a system theoretic perspective, underlying the limitations of traditional methods of tweezers characterization that are based on the first principle. The role of feedback in Optical tweezers is presented along with the fundamental limitations that the plant model imposes on optical tweezers performance to be used as a force sensor for fast dynamics input force. The purpose of optical tweezers as a pico-newton force probe is emphasized and a classical controls based method to improve the bandwidth of force estimation using an ad-hoc approach of system inversion is presented. The efficacy of system inversion based method in improving the force probe capability of feedback enhanced optical tweezers is validated by experimental results. It is shown experimentally that the system inversion method results in an order of magnitude improvement in the bandwidth of external force estimation. Finally, a robust control strategy is presented, where the problem of estimation of high bandwidth force is casted as an H-infinity optimization problem along with other performance objectives. This strategy is then compared with the traditional method using PI-controllers and experimental results presented. The robust control strategy is found to further improve the ability of optical tweezers as a force sensor for fast changing force profile by approximately three times over the system inversion approach.

Sehgal, Hullas


Invited Article: A review of haptic optical tweezers for an interactive microworld exploration  

NASA Astrophysics Data System (ADS)

This paper is the first review of haptic optical tweezers, a new technique which associates force feedback teleoperation with optical tweezers. This technique allows users to explore the microworld by sensing and exerting picoNewton-scale forces with trapped microspheres. Haptic optical tweezers also allow improved dexterity of micromanipulation and micro-assembly. One of the challenges of this technique is to sense and magnify picoNewton-scale forces by a factor of 1012 to enable human operators to perceive interactions that they have never experienced before, such as adhesion phenomena, extremely low inertia, and high frequency dynamics of extremely small objects. The design of optical tweezers for high quality haptic feedback is challenging, given the requirements for very high sensitivity and dynamic stability. The concept, design process, and specification of optical tweezers reviewed here are focused on those intended for haptic teleoperation. In this paper, two new specific designs as well as the current state-of-the-art are presented. Moreover, the remaining important issues are identified for further developments. The initial results obtained are promising and demonstrate that optical tweezers have a significant potential for haptic exploration of the microworld. Haptic optical tweezers will become an invaluable tool for force feedback micromanipulation of biological samples and nano- and micro-assembly parts.

Pacoret, Cécile; Régnier, Stéphane



Round-tip dielectrophoresis-based tweezers for single micro-object manipulation.  


In this paper, we present an efficient methodology to manipulate a single micro-object using round-tip positive dielectrophoresis-based tweezers. The tweezers consist of a glass needle with a round-tip and a pair of thin gold-film electrodes. The round-tip, which has a radius of 3µm, is formed by melting a finely pulled glass needle and concentrates the electric field at the tip of the tweezers, which allows the individual manipulation of single micro-objects. The tweezers successfully captured, conveyed, and positioned single cell-sized liposomes with diameters of 5-23µm, which are difficult to manipulate with conventional manipulation methodologies, such as optical tweezers or glass micropipettes, due to the similarities between their optical properties and those of the media, as well as the ease with which they are deformed or broken. We used Stokes' drag theory to experimentally evaluate the positive dielectrophoresis (pDEP) force generated by the tweezers as a function of the liposome size, the content of the surrounding media, and the applied AC voltage and frequency. The results agreed with the theoretically deduced pDEP force. Finally, we demonstrated the separation of labeled single cells from non-labeled cells with the tweezers. This device can be used as an efficient tool for precisely and individually manipulating biological micro-objects that are typically transparent and flexible. PMID:23570681

Kodama, Taiga; Osaki, Toshihisa; Kawano, Ryuji; Kamiya, Koki; Miki, Norihisa; Takeuchi, Shoji



Invited Article: A review of haptic optical tweezers for an interactive microworld exploration.  


This paper is the first review of haptic optical tweezers, a new technique which associates force feedback teleoperation with optical tweezers. This technique allows users to explore the microworld by sensing and exerting picoNewton-scale forces with trapped microspheres. Haptic optical tweezers also allow improved dexterity of micromanipulation and micro-assembly. One of the challenges of this technique is to sense and magnify picoNewton-scale forces by a factor of 10(12) to enable human operators to perceive interactions that they have never experienced before, such as adhesion phenomena, extremely low inertia, and high frequency dynamics of extremely small objects. The design of optical tweezers for high quality haptic feedback is challenging, given the requirements for very high sensitivity and dynamic stability. The concept, design process, and specification of optical tweezers reviewed here are focused on those intended for haptic teleoperation. In this paper, two new specific designs as well as the current state-of-the-art are presented. Moreover, the remaining important issues are identified for further developments. The initial results obtained are promising and demonstrate that optical tweezers have a significant potential for haptic exploration of the microworld. Haptic optical tweezers will become an invaluable tool for force feedback micromanipulation of biological samples and nano- and micro-assembly parts. PMID:24007046

Pacoret, Cécile; Régnier, Stéphane



Antigen detection at atomolar concentration using optical tweezers  

NASA Astrophysics Data System (ADS)

Methods that avoid intermediate amplification steps to detect protein markers of pathological disturbances would be of wide interest in the clinical environment. This is particularly the case in cancer diagnosis, where protein fragments are released into the blood by the emerging cancer cells. These fragments generate an antigen-antibody reaction, and the concentration of the antigen is known to modulate this interaction. Here we report on the development of a novel optical tweezers-based procedure to measure minute amount of antigen in a biological fluid. The force was applied on a 3?m polystyrene bead coated with Bovine Serum Albumin (BSA) attached on a 1.5 ?m diameter borosilicate rod tip coated with anti-BSA antibody. First, we verified that the binding strength was dependent on the protein concentration on the bead. We then assessed the sensitivity range by finding the minimal BSA concentration in solution that can still interfere with the bead-rod linkage. On the whole, the results demonstrated that proteinous antigen present in a biological fluid could possibly be detectable at atomolar concentration through the use of an optical tweezers.

Laliberté, Mathieu; Bordeleau, François; Marceau, Normand; Sheng, Yunlong



Orthogonal actuation of a supramolecular double-porphyrin tweezer.  


A supramolecular three-component double-porphyrin tweezer (PT) is prepared quantitatively using heteroleptic complex formation along the HETTAP methodology. Insertion of guest molecules, such as DABCO or pyrazine, into the coupled porphyrin cavities of PT leads to an actuation of the double-porphyrin tweezer function. Evidence from (1)H NMR, VT NMR, and UV-vis titration suggests a rapid association/dissociation of the DABCO molecules at the central porphyrin. Upon addition of an equimolar mixture of DABCO and pyrazine to PT, a dynamic five-component self-assembled structure was furnished exclusively. (1)H NMR and K(assoc) values validate the greater stability of the heteroloaded PT-(DABCO)(py) system in comparison to the two homoloaded systems, PT-(DABCO)(2) and PT-(py)(2). The higher stability of PT-(DABCO)(py) seems to be the result of charge transfer from DABCO to the vacant pi* orbital of pyrazine across the porphyrin plane. PMID:20677818

Schmittel, Michael; Samanta, Soumen K



Combining confocal microscopy with precise force-scope optical tweezers  

NASA Astrophysics Data System (ADS)

We demonstrate an example of 'confocal-tweezers' wherein confocal images and precise optical force measurements, using photodiodes, are obtained simultaneously in the x-y plane without moving the objective lens. The optical trap is produced using a 1.064?m cw laser and is combined with Leica's TCS SP5 broadband confocal microscope to trap and image living cells. The unique method by which the confocal images are created facilitates the acquisition of images in areas far from the trapping location. In addition, because the scanning process involves moving galvanic mirrors independently of the objective, the trap is held stable in position and is not subject to any error in position for the x-y scan. We have successfully trapped and confocally imaged 80nm gold colloids, 150nm gold colloids and 1?m polystyrene beads whilst making quantitative measurements of the force applied by the trap on each bead. To the best of our knowledge this is the first time that anyone has combined precise force measuring optical tweezers with confocal microscopy. We also discuss some of the technical challenges involved in advancing the experimental set up to make quantitative force measurements in combination with 3D stacking. Having proven the potential of this system in 2D, we hope to develop it further to investigate the nano-mechanics of cell division through the attachment of gold beads to fluorescently labelled organelles in S. pombe yeast cells.

Richardson, Andrew C.; Reihani, Nader; Oddershede, Lene B.



Full-field OCT combined with optical tweezer  

NASA Astrophysics Data System (ADS)

We present an optical tweezer technique assisted full-field optical coherence tomography (FF-OCT) system. The proposed scheme enables ultrahigh-resolution OCT imaging of a floating object optically trapped by single-beam gradient force in medium. The set up consists of a Linnik type of white light interference microscope combined with an optical tweezer system. The optical trap is formed by tightly focusing a 1064 nm Q-switching pulsed laser beam with a microscope objective lens of high numerical aperture (1.0 NA) in sample arm of the OCT interferometer. This co-sharing of probe channel between two of systems enables concurrent actions of trapping and OCT imaging for the sample. OCT imaging of the sample in depth can achieve by positioning the coherence gating with displacement of reference arm in the OCT interferometer. To demonstrate the efficacy of the system, micron-sized dielectric particles and living cells in solution are simultaneously trapped and optically sliced with cellular resolution.

Choi, Woo June; Park, Kwan Seob; Eom, Tae Joong; Oh, Myung-Kyu; Lee, Byeong-Ha



Directing growth cones of optic axons growing with laser scissors and laser tweezers  

NASA Astrophysics Data System (ADS)

We have combined a laser scissors and a laser tweezers to study, (1) the response of nerve fiber growth cones to laser-induced damage on single axons, and (2) localized microfluidic flow generated by laser-driven spinning birefringent particles. In the laser scissors study, sub-axotomy damage elicits a growth cone response whether damage is on the same or an adjacent axon. In laser tweezers study, the axon growth cones turn in response to the optically driven microfluidic flow. In summary, both the laser scissors and the laser tweezers studies elicit growth cone turning responses.o

Wu, Tao; Nieminen, Timo A.; Mohanty, Samarendra; Miotke, Jill; Meyer, Ronald L.; Rubinsztein-Dunlop, Halina; Berns, Michael W.



Fiber-pigtailed optical tweezer for single-atom trapping and single-photon generation  

NASA Astrophysics Data System (ADS)

We demonstrate a miniature, fiber-coupled optical tweezer to trap a single atom. The same fiber is used to trap a single atom and to read out its fluorescence. To obtain a low background level, the tweezer light is chopped, and we measure the influence of the chopping frequency on the atom's lifetime. We use the single atom as a single-photon source at 780 nm and measure the second-order correlation function of the emitted photons. Because of its miniature, robust, fiber-pigtailed design, this tweezer can be implemented in a broad range of experiments where single atoms are used as a resource.

Garcia, S.; Maxein, D.; Hohmann, L.; Reichel, J.; Long, R.



Inducing trauma into neuroblastoma cells and synthetic neural networks using optical tweezers  

NASA Astrophysics Data System (ADS)

The laser tweezers have become a very useful tool in the fields of physics, chemistry, and biology. My intent is to use the laser tweezers to induce trauma into neuroblastoma cells, cells that resemble neural cells when treated with retinoic acid, to try to surmise what happens when neural cells and networks are disrupted or destroyed. The issues presented will deal with the obtaining, maintenance, and differentiation of the cells, as well as the inner operations of the laser tweezers themselves, and what kind of applications it has been applied to, as well as to my work in this project.

Schneider, Patrick William


Optical sorting of particles by dual-channel line optical tweezers  

NASA Astrophysics Data System (ADS)

A novel configuration of dual-channel line optical tweezers with a ‘Y’ shape is constructed for sorting of particles within a microfluidic chip. When yeast cells with different size pass the intersection of the specially designed line optical tweezers, they are separated and transported to different channels due to a difference in the forces exerted by the line tweezers that depends on the size of the cells. The influences of some experimental conditions, such as laser power and flow velocity, on the sorting efficiency are discussed.

Ma, Baiheng; Yao, Baoli; Peng, Fei; Yan, Shaohui; Lei, Ming; Rupp, Romano



Extending a release-and-recapture scheme to single atom optical tweezer for effective temperature evaluation  

NASA Astrophysics Data System (ADS)

By recording the fluorescence fraction of the cold atoms remaining in the magneto-optical trap (MOT) as a function of the release time, the release-and-recapture (R&R) method is utilized to evaluate the effective temperature of the cold atomic ensemble. We prepare a single atom in a large-magnetic-gradient MOT and then transfer the trapped single atom into a 1064-nm microscopic optical tweezer. The energy of the single atom trapped in the tweezer is further reduced by polarization gradient cooling (PGC) and the effective temperature is evaluated by extending the R&R technique to a single atom tweezer. The typical effective temperature of a single atom in the tweezer is improved from about 105 ?K to about 17 ?K by applying the optimum PGC phase.

He, Jun; Yang, Bao-Dong; Zhang, Tian-Cai; Wang, Jun-Min



Interrogating biology with force: single molecule high-resolution measurements with optical tweezers.  


Single molecule force spectroscopy methods, such as optical and magnetic tweezers and atomic force microscopy, have opened up the possibility to study biological processes regulated by force, dynamics of structural conformations of proteins and nucleic acids, and load-dependent kinetics of molecular interactions. Among the various tools available today, optical tweezers have recently seen great progress in terms of spatial resolution, which now allows the measurement of atomic-scale conformational changes, and temporal resolution, which has reached the limit of the microsecond-scale relaxation times of biological molecules bound to a force probe. Here, we review different strategies and experimental configurations recently developed to apply and measure force using optical tweezers. We present the latest progress that has pushed optical tweezers' spatial and temporal resolution down to today's values, discussing the experimental variables and constraints that are influencing measurement resolution and how these can be optimized depending on the biological molecule under study. PMID:24047980

Capitanio, Marco; Pavone, Francesco S



Femtosecond optical tweezers for in-situ control of two-photon fluorescence  

Microsoft Academic Search

We perform a comparison of optical tweezing using continuous wave (cw) and femtosecond lasers. Measurement of the relative Q-values in the femtosecond and cw regimes shows that femtosecond optical tweezers are just as effective as cw optical tweezers. We also demonstrate simultaneous optical tweezing and in-situ control of two-photon fluorescence (at 400nm) from dye-doped polymer microspheres. By switching the 800

B. Agate; C. T. A. Brown; W. Sibbett; K. Dholakia



The manipulation and assembly of CuO nanorods with line optical tweezers  

Microsoft Academic Search

We present a simple technique for manipulating and assembling one-dimensional (1D) CuO nanorods. Our technique exploits the optical trapping ability of line optical tweezers to trap, manipulate and rotate nanorods without physical contact. With this simple and versatile method, nanorods can be readily arranged into interesting configurations. The optical line tweezers could also be used to manipulate an individual nanorod

Ting Yu; Fook-Chiong Cheong; Chorng-Haur Sow



New theoretical and experimental methods for the design of fiber optic tweezers  

NASA Astrophysics Data System (ADS)

This paper presents a study of optical forces acting on dielectric particles in media of distinct refractive index. The radiation pressure forces produced by optical tweezers are calculated using the finite difference time domain method as well as the Lorentz force on electric dipoles. The model considers a 2-dimension structure composed of a waveguide and a dielectric microparticle. Furthermore, the paper presents preliminary experimental results concerning the implementation of fiber optical tweezers system based on polymeric lensed fibers.

Rodrigues Ribeiro, R. S.; Guerreiro, A.; Ecoffet, C.; Soppera, O.; Jorge, P. A. S.



Chromosomal analysis and identification based on optical tweezers and Raman spectroscopy: comment  

NASA Astrophysics Data System (ADS)

The authors of the work: ‘Chromosomal analysis and identification based on optical tweezers and raman spectroscopy’ [Opt. Express 14, 5385 (2006], claim that they have been able to identify and differentiate between three human chromosomes with an optical-tweezer Raman Spectroscopic experimental (LTRS) set-up. The results and conclusions as they are presented in the paper are questionable, however, when the spectral data and data analysis are studied in greater detail.

Bak, Jimmy; Jørgensen, Thomas M.



Robust control approach to force estimation in a constant position optical tweezers  

NASA Astrophysics Data System (ADS)

Feedback enhanced optical tweezers with position regulation capability enable detection and estimation of forces in the pico-Newton regime. In this article we delineate the fundamental limitations and challenges of existing approaches for regulating position and force estimation in an optical tweezer. A modern control systems approach is shown to improve the bandwidth of force estimation by three to four times which is corroborated experimentally.

Aggarwal, Tanuj; Sehgal, Hullas; Salapaka, Murti



Measurement of interaction forces between red blood cells in aggregates by optical tweezers  

NASA Astrophysics Data System (ADS)

We have fabricated double-beam optical tweezers and demonstrated the possibility of their use for measuring the interaction forces between red blood cells (erythrocytes). It has been established experimentally that prolonged trapping of red blood cells in a tightly focused laser beam does not cause any visible changes in their shape or size. We have measured the interaction between red blood cells in the aggregate, deformed by optical tweezers.

Maklygin, A. Yu; Priezzhev, A. V.; Karmenian, A.; Nikitin, Sergei Yu; Obolenskii, I. S.; Lugovtsov, Andrei E.; Li, Kisun



Compact microscope-based 850-nm optical tweezers  

NASA Astrophysics Data System (ADS)

Emission from a single mode 100 mW laser diode at 850 nm is used for realizing optical tweezers: the laser beam is introduced into a microscope and focused by the objective into the object plane. Injection of the beam into a 40X microscope objective has been studied and the position and the size of the waist measured. The trap performance was studied as a function of the dimensions of the trapped particles. Trapping of polystyrene latex spheres of different size (from 0.2 micrometer to 6 micrometer) was observed in different conditions of laser power and transverse velocity of the spheres. Biological objects, Tetraselmis, of large dimension (around 10 micrometer) were also studied. We demonstrate the existence of an optimal range of size of the particles to be trapped. Furthermore we measure minimum trapping power required for trapping and the maximum speed of the trapped objects as a function of the dimensions.

Frediani, Carlo; Grego, S.; Guidoni, L.; Arimondo, Ennio



Non-conservative forces in optical tweezers and Brownian vortexes  

NASA Astrophysics Data System (ADS)

Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static, but non-conservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle's thermally-driven trajectory is not simply a deterministic response to the solenoidal component of the force, but rather reflects an interplay between advection and diffusion in which thermal fluctuations extract work from the non-conservative force field. As an example of this previously unrecognized class of stochastic machines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that non-conservative optical forces bias the particle's fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power.

Sun, Bo; Grosberg, Alexander Y.; Grier, David G.



Operational Regimes and Physics Present in Optoelectronic Tweezers  

PubMed Central

Optoelectronic tweezers (OET) are a powerful light-based technique for the manipulation of micro- and nanoscopic particles. In addition to an optically patterned dielectrophoresis (DEP) force, other light-induced electrokinetic and thermal effects occur in the OET device. In this paper, we present a comprehensive theoretical and experimental investigation of various fluidic, optical, and electrical effects present during OET operation. These effects include DEP, light-induced ac electroosmosis, electrothermal flow, and buoyancy-driven flow. We present finite-element modeling of these effects to establish the dominant mode for a given set of device parameters and bias conditions. These results are confirmed experimentally and present a comprehensive outline of the operational regimes of the OET device.

Valley, Justin K.; Jamshidi, Arash; Ohta, Aaron T.; Hsu, Hsan-Yin; Wu, Ming C.



Further Development of the Laser Tweezers Technique for Biomedical Applications  

NASA Astrophysics Data System (ADS)

The results of the experimental work aimed at a functional enhancement of the existing laser tweezers system by introducing a pixel-addressable liquid-crystal spatial light modulator (Holoeye HEO-1080P) are presented. The use of the modulator allows us to generate light fields of complicated structure including ones with the vortex component and control the objects positions in real time. The special software is developed to form an array of optical traps with the number of elements up to thirty two with the capability of individual or subgroup control. The method of a spatial separation of the modulator aperture is implemented. The ability to control the lateral power distribution of the light field as well as the value of its orbital moment brings new possibilities of a precise manipulation of microobjects including biological ones.

Afanasiev, K.; Korobtsov, A.; Kotova, S.; Losevsky, N.; Mayorova, A.; Patlan, V.; Volostnikov, V.



Combined holographic-mechanical optical tweezers: Construction, optimization, and calibration  

SciTech Connect

A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers setup. This provides great flexibility as the SLM creates an array of traps, which can be moved smoothly and quickly with the GMM. To optimize performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45 deg., smaller angles give a full 2{pi} phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.

Hanes, Richard D. L.; Jenkins, Matthew C.; Egelhaaf, Stefan U. [Condensed Matter Physics Laboratory, Heinrich-Heine University, 40225 Duesseldorf (Germany)



Peculiarities of RBC aggregation studied by double trap optical tweezers  

NASA Astrophysics Data System (ADS)

Aggregation peculiarities of red blood cells (RBCs) in autologous plasma are studied using double trap optical tweezers technique. The positions of RBCs are controlled with submicrometer accuracy by two optical traps formed by strongly focused laser beams (?=1064 nm). Quantitative measurements of interaction forces between RBCs in pair aggregates are performed. Depending on the RBCs aggregation force, four different end-points of disaggregation induced by optical trap movement are revealed. Analysis of experimental force dependence on the distance between two RBCs during disaggregation is in a good agreement with the model of ring-shaped interaction surfaces of RBCs in pair aggregate. Aggregation velocities measured are shown to be strongly different for healthy and pathologic (System Lupus Erythematosis - SLE) blood samples.

Khokhlova, Maria D.; Lyubin, Evgeny V.; Zhdanov, Alexander G.; Rykova, Sofia Yu.; Krasnova, Tatyana N.; Sokolova, Irina A.; Fedyanin, Andrey A.



Probing Micromechanical Properties of Biological Cells by Oscillatory Optical Tweezers  

NASA Astrophysics Data System (ADS)

We used oscillatory optical tweezers to probe the micromechanical properties of cultured alveolar epithelial cells in vitro. The frequency-dependent viscoelasticity of these cells was measured by optical trapping and forced oscillation of either a submicron endogenous intracellular organelle (intra-cellular) or a 1.5?m silica bead attached to the cytoskeleton through trans-membrane integrin receptors (extra-cellular). Both the storage modulus and the magnitude of the complex shear modulus followed weak power-law dependence with frequency. These data are comparable to data obtained by other measurement techniques. The exponents of power-law dependence of the data from the intra- and extra- cellular measurements are similar, whereas, the differences in the magnitudes of the moluli from the two measurements are statistically significant.

Zaorski, Angela; Wei, Ming-Tzo; Yalcin, Huseyin C.; Wang, Jing; Ghadiali, Samir N.; Chiou, Arthur; Ou-Yang, H. Daniel



Dynamic excitations in membranes induced by optical tweezers.  

PubMed Central

We present the phenomenology of transformations in lipid bilayers that are excited by laser tweezers. A variety of dynamic instabilities and shape transformations are observed, including the pearling instability, expulsion of vesicles, and more exotic ones, such as the formation of passages. Our physical picture of the laser-membrane interaction is based on the generation of tension in the bilayer and loss of surface area. Although tension is the origin of the pearling instability, it does not suffice to explain expulsion of vesicles, where we observe opening of giant pores and creeping motion of bilayers. We present a quantitative theoretical framework to understand most of the observed phenomenology. The main hypothesis is that lipid is pulled into the optical trap by the familiar dielectric effect, is disrupted, and finally is repackaged into an optically unresolvable suspension of colloidal particles. This suspension, in turn, can produce osmotic pressure and depletion forces, driving the observed transformations.

Bar-Ziv, R; Moses, E; Nelson, P



Fiber optical tweezers for microscale and nanoscale particle manipulation and force sensing  

NASA Astrophysics Data System (ADS)

Optical tweezers have been an important tool in biology and physics for studying single molecules and colloidal systems. Most of current optical tweezers are built with microscope objectives, which are: i) expensive, ii) bulky and hard to integrate, iii) sensitive to environmental fluctuations, iv) limited in terms of working distances from the substrate, and v) rigid with the requirements on the substrate (transparent substrate made with glass and with a fixed thickness). These limitations of objective-based optical tweezers prevent them from being miniaturized. Fiber optical tweezers can provide a solution for cost reduction and miniaturization, and these optical tweezers can be potentially used in microfluidic systems. However, the existing fiber optical tweezers have the following limitations: i) low trapping efficiency due to weakly focused beams, ii) lack of the ability to control the positions of multiple particles simultaneously, and iii) limited functionalities. The overall objective of this dissertation work is to further the fundamental understanding of fiber optical tweezers through experimental study and modeling, and to develop novel fiber optical tweezers systems to enhance the capability and functionalities of fiber optical tweezers as microscale and nanoscale manipulators/sensors. The contributions of this dissertation work are summarized as follows. i) An enhanced understanding of the inclined dual-fiber optical tweezers (DFOTs) system has been achieved. Stable three dimensional (3D) optical trapping of a single micron-sized particle has been experimentally demonstrated. This is the first time that the trapping efficiency has been calibrated and the stiffness of the trap has been obtained in the experiments, which has been carried out by using two methods: the drag force method and power spectrum analysis. Such calibration enables the system to be used as a picoNewton-level force sensor in addition to a particle manipulator. The influence of system parameters on the trapping performance has been carefully investigated through both experimental and numerical studies. ii) Multiple traps have been created and carefully studied with the inclined DFOTs for the first time. Three traps, one 3D trap and two 2D traps, have been experimentally created at different vertical levels with adjustable separations and positions. iii) Multiple functionalities have been achieved and studied for the first time with the inclined DFOTs. Particle separation, grouping, stacking, rod alignment, rod rotation, and optical binding have been experimentally demonstrated. The multiple functionalities allow the inclined DFOTs to find applications in the study of interaction forces in colloidal systems as well as parallel particle manipulation in drug delivery systems. iv) Far-field superfocusing effect has been investigated and successfully demonstrated with a fiber-based surface plasmonic (SP) lens for the first time. A planar SP lens with a set of concentric nanoscale rings on a fiber endface has been developed. For the first time, a focus size that is comparable to the smallest achievable focus size of high NA objective lenses has been achieved with the fiber-based SP lens. The fiber-based SP lens can bridge the nanoscale particles/systems and the macroscale power sources/detectors, which has been a long standing challenge for nanophotonics. In addition to optical trapping, the fiber-based SP lens will impact many applications including high-resolution lithography, high-resolution fluorescence detection, and sub-wavelength imaging. v) Trapping ability enhanced with the fiber-based SP lens has been successfully demonstrated. With the help of the fiber-based SP lens, the trapping efficiency of fiber optical tweezers has been significantly enhanced, which is comparable with that of objective-based optical tweezers. A submicron-sized bacterium has been successfully trapped in three dimensions for the first time with optical tweezers based on single fibers.

Liu, Yuxiang


Mapping force of interaction between PLGA nanoparticle with cell membrane using optical tweezers  

NASA Astrophysics Data System (ADS)

Drug delivery using magnetic (Fe3O4) Poly Lactic-co-Glycolic Acid (PLGA) nanoparticles is finding increasing usage in therapeutic applications due to its biodegradability, biocompatibility and targeted localization. Since optical tweezers allow non-contact, highly sensitive force measurement, we utilized optical tweezers for studying interaction forces between the Fe3O4-PLGA nanoparticles with prostate cancer PC3 cells. Presence of Fe3O4 within the PLGA shell allowed efficient trapping of these nanoparticles in near-IR optical tweezers. The conglomerated PLGA nanoparticles could be dispersed by use of the optical tweezers. Calibration of trapping stiffness as a function of laser beam power was carried out using equipartition theorem method, where the mean square displacement was measured with high precision using time-lapse fluorescence imaging of the nanoparticles. After the trapped PLGA nanoparticle was brought in close vicinity of the PC3 cell membrane, displacement of the nanoparticle from trap center was measured as a function of time. In short time scale (< 30sec), while the force of interaction was within 0.2 pN, the force increased beyond 1pN at longer time scales (˜ 10 min). We will present the results of the time-varying force of interactions between PLGA nanoparticles with PC3 cells using optical tweezers.

Chhajed, Suyash; Gu, Ling; Homayoni, Homa; Nguyen, Kytai; Mohanty, Samarendra



Axial optical trapping forces on two particles trapped simultaneously by optical tweezers  

SciTech Connect

Optical tweezers, which utilize radiation pressure to control and manipulate microscopic particles, are used for a large number of applications in biology and colloid science. In most applications a single optical tweezers is used to control one single particle. However, two or more particles can be trapped simultaneously. Although this characteristic has been used in applications, no theoretical analysis of the trapping force or the status of the trapped particles is available to our knowledge. We present our calculation, using a ray optics model, of the axial trapping forces on two rigid particles trapped in optical tweezers. The spherical aberration that results from a mismatch of the refractive indices of oil and water is also considered. The results show that the forces exerted by the optical tweezers on the two particles will cause the two particles to touch each other, and the two particles can be stably trapped at a joint equilibrium point. We also discuss the stability of axial trapping. The calculation will be useful in applications of optical tweezers to trap multiple particles.

Xu Shenghua; Li Yinmei; Lou Liren



Multiplexed single-molecule measurements with magnetic tweezers.  


We present a method for performing multiple single-molecule manipulation experiments in parallel with magnetic tweezers. We use a microscope with a low magnification, and thus a wide field of view, to visualize multiple DNA-tethered paramagnetic beads and apply an optimized image analysis routine to track the three-dimensional position of each bead simultaneously in real time. Force is applied to each bead using an externally applied magnetic field. Since variations in the field parameters are negligible across the field of view, nearly identical manipulation of all visible beads is possible. However, we find that the error in the position measurement is inversely proportional to the microscope's magnification. To mitigate the increased error caused by demagnification, we have developed a strategy based on tracking multiple fixed beads. Our system is capable of simultaneously manipulating and tracking up to 34 DNA-tethered beads at 60 Hz with approximately 1.5 nm resolution and with approximately 10% variation in applied force. PMID:19044437

Ribeck, Noah; Saleh, Omar A



Particle interaction measurements using laser tweezers optical trapping.  

SciTech Connect

Laser tweezers optical trapping provides a unique noninvasive capability to trap and manipulate particles in solution at the focal point of a laser beam passed through a microscope objective. Additionally, combined with image analysis, interaction forces between colloidal particles can be quantitatively measured. By looking at the displacement of particles within the laser trap due to the presence of a neighboring particle or looking at the relative diffusion of two particles held near each other by optical traps, interparticle interaction forces ranging from pico- to femto-Newtons can be measured. Understanding interaction forces is critical for predicting the behavior of particle dispersions including dispersion stability and flow rheology. Using a new analysis method proposed by Sainis, Germain, and Dufresne, we can simultaneously calculate the interparticle velocity and particle diffusivity which allows direct calculation of the interparticle potential for the particles. By applying this versatile tool, we measure difference in interactions between various phospholipid bilayers that have been coated onto silica spheres as a new type of solid supported liposome. We measure bilayer interactions of several cell membrane lipids under various environmental conditions such as pH and ionic strength and compare the results with those obtained for empty liposomes. These results provide insight into the role of bilayer fluctuations in liposome fusion, which is of fundamental interest to liposome based drug delivery schemes.

Koehler, Timothy P.; Brinker, C. Jeffrey; Brotherton, Christopher M.; Grillet, Anne M.; Molecke, Ryan A. (University of New Mexico, Albuquerque, NM)



Torsional sensing of small-molecule binding using magnetic tweezers  

PubMed Central

DNA-binding small molecules are widespread in the cell and heavily used in biological applications. Here, we use magnetic tweezers, which control the force and torque applied to single DNAs, to study three small molecules: ethidium bromide (EtBr), a well-known intercalator; netropsin, a minor-groove binding anti-microbial drug; and topotecan, a clinically used anti-tumor drug. In the low-force limit in which biologically relevant torques can be accessed (<10?pN), we show that ethidium intercalation lengthens DNA ?1.5-fold and decreases the persistence length, from which we extract binding constants. Using our control of supercoiling, we measure the decrease in DNA twist per intercalation to be 27.3?±?1° and demonstrate that ethidium binding delays the accumulation of torsional stress in DNA, likely via direct reduction of the torsional modulus and torque-dependent binding. Furthermore, we observe that EtBr stabilizes the DNA duplex in regimes where bare DNA undergoes structural transitions. In contrast, minor groove binding by netropsin affects neither the contour nor persistence length significantly, yet increases the twist per base of DNA. Finally, we show that topotecan binding has consequences similar to those of EtBr, providing evidence for an intercalative binding mode. These insights into the torsional consequences of ligand binding can help elucidate the effects of small-molecule drugs in the cellular environment.

Lipfert, Jan; Klijnhout, Sven; Dekker, Nynke H.



Probing the bulk viscosity of particles using aerosol optical tweezers  

NASA Astrophysics Data System (ADS)

Holographic aerosol optical tweezers can be used to trap arrays of aerosol particles allowing detailed studies of particle properties and processes at the single particle level. Recent observations have suggested that secondary organic aerosol may exist as ultra-viscous liquids or glassy states at low relative humidity, potentially a significant factor in influencing their role in the atmosphere and their activation to form cloud droplets. A decrease in relative humidity surrounding a particle leads to an increased concentration of solute in the droplet as the droplet returns to equilibrium and, thus, an increase in the bulk viscosity. We demonstrate that the timescales for condensation and evaporation processes correlate with particle viscosity, showing significant inhibition in mass transfer kinetics using ternary sucrose/sodium chloride/water droplets as a proxy to atmospheric multi-component aerosol. We go on to study the fundamental process of aerosol coagulation in aerosol particle arrays, observing the relaxation of non-spherical composite particles formed on coalescence. We demonstrate the use of bright-field imaging and elastic light scattering to make measurements of the timescale for the process of binary coalescence contrasting the rheological properties of aqueous sucrose and sodium chloride aerosol over a range of relative humidities.

Power, Rory; Bones, David L.; Reid, Jonathan P.



Multiplexed single-molecule measurements with magnetic tweezers  

SciTech Connect

We present a method for performing multiple single-molecule manipulation experiments in parallel with magnetic tweezers. We use a microscope with a low magnification, and thus a wide field of view, to visualize multiple DNA-tethered paramagnetic beads and apply an optimized image analysis routine to track the three-dimensional position of each bead simultaneously in real time. Force is applied to each bead using an externally applied magnetic field. Since variations in the field parameters are negligible across the field of view, nearly identical manipulation of all visible beads is possible. However, we find that the error in the position measurement is inversely proportional to the microscope's magnification. To mitigate the increased error caused by demagnification, we have developed a strategy based on tracking multiple fixed beads. Our system is capable of simultaneously manipulating and tracking up to 34 DNA-tethered beads at 60 Hz with {approx}1.5 nm resolution and with {approx}10% variation in applied force.

Ribeck, Noah [Physics Department, University of California, Santa Barbara, Santa Barbara, California 93106 (United States); Saleh, Omar A. [Materials Department and Biomolecular Science and Engineering Program, University of California, Santa Barbara, Santa Barbara, California 93106 (United States)



Manipulation of Suspended Single Cells by Microfluidics and Optical Tweezers  

PubMed Central

Chondrocytes and osteoblasts experience multiple stresses in vivo. The optimum mechanical conditions for cell health are not fully understood. This paper describes the optical and microfluidic mechanical manipulation of single suspended cells enabled by the ?PIVOT, an integrated micron resolution particle image velocimeter (?PIV) and dual optical tweezers instrument (OT). In this study, we examine the viability and trap stiffness of cartilage cells, identify the maximum fluid-induced stresses possible in uniform and extensional flows, and compare the deformation characteristics of bone and muscle cells. These results indicate cell photodamage of chondrocytes is negligible for at least 20 min for laser powers below 30 mW, a dead cell presents less resistance to internal organelle rearrangement and deforms globally more than a viable cell, the maximum fluid-induced shear stresses are limited to ~15 mPa for uniform flows but may exceed 1 Pa for extensional flows, and osteoblasts show no deformation for shear stresses up to 250 mPa while myoblasts are more easily deformed and exhibit a modulated response to increasing stress. This suggests that global and/or local stresses can be applied to single cells without physical contact. Coupled with microfluidic sensors, these manipulations may provide unique methods to explore single cell biomechanics.

Neve, Nathalie; Kohles, Sean S.; Winn, Shelley R.; Tretheway, Derek C.



Graded-index fiber tip optical tweezers: numerical simulation and trapping experiment.  


Optical fiber tweezers based on a graded-index multimode fiber (GIMMF) tip is proposed. Light propagation characteristics and gradient force distribution near the GIMMF tip are numerically investigated, which are further compared with that of optical fiber tips based on conventional single mode fibers. The simulated results indicated that by selecting optimal GIMMF length, the gradient force of the GIMMF tip tweezers is about 4 times higher than that of the SMF tip tweezers with a same shape. To prove the feasibility of such a new concept, optical trapping of yeast cells with a diameter of ~5 ?m using the chemically-etched GIMMF tip is experimentally demonstrated and the trapping force is also calculated. PMID:23842403

Gong, Yuan; Ye, Ai-Yan; Wu, Yu; Rao, Yun-Jiang; Yao, Yao; Xiao, Song



Silicon photonics for functional on-chip optical tweezers devices and circuits  

NASA Astrophysics Data System (ADS)

Silicon photonics using waveguide- and microresonator-based devices are finding technologically important applications in the field of optofluidics. By integrating microfluidic channels on top of silicon-based planar devices, silicon photonic devices can function as on-chip optical tweezers to manipulate micro/nanoparticles. In this paper, we will highlight our recent progress in the field of optofluidics using silicon nitride devices for on-chip optical manipulation including the experimental demonstrations of: (i) planar optical tweezers using waveguide junctions with and without tapers, (ii) microparticle buffering and dropping on microring resonator devices upon linearly polarized light and (iii) microparticle trapping and assembling on circular microdisk resonators. Such devices can function as basic building blocks for "optical tweezers circuits" in lab-on-chip applications.

Cai, Hong; Wang, Jiawei; Poon, Andrew W.



Dynamic Simulation of Trapping and Controlled Rotation of a Microscale Rod Driven by Line Optical Tweezers  

NASA Astrophysics Data System (ADS)

Since the invention of optical tweezers, several biological and engineering applications, especially in micro-nanofluid, have been developed. For example, development of optically driven micromotors, which has an important role in microfluidic applications, has vastly been considered. Despite extensive experimental studies in this field, there is a lack of theoretical work that can verify and analyze these observations. This work develops a dynamic model to simulate trapping and controlled rotation of a microscale rod under influence of the optical trapping forces. The laser beam, used in line optical tweezers with a varying trap's length, was modeled based on a ray-optics approach. Herein, the effects of viscosity of the surrounding fluid (water), gravity, and buoyancy were included in the proposed model. The predicted results are in overall agreement with the experimental observation, which make the theoretical model be a viable tool for investigating the dynamic behavior of small size objects manipulated by optical tweezers in fluid environments.

Haghshenas-Jaryani, Mahdi; Bowling, Alan; Mohanty, Samarendra



A computational tool to characterize particle tracking measurements in optical tweezers  

NASA Astrophysics Data System (ADS)

Here, we present a computational tool for optical tweezers which calculates the particle tracking signal measured with a quadrant detector and the shot-noise limit to position resolution. The tool is a piece of Matlab code which functions within the freely available Optical Tweezers Toolbox. It allows the measurements performed in most optical tweezer experiments to be theoretically characterized in a fast and easy manner. The code supports particles with arbitrary size, any optical fields and any combination of objective and condenser, and performs a full vector calculation of the relevant fields. Example calculations are presented which show the tracking signals for different particles, and the shot-noise limit to position sensitivity as a function of the effective condenser NA.

Taylor, Michael A.; Bowen, Warwick P.



RBCs under optical tweezers as cellular motors and rockers: microfluidic applications  

NASA Astrophysics Data System (ADS)

Recently, we have reported self-rotation of normal red blood cells (RBC), suspended in hypertonic buffer, and trapped in unpolarized laser tweezers. Here, we report use of such an optically driven RBC-motor for microfluidic applications such as pumping/centrifugation of fluids. Since the speed of rotation of the RBC-motor was found to vary with the power of the trapping beam, the flow rate could be controlled by controlling the laser power. In polarized optical tweezers, preferential alignment of trapped RBC was observed. The aligned RBC (simulating a disk) in isotonic buffer, could be rotated in a controlled manner for use as a microfluidic valve by rotation of the plane of polarization of the trapping beam. The thickness of the discotic RBC could be changed by changing the osmolarity of the solution and thus the alignment torque on the RBC due to the polarization of the trapping beam could be varied. Further, in polarized tweezers, the RBCs in hypertonic buffer showed rocking motion while being in rotation. Here, the RBC rotated over a finite angular range, stopped for some time at a particular angle, and then started rotating till it was back to the aligned position and this cycle was found repetitive. This can be attributed to the fact that though the RBCs were found to experience an alignment torque to align with plane of polarization of the tweezers due to its form birefringence, it was smaller in magnitude as compared to the rotational torque due to its structural asymmetry in hypertonic solution. Changes in the laser power caused a transition from/to rocking to/from motor behavior of the RBC in a linearly polarized tweezers. By changing the direction of polarization caused by rotation of an external half wave plate, the stopping angle of rocking could be changed. Further, RBCs suspended in intermediate hypertonic buffer and trapped with polarized tweezers showed fluttering about the vertical plane.

Mohanty, Samarendra; Mohanty, Khyati; Gupta, Pradeep



Applications of optical tweezers and an integrated force measurement module for biomedical research  

NASA Astrophysics Data System (ADS)

Optical tweezers are useful for manipulating biological samples and measuring biological forces. In the present study, we have integrated a forward scatter analysis (FORSA) module in the single-beam gradient force optical tweezers. The entire set-up was then incorporated onto an inverted microscope. In the FORSA module an Helium-Neon probing laser was spotted (at a slightly out-of-focus way) onto the object being trapped by the infrared laser-based tweezers and generated a diffraction pattern. Imagines of the diffraction pattern were captured by a charge- coupled device (CCD), and digitized and processed by a computer. Wed demonstrated that tracking the amplified diffraction pattern war much more precise to determine the movement of the object within the trap than analyzing the minute motion of the object itself. Displacement of the object could then be translated into the force being applied by the tweezers. Also, using an algorithm developed in the lab, we were able to follow the movement of the scattering pattern at a temporal resolution close to video rate. We have used this system to investigate the binding force associate with cell-cell interactions and modular interactions. In these studies. A cell was carefully positioned to make contact with another cell or a microparticle coated with proteins of interest by optical tweezers in a well-controlled manner. During these events, we noted a progressive increase of cell adhesion at the immediate early period (i.e., a few minutes after initial contact) of cell-cell interactions. Also, binding of a disintegrin, rhodostomin, and its mutant to the counterpart integrin on the cell surface could be assessed with great convenience and accuracy. Our results demonstrated that addition of the forward scatter analysis module to convention optical tweezers provides an effective and convenient way for monitoring biological activities in situ and measuring changes of biological forces with precision.

Tsai, Jin-Wu; Liao, Bing-Yao; Huang, Chun-Cheng; Hwang, Wen-Liang; Wang, Da-Wei; Chiou, Arthur E.; Lin, Chi-Hung



Rate of growth pattern of yeast cells studied under optical tweezers  

NASA Astrophysics Data System (ADS)

Cell growth and division has been of scientists' interest for over generations. Several mathematical models have been reported derived from conventional method of cell culture. Here we applied optical tweezers to guide cell division directionally. The patterns of Saccharonmyces bayanus yeast growth was studied under 1064 nm line optical tweezers generated by time-shared multiple optical traps. Yeast growth was found following the path of the generated laser patterns in linear, circular, square and L shapes, speculatively as a result of localized heating effect due to absorption at the focal point.

Charrunchon, Sookpichaya; Limtrakul, Jumras; Chattham, Nattaporn



Improved High-Force Magnetic Tweezers for Stretching and Refolding of Proteins and Short DNA  

PubMed Central

Although magnetic tweezers have many unique advantages in terms of specificity, throughput, and force stability, this tool has had limited application on short tethers because accurate measurement of force has been difficult for short tethers under large tension. Here, we report a method that allows us to apply magnetic tweezers to stretch short biomolecules with accurate force calibration over a wide range of up to 100 pN. We demonstrate the use of the method by overstretching of a short DNA and unfolding/refolding a protein of filamin A immunoglobulin domains 1–8. Other potential applications of this method are also discussed.

Chen, Hu; Fu, Hongxia; Zhu, Xiaoying; Cong, Peiwen; Nakamura, Fumihiko; Yan, Jie



Ring-shaped NdFeB-based magnetic tweezers enables oscillatory microrheology measurements  

NASA Astrophysics Data System (ADS)

We present the design and characterization of a magnetic tweezers device that employs a ring-shaped neodymium iron boron (NdFeB) magnet. Because the gradient of the magnetic field generated by ring magnets changes sign along its symmetry axis, magnetic tweezers devices that employ ring magnets can both push and pull on microscale magnetic beads, opening new avenues for the micromanipulation of soft materials. We demonstrate the application of such a device to oscillatory microrheology measurements of soft networks of microtubules, an essential cellular biopolymer.

Lin, Jun; Valentine, Megan T.



Mechanical and electrical properties of red blood cells using optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are a very sensitive tool, based on photon momentum transfer, for individual, cell by cell, manipulation and measurements, which can be applied to obtain important properties of erythrocytes for clinical and research purposes. Mechanical and electrical properties of erythrocytes are critical parameters for stored cells in transfusion centers, immunohematological tests performed in transfusional routines and in blood diseases. In this work, we showed methods, based on optical tweezers, to study red blood cells and applied them to measure apparent overall elasticity, apparent membrane viscosity, zeta potential, thickness of the double layer of electrical charges and adhesion in red blood cells.

Fontes, A.; Barjas Castro, M. L.; Brandão, M. M.; Fernandes, H. P.; Thomaz, A. A.; Huruta, R. R.; Pozzo, L. Y.; Barbosa, L. C.; Costa, F. F.; Saad, S. T. O.; Cesar, C. L.



On-site manipulation of single whole-genome DNA molecules using optical tweezers  

NASA Astrophysics Data System (ADS)

In this letter, we describe a noninvasive methodology for manipulating single Mb-size whole-genome DNA molecules. Cells were subjected to osmotic shock and the genome DNA released from the burst cells was transferred to a region of higher salt concentration using optical tweezers. The transferred genome DNA exhibits a conformational transition from a compact state into an elongated state, accompanied by the change in its environment. The applicability of optical tweezers to the on-site manipulation of giant genome DNA is suggested, i.e., lab-on-a-plate.

Oana, Hidehiro; Kubo, Koji; Yoshikawa, Kenichi; Atomi, Haruyuki; Imanaka, Tadayuki



Investigating intermolecular forces associated with thrombus initiation using optical tweezers  

NASA Astrophysics Data System (ADS)

Thrombus formation occurs when a platelet membrane receptor, glycoprotein (GP) Ib-IX-V complex, binds to its ligand, von Willebrand factor (vWf), in the subendothelium or plasma. To determine which GP Ib-IX-V amino acid sequences are critical for bond formation, we have used optical tweezers to measure forces involved in the binding of vWf to GP Ib-IX-V variants. Inasmuch as GP Ib(alpha) subunit is the primary component in human GP Ib-IX-V complex that binds to vWf, and that canine GP Ib(alpha) , on the other hand, does not bind to human vWf, we progressively replaced human GP Ib(alpha) amino acid sequences with canine GP Ib(alpha) sequences to determine the sequences essential for vWf/GP Ib(alpha) binding. After measuring the adhesive forces between optically trapped, vWf-coated beads and GP Ib(alpha) variants expressed on mammalian cells, we determined that leucine- rich repeat 2 of GP Ib(alpha) was necessary for vWf/GP Ib-IX- V bond formation. We also found that deletion of the N- terminal flanking sequence and leucine-rich repeat 1 reduced adhesion strength to vWf but did not abolish binding. While divalent cations are known to influence binding of vWf, addition of 1mM CaCl2 had no effect on measured vWf/GP Ib(alpha) bond strengths.

Arya, Maneesh; Lopez, Jose A.; Romo, Gabriel M.; Dong, Jing-Fei; McIntire, Larry V.; Moake, Joel L.; Anvari, Bahman



Mechanical properties of stored red blood cells using optical tweezers  

NASA Astrophysics Data System (ADS)

We have developed a method for measuring the red blood cell (RBC) membrane overall elasticity ? by measuring the deformation of the cells when dragged at a constant velocity through a plasma fluid by an optical tweezers. The deformability of erythrocytes is a critical determinant of blood flow in the microcirculation. We tested our method and hydrodynamic models, which included the presence of two walls, by measuring the RBC deformation as a function of drag velocity and of the distance to the walls. The capability and sensitivity of this method can be evaluated by its application to a variety of studies, such as, the measurement of RBC elasticity of sickle cell anemia patients comparing homozygous (HbSS), including patients taking hydroxyrea (HU) and heterozygous (HbAS) with normal donors and the RBC elasticity measurement of gamma irradiated stored blood for transfusion to immunosupressed patients as a function of time and dose. These studies show that the technique has the sensitivity to discriminate heterozygous and homozygous sickle cell anemia patients from normal donors and even follow the course of HU treatment of Homozygous patients. The gamma irradiation studies show that there is no significant change in RBC elasticity over time for up to 14 days of storage, regardless of whether the unit was irradiated or not, but there was a huge change in the measured elasticity for the RBC units stored for more than 21 days after irradiation. These finds are important for the assessment of stored irradiated RBC viability for transfusion purposes because the present protocol consider 28 storage days after irradiation as the limit for the RBC usage.

Fontes, Adriana; Alexandre de Thomaz, Andre; de Ysasa Pozzo, Liliana; de Lourdes Barjas-Castro, Maria; Brandao, Marcelo M.; Saad, Sara T. O.; Barbosa, Luiz Carlos; Cesar, Carlos Lenz



Refractive multiple optical tweezers for parallel biochemical analysis in micro-fluidics  

NASA Astrophysics Data System (ADS)

We present a multiple laser tweezers system based on refractive optics. The system produces an array of 100 optical traps thanks to a refractive microlens array, whose focal plane is imaged into the focal plane of a high-NA microscope objective. This refractive multi-tweezers system is combined to micro-fluidics, aiming at performing simultaneous biochemical reactions on ensembles of free floating objects. Micro-fluidics allows both transporting the particles to the trapping area, and conveying biochemical reagents to the trapped particles. Parallel trapping in micro-fluidics is achieved with polystyrene beads as well as with native vesicles produced from mammalian cells. The traps can hold objects against fluid flows exceeding 100 micrometers per second. Parallel fluorescence excitation and detection on the ensemble of trapped particles is also demonstrated. Additionally, the system is capable of selectively and individually releasing particles from the tweezers array using a complementary steerable laser beam. Strategies for high-yield particle capture and individual particle release in a micro-fluidic environment are discussed. A comparison with diffractive optical tweezers enhances the pros and cons of refractive systems.

Merenda, Fabrice; Rohner, Johann; Pascoal, Pedro; Fournier, Jean-Marc; Vogel, Horst; Salathé, René P.



Research Advances: Nanoscale Molecular Tweezers; Cinnamon as Pesticide?; Recently Identified Dietary Sources of Antioxidants  

NASA Astrophysics Data System (ADS)

This Report from Other Journals surveys articles of interest to chemists that have been recently published in other science journals. Topics surveyed include reports that receptors have been designed to act as molecular tweezers; cinnamon has potential in the fight against mosquitoes; and high levels of antioxidants are found in some surprising foods. See Featured Molecules .

King, Angela G.



Molecular tweezers modulate 14-3-3 protein-protein interactions  

NASA Astrophysics Data System (ADS)

Supramolecular chemistry has recently emerged as a promising way to modulate protein functions, but devising molecules that will interact with a protein in the desired manner is difficult as many competing interactions exist in a biological environment (with solvents, salts or different sites for the target biomolecule). We now show that lysine-specific molecular tweezers bind to a 14-3-3 adapter protein and modulate its interaction with partner proteins. The tweezers inhibit binding between the 14-3-3 protein and two partner proteins—a phosphorylated (C-Raf) protein and an unphosphorylated one (ExoS)—in a concentration-dependent manner. Protein crystallography shows that this effect arises from the binding of the tweezers to a single surface-exposed lysine (Lys214) of the 14-3-3 protein in the proximity of its central channel, which normally binds the partner proteins. A combination of structural analysis and computer simulations provides rules for the tweezers' binding preferences, thus allowing us to predict their influence on this type of protein-protein interactions.

Bier, David; Rose, Rolf; Bravo-Rodriguez, Kenny; Bartel, Maria; Ramirez-Anguita, Juan Manuel; Dutt, Som; Wilch, Constanze; Klärner, Frank-Gerrit; Sanchez-Garcia, Elsa; Schrader, Thomas; Ottmann, Christian



Construction of a cost effective optical tweezers for manipulation of birefringent materials using circularly polarized light  

Microsoft Academic Search

Light manipulation is a very powerful tool in physics, biology, and chemistry. There are several physical principles underlying the apparatus known as the ``optical tweezers,'' the term given to using focused light to manipulate and control small objects. By carefully controlling the orientation and position of a focused laser beam, dielectric particles can be effectively trapped and manipulated. We have

Allison McMahon; Toni Sauncy



Red blood cell micromanipulation with elliptical laser beam profile optical tweezers in different osmolarity conditions  

NASA Astrophysics Data System (ADS)

In this work optical tweezers with elliptical beam profiles have been developed in order to examine the effect of optical force on fresh red blood cells (RBC) in isotonic, hypertonic and hypotonic buffer solutions. Considering that the optical force depends essentially on the cell surface and the cytoplasmic refractive index, it is obvious that biochemical modifications associated with different states of the cell will influence its behaviour in the optical trap. Line optical tweezers were used to manipulate simultaneously more than one red blood cell. After we have been manipulated a RBC with an elliptical laser beam profile in an isotonic or hypertonic buffer, we noticed that it rotates by itself when gets trapped by optical tweezers and undergoes folding. Further shape deformations can be observed attributed to the competition between alignment and rotational torque which are transferred by laser light to the cell. In hypotonic buffer RBCs become spherical and do not rotate or fold since the resultant force due to rays emerging from diametrically opposite points of the cell leads to zero torque. Manipulation of fresh red blood cells in isotonic solution by line optical tweezers leads to folding and elongation of trapped RBCs. Membrane elasticity properties such as bending modulus can be estimated by measuring RBC's folding time in function with laser power.

Spyratou, E.; Makropoulou, M.; Serafetinides, A. A.



Optical tweezers with multiple optical forces using double-hologram interference  

Microsoft Academic Search

In earlier work, we introduced new ways of generating a series of interference patterns formed from Laguerre Gaussian (LG) beams, which are being used as advanced optical tweezers in creating and manipulating three-dimensional structures. In this work, we have succeeded in demonstrating, for the first time to our knowledge, double LG and LG beams with a Gaussian-beam interference using a

Woei Ming Lee; X.-C. Yuan; D. Y. Tang



Physical Properties of Escherichia coli P Pili Measured by Optical Tweezers  

Microsoft Academic Search

The mechanical behavior of individual P pili of uropathogenic Escherichia coli has been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of ?103 PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. They are particularly important in the pathogenesis of E. coli colonizing the upper

Jana Jass; Staffan Schedin; Erik Fällman; Jörgen Ohlsson; Ulf J. Nilsson; Bernt Eric Uhlin; Ove Axner



Tapered fiber optical tweezers for microscopic particle trapping: fabrication and application  

Microsoft Academic Search

A novel single tapered fiber optical tweezers is proposed and fabricated by heating and drawing technology. The microscopic particle tapping performance of this special designed tapered fiber probe is demonstrated and investigated. The distribution of the optical field emerging from the tapered fiber tip is numerically calculated based on the beam propagation method. The trapping force FDTD analysis results, both

Zhihai Liu; Chengkai Guo; Jun Yang; Libo Yuan



Nonlinear Elastic and Viscoelastic Deformation of the Human Red Blood Cell with Optical Tweezers  

Microsoft Academic Search

Studies of the deformation characteristics of single biological cells can offer insights into the connec- tions among mechanical state, biochemical response and the onset and progression of diseases. Deformation im- posed by optical tweezers provides a useful means for the study of single cell mechanics under a variety of well-controlled stress-states. In this paper, we first crit- ically review recent

J. P. Mills; L. Qie; M. Dao; C. T. Lim; S. Suresh



Mechanics of the human red blood cell deformed by optical tweezers  

Microsoft Academic Search

The mechanical deformation characteristics of living cells are known to influence strongly their chemical and biological functions and the onset, progression and consequences of a number of human diseases. The mechanics of the human red blood cell (erythrocyte) subjected to large deformation by optical tweezers forms the subject of this paper. Video photography of the cell deformed in a phosphate

M. Dao; C. T. Lim; S. Suresh



Elasticity of the Red Cell Membrane and Its Relation to Hemolytic Disorders: An Optical Tweezers Study  

Microsoft Academic Search

We have used optical tweezers to study the elasticity of red cell membranes; force was applied to a bead attached to a permeabilized spherical ghost and the force-extension relation was obtained from the response of a second bead bound at a diametrically opposite position. Interruption of the skeletal network by dissociation of spectrin tetramers or extraction of the actin junctions

John Sleep; David Wilson; Robert Simmons; Walter Gratzer



Distinct Membrane Mechanical Properties of Human Mesenchymal Stem Cells Determined Using Laser Optical Tweezers  

Microsoft Academic Search

The therapeutic efficacy of mesenchymal stem cells (MSCs) in tissue engineering and regenerative medicine is determined by their unique biological, mechanical, and physicochemical characteristics, which are yet to be fully explored. Cell membrane mechanics, for example, has been shown to critically influence MSC differentiation. In this study, we used laser optical tweezers to measure the membrane mechanics of human MSCs

Igor Titushkin; Michael Cho



Optical tweezers with fluorescence detection for temperature-dependent microrheological measurements  

NASA Astrophysics Data System (ADS)

We introduce a setup of optical tweezers, capable of carrying out temperature-dependent rheological measurements of soft materials. In our setup, the particle displacement is detected by imaging a bright spot due to fluorescence emitted from a dye-labeled particle against a dark background onto a quadrant photodiode. This setup has a relatively wide space around the sample that allows us to further accessorize the optical tweezers by a temperature control unit. The applicability of the setup was examined on the basis of the rheological measurements using a typical viscoelastic system, namely a worm-like micelle solution. The temperature and frequency dependences of the local viscoelastic functions of the worm-like micelle solution obtained by this setup were in good accordance with those obtained by a conventional oscillatory rheometer, confirming the capability of the optical tweezers as a tool for the local rheological measurements of soft materials. Since the optical tweezers measurements only require a tiny amount of sample (~40 ?L), the rheological measurements using our setup should be useful for soft materials of which the available amount is limited.

Shundo, Atsuomi; Hori, Koichiro; Penaloza, David P.; Tanaka, Keiji



Micromanipulation of statoliths in gravity-sensing Chara rhizoids by optical tweezers  

Microsoft Academic Search

Infrared laser traps (optical tweezers) were used to micromanipulate statoliths in gravity-sensing rhizoids of the green alga Chara vulgaris Vail. We were able to hold and move statoliths with high accuracy and to observe directly the effects of statolith position on cell growth in horizontally positioned rhizoids. The first step in gravitropism, namely the physical action of gravity on statoliths,

G. Leitz; E. Schnepf; K. O. Greulich



TTFV-Based Molecular Tweezers and Macrocycles as Receptors for Fullerenes.  


Hybrids of tetrathiafulvalene vinylogues (TTFVs) and planar arenes were synthesized via the click reaction to form tweezer-like and macrocyclic structures. These compounds were investigated as receptors for fullerenes (C60 and C70) by UV-vis absorption and fluorescence spectroscopy. PMID:23964798

Mulla, Karimulla; Shaik, Haseena; Thompson, David W; Zhao, Yuming



Optical tweezers study of viscoelastic properties in the outer hair cell plasma membrane  

Microsoft Academic Search

An optical tweezers system was used to study the mechanical characteristics of the outer hair cell (OHC) lateral wall by forming plasma membrane tethers. A 2nd order generalized Kelvin model was applied to describe the viscoelastic behavior of OHC membrane tethers. The measured parameters included equilibrium tethering force, (Feq), force relaxation times (tau), stiffness values (kappa), and coefficients of friction

David R. Murdock; Sergey A. Ermilov; Feng Qian; William E. Brownell; Bahman Anvari



High-resolution, long-term characterization of bacterial motility using optical tweezers  

Microsoft Academic Search

We present a single-cell motility assay, which allows the quantification of bacterial swimming in a well-controlled environment, for durations of up to an hour and with a temporal resolution greater than the flagellar rotation rates of ?100 Hz. The assay is based on an instrument combining optical tweezers, light and fluorescence microscopy, and a microfluidic chamber. Using this device we

Taejin L Min; Patrick J Mears; Lon M Chubiz; Christopher V Rao; Yann R Chemla; Ido Golding



Mechanical characterization of human red blood cells by robotic manipulation with optical tweezers  

Microsoft Academic Search

Human red blood cells (RBCs) are responsible to transport oxygen and carbon dioxide for human bodies. The physiological functions of RBCs are greatly influenced by their mechanical properties. Any alteration of the cell mechanics may cause human diseases. In this paper, to understand the correlation between the cell properties and their osmotic environments, robotic manipulation technology with optical tweezers is

Youhua Tan; Dong Sun; Wenhao Huang; Hanxiong Li



A theoretical study of the feasibility of acoustical tweezer: Ray acoustics approach  

Microsoft Academic Search

Optical tweezer has been found to have many biomedical applications in trapping macromolecules and cells. For the trapping mechanism, there has to be a sharp spatial change in axial optical intensity and the particle size must be much greater than the wavelength. Similar phenomenon may exist in acoustics. This work was undertaken to demonstrate theoretically that it is possible to

Jungwoo Lee; Kanglyeol Ha; K. Kirk Shung



Thermodynamic DNA Looping by a Two-Site Restriction Endonuclease Studied using Optical Tweezers  

Microsoft Academic Search

Many enzyme-DNA interactions involve multimeric protein complexes that bind at two distant sites such that the DNA is looped. An example is the type IIe restriction enzyme Sau3AI, which requires two recognition sites to cleave the DNA. Here we study this process at the single DNA level using force measuring optical tweezers. We characterize cleavage rates of single DNA molecules

Gregory J. Gemmen



Quadruple ??stack of two perylene bisimide tweezers: a bimolecular complex with kinetic stability.  


Self-assembly: A tweezer-type perylene bisimide (PBI) dyad self-assembles into a defined bimolecular complex composed of a quadruple PBI ??stack with remarkable kinetic stability, which is unprecedented for ?-stacked dye aggregates (see picture). These persistent supramolecular species are of considerable interest for the elucidation of functional properties of dye aggregates. PMID:23757369

Shao, Changzhun; Stolte, Matthias; Würthner, Frank



Algorithms for On-Line Monitoring of Micro Spheres in an Optical Tweezers-Based Assembly Cell  

Microsoft Academic Search

Optical tweezers have emerged as a powerful tool for micro and nanomanipulation. Using optical tweezers to perform automated assembly requires on-line monitoring of components in the assembly workspace. This paper presents algorithms for estimating 3-dimensional positions of micro-spheres in the assembly workspace. Algorithms presented in this paper use images obtained by optical section microscopy. The images are first segmented to

Tao Peng; Arvind Balijepalli; Satyandra K. Gupta; Tom LeBrun



Improved direct binary search-based algorithm for generating holograms for the application of holographic optical tweezers  

NASA Astrophysics Data System (ADS)

This paper presents an improved direct binary search (DBS)-based algorithm for generating holograms to holographic optical tweezers. The simulations show that the improved algorithm greatly enhances computation speed while maintaining high hologram efficiency and high-intensity homogeneous target spots. The improved algorithm was applied to generate holographic optical tweezers in several experiments. The experiments demonstrate that real-time trap and manipulation can be realized with the improved algorithm if the number of trapped microparticles is small.

Zhao, Xudong; Li, Jing; Tao, Tao; Long, Qian; Wu, Xiaoping



Flexible particle manipulation techniques with conical refraction-based optical tweezers  

NASA Astrophysics Data System (ADS)

We present an optimized optical tweezers system based upon the conical refraction of circularly polarized light in a biaxial crystal. The described optical arrangement avoids distortions to the Lloyd plane rings that become apparent when working with circularly polarized light in conventional optical tweezers. We demonstrate that the intensity distribution of the conically diffracted light permits optical manipulation of high and low refractive index particles simultaneously. Such trapping is in three dimensions and not limited to the Lloyd plane rings. By removal of a quarter waveplate the system also permits the study of linearly polarized conical refraction. We show that particle position in the Raman plane is determined by beam power, and indicates that true optical tweezing is not taking place in this part of the beam.

McDougall, C.; Henderson, Robert; Carnegie, David J.; Sokolovskii, Grigorii S.; Rafailov, Edik U.; McGloin, David



Internal Structure, Fluctuations and Micromechanical Properties of Bovine Arterial Endothelial Cells: An Optical Tweezers Study  

NASA Astrophysics Data System (ADS)

The purpose of this study is to probe the micromechanical properties of cultured bovine arterial endothelial cells by using optical tweezers to trap endogenous granular structures in the cells. A novel application of oscillating optical tweezers and coherent detection of the forced oscillation of the trapped particle enables us to measure the viscoelastic properties in soft matter with a broad frequency range and with a high data sampling rate. This study was designed to determine the difference between the viscoelasticity of the cytoskeleton around granular structures in close vicinity of the nucleus and around the cell's edge. Time dependent measurements of the mechanical properties at a fixed oscillation frequency revealed pronounced fluctuation in living cells, indicating local dynamics of the cytoskeleton around the probed particle. Possible causes for the fluctuations will be discussed.

Perretta, Carolyn; Farrell, Sheena; Latinovic, Olga; Ou-Yang, H. Daniel



Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers  

PubMed Central

A cell of the bacterium Escherichia coli was tethered covalently to a glass coverslip by a single flagellum, and its rotation was stopped by using optical tweezers. The tweezers acted directly on the cell body or indirectly, via a trapped polystyrene bead. The torque generated by the flagellar motor was determined by measuring the displacement of the laser beam on a quadrant photodiode. The coverslip was mounted on a computer-controlled piezo-electric stage that moved the tether point in a circle around the center of the trap so that the speed of rotation of the motor could be varied. The motor generated ?4500 pN nm of torque at all angles, regardless of whether it was stalled, allowed to rotate very slowly forwards, or driven very slowly backwards. This argues against models of motor function in which rotation is tightly coupled to proton transit and back-transport of protons is severely limited.

Berry, Richard M.; Berg, Howard C.



Construction of a cost effective optical tweezers for manipulation of birefringent materials using circularly polarized light  

NASA Astrophysics Data System (ADS)

Light manipulation is a very powerful tool in physics, biology, and chemistry. There are several physical principles underlying the apparatus known as the ``optical tweezers,'' the term given to using focused light to manipulate and control small objects. By carefully controlling the orientation and position of a focused laser beam, dielectric particles can be effectively trapped and manipulated. We have designed a cost efficient and effective undergraduate optical tweezers apparatus by using standard ``off the shelf'' components and starting with a standard undergraduate laboratory microscope. Images are recorded using a small CCD camera interfaced to a computer and controlled by LabVIEW^TM software. By using wave plates to produce circular polarized light, rotational motion can be induced in small particles of birefringent materials such as calcite and mica.

McMahon, Allison; Sauncy, Toni



Raman sorting and identification of single living micro-organisms with optical tweezers  

NASA Astrophysics Data System (ADS)

We report on a novel technique for sorting and identification of single biological cells and food-borne bacteria based on laser tweezers and Raman spectroscopy (LTRS). With this technique, biological cells of different physiological states in a sample chamber were identified by their Raman spectral signatures and then they were selectively manipulated into a clean collection chamber with optical tweezers through a microchannel. As an example, we sorted the live and dead yeast cells into the collection chamber and validated this with a standard staining technique. We also demonstrated that bacteria existing in spoiled foods could be discriminated from a variety of food particles based on their characteristic Raman spectra and then isolated with laser manipulation. This label-free LTRS sorting technique may find broad applications in microbiology and rapid examination of food-borne diseases.

Xie, Changan; Chen, De; Li, Yong-Qing



An SLM-based Shack-Hartmann wavefront sensor for aberration correction in optical tweezers  

NASA Astrophysics Data System (ADS)

Holographic optical tweezers allow the creation of multiple optical traps in 3D configurations through the use of dynamic diffractive optical elements called spatial light modulators (SLMs). We show that, in addition to controlling traps, the SLM in a holographic tweezers system can be both the principal element of a wavefront sensor and the corrective element in a closed-loop adaptive optics system. This means that aberrations in such systems can be estimated and corrected without altering the experimental setup. Aberrations are estimated using the Shack-Hartmann method, where an array of spots is projected into the sample plane and the distortion of this array is used to recover the aberration. The system can recover aberrations of up to ten wavelengths peak-peak, and is sensitive to aberrations much smaller than a wavelength. The spot pattern could also be analysed by eye, as a tool for aligning the system.

Bowman, Richard W.; Wright, Amanda J.; Padgett, Miles J.



Automatic transportation of biological cells with a robot-tweezer manipulation system  

Microsoft Academic Search

The positioning of biological cells has become increasingly important in biomedical research such as drug discovery, cell-to-cell interaction, and tissue engineering. Significant demand for both accuracy and productivity in cell manipulation highlights the need for automated cell transportation with integrated robotics and micro\\/nano-manipulation technologies. Optical tweezers, which use highly focused low-power laser beams to trap and manipulate particles at the

Songyu Hu; Dong Sun



Kinetics of Microtubule-AtMAP65-1 Bond Studied with Dual-Optical Tweezers  

Microsoft Academic Search

The unbinding force of microtubule-AtMAP65-1 bond is measured with dual-optical tweezers. Force histograms reveal quantized force distributions under physiological condition and with 100 mM NaCl treatment. Based on Bell-Evans-model of multiple bonds, histograms are fitted and kinetic parameters are obtained. Under the force loading rate of 9 pN\\/s, the most probable unbinding forces for the single bond are 16.8± 0.8

E Qu; Honglian Guo; Chunhua Xu; Zhaolin Li; Ming Yuan; Bingying Cheng; Daozhong Zhang



3D manipulation of particles into crystal structures using holographic optical tweezers  

Microsoft Academic Search

We have developed holographic optical tweezers that can manipulate many particles simultaneously in three dimensions in order to create micro-crystal structures that extend over many tens of microns. The technique uses specific hologram-design algorithms to create structures that can be dynamically scaled or rotated about arbitrary axes. We believe the generation and control of pre-determined crystal-like structures have significant potential

Jonathan Leach; Gavin Sinclair; Pamela Jordan; Johannes Courtial; Miles J. Padgett; Jon Cooper; Zsolt J. Laczik



A New Determination of the Shear Modulus of the Human Erythrocyte Membrane Using Optical Tweezers  

Microsoft Academic Search

Optical tweezers are used to apply calibrated forces to human erythrocytes, via small silica beads bound to their membrane. The shear modulus ? of the membrane is inferred from measurements of the cell deformation in the small strain linear regime. We find the same result ?=2.5±0.4?N\\/m for both discotic and nearly spherical swollen cells. This value is smaller than the

Sylvie Hénon; Guillaume Lenormand; Alain Richert; François Gallet



Holographic optical tweezers obtained by using the three-dimensional Gerchberg-Saxton algorithm  

NASA Astrophysics Data System (ADS)

An extension of the Gerchberg-Saxton algorithm from two dimensions to three is used to configure a continuous optical trap geometry. Intensity tailoring in a continuous, three-dimensional (3D) volume rather than in multiple discrete two-dimensional planes yields flexible 3D holographic optical tweezers. A numerical simulation and optical demonstrations of continuous 3D beam shaping and particle trapping confirm the capabilities of the method.

Chen, Hao; Guo, Yunfeng; Chen, Zhaozhong; Hao, Jingjing; Xu, Ji; Wang, Hui-Tian; Ding, Jianping



Short-term binding of fibroblasts to fibronectin: optical tweezers experiments and probabilistic analysis  

Microsoft Academic Search

The biophysical properties of the interaction between fibronectin and its membrane receptor were inferred from adhesion tests\\u000a on living cells. Individual fibroblasts were maintained on fibronectin-coated glass for short time periods (1–16?s) using\\u000a optical tweezers. After contact, the trap was removed quickly, leading to either adhesion or detachment of the fibroblast.\\u000a Through a stochastic analysis of bond kinetics, we derived

Olivier Thoumine; Pierre Kocian; Arlette Kottelat; Jean-Jacques Meister



New opto-plasmonic tweezers for manipulation and rotation of biological cells--design and fabrication.  


Opto-Plasmonic Tweezers are proposed as a new optical manipulator and rotator for biological cells. The approach utilizes polarized light to excite localized surface plasmon resonance (LSPR) on an array of Au nanostructure. Large dielectrophoretic trapping force is expected to be induced by the highly non-uniform scattering field from the resonant oscillating dipoles. Fine orientation control of the cells can be realized by tuning the polarization state of the input light. PMID:17946622

Miao, Xiaoyu; Lin, Lih Y




Microsoft Academic Search

Optical tweezers are often used in connection with other techniques to study physical properties of biological systems. In\\u000a particular, this combination has often been used to study elastic properties of individual strands of nucleic acids. The DNA\\u000a used in this study is the shortest so far reported, only 1.1 ?m, 20 times its persistence length. We use two different experimental



Optical tweezers to study single Protein A\\/Immunoglobulin G interactions at varying conditions  

Microsoft Academic Search

Optical tweezers (OT) are ideally suited to study the interaction of single receptor-ligand bonds. Here we introduce a newly\\u000a developed assay using OT to investigate the interactions between Protein A from Staphylococcus\\u000a aureus and Immunoglobulin G from rabbit serum (RIgG). We demonstrate that the rupture forces depend on the loading rate and on the\\u000a sodium chloride concentration. The measured loading

Mathias Salomo; Ulrich F. Keyser; Marc Struhalla; Friedrich Kremer



Red blood cell membrane viscoelasticity, agglutination and zeta potential measurements with double optical tweezers  

NASA Astrophysics Data System (ADS)

The red blood cell (RBC) viscoelastic membrane contains proteins and glycolproteins embedded in, or attached, to a fluid lipid bilayer and are negatively charged, which creates a repulsive electric (zeta) potential between the cells and prevents their aggregation in the blood stream. There are techniques, however, to decrease the zeta potential to allow cell agglutination which are the basis of most of the tests of antigen-antibody interactions in blood banks. This report shows the use of a double optical tweezers to measure RBC membrane viscosity, agglutination and zeta potential. In our technique one of the optical tweezers trap a silica bead that binds strongly to a RBC at the end of a RBCs rouleaux and, at the same time, acts as a pico-Newton force transducer, after calibration through its displacement from the equilibrium position. The other optical tweezers trap the RBC at the other end. To measure the membrane viscosity the optical force is measured as a function of the velocity between the RBCs. To measure the adhesion the tweezers are slowly displaced apart until the RBCs disagglutination happens. The RBC zeta potential is measured in two complimentary ways, by the force on the silica bead attached to a single RBC in response to an applied electric field, and the conventional way, by the measurement of terminal velocity of the RBC after released from the optical trap. These two measurements provide information about the RBC charges and, also, electrolytic solution properties. We believe this can improve the methods of diagnosis in blood banks.

Fontes, Adriana; Fernandes, Heloise P.; Barjas-Castro, Maria L.; de Thomaz, André A.; de Ysasa Pozzo, Liliana; Barbosa, Luiz C.; Cesar, Carlos L.



Rolling, aligning, and trapping droplets on a laser beam using marangoni optofluidic tweezers  

Microsoft Academic Search

Optical methods for droplet m attractive because they offer dyanmic on-chip structures; however, forces from tend to be in the pN range. We demonst of oil-in-water droplets on a focused lase Marangoni optofluidic tweezers (MOT) Marangoni flow generated by a laser-indu singularity at the oil-water interface. Th the flow aligns the droplet centroid to th point the flow becomes symmetric

G. K. Kurup; Amar S. Basu



Optical tweezers: Characterization and systems approach to high bandwidth force estimation  

Microsoft Academic Search

In recent times, the hard boundaries between classical fields of sciences have almost disappeared. There is a cross-pollination of ideas between sciences, engineering and mathematics. This work investigates a modern tool of micro-manipulation of microscopic particles that is used primarily by bio-physicists and bio-chemists for single cell, single molecule studies. This tool called the Optical Tweezers can trap microscopic dielectric

Hullas Sehgal



High-resolution optical tweezers for investigating DNA-binding/translocating molecular motors  

NASA Astrophysics Data System (ADS)

A double-trap optical tweezers instrument was constructed and its spatial resolution measured. The instrument features real-time control that allows feedback based position- and force-clamping experiments. To study RNA-polymerization by QDE-1, an RNA-dependent RNA-polymerase, we tethered a 7250 nt single-stranded DNA molecule between two optically trapped microspheres. Preliminary constant-force extension trajectories and force-extension curves were collected.

Wallin, Anders E.; Ojala, Heikki; Ziedaite, Gabija; Degerth, Linda; Bamford, Dennis; Haeggström, Edward



Analysis of Cell Mechanics in Single Vinculin-Deficient Cells Using a Magnetic Tweezer  

Microsoft Academic Search

A magnetic tweezer was constructed to apply controlled tensional forces (10 pN to greater than 1 nN) to transmembrane receptors via bound ligand-coated microbeadswhile optically measuring lateral bead displacements within individual cells. Use of this system with wild-type F9 embryonic carcinoma cells and cells from a vinculin knockout mouse F9 Vin (?\\/?) revealed much larger differences in the stiffness of

Francis J. Alenghat; Ben Fabry; Kenneth Y. Tsai; Wolfgang H. Goldmann; Donald E. Ingber



Optical tweezers induced photodamage in living cells quantified with digital holographic phase microscopy  

NASA Astrophysics Data System (ADS)

Optical tweezers are a versatile technique to manipulate living biological specimen in a contact-less way. The interaction with living cells can be performed, for example, through direct manipulation of cell organelles or by movement of an internalized particle within the cytoplasm. However, the risk of damage that the trapping beam may induce in the biological sample due to the energy deposition has to be considered. This optically induced damage or photodamage depends mainly on the wavelength of the trapping beam, the exposure time and the biological specimen that is investigated. In this work, we explore a method to analyse the photo damage in living cells in a multimodal biophotonic workstation that is based on combining a holographic optical tweezers (HOT) microscope with a self-interference digital holographic microscopy (DHM) module. A time-dependent investigation shows that no observable changes in the cell morphology are induced at room conditions with the used laser power of the trapping beam during periods of time < 20 min of laser application. In addition, results from investigations of the photodamage increasing the working temperature to 37°C demonstrate that the optical tweezers beam can provoke severe but reversible morphology changes in the cell.

Barroso Peña, Álvaro; Kemper, Björn; Woerdemann, Mike; Vollmer, Angelika; Ketelhut, Steffi; von Bally, Gert; Denz, Cornelia



Chromosomal analysis and identification based on optical tweezers and Raman spectroscopy  

NASA Astrophysics Data System (ADS)

The ability to identify specific chromosomes with certainty has been established by the development of several cytogenetic techniques based on staining. Here, we report the use of a new optical technique, laser tweezers and Raman spectroscopy (LTRS), to capture and manipulate chromosomes in order to obtain their spectral patterns for molecular analysis without the need for staining. The purpose of this study was to obtain Raman spectroscopy patterns for chromosomes number 1, 2, and 3 and to test if the Raman spectroscopy pattern could be used to distinguish these three chromosomes. In our experiment, optical tweezers were used to capture the individual chromosomes and the Raman spectral patterns were collected for the trapped chromosomes. Then, the captured chromosome was manipulated with the optical tweezers and moved to another chamber through a micro - channel, in which the chromosomes were G banded for positive identification as chromosome number 1, 2, or 3. Generalized discriminate analysis (GDA) was used to compare the Raman signatures. This analysis revealed that chromosomes 1, 2, and 3 could be distinguished and identified based on their Raman spectra. Development of this approach will lead to more rapid automatic methods for chromosome analysis and identification without the use of prior staining. Moreover, the Raman spectral patterns may lend themselves to more detailed analysis of chromosomal structure than is currently available with standard staining protocols. Such analysis may some day be useful for rapid, automated screening and diagnosis for certain cancers.

Ojeda, Jenifer F.; Xie, Changan; Li, Yong-Qing; Bertrand, Fred E.; Wiley, John; McConnell, Thomas J.



Single-cell optoporation and transfection using femtosecond laser and optical tweezers  

PubMed Central

In this paper, we demonstrate a new single-cell optoporation and transfection technique using a femtosecond Gaussian laser beam and optical tweezers. Tightly focused near-infrared (NIR) femtosecond laser pulse was employed to transiently perforate the cellular membrane at a single point in MCF-7 cancer cells. A distinct technique was developed by trapping the microparticle using optical tweezers to focus the femtosecond laser precisely on the cell membrane to puncture it. Subsequently, an external gene was introduced in the cell by trapping and inserting the same plasmid-coated microparticle into the optoporated cell using optical tweezers. Various experimental parameters such as femtosecond laser exposure power, exposure time, puncture hole size, exact focusing of the femtosecond laser on the cell membrane, and cell healing time were closely analyzed to create the optimal conditions for cell viability. Following the insertion of plasmid-coated microparticles in the cell, the targeted cells exhibited green fluorescent protein (GFP) under the fluorescent microscope, hence confirming successful transfection into the cell. This new optoporation and transfection technique maximizes the level of selectivity and control over the targeted cell, and this may be a breakthrough method through which to induce controllable genetic changes in the cell.

Waleed, Muhammad; Hwang, Sun-Uk; Kim, Jung-Dae; Shabbir, Irfan; Shin, Sang-Mo; Lee, Yong-Gu



Dislocation reactions, grain boundaries, and irreversibility in two-dimensional lattices using topological tweezers.  


Dislocations, disclinations, and grain boundaries are topological excitations of crystals that play a key role in determining out-of-equilibrium material properties. In this article we study the kinetics, creation, and annihilation processes of these defects in a controllable way by applying "topological tweezers," an array of weak optical tweezers which strain the lattice by weakly pulling on a collection of particles without grabbing them individually. We use topological tweezers to deterministically control individual dislocations and grain boundaries, and reversibly create and destroy dislocation pairs in a 2D crystal of charged colloids. Starting from a perfect lattice, we exert a torque on a finite region and follow the complete step-by-step creation of a disoriented grain, from the creation of dislocation pairs through their reactions to form a grain boundary and their reduction of elastic energy. However, when the grain is rotated back to its original orientation the dislocation reactions do not retrace. Rather, the process is irreversible; the grain boundary expands instead of collapsing. PMID:24009341

Irvine, William T M; Hollingsworth, Andrew D; Grier, David G; Chaikin, Paul M



Single-cell optoporation and transfection using femtosecond laser and optical tweezers.  


In this paper, we demonstrate a new single-cell optoporation and transfection technique using a femtosecond Gaussian laser beam and optical tweezers. Tightly focused near-infrared (NIR) femtosecond laser pulse was employed to transiently perforate the cellular membrane at a single point in MCF-7 cancer cells. A distinct technique was developed by trapping the microparticle using optical tweezers to focus the femtosecond laser precisely on the cell membrane to puncture it. Subsequently, an external gene was introduced in the cell by trapping and inserting the same plasmid-coated microparticle into the optoporated cell using optical tweezers. Various experimental parameters such as femtosecond laser exposure power, exposure time, puncture hole size, exact focusing of the femtosecond laser on the cell membrane, and cell healing time were closely analyzed to create the optimal conditions for cell viability. Following the insertion of plasmid-coated microparticles in the cell, the targeted cells exhibited green fluorescent protein (GFP) under the fluorescent microscope, hence confirming successful transfection into the cell. This new optoporation and transfection technique maximizes the level of selectivity and control over the targeted cell, and this may be a breakthrough method through which to induce controllable genetic changes in the cell. PMID:24049675

Waleed, Muhammad; Hwang, Sun-Uk; Kim, Jung-Dae; Shabbir, Irfan; Shin, Sang-Mo; Lee, Yong-Gu



Spherical vortex beams of high radial degree for enhanced single-beam tweezers  

NASA Astrophysics Data System (ADS)

We present, in our knowledge, the first theoretical demonstration of the possibility to trap and manipulate particles in three dimensions with the radiation pressure exerted by a single acoustical beam. Numerical examples demonstrate that single-beam acoustical tweezers operating in three dimensions are feasible with a large variety of materials and may widely extend the range of forces and operation regions that are currently available with optical tweezers. To do so, a method to model the focusing properties of acoustical beams with complex wavefronts using a spherical transducer is proposed. Then, the radiation forces exerted by various beams going from the classical vortex to the high radial degree spherical vortex beam that we introduce here are studied. While the first is shown to trap moderately small particles, the latter will stiffly trap large solid spheres in three dimensions. Even though this demonstration is carried out using a formalism suited to acoustics, it is easily applicable to trap non-transparent particles with optical tweezers that remain an issue.

Baresch, Diego; Thomas, Jean-Louis; Marchiano, Régis



Scanning a DNA molecule for bound proteins using hybrid magnetic and optical tweezers.  


The functional state of the genome is determined by its interactions with proteins that bind, modify, and move along the DNA. To determine the positions and binding strength of proteins localized on DNA we have developed a combined magnetic and optical tweezers apparatus that allows for both sensitive and label-free detection. A DNA loop, that acts as a scanning probe, is created by looping an optically trapped DNA tether around a DNA molecule that is held with magnetic tweezers. Upon scanning the loop along the ?-DNA molecule, EcoRI proteins were detected with ~17 nm spatial resolution. An offset of 33 ± 5 nm for the detected protein positions was found between back and forwards scans, corresponding to the size of the DNA loop and in agreement with theoretical estimates. At higher applied stretching forces, the scanning loop was able to remove bound proteins from the DNA, showing that the method is in principle also capable of measuring the binding strength of proteins to DNA with a force resolution of 0.1 pN/[Formula: see text]. The use of magnetic tweezers in this assay allows the facile preparation of many single-molecule tethers, which can be scanned one after the other, while it also allows for direct control of the supercoiling state of the DNA molecule, making it uniquely suitable to address the effects of torque on protein-DNA interactions. PMID:23755219

van Loenhout, Marijn T J; De Vlaminck, Iwijn; Flebus, Benedetta; den Blanken, Johan F; Zweifel, Ludovit P; Hooning, Koen M; Kerssemakers, Jacob W J; Dekker, Cees



Micromanipulation and physiological monitoring of cells using two-photon excited fluorescence in cw laser tweezers  

NASA Astrophysics Data System (ADS)

We report the observation of two-photon fluorescence excitation and cell confinement, simultaneously, in a continuous-wave (cw) single-beam gradient force optical trap, and demonstrate its use as an in-situ probe to study the physiological state of an optically confined cell sample. At the wavelength of 1064 nm, a single focused gaussian laser beam is used to simultaneously confine, and excite visible fluorescence from, a human sperm cell that has been tagged with propidium iodide, a exogenous fluorescent dye that functions as a viability assay of cellular physiological state. The intensity at the dye peak emission wavelength of 620 nm exhibits a near-square-law dependence on incident trapping beam photon laser power, a behavior consistent with a two-photon absorption process. In addition, for a sperm cell held stationary in the optical tweezers for a period of several minutes at a constant trapping power, red fluorescence emission was observed to increase the time, indicating that the cell has gradually transitioned between a live and dead state. Two-photon excited fluorescence was also observed in chinese hamster ovary cells that were confined by cw laser tweezers and stained with either propidium iodide or Snarf, a pH-sensitive dye probe. These results suggest that, for samples suitably tagged with fluorescent probes and vital stains, optical tweezers can be used to generate their own in-situ diagnostic optical probes of cellular viability or induced photodamage, via two-photon processes.

Sonek, Gregory J.; Liu, Yagang; Berns, Michael W.; Tromberg, Bruce J.



Dielectrophoretic Tweezers as a Platform for Molecular Force Spectroscopy in a Highly Parallel Format  

PubMed Central

We demonstrated the application of a simple electrode geometry for dielectrophoresis (DEP) on colloidal probes as a form of molecular force spectroscopy in a highly parallel format. The electric field between parallel plates is perturbed with dielectric microstructures, generating uniform DEP forces on colloidal probes in the range of several hundred piconewtons across a macroscopic sample area. We determined the approximate crossover frequency between negative and positive DEP using electrodes without dielectric microstructures—a simplification over standard experimental methods involving quadrupoles or optical trapping. 2D and 3D simulations of the electric field distributions validated the experimental behavior of several of our DEP tweezers geometries and provided insight into potential improvements. We applied the DEP tweezers to the stretching of a short DNA oligomer and detected its extension using total-internal reflection fluorescence microscopy. The combination of a simple cell fabrication, a uniform distribution of high axial forces, and a facile optical detection of our DEP tweezers makes this form of molecular force spectroscopy ideal for highly parallel detection of stretching or unbinding kinetics of biomolecules.

Cheng, Peng; Barrett, Michael J.; Oliver, Piercen M.; Cetin, Deniz; Vezenov, Dmitri



Differential detection of dual traps improves the spatial resolution of optical tweezers  

PubMed Central

The drive toward more sensitive single-molecule manipulation techniques has led to the recent development of optical tweezers capable of resolving the motions of biological systems at the subnanometer level, approaching the fundamental limit set by Brownian fluctuations. One successful approach has been the dual-trap optical tweezers, in which the system of study is held at both ends by microspheres in two separate optical traps. We present here a theoretical description of the Brownian limit on the spatial resolution of such systems and verify these predictions by direct measurement in a Brownian noise-limited dual-trap optical tweezers. We find that by detecting the positions of both trapped microspheres, correlations in their motions can be exploited to maximize the resolving power of the instrument. Remarkably, we show that the spatial resolution of dual optical traps with dual-trap detection is always superior to that of more traditional, single-trap designs, despite the added Brownian noise of the second trapped microsphere.

Moffitt, Jeffrey R.; Chemla, Yann R.; Izhaky, David; Bustamante, Carlos



[Raman tweezers-based analysis of carotenoid synthesis in Rhodotorula glutinis].  


Carotenoid synthesis in Rhodotorula glutinis was investigated with Raman tweezers in order to find the effect of nitrogen and carbon resource on carotenoid yield. The cells in fermentation terminus were harvested, and then divided into two parts, one for UV analysis, the other for Raman tweezers detection. Original spectra were preprocessed by carrying out background elimination and baseline correction, and the averaged spectra of cells cultivated in different fermentation medium were analyzed qualitatively. The results showed that the Raman intensity of carotenoid were obviously different. There was a high correlation between UV results and Raman peak height data, the correlation coefficients of fitted parameters were 0.907 8 and 0.912 1, respectively. Quantitative analysis of 1 508 cm(-1) peak height indicated that the appropriate nitrogen and carbon resources for the growth of Rhodotorula glutinis cells and synthesis of carotenoid were yeast extract + tryptone, and glucose, respectively. The above results suggest that Raman tweezers can provide information about carotenoids in Rhodotorula glutinis cells and serve as an effective tool for real time measurement of carotenoid synthesis and optimization of fermentation medium. PMID:21714247

Yuan, Yu-Feng; Tao, Zhan-Hua; Liu, Jun-Xian; Wang, Gui-Wen; Li, Yong-Qing



3D multiple optical tweezers based on time-shared scanning with a fast focus tunable lens  

NASA Astrophysics Data System (ADS)

Three-dimensional controlled manipulation of individual micro-objects requires multiple optical tweezers that can be independently controlled in a 3D working space with high spatiotemporal resolution. Here, the author presents 3D multiple optical tweezers based on a time-shared scanning technique with an electrically focus tunable lens for axial steering and a two-axis steering mirror for lateral steering. Four typical examples of 3D controlled manipulation, including the rotation of a single bead on its axis, are demonstrated in real time. The optical system design and the control method are also described.

Tanaka, Yoshio



The design and biological applications of dual-beam oscillating optical tweezer-based imaging cytorheometer  

NASA Astrophysics Data System (ADS)

Because of its non-invasive nature, optical tweezers have emerged as a popular tool for the studies of complex fluids and biological cells and tissues. The capabilities of optical tweezer-based experimental instruments continue to evolve for better and broader applications, through new apparatus designs and integrations with microscopic imaging techniques. In this paper, we present the design, calibration and applications of a powerful microrheometer that integrates a novel high temporal and spatial resolution dual-beam oscillating optical tweezer-based cytorheometer (DOOTC) with spinning disk confocal microscopy. The oscillating scheme detects the position of micron-size probe particles via a phase-sensitive lock-in amplifier to greatly enhance sensitivity. The dual-beam scheme ensures that the cytorheometer is insensitive to sample specimen background parameter variances, and thus enables the investigation of micromechanical properties of biological samples, which are intrinsically inhomogeneous. The cytorheometer system is demonstrated to be capable of measuring dynamic local mechanical moduli in the frequency range of 0.1-150 Hz at up to 2 data point per second and with nanometer spatial resolutions, while visualizing and monitoring structural properties in situ. We report the results of system applications in the studies of bovine skin gelatin gel, purified microtubule assemblies, and human alveolar epithelial cells. The time evolution of the storage moduli G' and the loss moduli G'' of the gel is recorded for undisturbed gel-forming process with high temporal resolution. The micromechanical modulus G* of polymerized microtubule network as a function of frequency are shown to be both inhomogeneous and anisotropic consistent with local structures revealed by confocal imaging. The mechanical properties of A549 human lung cells as a function of temperature will be reported showing significant decrease in cell stiffness at higher temperature.

Ou-Yang, H. D.; Wang, J.



The self-orientation of mammalian cells in optical tweezers—the importance of the nucleus  

NASA Astrophysics Data System (ADS)

Here we present the first evidence showing that eukaryotic cells can be stably trapped in a single focused Gaussian beam with an orientation that is defined by the nucleus. A mammalian eukaryotic cell (in suspension) is trapped and is re-oriented in the focus of a linearly polarized Gaussian beam with a waist of dimension smaller than the radius of the nucleus. The cell reaches a position relative to the focus that is dictated by the nucleus and nuclear components. Our studies illustrate that the force exerted by the optical tweezers at locations within the cell can be predicted theoretically; the data obtained in this way is consistent with the experimental observations.

Perney, Nicolas M. B.; Horak, Peter; Hanley, Neil A.; Melvin, Tracy



Measuring stall forces in vivo with optical tweezers through light momentum changes  

NASA Astrophysics Data System (ADS)

The stall forces of processive molecular motors have been widely studied previously in vitro. Even so, in vivo experiments are required for determining the actual performance of each molecular motor in its natural environment. We report the direct measurement of light momentum changes in single beam optical tweezers as a suitable technique for measuring forces inside living cells, where few alternatives exist. The simplicity of this method, which does not require force calibration for each trapped object, makes it convenient for measuring the forces involved in fast dynamic biological processes such us intracellular traffic. Here we present some measurements of the stall force of processive molecular motors inside living Allium cepa cells.

Mas, J.; Farré, A.; López-Quesada, C.; Fernández, X.; Martín-Badosa, E.; Montes-Usategui, M.



Multiplexing and switching of virtual electrodes in optoelectronic tweezers based on lithium niobate.  


We introduce a method for trapping and arranging microparticles in arbitrary two-dimensional patterns with high flexibility. For this purpose, optoelectronic tweezers based on lithium niobate as photoconductor are used to create virtual electrodes through modulated illumination. The evolving field gradients arrange microparticles due to dielectrophoretic (DEP) forces and enable an all-optical approach for DEP. In order to increase flexibility further, we investigate multiplexed electrode structures for in situ reconfiguration of particle arrangements. Using the all-optical erasure of previously written virtual electrodes, we demonstrate electrode switching and sequential particle trapping in a microchannel for microfluidic applications. PMID:23041845

Glaesener, Stefan; Esseling, Michael; Denz, Cornelia



Microfluidic integrated optoelectronic tweezers for single-cell preparation and analysis.  


We report a novel microfluidic integrated optoelectronic tweezers (OET) platform for single-cell sample preparation and analysis. Integration of OET and microfluidics is achieved by embedding single-wall carbon nanotube (SWNT) electrodes into multilayer PDMS structures. This integrated platform allows users to selectively pick up individual cells from a population with light beams based on their optical signatures such as size, shape, and fluorescence, and transport them into isolated chambers using light induced dielectrophoretic forces. Isolated cells can be encapsulated into nanoliter liquid plugs and transported out of the platform for downstream molecule analysis using standard commercial instruments. PMID:23884358

Huang, Kuo-Wei; Wu, Yi-Chien; Lee, Ji-Ann; Chiou, Pei-Yu



Probing cell biophysical behavior based on actin cytoskeleton modeling and stretching manipulation with optical tweezers  

NASA Astrophysics Data System (ADS)

This letter presents an approach to utilizing the actin cytoskeleton model and optical tweezers technology to probe the distinct underlying F-actin remodeling mechanism and showing quantitatively how cell mechanical behavior is associated with alterations in the cell functions. The structural parameters of F-actin were extracted by fitting the modeling results with the experimental results obtained by cell stretching manipulation. Alterations of cell mechanical behaviors under distinct diseased cellular stages were further interpreted. Jurkat and K562 cells were used as sample cells. This letter successfully illustrates the correlation of the cell mechanical behavior and cell functional alterations in a quantitative way.

Wang, Kaiqun; Cheng, Jinping; Han Cheng, Shuk; Sun, Dong



Fast acoustic tweezers for the two-dimensional manipulation of individual particles in microfluidic channels  

NASA Astrophysics Data System (ADS)

This paper presents a microfluidic device that implements standing surface acoustic waves in order to handle single cells, droplets, and generally particles. The particles are moved in a very controlled manner by the two-dimensional drifting of a standing wave array, using a slight frequency modulation of two ultrasound emitters around their resonance. These acoustic tweezers allow any type of motion at velocities up to few ×10 mm/s, while the device transparency is adapted for optical studies. The possibility of automation provides a critical step in the development of lab-on-a-chip cell sorters and it should find applications in biology, chemistry, and engineering domains.

Tran, S. B. Q.; Marmottant, P.; Thibault, P.



Optical determination of motility forces in human spermatozoa with laser tweezers  

NASA Astrophysics Data System (ADS)

Laser tweezers may act as optical force transducers. We report on the determination of intrinsic motility forces of human spermatozoa by employing an 800 nm optical trap. The cellular forces were calculated from calibrated trapping forces. The determination of trapping forces based on a hydrodynamic model for ellipsoidal specimens, the measurement of the minimum laser power required to confine a single cell in the trap, and the calculation of viscus forces during the movement of optically trapped sperm heads through a laminar fluid. A mean motility force of 44 plus or minus 24 pN was calculated for spermatozoa of healthy donors.

Koenig, Karsten; Svaasand, Lars O.; Tadir, Yona; Tromberg, Bruce J.; Berns, Michael W.



Simultaneous rotation, orientation and displacement control of birefringent microparticles in holographic optical tweezers.  


We report the experimental implementation of a new method for generating multiple dynamical optical tweezers, where each one of them is generated with an independent linear polarization state with arbitrary orientation. This also allows an independent simultaneous polarization-rotation control. The laser beam, both for generating multiple traps and polarization control, has been modulated using a single reflective nematic liquid crystal with parallel alignment. We present experimental results of controlled displacement, orientation and rotation of birefringent particles. In addition, a simple method for estimating and canceling out the primary astigmatism present in the system is presented. PMID:23388900

Arias, A; Etcheverry, S; Solano, P; Staforelli, J P; Gallardo, M J; Rubinsztein-Dunlop, H; Saavedra, C



Laser-induced fusion of human embryonic stem cells with optical tweezers  

NASA Astrophysics Data System (ADS)

We report a study on the laser-induced fusion of human embryonic stem cells (hESCs) at the single-cell level. Cells were manipulated by optical tweezers and fused under irradiation with pulsed UV laser at 355 nm. Successful fusion was indicated by green fluorescence protein transfer. The influence of laser pulse energy on the fusion efficiency was investigated. The fused products were viable as gauged by live cell staining. Successful fusion of hESCs with somatic cells was also demonstrated. The reported fusion outcome may facilitate studies of cell differentiation, maturation, and reprogramming.

Chen, Shuxun; Cheng, Jinping; Kong, Chi-Wing; Wang, Xiaolin; Han Cheng, Shuk; Li, Ronald A.; Sun, Dong



HPLC study of the host–guest complexation between fluorescent glutathione derivatives and ?-cyclodextrin  

Microsoft Academic Search

RP-HPLC and the van’t Hoff law were used to study the association in which ?-cyclodextrin forms inclusion complexes with aminothiol–phthaldialdehyde\\u000a derivatives prepared from either glutathione (GSH) or ?-glutamylcysteine (?-glucys) and either naphthalene-2,3-dicarboxaldehyde\\u000a (NDA) or o-phthaldialdehyde (OPA). Elution was carried out at pH 8.5, the derivatization pH which gave the highest fluorescence signal\\u000a during batch experiments. The variation of the retention

Stéphanie Marchand; Aldona Guzek; Pierre Leroy



Transfer-printing and host-guest properties of 3D supramolecular particle structures.  


Mechanically robust and crystalline supramolecular particle structures have been constructed by decoupling nanoparticle assembly and supramolecular glue infiltration into a sequential process. First, beta-cyclodextrin (CD)-functionalized polystyrene particles (d approximately 500 nm) were assembled on a CD-functionalized surface via convective assembly to form highly ordered, but mechanically unstable, particle crystals. Subsequently, the crystals were infiltrated by a solution of adamantyl-functionalized dendrimers, functioning as a supramolecular glue to bind neighboring particles together and to couple the entire particle crystal to the CD surface, both in a noncovalent manner. The supramolecular particle crystals are highly robust, as witnessed by their ability to withstand agitation by ultrasonication. When assembled on a poly(dimethylsiloxane) (PDMS) stamp, the dendrimer-infiltrated particle crystals could be transfer-printed onto a CD-functionalized target surface. By variation of the geometry and size of the PDMS stamps, single particle lines, interconnected particle rings, and V-shaped particle assemblies were obtained. The particle structures served as 3D receptors for the binding of (multiple) complementary guest molecules, indicating that the supramolecular host functionalities of the particle crystals were retained throughout the fabrication process. PMID:20356024

Ling, Xing Yi; Phang, In Yee; Reinhoudt, David N; Vancso, G Julius; Huskens, Jurriaan



Cooperative assembly of discrete stacked aggregates driven by supramolecular host-guest complexation.  


p-Sulfonatocalix[4]arene (SC4) interacts with the aromatic dye crystal violet (CV) to form complexes with stoichiometries ranging from SC4:CV = 1:1 up to 1:5 both in solution and in the gas phase. While the 1:1 complex is of the inclusion type, as frequently observed for other guests, in the higher-order complexes the CV molecules interact with SC4 in a peripheral manner. The formation of such complexes is driven by ionic interactions established between the dye and the calixarene and by CV-CV stacking interactions. The application of an advanced fitting procedure made possible a quantitative analysis of the UV-vis data and allowed the determination of the stepwise binding constants. This unprecedented approach provides evidence that the formation of the highest-order complexes occurs through a cooperative mechanism. Moreover, the development of a quantitative analytical model enables the possibility of using this type of system for water-soluble sensing assays, as is also exemplified in the present work. PMID:23962101

Basílio, Nuno; Piñeiro, Angel; Da Silva, José P; García-Río, Luis



Self-assembled hexanuclear organometallic cages: synthesis, characterization, and host-guest properties.  


A series of iridium- and rhodium-based hexanuclear organometallic cages containing 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone, 9,10-dihydroxy-1,4-anthraquinone, and 6,11-dihydroxynaphthacene-5,12-dione ligands were synthesized from the self-assembly of the corresponding molecular "clips" and 2,4,6-tri(4-pyridyl)-1,3,5-triazine ligands in good yields. These organometallic cages can form inclusion systems with a wide variety of ?-donor substrates, including coronene, pyrene, [Pt(acac)(2)], and hexamethoxytriphenylene. The 1:1 complexation of the resulting supramolecular assemblies was confirmed by (1)H NMR spectroscopy. Large complexation shifts (??>1 ppm) were observed in the (1)H NMR spectra of guests in the presence of cage [Cp*(6)M(6)(?-DHNA)(3)(tpt)(2)](OTf)(6) (6a; M=Ir, tpt=2,4,6-tri(4-pyridyl)-1,3,5-triazine). The formation of discrete 1:1 donor-acceptor complexes, pyrene?6b (M=Rh), coronene?6a, coronene?6b, and [Pt(acac)(2)]?6a was confirmed by their single-crystal X-ray analyses. In these systems, the most important driving force for the formation of guest-host complexes is clearly the donor-acceptor ?···? stacking interaction, including charge-transfer interactions between the electron-donating and electron-accepting aromatic components. These structures provide compelling evidence for the existence of strong attractive forces between the electron-deficient triazine core and electron-rich guest. The results presented here may provide useful guidance for designing artificial receptors for functional biomolecules. PMID:22392820

Han, Ying-Feng; Li, Hao; Zheng, Zhi-Fang; Jin, Guo-Xin



Optical Detection of Aqueous Phase Analytes via Host-Guest Interactions on a Lipid Membrane Surface  

SciTech Connect

The organization and assembly of molecules in cellular membranes is orchestrated through the recognition and binding of specific chemical signals. A simplified version of the cellular membrane system has been developed using a synthetically prepared membrane receptor incorporated into a biologically derived lipid bilayer. Through an interplay of electrostatic and van der Wards interactions, aggregation or dispersion of molecular components could be executed on command using a specific chemical signal. A pyrene fluorophore was used as an optical probe to monitor the aggregational state of the membrane receptors in the bilayer matrix. The pyrene excimer emission to monomer emission (E/M) intensity ratio gave a relative assessment of the local concentration of receptors in the membrane. Bilayers were prepared with receptors selective for the divalent metal ions of copper, mercury, and lead. Addition of the metal ions produced a rapid dispersion of aggregated receptor components at nano- to micro-molar concentrations. The process was reversible by sequestering the metal ions with EDTA. Receptors for proteins and polyhistidine were also prepared and incorporated into phosphatidylcholine lipid bilayers. In this case, the guest molecules bound to the membrane through multiple points of interaction causing aggregation of initially dispersed receptor molecules. The rapid, selective, and sensitive fluorescence optical response of these lipid assemblies make them attractive in sensor applications for aqueous phase metal ions and polypeptides.

Sasaki, D.Y.; Waggoner, T.A.



Light-harvesting host-guest antenna materials for solar energy conversion devices  

NASA Astrophysics Data System (ADS)

In natural photosynthesis, light is absorbed by photonic antenna systems consisting of a few hundred chlorophyll molecules. These devices allow fast energy transfer from an electronically excited molecule to an unexcited neighbour molecule in such a way that the excitation energy reaches the reaction centre with high probability. Trapping occurs there. The anisotropic arrangement of the chlorophyll molecules is important for efficient energy migration. In natural antennae the formation of aggregates is prevented by fencing the chlorophyll molecules in polypeptide cages. A similar approach is possible by enclosing dyes inside a microporous material and by choosing conditions such that the cavities are able to uptake only monomers but not aggregates. In most of our experiments we have been using zeolite L as a host because it was found to be very versatile. Its crystals are of cylindrical shape and consist of an extended one-dimensional tube system. They can be prepared in wide size range. We have filled the individual tubes with successive chains of different dye molecules and we have shown that photonic antenna materials can be prepared. Moreover, fluorescent dye molecules can be bound covalently to the channel entrances. Dependent on the spectral properties of these stopcock molecules, the electronic excitation energy is transported radiationless to the stopcock fixed at the ends of the nanochannels or injected from the stopcock to the dyes inside the zeolite. The radiationless energy migration is in competition with spontaneous emission, thermal deactivation, quenching, and photochemically induced degradation. Fast energy migration is therefore crucial for an efficient antenna material. - The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within the volume of a dye-loaded zeolite L crystal and radiationless transport to both ends of the cylinder or from the ends to the centre. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the zeolite L channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device via a stopcock intermediate. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation energy transfer phenomena, and challenges for developing new photonic devices for solar energy conversion and storage.

Huber, Stefan; Calzaferri, Gion



Substrate induced phosphorescence from cyclodextrin·lumophore host-guest complexes  

Microsoft Academic Search

Hydrogen bonding substrates (S) trigger bright phosphorescence upon their addition to aqueous solutions containing 1-bromonaphthalene (1-BrNp) and a glucosyl modified cyclodextrin (G?-CD). Steady-state and time-resolved luminescence measurements establish that the phosphorescence arises from 1-BrNp as part of a 1-BrNp·G?-CD·S complex. In all cases, the substrate comprises a bulky t-butyl or cyclohexyl group spaced from the functional group of an alcohol,

Wanda K. Hartmann; Mike H. B. Gray; Adrian Ponce; Daniel G. Nocera; Peter A. Wong



Supramolecular hydrogels from in situ host-guest inclusion between chemically modified cellulose nanocrystals and cyclodextrin.  


When grafted ?-cyclodextrin is used as targeting sites, Pluronic polymers have been introduced on the surface of cellulose nanocrystals by means of inclusion interaction between ?-cyclodextrin and hydrophobic segment of the polymer. Because of the steric stabilization effect, surface poly(ethylene glycol) chains facilitate the dispersion and compatibility of nanocrystals, which also enhance the loading levels of nanocrystals in the hydrogel system. Meanwhile, uncovered poly(ethylene glycol) segments render the participating inclusion of ?-cyclodextrin for the architecture of in situ hydrogels. Surface grafting and inclusion reactions were proved by solid (13)C NMR and FTIR. Grafting efficiency of ?-cyclodextrin and inclusion efficiency of Pluronic on the surface of nanocrystals were confirmed by UV spectroscopy and elemental analysis. A significant enhancement of the structural and thermal stability of in situ hydrogels with high loading levels of modified nanocrystals (>5.77 wt %) was observed by rheological analysis. Further study reveals the performance and behavior of hydrogels under a different pH environment. Finally, in situ hydrogels were used as drug carrier for in vitro release of doxorubicin and exhibit the behavior of prolonged drug release with special release kinetics. PMID:23347071

Lin, Ning; Dufresne, Alain



Supramolecular cross-linked networks via host-guest complexation with cucurbit[8]uril.  


The ability to finely tune the solution viscosity of an aqueous system is critical in many applications ranging from large-scale fluid-based industrial processes to free-standing hydrogels important in regenerative medicine, controlled drug delivery, and 'green' self-healing materials. Herein we demonstrate the use of the macrocyclic host molecule cucurbit[8]uril (CB[8]) to facilitate reversible cross-linking of multivalent copolymers with high binding constants (K(a) > 10(11)-10(12) M(-2)) leading to a supramolecular hydrogel. Multivalent copolymers were prepared by free radical polymerization techniques and contained either pendant methyl viologen (a good first guest for CB[8]) or naphthoxy derivatives (good second guests for CB[8]). A colorless solution of the two multivalent copolymers bearing first and second guests, respectively, can be transformed into a highly viscous, colored supramolecular hydrogel with the cross-link density being easily controlled through CB[8] addition. Moreover, the cross-links (1:1:1 supramolecular ternary complexes of CB[8]/viologen/naphthoxy) are dynamic and stimuli-responsive, and the material properties can be modulated by temperature or other external stimuli. Rheological characterization of the bulk material properties of these dynamically cross-linked networks provided insight into the kinetics of CB[8] ternary complexation responsible for elastically active cross-linking with a second guest dissociation rate constant (k(d)) of 1200 s(-1) for the ternary complex. These materials exhibited intermediate mechanical properties at 5 wt % in water (plateau modulus = 350-600 Pa and zero-shear viscosity = 5-55 Pa·s), which is complementary to existing supramolecular hydrogels. Additionally, these supramolecular hydrogels exhibited thermal reversibility and subsequent facile modulation of microstructure upon further addition of CB[8] and thermal treatment. The fundamental knowledge gained from the study of these dynamic materials will facilitate progress in the field of smart, self-healing materials, self-assembled hydrogels, and controlled solution viscosity. PMID:20845973

Appel, Eric A; Biedermann, Frank; Rauwald, Urs; Jones, Samuel T; Zayed, Jameel M; Scherman, Oren A



Host-guest molecular interactions in vanillin/amylose inclusion complexes.  


The interaction of 4-hydroxy-3-methoxybenzaldehyde (vanillin) and Hylon VII due to the formation of an inclusion complex is studied using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), and circular dichroism (CD). The results confirm the close interaction among the different functional groups of vanillin and its host. In addition, a second case study was carried out with an amylose from a different source (100% amylose [APT III]). As a result, remarkable differences were found in the vanillin complexation capability of this amylose, which is only shown in solution by circular dichroism spectroscopy studies through a clear Cotton effect. This finding confirms the value of using CD studies, which shows that, depending on the amylose source, inclusion complexes can be found in solution, or both in solution and the coexisting precipitates, as shown using other techniques, such as X-ray diffraction (XRD) or differential scanning calorimetry (DSC). Moreover, solubility assays and complexation of both starches with iodine and subsequent absorption spectroscopy studies gives more information regarding the possible source of the starch encapsulation capability. Thus, Hylon VII shows higher capacity as vanillin encapsulant than APT III, showing the formation of inclusion complexes both in solution and solid phase, whereas APT III complexes are only perceivable in solution. PMID:23876727

Rodríguez, Silvio D; Bernik, Delia L



Specific host-guest interactions in a protein-based artificial transaminase.  


Artificial enzymes can be created by covalent attachment of a catalytic active group to a protein scaffold. Recently, we assembled an artificial transaminase by conjugation of intestinal fatty acid binding protein (IFABP) with a pyridoxamine derivative via a disulfide bond; the resulting construct catalyzed a transamination reaction 200-fold faster than free pyridoxamine. To identify the origin of this increased catalytic efficiency computer modeling was first used to identify two putative residues, Y14 and R126, that were in close proximity to the gamma-carboxylate group of the substrate, alpha-ketoglutartate. These positions were mutated to phenylalanine and methionine, respectively, and used to prepare semisynthetic transaminases by conjugation to pyridoxamine (Px) or an N-methylated derivative (MPx). Kinetic analysis of the resulting constructs showed that the R126M mutation reduced substrate affinity 3- to 6-fold while the additional Y14F mutation had a negligible effect. These results are consistent with a model for substrate recognition that involves an electrostatic interaction between the cationic guanidinium group of R126 and the anionic carboxylate from the substrate. Interestingly, one of the conjugates that contains an N-methylated pyridoxamine catalyzes a transamination reaction with a k(cat)' value of 1.1h(-1) which is the fastest value for k(cat) we have thus far obtained and is 34-fold greater than that for the free cofactor in the absence of the protein. PMID:11553487

Häring, D; Distefano, M D



Highly Stable Host-Guest Photorefractive Polymer Composite with Low Glass Transition Temperature  

NASA Astrophysics Data System (ADS)

We studied the phase stability and photorefractive properties of a new poly(N-vinylcarbazole) (PVK)-based photorefractive polymer composite by modifying the structure of a nonlinear optical chromophore (NLO), 4-butoxy-3-propyl-1-(4'-nitrophenyazo)benzene. The shelf life of a sample with a modified NLO, 4-(2-ethylhexyloxy)3-propyl-1-(4'-nitrophenyazo) benzene was extended by more than five months even though it had a low glass transition temperature (Tg) of -19°C. This material also had a short photorefractive response time constant of 33 ms and a high diffraction efficiency of 49% at an electric field of 100 V/?m and a total writing intensity of 942 mW/cm2. These desirable characteristics are believed to be due to the following reasons: first, the new chromophore acts as a plasticizer, thereby enhancing the orientation of the NLO and second, the solubility of the chromophore in a polymer matrix increases, inhibiting crystallization and providing a high optical quality.

Jung, Gyeong Bok; Akazawa, Takayuki; Mutai, Toshiki; Fujimura, Ryushi; Ashihara, Satoshi; Shimura, Tsutomu; Araki, Koji; Kuroda, Kazuo



Host-guest chemistry of copper(II)-histidine complexes encaged in zeolite Y.  


Structural analysis has been carried out on copper(II)-histidine (Cu(2+)/His) complexes after immobilization in the pore system of the zeolites NaY and de-aluminated NaY (DAY). The aim of this study was to determine the geometrical structure of Cu(2+)/His complexes after encaging, to obtain insight into both the effect of the zeolite matrix on the molecular structure and redox properties of the immobilized complexes. In addition to N(2) physisorption and X-ray fluorescence (XRF) analyses, a combination of UV/Vis/NIR, ESR, X-ray absorption (EXAFS and XANES), IR, and Raman spectroscopy was used to obtain complementary information on both the first coordination shell of the copper ion and the orientation of the coordinating His ligands. It was demonstrated that two complexes (A and B) are formed, of which the absolute and relative abundance depends on the Cu(2+)/His concentration in the ion-exchange solution and on the Si/Al ratio of the zeolite material. In complex A, one His ligand coordinates in a tridentate facial-like manner through N(am), N(im), and O(c), a fourth position being occupied by an oxygen atom from a zeolite Brønsted site. In complex B, two His ligands coordinate as bidentate ligands; one histamine-like (N(am), N(im)) and the other one glycine-like (N(am), O(c)). In particular the geometrical structure of complex A differs from the preferred structure of Cu(2+)/His complexes in aqueous solutions; this fact implies that the zeolite host material actively participates in the coordination and orientation of the guest molecules. The tendency for complex A to undergo reduction in inert atmosphere to Cu(1+) (as revealed by dynamic XANES studies) suggests activation of complex A by the interaction with the zeolite material. EXAFS analysis confirms the formation of a distorted four coordinate geometry of complex A, suggesting that the combination of zeolite and one His ligand force the Cu(2+) complex into an activated, entactic state. PMID:16807946

Mesu, J Gerbrand; Visser, Tom; Beale, Andrew M; Soulimani, Fouad; Weckhuysen, Bert M



Electrochemiluminescent cells based on zeolite-encapsulated host-guest systems: encapsulated ruthenium tris-bipyridyl.  


An electrochemiluminescent cell has been developed that has an active layer consisting of ruthenium tris-bipyridyl encapsulated inside zeolite Y supercages. Operation of the cell requires the addition of polyethylene glycol as the solid electrolyte. The cell, which exhibits electrical conductivity behavior typical of a semiconductor, has an optimum operating voltage of 3 V. Ion exchange of sodium by cesium and vapor deposition of calcium metal inside the zeolite pores enhance the electrochemiluminescent efficiency of the cell by a factor of 4. PMID:17285650

Alvaro, Mercedes; Cabeza, Jose F; Fabuel, David; Corma, Avelino; García, Hermenegildo



Control of H- and J-aggregate formation via host-guest complexation using cucurbituril hosts.  


The binding interactions between two cyanine dyes, pseudoisocyanine (PIC) and pinacyanol (PIN), and the cucurbit[n]uril hosts, cucurbit[7]uril (CB7) and cucurbit[6]uril (CB6), were investigated by electronic absorption spectroscopy and DFT computational methods. The CB7 host forms more stable complexes with both dyes than CB6 and the computational studies suggest that the cavity of the smaller host CB6 is not threaded by the dyes. The equilibrium association constants (K) for complexation by CB7 were measured and found to be 2.05 x 10(4) and 3.84 x 10(5) M(-1) for PIC and PIN, respectively, in aqueous media at 23 degrees C. CB7 complexation was found to effectively disrupt the intermolecular forces responsible for the aggregation of both dyes. Thus, CB7 completely disrupts the J-aggregates formed by PIC and the H-aggregates (as well as lower concentrations of J-aggregates) formed by PIN. In both cases a competing guest, 1-aminoadamantane (AD), could be used to adjust the extent of aggregation of the cyanine dye. AD regulates aggregate formation because it forms an extremely stable complex with CB7 (K approximately = 10(12) M(-1)) and exerts a tight control on the CB7 concentration available to interact and bind with the dye. PMID:19007116

Gadde, Suresh; Batchelor, Elizabeth K; Weiss, Joshua P; Ling, Yonghua; Kaifer, Angel E



Quantification of surface functional groups on polymer microspheres by supramolecular host-guest interactions.  


We introduce a method to determine the number of accessible functional groups on a polymer microsphere surface based on the interaction between the macrocyclic host cucurbit[7]uril (CB7) and a guest reacted to the microsphere surface. After centrifugation, CB7 in the supernatant is quantified by addition of a fluorescent dye. The difference between added and detected CB7 affords the number of accessible surface functional groups. PMID:21647510

Hennig, Andreas; Hoffmann, Angelika; Borcherding, Heike; Thiele, Thomas; Schedler, Uwe; Resch-Genger, Ute



Modulation in prototropism of the photosensitizer Harmane by host:guest interactions between ?-cyclodextrin and surfactants.  


The present contribution demonstrates the photophysics of a prospective cancer cell photosensitizer Harmane (HM) belonging to the family of ?-carboline in mixed microheterogeneous environments of ?-cyclodextrin (?-CD) and surfactants having varying surface charges using steady-state and time-resolved fluorescence spectroscopic techniques. The remarkable modulations in prototropic activities of the micelle-bound drug in the presence of ?-CD evinces for disruption of the micellar structural integrity by ?-CD. The results are meticulously discussed in relevance to the effect of a potential drug delivery vehicle (CD) on the membrane-mimetic micellar system. Further, application of an extrinsic fluorescence probe for monitoring such interactions is fraught by the possibilities of no less than three equilibria that can operate simultaneously viz., (i) surfactant-cyclodextrin, (ii) surfactant-fluorophore and (iii) cyclodextrin-fluorophore. This aspect highlights the enormous importance of the issue of suitability of the fluorescence probe to study such complicated systems and interaction phenomena. Also the varying interaction scenario of ?-CD with the nature of the surfactant highlights the importance of precise knowledge of the strength and locus of drug binding in delineating such complex interactions. The results of the present investigation advocate for the potential applicability of the drug (HM) itself as a fluorescence reporter in study of such complex microheterogeneous interactions. PMID:24060109

Paul, Bijan K; Ray, Debarati; Ganguly, Aniruddha; Guchhait, Nikhil



A cyclodextrin host-guest recognition approach to a label-free electrochemical DNA hybridization biosensor.  


A novel label-free electrochemical DNA hybridization biosensor using a ?-cyclodextrin/poly(N-acetylaniline)/carbon nanotube composite modified screen printed electrode (CD/PNAANI/CNT/SPE) has been developed. The proposed DNA hybridization biosensor relies on the intrinsic oxidation signals of guanine (G) and adenine (A) from single-stranded DNA entered into the cyclodextrin (CD) cavity. Due to the binding of G and A bases to complementary cytosine and thymine bases in dsDNA, the signals obtained for ssDNA were much higher than that of dsDNA. The synergistic effect of the multi-walled carbon nanotubes provides a significantly enhanced voltammetric signal, and the CD encapsulation effect makes anodic peaks of G and A shift to less positive potentials than that at the bare SPE. The peak heights of G and A signals are dependent on both the number of the respective bases in oligonucleotides and the concentration of the target DNA sequences. Hybridization of complementary strands was monitored through the measurements of oxidation signal of purine bases, which enabled the detection of target sequences from 0.01 to 1.02 nmol ?l(-1) with the detection limit of target DNA as low as 5.0 pmol ?l(-1) (S/N = 3). Implementation of label-free and homogeneous electrochemical hybridization detection constitutes an important step toward low-cost, simple, highly sensitive and accurate DNA assay. Discrimination between complementary, noncomplementary, and two-base mismatch targets was easily accomplished using the proposed electrode. PMID:22398413

Abbaspour, Abdolkarim; Noori, Abolhassan



Host-Guest Interaction Mediated Polymeric Core-Shell Assemblies: Versatile Nanocarriers for Drug Delivery  

PubMed Central

Novel hydrophilic-hydrophilic block copolymer with one block containing ?-cyclodextrin was synthesized. Core-shell structured nano-assemblies with chemical sensitivity could be constructed by this copolymer in the presence of hydrophobic compounds. By selecting appropriate guest components, polyion complex micelles could also be assembled. These results suggest the potential versatile applications of this type of copolymers in pharmaceutics, nanomedicine, and nano-biotechnology.

Zhang, Jianxiang; Ma, Peter X.



Comparison of host-guest Langmuir-Blodgett multilayer formation by two different amphiphilic cyclodextrins  

SciTech Connect

We report here our results for Langmuir monolayers of the derivatives of cyclodextrin shown: hexakis(6-deoxy-6-dodecylamino)-{alpha}-cyclodextrin (1a), heptakis(6-deoxy-6-dodecylamino)-{beta}-cyclodextrin (1b), and heptakis(6-deoxy-6-dodecylthio)-{beta}-cyclodextrin (2b ), which was found to be partially substituted. Langmuir films of these derivatives were examined using {Pi}-A isotherm measurements and Brewster angle microscopy. Langmuir-Blodgett (LB) multilayer films of these derivatives were deposited from subphases containing p-nitrophenol to determine the extent of incorporation of the guest molecule in the LB film. The transfer ratios of the film exhibited a noteworthy evolution with the transfer pressure. The variation in the extent of guest molecule incorporation is discussed and compared with the binding behavior in solution of unmodified cyclodextrins. 29 refs., 4 figs.

Parazak, D.P.; Khan, A.R.; D`Souza, V.T.; Stine, K.J. [Univ. of Missouri, St. Louis, MO (United States)



Highly ordered alignment of a vinyl polymer by host-guest cross-polymerization  

NASA Astrophysics Data System (ADS)

Chain alignment can significantly influence the macroscopic properties of a polymeric material, but no general and versatile methodology has yet been reported to obtain highly ordered crystalline packing of polymer chains, with high stability. Here, we disclose a strategy that relies on ‘ordered crosslinks’ to produce polymeric materials that exhibit a crystalline arrangement. Divinyl crosslinkers (2,5-divinyl-terephthalate) were first embedded, as substitutional ligands, into the structure of a porous coordination polymer (PCP), [Cu(terephthalate)triethylenediamine0.5]n. A representative vinyl monomer, styrene, was subsequently polymerized inside the channels of the host PCP. The polystyrene chains that form within the PCP channels also crosslink with the divinyl species. This bridges together the polymer chains of adjacent channels and ensures that, on selective removal of the PCP, the polymer chains remain aligned. Indeed, the resulting material exhibits long-range order and is stable to thermal and solvent treatments, as demonstrated by X-ray powder diffraction and transmission electron microscopy.

Distefano, Gaetano; Suzuki, Hirohito; Tsujimoto, Masahiko; Isoda, Seiji; Bracco, Silvia; Comotti, Angiolina; Sozzani, Piero; Uemura, Takashi; Kitagawa, Susumu



Optical Tweezers as a New Biomedical Tool to Measure Zeta Potential of Stored Red Blood Cells  

PubMed Central

During storage, red blood cells (RBCs) for transfusion purposes suffer progressive deterioration. Sialylated glycoproteins of the RBC membrane are responsible for a negatively charged surface which creates a repulsive electrical zeta potential. These charges help prevent the interaction between RBCs and other cells, and especially among each RBCs. Reports in the literature have stated that RBCs sialylated glycoproteins can be sensitive to enzymes released by leukocyte degranulation. Thus, the aim of this study was, by using an optical tweezers as a biomedical tool, to measure the zeta potential in standard RBCs units and in leukocyte reduced RBC units (collected in CPD-SAGM) during storage. Optical tweezers is a sensitive tool that uses light for measuring cell biophysical properties which are important for clinical and research purposes. This is the first study to analyze RBCs membrane charges during storage. In addition, we herein also measured the elasticity of RBCs also collected in CPD-SAGM. In conclusion, the zeta potential decreased 42% and cells were 134% less deformable at the end of storage. The zeta potential from leukodepleted units had a similar profile when compared to units stored without leukoreduction, indicating that leukocyte lyses were not responsible for the zeta potential decay. Flow cytometry measurements of reactive oxygen species suggested that this decay is due to membrane oxidative damages. These results show that measurements of zeta potentials provide new insights about RBCs storage lesion for transfusion purposes.

Silva, Carlos A. L.; Fernandes, Heloise P.; Filho, Milton M.; Lucena, Sheyla C.; Costa, Ana Maria D. N.; Cesar, Carlos L.; Barjas-Castro, Maria L.; Santos, Beate S.; Fontes, Adriana



Laser scanning confocal microscopy and laser tweezers based experiments to understand dentine-bacteria interactions  

NASA Astrophysics Data System (ADS)

Failure of endodontic treatment is commonly due to Enterococcal infection. In this study influence of chemical treatments of type-I collagen membrane by chemical agents commonly used in endodontic treatment on Enterococcus faecalis cell adherence was evaluated. In order to determine the change in number of adhering bacteria after chemical treatment, confocal laser scanning microscopy was used. For this, overnight culture of E faecalis in All Culture broth was applied to chemically treated type-I collagen membrane. It was found that Ca(OH)2 treated groups had statistically significant (p value=0.05) increase in population of bacteria adherence. The change in adhesion force between bacteria and collagen was determined by using optical tweezers (1064 nm). For this experiment, Type-I collagen membrane was soaked for 5 mins in a media that contained 50% all culture media and 50% saturated Ca(OH)2 . The membrane was spread on the coverslip, on which diluted bacterial suspension was added. The force of laser tweezers on the bacteria was estimated at different trap power levels using viscous drag method and trapping stiffness was calculated using Equipartition theorem method. Presence of Ca(OH)2 was found to increase the cell-substrate adherence force from 0.38pN to >2.1pN. Together, these experiments show that it was highly probable that the increase in adherence to collagen was due to a stronger adhesion in the presence of Ca (OH)2.

Peng, Sum Chee; Mohanty, Samarendra; Gupta, P. K.; Kishen, Anil



Combined versatile high-resolution optical tweezers and single-molecule fluorescence microscopy  

PubMed Central

Optical trapping and single-molecule fluorescence are two major single-molecule approaches. Their combination has begun to show greater capability to study more complex systems than either method alone, but met many fundamental and technical challenges. We built an instrument that combines base-pair resolution dual-trap optical tweezers with single-molecule fluorescence microscopy. The instrument has complementary design and functionalities compared with similar microscopes previously described. The optical tweezers can be operated in constant force mode for easy data interpretation or in variable force mode for maximum spatiotemporal resolution. The single-molecule fluorescence detection can be implemented in either wide-field or confocal imaging configuration. To demonstrate the capabilities of the new instrument, we imaged a single stretched ? DNA molecule and investigated the dynamics of a DNA hairpin molecule in the presence of fluorophore-labeled complementary oligonucleotide. We simultaneously observed changes in the fluorescence signal and pauses in fast extension hopping of the hairpin due to association and dissociation of individual oligonucleotides. The combined versatile microscopy allows for greater flexibility to study molecular machines or assemblies at a single-molecule level.

Sirinakis, George; Ren, Yuxuan; Gao, Ying; Xi, Zhiqun; Zhang, Yongli



Formation of an artificial blood vessel: adhesion force measurements with optical tweezers  

NASA Astrophysics Data System (ADS)

We are investigating the formation of a tissue capsule around a foreign body. This tissue capsule can be used as an autologous graft for the replacement of diseased blood vessels or for bypass surgery. The graft is grown in the peritoneal cavity of the recipient and the formation starts with the adhesion of cells to the foreign body. We identify the cell type and measure the adhesion of these cells to foreign materials using optical tweezers. Cell adhesion to macroscopic samples and microspheres is investigated. No difference in the adhesion force was measurable for polyethylene, silicon and Tygon on a scale accessible to optical tweezers. The density of adherent cells was found to vary strongly, being highest on polyethylene. The mean rupture forces for cell-microsphere adhesion ranged from 24 to 39 pN and changed upon preadsorption of bovine serum albumin. For plain microspheres, the highest mean rupture force was found for PMMA, which also showed the highest adhesion probability for the cell-microsphere interaction.

Knoener, Gregor; Campbell, Julie H.; Heckenberg, Norman R.; Rubinsztein-Dunlop, Halina



Counter-propagating dual-trap optical tweezers based on linear momentum conservation  

NASA Astrophysics Data System (ADS)

We present a dual-trap optical tweezers setup which directly measures forces using linear momentum conservation. The setup uses a counter-propagating geometry, which allows momentum measurement on each beam separately. The experimental advantages of this setup include low drift due to all-optical manipulation, and a robust calibration (independent of the features of the trapped object or buffer medium) due to the force measurement method. Although this design does not attain the high-resolution of some co-propagating setups, we show that it can be used to perform different single molecule measurements: fluctuation-based molecular stiffness characterization at different forces and hopping experiments on molecular hairpins. Remarkably, in our setup it is possible to manipulate very short tethers (such as molecular hairpins with short handles) down to the limit where beads are almost in contact. The setup is used to illustrate a novel method for measuring the stiffness of optical traps and tethers on the basis of equilibrium force fluctuations, i.e., without the need of measuring the force vs molecular extension curve. This method is of general interest for dual trap optical tweezers setups and can be extended to setups which do not directly measure forces.

Ribezzi-Crivellari, M.; Huguet, J. M.; Ritort, F.



Investigation of the mechanical property of individual cell using axial optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers is a technique that can trap and manipulate small objects using a highly focused laser beam. Because optical tweezers can also be used to measure small forces, it has been extensively used for the measurement of the mechanical forces of cells. Previous research works typically study particle manipulation and cell force measurement in the lateral direction, hence excluding valuable insights about the axial mechanical properties of cells. Other works that investigate axial cell force measurements utilize spatial light modulators and other devices that are expensive and complicate the setup. Thus, in our study, we designed a simple scheme that can axially manipulate particles by adjusting the position of one lens, called L1-lens, in our setup. Image processing techniques were utilized to determine the changes in the axial particle translation, providing nanometer sensitivity. We investigated the capability of our system using two different-sized particles and results show that for a given L1-lens default position and movement, a 2-micron particle and a 4.26-micron particle were moved axially for 7.68 µm and 4.83 µm, respectively. Axial trapping stiffness was also measured for the stated bead sizes in different magnification. Using the computed trapping sti_ness, we will investigate the axial reactive forces of cells.

Dy, Mary-Clare; Sugiura, Tadao; Minato, Kotaro



In situ microparticle analysis of marine phytoplankton cells with infrared laser-based optical tweezers  

NASA Astrophysics Data System (ADS)

We describe the application of infrared optical tweezers to the in situ microparticle analysis of marine phytoplankton cells. A Nd:YAG laser (lambda=3D 1064 nm) trap is used to confine and manipulate single Nannochloris and Synechococcus cells in an enriched seawater medium while spectral fluorescence and Lorenz-Mie backscatter signals are simultaneously acquired under a variety of excitation and trapping conditions. Variations in the measured fluorescence intensities of chlorophyll a (Chl a) and phycoerythrin pigments in phytoplankton cells are observed. These variations are related, in part, to basic intrasample variability, but they also indicate that increasing ultraviolet-exposure time and infrared trapping power may have short-term effects on cellular physiology that are related to Chl a photobleaching and laser-induced heating, respectively. The use of optical tweezers to study the factors that affect marine cell physiology and the processes of absorption, scattering, and attenuation by individual cells, organisms, and particulate matter that contribute to optical closure on a microscopic scale are also described. (c)1995 Optical Society of America

Sonek, G. J.; Liu, Y.; Iturriaga, R. H.



Simulation of heart infarction by laser microbeams and induction of arrhythmias by optical tweezers  

NASA Astrophysics Data System (ADS)

Laser microbeam and optical tweezers were used for micromanipulation of a heart tissue model consisting of embryonic chicken cardiomyocytes and bibroblasts. Using the laser microbeam a would was created, i.e. a sort of artificial heart infarction was generated. The first steps of wound repair were observed by live cell imaging. A complete filling of teh would primarily by migrating fibroblasts but not by cardiomyocytes was detected 18 hours after wounding. In another set of experiments erythrocyte mediated force application (EMFA) by optical tweezers was applied for optomechanical manipulatoin of cardiomyocytes and fibroblasts. Here we demonstrate induction of dramatic distrubances of calcium waves in a group of synchronously beating cardiomyocytes by an optomechanical input that results in cellular deformation. Surprisingly, it was found that putatively non-excitable fibroblasts respond to this mechanical stress with calcium oscillations. The results reported here indicate that the induction of artificial heart infarction can provide insights into healing processes after mycardial injury. EMFA is capable to examine effects of myocardial overload and to provide important information about processes triggered by mechanical stress on the level of single or very few cells. As a perspective, the preseneted techniques may be used to study the influence of drugs on wound healing and coordination of beating in the heart.

Perner, Birgit; Monajembashi, Shamci; Rapp, Alexander; Wollweber, Leo; Greulich, Karl Otto



Electrochemical detection of single microbeads manipulated by optical tweezers in the vicinity of ultramicroelectrodes.  


Latex micrometric beads are manipulated by optical tweezers in the vicinity of an ultramicroelectrode (UME). They are optically trapped in solution and approached the electrode surface. After the electrochemical measurement, they are optically removed from the surface. The residence time of the particle on the electrode is thus controlled by the optical tweezers. The detection is based on diffusional hindrance by the insulating objects which alters the fluxes of the redox Ru(NH3)6(3+) species toward the UME and thus its mass-transfer limited current. We have optically deposited successively 1, 2, and 3 beads of 3-?m radius on the UME surface, and we have recorded the variations of the current depending on their landing locations that were optically controlled. Finally we decreased the current by partially blocking the electroactive surface with a six-bead assembly. The variation of the steady-state current and the approach curves allow for the indirect electrochemical localization of the bead in the vicinity of the UME, not only when the bead is in contact but also when it is levitated at distances lower than the UME radius. These experiments show that single particles or more complex structures may be manipulated in situ in a contactless mode near the UME surface. From comparison with simulations, the electrochemical detection affords an indirect localization of the object in the UME environment. The developed approach offers a potential application for interrogating the electrochemical activity of single cells and nanoparticles. PMID:24020821

Suraniti, Emmanuel; Kanoufi, Frédéric; Gosse, Charlie; Zhao, Xuan; Dimova, Rumiana; Pouligny, Bernard; Sojic, Neso



Combined versatile high-resolution optical tweezers and single-molecule fluorescence microscopy  

NASA Astrophysics Data System (ADS)

Optical trapping and single-molecule fluorescence are two major single-molecule approaches. Their combination has begun to show greater capability to study more complex systems than either method alone, but met many fundamental and technical challenges. We built an instrument that combines base-pair resolution dual-trap optical tweezers with single-molecule fluorescence microscopy. The instrument has complementary design and functionalities compared with similar microscopes previously described. The optical tweezers can be operated in constant force mode for easy data interpretation or in variable force mode for maximum spatiotemporal resolution. The single-molecule fluorescence detection can be implemented in either wide-field or confocal imaging configuration. To demonstrate the capabilities of the new instrument, we imaged a single stretched ? DNA molecule and investigated the dynamics of a DNA hairpin molecule in the presence of fluorophore-labeled complementary oligonucleotide. We simultaneously observed changes in the fluorescence signal and pauses in fast extension hopping of the hairpin due to association and dissociation of individual oligonucleotides. The combined versatile microscopy allows for greater flexibility to study molecular machines or assemblies at a single-molecule level.

Sirinakis, George; Ren, Yuxuan; Gao, Ying; Xi, Zhiqun; Zhang, Yongli



Application of laser tweezers Raman spectroscopy techniques to the monitoring of single cell response to stimuli  

NASA Astrophysics Data System (ADS)

Laser tweezers Raman spectroscopy (LTRS) combines optical trapping with micro-Raman spectroscopy to enable label-free biochemical analysis of individual cells and small biological particles in suspension. The integration of the two technologies greatly simplifies the sample preparation and handling of suspension cells for spectroscopic analysis in physiologically meaningful conditions. In our group, LTRS has been used to study the effects of external perturbations, both chemical and mechanical, on the biochemistry of the cell. Single cell dynamics can be studied by performing longitudinal studies to continuously monitor the response of the cell as it interacts with its environment. The ability to carry out these measurements in-vitro makes LTRS an attractive tool for many biomedical applications. Here, we discuss the use of LTRS to study the response of cancer cells to chemotherapeutics and bacteria cells to antibiotics and show that the life cycle and apoptosis of the cells can be detected. These results show the promise of LTRS for drug discovery/screening, antibiotic susceptibility testing, and chemotherapy response monitoring applications. In separate experiments, we study the response of red blood cells to the mechanical forces imposed on the cell by the optical tweezers. A laser power dependent deoxygenation of the red blood cell in the single beam trap is reported. Normal, sickle cell, and fetal red blood cells have a different behavior that enables the discrimination of the cell types based on this mechanochemical response. These results show the potential utility of LTRS for diagnosing and studying red blood cell diseases.

Chan, James W.; Liu, Rui; Matthews, Dennis L.



Magnetic Tweezers-Based Force Clamp Reveals Mechanically Distinct apCAM Domain Interactions  

PubMed Central

Cell adhesion molecules of the immunoglobulin superfamily (IgCAMs) play a crucial role in cell-cell interactions during nervous system development and function. The Aplysia CAM (apCAM), an invertebrate IgCAM, shares structural and functional similarities with vertebrate NCAM and therefore has been considered as the Aplysia homolog of NCAM. Despite these similarities, the binding properties of apCAM have not been investigated thus far. Using magnetic tweezers, we applied physiologically relevant, constant forces to apCAM-coated magnetic particles interacting with apCAM-coated model surfaces and characterized the kinetics of bond rupture. The average bond lifetime decreased with increasing external force, as predicted by theoretical considerations. Mathematical simulations suggest that the apCAM homophilic interaction is mediated by two distinct bonds, one involving all five immunoglobulin (Ig)-like domains in an antiparallel alignment and the other involving only two Ig domains. In summary, this study provides biophysical evidence that apCAM undergoes homophilic interactions, and that magnetic tweezers-based, force-clamp measurements provide a rapid and reliable method for characterizing relatively weak CAM interactions.

Kilinc, Devrim; Blasiak, Agata; O'Mahony, James J.; Suter, Daniel M.; Lee, Gil U.



Optical Tweezers Experiments Resolve Distinct Modes of DNA-Protein Binding  

PubMed Central

Optical tweezers are ideally suited to perform force microscopy experiments that isolate a single biomolecule, which then provides multiple binding sites for ligands. The captured complex may be subjected to a spectrum of forces, inhibiting or facilitating ligand activity. In the following experiments, we utilize optical tweezers to characterize and quantify DNA binding of various ligands. High Mobility Group Type B (HMGB) proteins, which bind to double-stranded DNA, are shown to serve the dual purpose of stabilizing and enhancing the flexibility of double stranded DNA. Unusual intercalating ligands are observed to thread into and lengthen the double-stranded structure. Proteins binding to both double- and single-stranded DNA, such as the alpha polymerase subunit of E. coli Pol III, are characterized and the subdomains containing the distinct sites responsible for binding are isolated. Finally, DNA binding of bacteriophage T4 and T7 single-stranded DNA (ssDNA) binding proteins are measured for a range of salt concentrations, illustrating a binding model for proteins that slide along double-stranded DNA, ultimately binding tightly to ssDNA. These recently developed methods quantify both the binding activity of the ligand as well as the mode of binding.

McCauley, Micah J.; Williams, Mark C.



Optical tweezers experiments resolve distinct modes of DNA-protein binding.  


Optical tweezers are ideally suited to perform force microscopy experiments that isolate a single biomolecule, which then provides multiple binding sites for ligands. The captured complex may be subjected to a spectrum of forces, inhibiting or facilitating ligand activity. In the following experiments, we utilize optical tweezers to characterize and quantify DNA binding of various ligands. High mobility group type B (HMGB) proteins, which bind to double-stranded DNA, are shown to serve the dual purpose of stabilizing and enhancing the flexibility of double stranded DNA. Unusual intercalating ligands are observed to thread into and lengthen the double-stranded structure. Proteins binding to both double- and single-stranded DNA, such as the alpha polymerase subunit of E. coli Pol III, are characterized, and the subdomains containing the distinct sites responsible for binding are isolated. Finally, DNA binding of bacteriophage T4 and T7 single-stranded DNA (ssDNA) binding proteins is measured for a range of salt concentrations, illustrating a binding model for proteins that slide along double-stranded DNA, ultimately binding tightly to ssDNA. These recently developed methods quantify both the binding activity of the ligand as well as the mode of binding. PMID:19173290

McCauley, Micah J; Williams, Mark C



Design of hybrid optical tweezers system for controlled three-dimensional micromanipulation  

NASA Astrophysics Data System (ADS)

Three-dimensional (3D) micro/nano-manipulation using optical tweezers is a significant technique for various scientific fields ranging from biology to nanotechnology. For the dynamic handling of multiple/individual micro-objects in a true 3D working space, we present an improved hybrid optical tweezers system consisting of two multibeam techniques. These two techniques include the generalized phase contrast method with a spatial light modulator and the time-shared scanning method with a two-axis steering mirror and an electrically focus-tunable lens. Unlike our previously reported system that could only handle micro-objects in a two and half dimensional working space, the present system has high versatility for controlled manipulation of multiple micro-objects in a true 3D working space. The controlled rotation of five beads forming a pentagon, that of four beads forming a tetrahedron about arbitrary axes, and the fully automated assembly and subsequent 3D translation of micro-bead arrays are successfully demonstrated as part of the 3D manipulation experiment.

Tanaka, Yoshio; Tsutsui, Shogo; Kitajima, Hiroyuki



Measuring integrated cellular mechanical stress response at focal adhesions by optical tweezers  

NASA Astrophysics Data System (ADS)

The ability of cells to sustain mechanical stress is largely modulated by the cytoskeleton. We present a new application of optical tweezers to study cell's mechanical properties. We trap a fibronectin-coated bead attached to an adherent H4II-EC3 rat hepatoma cell in order to apply the force to the cell surface membrane. The bead position corresponding to the cell's local mechanical response at focal adhesions is measured with a quadrant detector. We assessed the cell response by tracking the evolution of the equilibrium force for 40 cells selected at random and selected a temporal window to assess the cell initial force expression at focal adhesions. The mean value of the force within this time window over 40 randomly selected bead/cell bounds was 52.3 pN. Then, we assessed the responses of the cells with modulation of the cytoskeletons, namely the ubiquitous actin-microfilaments and microtubules, plus the differentiation-dependent keratin intermediate filaments. Notably, a destabilization of the first two networks led to around 50 and 30% reductions in the mean equilibrium forces, respectively, relative to untreated cells, whereas a loss of the third one yielded a 25% increase. The differences in the forces from untreated and treated cells are resolved by the optical tweezers experiment.

Bordeleau, François; Bessard, Judicael; Marceau, Normand; Sheng, Yunlong



Using electrical and optical tweezers to facilitate studies of molecular motors†  

PubMed Central

Dielectrophoresis was used to stretch and suspend actin filaments across a trench etched between two electrodes patterned on a glass slide. Optical tweezers were used to bring a motor protein-coated bead into close proximity to a pre-selected, suspended actin filament, facilitating the attachment of the myosin-coated bead to the filament. The clearance beneath the filament allowed the bead to move freely along and around its filamentous track, unhindered by solid surfaces. Using defocused images, the three-dimensional position of the bead was tracked as a function of time to obtain its trajectory. Experiments were carried out with myosin V and myosin X. Both motor proteins followed left-handed helical paths with the myosin X motor exhibiting a shorter pitch than the myosin V. The combined use of electrostatic and optical tweezers facilitates the preparation of motility assays with suspended tracks. Variants of this technique will enable higher complexity experiments in vitro to better understand the behavior of motors in cells.

Arsenault, Mark E.; Sun, Yujie; Bau, Haim H.; Goldman, Yale E.



Optical tweezers and cell biomechanics in macro- and nano-scale  

NASA Astrophysics Data System (ADS)

The mechanical properties of cells, as well as their dysfunction, have been implicated in many aspects of human physiology and patho-physiology. Hence, new biophysical techniques, as optical tweezers, are of great importance for biomechanical measurements in both cells and cell simulators (e.g. liposomes). Liposomes are used, among other applications, as drug delivery nanosystems in cancer therapy. In this work, experimental measurements of the optical forces exerted by line optical tweezers on trapped cells (erythrocytes) and liposomes, using the dielectrophoresis method for calibration, are presented. Folding and elongation of trapped red blood cells was observed, in the direction of the electric field of incident beam, while, upon removal of the optical trap, the red blood cells were observed to unfold to their original biconcave shape. By measuring the folding and unfolding times, membrane elasticity properties such as bending modulus were estimated. Shear and bending modulus of liposomes were also estimated by measuring the liposome deformations, induced by optical forces along the beam long axis. The optical force is quasi-linearly increased with the increase of liposome diameter. In the elasticity regime, when the laser was turned off, the liposome acquired gradually its initial shape without any hysteresis.

Serafetinides, Alexander A.; Makropoulou, Mersini; Spyratou, Ellas



Elastic light scattering measurements from multiple red blood cells in elliptical optical tweezers  

NASA Astrophysics Data System (ADS)

Different theoretical models have been developed to understand light propagation in biological media and to facilitate the analysis of experimental data, both at the cellular level and in bulk tissues. Optical tweezers, combined with a light scattering measurement facility, enable the measurement of elastic light scattering distributions from single particles and cells. The aim of this paper is to present elastic light scattering measurement results from several red blood cells (RBCs) held in elliptical optical tweezers and to compare these results with theoretical predictions found in literature. Both faceon and rim-on incidence of He-Ne laser light (vertical polarization) in relation to the measured RBCs was considered. In the face-on case, light scattering intensity was larger from two RBCs than from one, but almost no difference was found when using three RBCs instead of two. In rim-on incidence, clear changes in the shape of the scattering light intensity field were found when the number of RBCs was increased from one to two. These results are supported by modelling results from literature.

Kauppila, Antti; Kinnunen, Matti; Karmenyan, Artashes; Myllylä, Risto



Optical trapping of a spherically symmetric sphere in the ray-optics regime: a model for optical tweezers upon cells  

SciTech Connect

Since their invention in 1986, optical tweezers have become a popular manipulation and force measurement tool in cellular and molecular biology. However, until recently there has not been a sophisticated model for optical tweezers on trapping cells in the ray-optics regime. We present a model for optical tweezers to calculate the optical force upon a spherically symmetric multilayer sphere representing a common biological cell. A numerical simulation of this model shows that not only is the magnitude of the optical force upon a Chinese hamster ovary cell significantly three times smaller than that upon a polystyrene bead of the same size, but the distribution of the optical force upon a cell is also much different from that upon a uniform particle, and there is a 30% difference in the optical trapping stiffness of these two cases. Furthermore, under a small variant condition for the refractive indices of any adjacent layers of the sphere, this model provides a simple approximation to calculate the optical force and the stiffness of an optical tweezers system.

Chang Yiren; Hsu Long; Chi Sien



Comparison of a high-speed camera and a quadrant detector for measuring displacements in optical tweezers  

Microsoft Academic Search

We compare the performance of a high-speed camera and a quadrant detector for measuring the displacement of micron-sized particles in optical tweezers. For trapping powers up to 100 mW, the standard deviation of the particle displacements measured by the two techniques shows excellent agreement. This comparison also provides a method for calibrating one technique against the other.

S. Keen; J. Leach; G. Gibson; M. J. Padgett



Observing dynamics of chromatin fibers in Xenopus egg extracts by single DNA manipulation using a transverse magnetic tweezer setup  

Microsoft Academic Search

We have studied assembly of chromatin on single DNAs using Xenopus egg extracts and a specially designed magnetic tweezer setup which generates controlled force in the focal plane of the objective, allowing us to visualize and measure DNA extension under a wide range of constant tensions. We found, in the absence of ATP, interphase extracts assembled nucleosomes against DNA tensions

Jie Yan; Dunja Skoko; John Marko; Tom Maresca; Rebecca Heald



Direct integration of micromachined pipettes in a flow channel for single DNA molecule study by optical tweezers  

Microsoft Academic Search

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap setup (optical tweezers) to study mechanical and structural properties of ?-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of

Cristina Rusu; Oever van't Ronny; M. J. de Boer; Henri V. Jansen; J. W. Berenschot; Martin L. Bennink; Johannes S. Kanger; B. G. de Grooth; Miko Elwenspoek; Jan Greve; Jürgen Brugger; Berg van den Albert



The stiffness of rabbit skeletal actomyosin cross-bridges determined with an optical tweezers transducer.  

PubMed Central

Muscle contraction is brought about by the cyclical interaction of myosin with actin coupled to the breakdown of ATP. The current view of the mechanism is that the bound actomyosin complex (or "cross-bridge") produces force and movement by a change in conformation. This process is known as the "working stroke." We have measured the stiffness and working stroke of a single cross-bridge (kappa xb, dxb, respectively) with an optical tweezers transducer. Measurements were made with the "three bead" geometry devised by Finer et al. (1994), in which two beads, supported in optical traps, are used to hold an actin filament in the vicinity of a myosin molecule, which is immobilized on the surface of a third bead. The movements and forces produced by actomyosin interactions were measured by detecting the position of both trapped beads. We measured, and corrected for, series compliance in the system, which otherwise introduces large errors. First, we used video image analysis to measure the long-range, force-extension property of the actin-to-bead connection (kappa con), which is the main source of "end compliance." We found that force-extension diagrams were nonlinear and rather variable between preparations, i.e., end compliance depended not only upon the starting tension, but also upon the F-actin-bead pair used. Second, we measured kappa xb and kappa con during a single cross-bridge attachment by driving one optical tweezer with a sinusoidal oscillation while measuring the position of both beads. In this way, the bead held in the driven optical tweezer applied force to the cross-bridge, and the motion of the other bead measured cross-bridge movement. Under our experimental conditions (at approximately 2 pN of pretension), connection stiffness (kappa con) was 0.26 +/- 0.16 pN nm-1. We found that rabbit heavy meromyosin produced a working stroke of 5.5 nm, and cross-bridge stiffness (kappa xb) was 0.69 +/- 0.47 pN nm-1.

Veigel, C; Bartoo, M L; White, D C; Sparrow, J C; Molloy, J E



Single-molecule manipulation of double-stranded DNA using optical tweezers: Interaction studies of DNA with RecA and YOYO-1  

Microsoft Academic Search

By using optical tweezers and a specially designed flow cell with an integrated glass micropipette, we constructed a setup similar to that of Smith et al. (Science 271:795-799, 1996) in which an individual double-stranded DNA (dsDNA) molecule can be captured between two polystyrene beads. The first bead is immobilized by the optical tweezers and the second by the micropipette. Movement

Martin L. Bennink; Orlando D. Scharer; Ronald Kanaar; Kumiko Sakata-Sogawa; Juleon M. Schins; Johannes S. Kanger; Grooth de Bart G; Jan Greve



High-force NdFeB-based magnetic tweezers device optimized for microrheology experiments.  


We present the design, calibration, and testing of a magnetic tweezers device that employs two pairs of permanent neodymium iron boron magnets surrounded by low-carbon steel focusing tips to apply large forces to soft materials for microrheology experiments. Our design enables the application of forces in the range of 1-1800 pN to ?4.5 ?m paramagnetic beads using magnet-bead separations in the range of 0.3-20 mm. This allows the use of standard coverslips and sample geometries. A high speed camera, custom LED-based illumination scheme, and mechanically stabilized measurement platform are employed to enable the measurement of materials with viscoelastic moduli as high as ?1 kPa. PMID:22667631

Lin, Jun; Valentine, Megan T



Coherence and Raman Sideband Cooling of a Single Atom in an Optical Tweezer  

NASA Astrophysics Data System (ADS)

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n¯x=n¯y=0.01, n¯z=8) even for a trap beam waist as small as w=900nm. The small atomic wave packet with ?x=?y=24nm and ?z=270nm represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces.

Thompson, J. D.; Tiecke, T. G.; Zibrov, A. S.; Vuleti?, V.; Lukin, M. D.



Force between colloidal particles in a nematic liquid crystal studied by optical tweezers  

NASA Astrophysics Data System (ADS)

We measure the dependence of the interparticle force F on the distance R between two colloidal particles with hyperbolic hedgehog defects in a nematic liquid crystal using optical tweezers. The particle-defect pair can be regarded as an elastic “dipole” in the electrostatic analogy. In a parallel configuration, where the dipole vectors are parallel with each other, F is attractive and proportional to R-4 . However, F becomes repulsive at small R due to the existence of a defect between the particles. In an antiparallel configuration, where the particles directly face each other, F is repulsive over the whole range of R and proportional to R-3.6 . In another antiparallel configuration, where two hyperbolic hedgehog defects directly face each other, F is proportional to R-3.6 and F at small R turns out to be attractive upon tilting the dipoles. Furthermore, we yield the force between particles connected by a stringlike defect called a bubblegum defect.

Takahashi, Kenji; Ichikawa, Masatoshi; Kimura, Yasuyuki



Coherence and Raman sideband cooling of a single atom in an optical tweezer.  


We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n(x)=n(y)=0.01, n(z)=8) even for a trap beam waist as small as w=900??nm. The small atomic wave packet with ?x=?y=24??nm and ?z=270??nm represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces. PMID:23581312

Thompson, J D; Tiecke, T G; Zibrov, A S; Vuleti?, V; Lukin, M D



Floating electrode optoelectronic tweezers: Light-driven dielectrophoretic droplet manipulation in electrically insulating oil medium  

NASA Astrophysics Data System (ADS)

We report an optical actuation mechanism, floating electrode optoelectronic tweezers (FEOET). FEOET enables light-driven transport of aqueous droplets immersed in electrically insulating oil on a featureless photoconductive glass layer with direct optical images. We demonstrate that a 681 ?m de-ionized water droplet immersed in corn oil medium is actuated by a 3.21 ?W laser beam with an average intensity as low as 4.08 ?W/mm2 at a maximum speed of 85.1 ?m/s on a FEOET device. FEOET provides a promising platform for massively parallel droplet manipulation with optical images on low cost, silicon-coated glass. The FEOET device structure, fabrication, working principle, numerical simulations, and operational results are presented in this letter.

Park, Sungyong; Pan, Chenlu; Wu, Ting-Hsiang; Kloss, Christoph; Kalim, Sheraz; Callahan, Caitlin E.; Teitell, Michael; Chiou, Eric P. Y.



Optically-driven red blood cell rotor in linearly polarized laser tweezers  

NASA Astrophysics Data System (ADS)

We have constructed a dual trap optical tweezers set-up around an inverted microscope where both the traps can be independently controlled and manipulated in all the three dimensions. Here we report our observations on rotation of red blood cells (RBCs) in a linearly polarized optical trap. Red blood cells deform and become twisted in hypertonic phosphate buffer saline and when trapped, experience an unbalanced radiation pressure force. The torque generated from the unbalanced force causes the trapped RBC to rotate. Addition of Ca^{++} ions in the solution, keeping the osmolarity same, makes the cell membranes stiffer and the cells deform less. Thus the speed of rotation of the red blood cells can be controlled, as less deformation and in turn less asymmetry in shape produces less torque under the radiation pressure resulting in slower rotation at the same laser power.

Khan, Manas; Mohanty, Samarendra K.; Sood, A. K.



Active Microrheology Using Optical Tweezers to Characterize Viscoelastic Properties of Entangled DNA  

NASA Astrophysics Data System (ADS)

We use active microrheology techniques to investigate the frequency-dependent linear elastic and viscous moduli (G', G'') of entangled DNA. Utilizing optical tweezers, single microspheres, embedded within solutions of entangled DNA of varying molecular lengths and solution concentrations, are driven sinusoidally over a frequency range of 0.6 - 95 Hz, while fluorescence microscopy is used to simultaneously visualize the deformation of a sparse number of DNA molecules entangled in the solution. DNA lengths of 11 kbp -- 115 kbp and solution concentrations of 1.0 -- 2.5 mg/ml are probed to determine the dependence of the viscoelasticity of entangled DNA on solution concentration and, for the first time, molecular length. Results are compared to theoretical predictions for entangled polymers, as well as previously reported macrorheology results.

Chapman, Cole D.; Lee, Kent; Henze, Dean; Smith, Douglas E.; Anderson, Rae M.



Modeling of a single red blood cell thermal reaction exposed to infrared laser tweezers  

NASA Astrophysics Data System (ADS)

Continuous-wave laser micro-beams are generally used as diagnostic tools in laser scanning microscopes or in the case of near-infrared (NIR) micro-beams, as optical traps for cell manipulation and force characterization. Because single beam traps are created with objectives of high numerical aperture, typical trapping intensities and photon flux densities are in the order of 106 W/cm2 and 103 cm-2s-1, respectively. The main idea of our theoretical study was to investigate the thermal reaction of RBCs irradiated by laser micro-beam. The study is supported by the fact that many experiments have been carried out with RBCs in laser NIR tweezers. In the present work it has been identified that the laser affects a RBC with a density of absorbed energy at approximately 107 J/cm3, which causes a temperature rise in the cell of about 7 - 12 °C.

Seteikin, A.; Krasnikov, I.; Bernhardt, I.



3D Manipulation of Protein Microcrystals with Optical Tweezers for X-ray Crystallography  

NASA Astrophysics Data System (ADS)

In some synchrotron facilities such as SPring-8, X-ray microbeams have been utilized for protein crystallography, allowing users to collect diffraction data from a protein microcrystal. Usually, a protein crystal is picked up manually from a crystallization droplet. However it is very difficult to manipulate the protein microcrystals which are very small and fragile against a shock and changes of temperature and solvent condition. We have been developing an automatic system applying the optical tweezers with two lensed fiber probes to manipulate the fragile protein microcrystal. The system succeeded in trapping a crystal and levitating it onto the cryoloop in the solvent. X-ray diffraction measurement for the manipulated protein microcrystals indicated that laser irradiation and trap with 1064nm wavelength hardly affected the result of X-ray structural analysis.

Hikima, T.; Hashimoto, K.; Murakami, H.; Ueno, G.; Kawano, Y.; Hirata, K.; Hasegawa, K.; Kumasaka, T.; Yamamoto, M.



Optical levitation and manipulation of stuck particles with pulsed optical tweezers  

NASA Astrophysics Data System (ADS)

We report on optical levitation and manipulation of microscopic particles that are stuck on a glass surface with pulsed optical tweezers. An infrared pulse laser at 1.06 ?m was used to generate a large gradient force (up to 10^-9 N) within a short duration (~45 ?s) that overcomes the adhesive interaction between the particles and the glass surface. Then a low-power continuous-wave diode laser at 785 nm was used to capture and manipulate the levitated particle. We have demonstrated that both stuck dielectric and biological micrometer-sized particles, including polystyrene beads, yeast cells, and Bacillus cereus bacteria, can be levitated and manipulated with this technique. We measured the single-pulse levitation efficiency for 2.0 ?m polystyrene beads as a function of the pulse energy and of the axial displacement from the stuck particle to the pulsed laser focus, which was as high as 88%.

Ashok Ambardekar, Amol; Li, Yong-Qing



Optical tweezers study of viscoelastic properties in the outer hair cell plasma membrane  

NASA Astrophysics Data System (ADS)

An optical tweezers system was used to study the mechanical characteristics of the outer hair cell (OHC) lateral wall by forming plasma membrane tethers. A 2nd order generalized Kelvin model was applied to describe the viscoelastic behavior of OHC membrane tethers. The measured parameters included equilibrium tethering force, (Feq), force relaxation times (?), stiffness values (?), and coefficients of friction (?). An analysis of force relaxation in membrane tethers indicated that the force decay is a biphasic process containing both an elastic and a viscous phase. In general, we observed an overall negative trend in the measured parameters upon application of the cationic amphipath chlorpromazine (CPZ). CPZ was found to cause up to a 40 pN reduction in Feq in OHCs. A statistically significant reduction in relaxation times and coefficients of friction was also observed, suggesting an increase in rate of force decay and a decrease in plasma membrane viscosity.

Murdock, David R.; Ermilov, Sergey A.; Qian, Feng; Brownell, William E.; Anvari, Bahman



Floating electrode optoelectronic tweezers: Light-driven dielectrophoretic droplet manipulation in electrically insulating oil medium  

PubMed Central

We report an optical actuation mechanism, floating electrode optoelectronic tweezers (FEOET). FEOET enables light-driven transport of aqueous droplets immersed in electrically insulating oil on a featureless photoconductive glass layer with direct optical images. We demonstrate that a 681 ?m de-ionized water droplet immersed in corn oil medium is actuated by a 3.21 ?W laser beam with an average intensity as low as 4.08 ?W?mm2 at a maximum speed of 85.1 ?m?s on a FEOET device. FEOET provides a promising platform for massively parallel droplet manipulation with optical images on low cost, silicon-coated glass. The FEOET device structure, fabrication, working principle, numerical simulations, and operational results are presented in this letter.

Park, Sungyong; Pan, Chenlu; Wu, Ting-Hsiang; Kloss, Christoph; Kalim, Sheraz; Callahan, Caitlin E.; Teitell, Michael; Chiou, Eric P.Y.



Magnetic tweezers measurements of the nanomechanical properties of DNA in the presence of drugs  

PubMed Central

Herein, we study the nanomechanical characteristics of single DNA molecules in the presence of DNA binders, including intercalating agents (ethidium bromide and doxorubicin), a minor groove binder (netropsin) and a typical alkylating damaging agent (cisplatin). We have used magnetic tweezers manipulation techniques, which allow us to measure the contour and persistence lengths together with the bending and torsional properties of DNA. For each drug, the specific variations of the nanomechanical properties induced in the DNA have been compared. We observed that the presence of drugs causes a specific variation in the DNA extension, a shift in the natural twist and a modification of bending dependence on the imposed twist. By introducing a naive model, we have justified an anomalous correlation of torsion data observed in the presence of intercalators. Finally, a data analysis criterion for discriminating between different molecular interactions among DNA and drugs has been suggested.

Salerno, Domenico; Brogioli, Doriano; Cassina, Valeria; Turchi, Diana; Beretta, Giovanni Luca; Seruggia, Davide; Ziano, Roberto; Zunino, Franco



A general method for manipulating DNA sequences from any organism with optical tweezers  

PubMed Central

Mechanical manipulation of single DNA molecules can provide novel information about DNA properties and protein–DNA interactions. Here we describe and characterize a useful method for manipulating desired DNA sequences from any organism with optical tweezers. Molecules are produced from either genomic or cloned DNA by PCR using labeled primers and are tethered between two optically trapped microspheres. We demonstrate that human, insect, plant, bacterial and viral sequences ranging from ?10 to 40 kilobasepairs can be manipulated. Force-extension measurements show that these constructs exhibit uniform elastic properties in accord with the expected contour lengths for the targeted sequences. Detailed protocols for preparing and manipulating these molecules are presented, and tethering efficiency is characterized as a function of DNA concentration, ionic strength and pH. Attachment strength is characterized by measuring the unbinding time as a function of applied force. An alternative stronger attachment method using an amino–carboxyl linkage, which allows for reliable DNA overstretching, is also described.

Fuller, Derek N.; Gemmen, Gregory J.; Rickgauer, John Peter; Dupont, Aurelie; Millin, Rachel; Recouvreux, Pierre; Smith, Douglas E.



High-force NdFeB-based magnetic tweezers device optimized for microrheology experiments  

SciTech Connect

We present the design, calibration, and testing of a magnetic tweezers device that employs two pairs of permanent neodymium iron boron magnets surrounded by low-carbon steel focusing tips to apply large forces to soft materials for microrheology experiments. Our design enables the application of forces in the range of 1-1800 pN to {approx}4.5 {mu}m paramagnetic beads using magnet-bead separations in the range of 0.3-20 mm. This allows the use of standard coverslips and sample geometries. A high speed camera, custom LED-based illumination scheme, and mechanically stabilized measurement platform are employed to enable the measurement of materials with viscoelastic moduli as high as {approx}1 kPa.

Lin Jun [Department of Mechanical Engineering, University of California, Santa Barbara, California 93106 (United States); Biomolecular Science and Engineering Program, University of California, Santa Barbara, California 93106 (United States); Valentine, Megan T. [Department of Mechanical Engineering, University of California, Santa Barbara, California 93106 (United States)



Monitoring and rapid quantification of total carotenoids in Rhodotorula glutinis cells using laser tweezers Raman spectroscopy.  


Rhodotorula glutinis is known to accumulate large amounts of carotenoids under certain culture conditions, which have very important industrial applications. So far, the molecular mechanism of regulating carotenogenesis is still not well understood. To better understand the carotenogenesis process, it requires methods that can detect carotenogenesis rapidly and reliably in single live cells. In this paper, a method based on laser tweezers Raman spectroscopy (LTRS) was developed to directly detect carotenoids, as well as other important biological molecules in single live R. glutinis cells. The data showed that the accumulation of carotenoids and lipids occurred mainly in the late exponential and stationary phases when the cell growth was inhibited by nutrient limitation. Meanwhile, the carotenoid concentration changed together with the concentration of nucleic acids, which increased in the first phase and decreased in the last phase of the culture. These data demonstrate that LTRS is a rapid, convenient, and reliable method to study the carotenogenesis process in vivo. PMID:21054502

Tao, Zhanhua; Wang, Guiwen; Xu, Xiaodong; Yuan, Yufeng; Wang, Xue; Li, Yongqing



Inferring kinetic pathways, rates, and force dependence from nonprocessive optical tweezers experiments: a maximum likelihood approach  

NASA Astrophysics Data System (ADS)

Optical tweezers experiments allow us to probe the role of force and mechanical work in a variety of biochemical processes. However, observable states do not usually correspond in a one-to-one fashion with the internal state of an enzyme or enzyme-substrate complex. Different kinetic pathways yield different distributions for the dwells in the observable states. Furthermore, the dwell-time distribution will be dependent upon force, and upon where in the biochemical pathway force acts. I will present a maximum-likelihood method for identifying rate constants and the locations of force-dependent transitions in transcription initiation by T7 RNA Polymerase. This method is generalizable to systems with more complicated kinetic pathways in which there are two observable states (e.g. bound and unbound) and an irreversible final transition.

Kalafut, Bennett; Visscher, Koen



Measurement of the membrane elasticity of red blood cell with osmotic pressure by optical tweezers.  


Cells have to undergo many changes in osmotic pressure during their long-term preservation, and will have injuries before they return to their normal states. Mechanics of a cell with deformation, either small or large, is usually used to describe the change of the cell quantitatively. However, there are few reports on the deformation of cells subjected to the change of osmotic pressures during preservation. Here, we report our study of the elasticity of the human red blood cells under osmotic pressures using optical tweezers. We find that the deformation characteristics of erythrocytes are strongly dependent on the osmotic pressure. We also find the RBCs will become stiff with increasing osmotic pressure, suggesting a potential reason for membrane injury during preservation. PMID:19448857

Wu, Jianguang; Li, Yinmei; Lu, Di; Liu, Zhong; Cheng, Zhengdong; He, Liqun


Trapping and rotating nanoparticles using a plasmonic nano-tweezer with an integrated heat sink.  


Although optical tweezers based on far-fields have proven highly successful for manipulating objects larger than the wavelength of light, they face difficulties at the nanoscale because of the diffraction-limited focused spot size. This has motivated interest in trapping particles with plasmonic nanostructures, as they enable intense fields confined to sub-wavelength dimensions. A fundamental issue with plasmonics, however, is Ohmic loss, which results in the water, in which the trapping is performed, being heated and to thermal convection. Here we demonstrate the trapping and rotation of nanoparticles using a template-stripped plasmonic nanopillar incorporating a heat sink. Our simulations predict an ~100-fold reduction in heating compared with previous designs. We further demonstrate the stable trapping of polystyrene particles, as small as 110 nm in diameter, which can be rotated around the nanopillar actively, by manual rotation of the incident linear polarization, or passively, using circularly polarized illumination. PMID:21915111

Wang, Kai; Schonbrun, Ethan; Steinvurzel, Paul; Crozier, Kenneth B



An active one-particle microrheometer: Incorporating magnetic tweezers to total internal reflection microscopy  

NASA Astrophysics Data System (ADS)

We present a novel microrheometer by incorporating magnetic tweezers in the total internal reflection microscopy (TIRM) that enables measuring of viscoelastic properties of materials near solid surface. An evanescent wave generated by a solid/liquid interface in the TIRM is used as the incident light source in the microrheometer. When a probe particle (of a few micrometers diameter) moves near the interface, it can interact with the evanescent field and reflect its position with respect to the interface by the scattered light intensity. The exponential distance dependence of the evanescent field, on the one hand, makes this technique extremely sensitive to small changes from z-fluctuations of the probe (with a resolution of several nanometers), and on the other, it does not require imaging of the probe with high lateral resolution. Another distinct advantage is the high sensitivity in determining the z position of the probe in the absence of any labeling. The incorporated magnetic tweezers enable us to effectively manipulate the distance of the embedded particle from the interface either by a constant or an oscillatory force. The force ramp is easy to implement through a coil current ramp. In this way, the local viscous and elastic properties of a given system under different confinements can therefore be measured by resolving the near-surface particle motion. To test the feasibility of applying this microrheology to soft materials, we measured the viscoelastic properties of sucrose and poly(ethylene glycol) solutions and compared the results to bulk rheometry. In addition, we applied this technique in monitoring the structure and properties of deformable microgel particles near the flat surface.

Gong, Xiangjun; Hua, Li; Wu, Chi; Ngai, To



Optoelectronic tweezers for the measurement of the relative stiffness of erythrocytes  

NASA Astrophysics Data System (ADS)

In this paper we describe the first use of Optoelectronic Tweezers (OET), an optically controlled micromanipulation method, to measure the relative stiffness of erythrocytes in mice. Cell stiffness is an important measure of cell health and in the case of erythrocytes, the most elastic cells in the body, an increase in cell stiffness can indicate pathologies such as type II diabetes mellitus or hypertension (high blood pressure). OET uses a photoconductive device to convert an optical pattern into and electrical pattern. The electrical fields will create a dipole within any polarisable particles in the device, such as cells, and non-uniformities of the field can be used to place unequal forces onto each side of the dipole thus moving the particle. In areas of the device where there are no field gradients, areas of constant illumination, the force on each side of the dipole will be equal, keeping the cell stationary, but as there are opposing forces on each side of the cell it will be stretched. The force each cell will experience will differ slightly so the stretching will depend on the cells polarisability as well as its stiffness. Because of this a relative stiffness rather than absolute stiffness is measured. We show that with standard conditions (20Vpp, 1.5MHz, 10mSm-1 medium conductivity) the cell's diameter changes by around 10% for healthy mouse erythrocytes and we show that due to the low light intensities required for OET, relative to conventional optical tweezers, multiple cells can be measured simultaneously.

Neale, Steven L.; Mody, Nimesh; Selman, Colin; Cooper, Jonathan M.



Optical tweezers based force measurement system for quantitating binding interactions: system design and application for the study of bacterial adhesion  

Microsoft Academic Search

An optical force measurement system for quantitating forces in the pN range between micrometer-sized objects has been developed. The system was based upon optical tweezers in combination with a sensitive position detection system and constructed around an inverted microscope. A trapped particle in the focus of the high numerical aperture microscope-objective behaves like an omnidirectional mechanical spring in response to

Erik Fällman; Staffan Schedin; Jana Jass; Magnus Andersson; Bernt Eric Uhlin; Ove Axner



From supramolecular porphyrin tweezers to dynamic A(n)B(m)C(l)D(k) multiporphyrin arrangements through orthogonal coordination.  


A dynamic, supramolecular, three-component A(n)B(m)C(l) bis(zinc porphyrin) tweezer has been prepared quantitatively using the heteroleptic bisphenanthroline (HETPHEN) concept. Upon addition of nitrogenous spacers of different length, namely, the extended bipyridine 3 a, 4,4'-bipyridine (3 b), and 1,4-diazabicyclo[2.2.2]octane (DABCO; 3 c), to set up an additional orthogonal binding motif (Zn(Por)-N(spacer)), three structurally different, still dynamic, four-component A(n)B(m)C(l)D(k) assemblies were cleanly formed, as indicated by UV/Vis and NMR titrations as well as by DOSY investigations. The structures were identified as a bridged monotweezer A(2)BC(2)D, a doubly bridged double tweezer A(4)B(2)C(4)D(2), and a triply bridged double tweezer A(4)B(2)C(4)D(3), the latter resembling a porphyrin stack. Notably, the same structures were equally formed directly from a mixture of the constituents A, B, C, and D put together in any sequence if the correct stoichiometry was applied. PMID:16862633

Kishore, Ravuri S K; Paululat, Thomas; Schmittel, Michael



Manipulating CD4+ T cells by optical tweezers for the initiation of cell-cell transfer of HIV-1  

PubMed Central

Cell-cell interactions through direct contact are very important for cellular communication and coordination – especially for immune cells. The human immunodeficiency virus type I (HIV-1) induces immune cell interactions between CD4+ cells to shuttle between T cells via a virological synapse. A goal to understand the process of cell-cell transmission through virological synapses is to determine the cellular states that allow a chance encounter between cells to become a stable cell-cell adhesion. Here we demonstrate the use of optical tweezers to manipulate uninfected primary CD4+ T cells near HIV Gag-iGFP transfected Jurkat T cells to probe the determinants that induce stable adhesion. When combined with fast 4D confocal fluorescence microscopy, optical tweezers can be utilized to not only facilitate cell-cell contact, but to also allow one to simultaneously track the formation of a virological synapse, and ultimately to enable us to precisely determine all events preceding virus transfer. HIV-1 infected T cell (green) decorated with uninfected primary T cells (red) by manipulating the primary cells with an optical tweezers system

McNerney, Gregory P.; Hubner, Wolfgang; Chen, Benjamin K.; Huser, Thomas



A SO2-selective electrode based on a Zn-porphyrin for wine analysis.  


This work describes the assessment of a SO2-selective electrode based on the use of the neutral carrier 5,10,15,20-tetraphenyl(porphyrinate)zinc(II) in a PVC membrane plasticized with 2-nitrophenyl phenyl ether. After being conditioned in 2 mol L(-1) diethylamine solution for 24 h, the electrode exhibited selective anionic response toward the analyte in a concentration interval of more than four decades, with an slope of -59.5 mV dec(-1), a practical detection limit of 3.7×10(-6) mol L(-1) and a low limit of linear range of 7.2×10(-6) mol L(-1). The response mechanism is based on the displacement of the diethylamine:metalloporphyrin complex equilibrium within membrane bulk, inducing a variation in the cationic-sites to ionophore ratio. In turn, free hydroxyl ions are complexed by the displaced ionophore in a ratio 1:1 and translated as single negative charge nernstian response. Finally, the selectivity of the electrode is evaluated in view of its application to wine analysis. Results had high accuracy and precision when compared with a reference method. PMID:23830421

Cuartero, María; Amorim, Célia G; Araújo, Alberto N; Ortuño, Joaquín A; Montenegro, Maria C B S M



On-chip pH measurement using functionalized gel-microbeads positioned by optical tweezers.  


This paper demonstrates local pH measurement in a microchip using a pH-sensing gel-microbead. To achieve this, the gel-microbead made of a hydrophilic photo-crosslinkable resin was functionalized with the pH indicator bromothymol blue (BTB). The primary constituent of this photo-crosslinkable resin is poly(ethylene glycol). Gel-microbeads impregnated with BTB were obtained by stirring the mixture solution, which was composed of the resin, BTB, and an electrolyte solution. The gel-microbead is polymerized by UV illumination. The polymerized gel-microbead can be manipulated by optical tweezers and made to adhere to a glass surface. The local pH was measured from the color of the gel-microbead impregnated with BTB by calibrated color information in the YCrCb color space. We succeeded in measuring the local pH value using the pH-sensing gel-microbead by manipulating and positioning it at the desired point in the microchip. PMID:18231676

Maruyama, Hisataka; Arai, Fumihito; Fukuda, Toshio



Interaction of Oxazole Yellow Dyes with DNA Studied with Hybrid Optical Tweezers and Fluorescence Microscopy  

PubMed Central

Abstract We have integrated single molecule fluorescence microscopy imaging into an optical tweezers set-up and studied the force extension behavior of individual DNA molecules in the presence of various YOYO-1 and YO-PRO-1 concentrations. The fluorescence modality was used to record fluorescent images during the stretching and relaxation cycle. Force extension curves recorded in the presence of either dye did not show the overstretching transition that is characteristic for bare DNA. Using the modified wormlike chain model to curve-fit the force extension data revealed a contour length increase of 6% and 30%, respectively, in the presence of YO-PRO-1 and YOYO-1 at 100 nM. The fluorescence images recorded simultaneously showed that the number of bound dye molecules increased as the DNA molecule was stretched and decreased again as the force on the complex was lowered. The binding constants and binding site sizes for YO-PRO-1 and YOYO-1 were determined as a function of the force. The rate of YO-PRO-1 binding and unbinding was found to be 2 orders of magnitude larger than that for YOYO-1. A kinetic model is proposed to explain this observation.

Murade, C.U.; Subramaniam, V.; Otto, C.; Bennink, Martin L.



Probing Protein Folding Kinetics with High-resolution, Stabilized Optical Tweezers  

NASA Astrophysics Data System (ADS)

Single-molecule techniques provide a powerful means of exploring molecular transitions such as the unfolding and refolding of a protein. However, the quantification of bi-directional transitions and near-equilibrium phenomena poses unique challenges, and is often limited by the detection resolution and long-term stability of the instrument. We have developed unique optical tweezers methods that address these problems, including an interference-based method for high-resolution 3D bead tracking (˜1 nm laterally, ˜0.3 nm vertically, at > 100 Hz), and a continuous autofocus system that stabilizes the trap height to within 1-2 nm longterm [1,2]. We have used our instruments to quantify the force-dependent unfolding and refolding kinetics of single protein domains (e.g. spectrin in collaboration with E. Evans). These single-molecule studies are presented, together with the accompanying probabilistic analysis that we have developed. References: 1. W.P. Wong, V. Heinrich, E. Evans, Mat. Res. Soc. Symp. Proc., 790, P5.1-P5.10 (2004). 2. V. Heinrich, W.P. Wong, K. Halvorsen, E. Evans, Langmuir, 24, 1194-1203 (2008).

Wong, Wesley; Halvorsen, Ken



Trap profiles of projector based optoelectronic tweezers (OET) with HeLa cells  

PubMed Central

In this paper we present trap profile measurements for HeLa cells in Optoelectronic Tweezers (OET) based on a data projector. The data projector is used as a light source to illuminate amorphous Si creating virtual electrodes which are used to trap particles through dielectrophoresis. We show that although the trap stiffness is typically greater at the edges of the optical spot it is possible to create a trap with constant trap stiffness by reducing the trap’s size until it is similar to the object being trapped. We have successfully created a trap for HeLa cells with a constant trap stiffness of 3×10?6 Nm?1 (capable of moving the cell up to 50 ?ms?1) with a 12 ?m diameter trap. We also calculate the depth of the potential well that the cell will experience due to the trap and find that it to be 1.6×10?16J (4×104 kBT).

Neale, Steven L.; Ohta, Aaron T.; Hsu, Hsan-Yin; Valley, Justin K.; Jamshidi, Arash; Wu, Ming C.



The interaction of Escherichia coli with its surrounding three dimensional substrate measured by oscillatory optical tweezers  

NASA Astrophysics Data System (ADS)

It has been known that the shape, the locomotion, and the growth of cells and bacteria are often affected by their interactions with extra cellular matrix (ECM). However, it is difficult to quantify such interactions with conventional biochemical methods. In this paper we report the application of oscillatory optical tweezers to trap and oscillate three types of E. coli, in 0.2% LB agar substrate to quantify the E. coli - substrate interactions in terms of the elasticity modulus G'. The three types of E. coli are BW25113 (wild-type, normal with flagellum), BW25113 (normal with flagellum, but subjected to UV light exposure for 1 hr to deactivate the flagellum), and JW1923 (a null-flagellum mutant of BW25113). Our results indicate that the value of G' for the later two is significantly higher than that for the normal wild-type (WT). We speculated that the interaction with the surrounding is perturbed, and hence reduced, mainly by the motion of the flagellum in the case of the WT.

Yen, Pei-Wen; Su, Pin-Tzu; Hung, Li-Jen; Wei, Ming-Tzo; Syu, Wan-Jr; Chiou, Arthur



Calibration of optical tweezers with positional detection in the back focal plane  

SciTech Connect

We explain and demonstrate a new method of force and position calibrations for optical tweezers with back-focal-plane photodetection. The method combines power spectral measurements of thermal motion and the response to a sinusoidal motion of a translation stage. It consequently does not use the drag coefficient of the trapped object as an input. Thus, neither the viscosity, nor the size of the trapped object, nor its distance to nearby surfaces needs to be known. The method requires only a low level of instrumentation and can be applied in situ in all spatial dimensions. It is both accurate and precise: true values are returned, with small error bars. We tested this experimentally, near and far from surfaces in the lateral directions. Both position and force calibrations were accurate to within 3%. To calibrate, we moved the sample with a piezoelectric translation stage, but the laser beam could be moved instead, e.g., by acousto-optic deflectors. Near surfaces, this precision requires an improved formula for the hydrodynamical interaction between an infinite plane and a microsphere in nonconstant motion parallel to it. We give such a formula.

Tolic-Noerrelykke, Simon F.; Schaeffer, Erik; Howard, Jonathon; Pavone, Francesco S.; Juelicher, Frank; Flyvbjerg, Henrik [Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, 01187 Dresden (Germany) and European Laboratory for Non-linear Spectroscopy, via Nello Carrara 1, 50019 Sesto Fiorentino, Florence (Italy) and Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden (Germany); European Laboratory for Non-linear Spectroscopy, via Nello Carrara 1, 50019 Sesto Fiorentino, Florence (Italy); Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, 01187 Dresden (Germany); Isaac Newton Institute for Mathematical Sciences, Cambridge CB3 0EH (United Kingdom); Biosystems Department, Risoe National Laboratory, DK-4000 Roskilde (Denmark) and Danish Polymer Centre, Risoe National Laboratory, DK-4000 Roskilde (Denmark)



STED nanoscopy combined with optical tweezers reveals protein dynamics on densely covered DNA.  


Dense coverage of DNA by proteins is a ubiquitous feature of cellular processes such as DNA organization, replication and repair. We present a single-molecule approach capable of visualizing individual DNA-binding proteins on densely covered DNA and in the presence of high protein concentrations. Our approach combines optical tweezers with multicolor confocal and stimulated emission depletion (STED) fluorescence microscopy. Proteins on DNA are visualized at a resolution of 50 nm, a sixfold resolution improvement over that of confocal microscopy. High temporal resolution (<50 ms) is ensured by fast one-dimensional beam scanning. Individual trajectories of proteins translocating on DNA can thus be distinguished and tracked with high precision. We demonstrate our multimodal approach by visualizing the assembly of dense nucleoprotein filaments with unprecedented spatial resolution in real time. Experimental access to the force-dependent kinetics and motility of DNA-associating proteins at biologically relevant protein densities is essential for linking idealized in vitro experiments with the in vivo situation. PMID:23934077

Heller, Iddo; Sitters, Gerrit; Broekmans, Onno D; Farge, Géraldine; Menges, Carolin; Wende, Wolfgang; Hell, Stefan W; Peterman, Erwin J G; Wuite, Gijs J L



Optical tweezers reveal a dynamic mechanical response of cationic peptide-DNA complexes  

NASA Astrophysics Data System (ADS)

Nonviral carriers have been developed to deliver nucleic acids by forming nanoscale complexes; however, there has been limited success in achieving high transfection efficiency. Our hypothesis is that a factor affecting gene delivery efficiency is the mechanical response of the condensed complex. To begin to test this hypothesis, we directly measured the mechanical properties of DNA-carrier complexes using optical tweezers. Histidine-lysine (HK) polymer, Asparagine-lysine (NK) polymer and poly-L-lysine were used to form complexes with a single DNA molecule. As carriers were introduced, a sudden decrease in DNA extension occurrs at a force level which is defined as critical force (Fc). Fc is carrier and concentration dependent. Pulling revealed reduction in DNA extension length for HK-DNA complexes. The characteristics of force profiles vary by agent and can be dynamically manipulated by changes in environmental conditions such as ionic strength of the buffer as well as pH. Heparin can remove cationic reagents which are otherwise irreversibly bound to DNA. The implications for optimizing molecular interactions to enhance transfection efficiency will be discussed.

Lee, Amy; Zheng, Tai; Sucayan, Sarah; Chou, Szu-Ting; Tricoli, Lucas; Hustedt, Jason; Kahn, Jason; Mixson, A. James; Seog, Joonil



Optical tweezers based measurement of PLGA-NP interaction with prostate cancer cells  

NASA Astrophysics Data System (ADS)

In order to quantify the binding capacities of polymeric, biodegradable and biocompatible poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs), conjugated with either R11 peptides or Folic Acid, the strength by detach from prostate cancer cells (PCCs) was measured via optical tweezers based measurements. Specific nanoparticle drug delivery eliminates the previously used diffuse, full-body application of potent cancer drugs by localizing drug delivery to malignant cells. Precise monitoring of NP position in the trap near the PCC membrane using a fluorescence imaging based method enabled calibration of the trap stiffness and subsequent force measurements. By defining the force with which the many diverse conjugates and coatings of different types of NPs bind the vast array of cancer cell types, chemotherapeutic drugs can be delivered in a specific manner with the optimal particle and corresponding conjugates. Further, and most significantly, the rupture force measurements will reveal whether or not targeted nanoparticles can overcome the force of blood attempting to pull the particle from designated cells. Our preliminary study revealed that the binding between PLGA-NPs and prostate cancer cells is enhanced by coating with folic acid or R11 peptides. These conjugates increase the force required to detach the particle thus allowing particles to overcome drag force of the blood in prostate capillary systems.

Blesener, Thea; Mondal, Argha; Menon, Jyothi U.; Nguyen, Kytai T.; Mohanty, Samarendra



Monitoring trehalose uptake and conversion by single bacteria using laser tweezers Raman spectroscopy.  


Having the ability to monitor metabolic activity at the scale of single bacterial cells noninvasively would enable us to follow changes in the distribution of activity in bacterial systems which is of major importance for topics such as integration of metabolism and development, metabolic engineering, microbial activity and drug resistance, cell-cell interactions, and quorum sensing. Here, we used laser tweezers Raman spectroscopy to monitor the in vivo real-time uptake and conversion of trehalose by single bacterial cells. This approach can be used for the quantitative determination of sugar uptake by a single bacterium and its metabolic response to the sugar application with time. We show that uptake of trehalose can be quantified in single living bacterial cells held in place by an optical trap while simultaneously collecting Raman spectra upon application of sugar to the medium. This technique yields real-time chemical information in a label-free manner, thus eliminating the limitations of toxicity of the isotopic probes common in studying transport processes. It can substitute the laborious and time-consuming analytical evaluation. Although the single-cell Raman spectroscopy method demonstrated here is focused on the study of trehalose uptake by Sinorhizobium meliloti, the demonstrated approach is applicable to many different organisms and carbohydrates in general. PMID:23796054

Avetisyan, Anna; Jensen, John Beck; Huser, Thomas



Development of microfluidic system and optical tweezers for electrophysiological investigations of an individual cell  

NASA Astrophysics Data System (ADS)

We present a new approach of combining Lab-on-a-chip technologies with optical manipulation technique for accurate investigations in the field of cell biology. A general concept was to develop and combine different methods to perform advanced electrophysiological investigations of an individual living cell under optimal control of the surrounding environment. The conventional patch clamp technique was customized by modifying the open system with a gas-tight multifunctional microfluidics system and optical trapping technique (optical tweezers). The system offers possibilities to measure the electrical signaling and activity of the neuron under optimum conditions of hypoxia and anoxia while the oxygenation state is controlled optically by means of a spectroscopic technique. A cellbased microfluidics system with an integrated patch clamp pipette was developed successfully. Selectively, an individual neuron is manipulated within the microchannels of the microfluidic system under a sufficient control of the environment. Experiments were performed to manipulate single yeast cell and red blood cell (RBC) optically through the microfluidics system toward an integrated patch clamp pipette. An absorption spectrum of a single RCB was recorded which showed that laser light did not impinge on the spectroscopic spectrum of light. This is promising for further development of a complete lab-on-a-chip system for patch clamp measurements.

Alrifaiy, A.; Bitaraf, N.; Lindahl, O.; Ramser, K.



Uncoiling mechanism of Klebsiella pneumoniae type 3 pili measured by using optical tweezers  

NASA Astrophysics Data System (ADS)

Pili are bacterial appendages that play many important roles in bacterial behaviors, physiology and interaction with hosts. Via pili, bacteria are able to adhere to, migrate onto, and colonize on host cells, mechanically. Different from the most studied type 1 and P type pili, which are rigid and thick with an average of 6~7 nm in diameter, type 3 pili are relatively tiny (3-5 nm in diameter) and flexible, and their biophysical properties remains unclear. By using optical tweezers, we found that the elongation processes of type 3 pili are divided into three phases: (1) elastic elongation, (2) uncoiling elongation, and (3) intrinsic elongation, separately. Besides, the uncoiling force of the recombinant pili displayed on the surface of E. coli [pmrkABCDV1F] is measured 20 pN in average stronger than that of E. coli [pmrkABCDV1]. This suggests that pilin MrkF is involved in determining the mechanical properties of the type 3 pili.

Chen, Feng-Jung; Chan, Chia-Han; Liu, Kuo-Liang; Huang, Ying-Jung; Peng, Hwei-Ling; Chang, Hwan-You; Yew, Tri-Rung; Hsu, Ken Y.; Hsu, Long



Ion-selective electrodes based on molecular tweezer-type neutral carriers.  


Potentiometric properties of cholic and deoxycholic acid derivatives substituted with various ion-recognizing moieties, such as dithiocarbamate, bipyridyl, glycolic and malonic diamides, urea and thiourea, and trifluoroacetophenons (TFAP), have been studied using solvent polymeric membranes. The dithiocarbamate and bipyridyl group containing ionophores exhibit high silver ion selectivity. The cholic acid derivatized with glycolic diamides exhibited high calcium selectivity, but its complex formulation constant was 10(5) times smaller than that of ETH 1001. The reduced calcium binding ability of the glycolic diamide-substituted ionophore was advantageous for eliminating anionic interference. The bi- or tripodal malonic diamide-substituted ionophores exhibited substantially increased magnesium selectivity. Anion-selective ionophores have been designed by substituting urea and thiourea group containing chains to the hydroxyl linkers of chenodeoxycholic acid frames; their selectivity closely followed the sequence of Hoffmeister series, except the unusually large response of the thiourea-substituted ionophore to sulfate. The most successful examples of cholic or deoxycholic acid frame-based ionophores are those functionalized with two carbonate-selective TFAP groups: bipodal TFAP groups behaves like a tweezers for the incoming carbonate, and exhibit analytically interference free and quantitative responses to the carbonate in serum and seawater samples. PMID:18969404

Shim, Jun Ho; Jeong, In Seok; Lee, Min Hyung; Hong, Hun Pyo; On, Jeung Hoon; Kim, Ki Soo; Kim, Hong-Seok; Kim, Byeong Hyo; Cha, Geun Sig; Nam, Hakhyun



Removal forces and adhesion properties of Saccharomyces cerevisiae on glass substrates probed by optical tweezer  

NASA Astrophysics Data System (ADS)

In agroindustry, the hygiene of solid surfaces is of primary importance in order to ensure that products are safe for consumers. To improve safety, one of the major ways consists in identifying and understanding the mechanisms of microbial cell adhesion to nonporous solid surfaces or filtration membranes. In this paper we investigate the adhesion of the yeast cell Saccharomyces cerevisiae (about 5 ?m in diameter) to a model solid surface, using well-defined hydrophilic glass substrates. An optical tweezer device developed by Piau [J. Non-Newtonian Fluid Mech. 144, 1 (2007)] was applied to yeast cells in contact with well-characterized glass surfaces. Two planes of observation were used to obtain quantitative measurements of removal forces and to characterize the corresponding mechanisms at a micrometer length scale. The results highlight various adhesion mechanisms, depending on the ionic strength, contact time, and type of yeast. The study has allowed to show a considerable increase of adhering cells with the ionic strength and has provided a quantitative measurement of the detachment forces of cultured yeast cells. Force levels are found to grow with ionic strength and differences in mobility are highlighted. The results clearly underline that a microrheological approach is essential for analyzing the adhesion mechanisms of biological systems at the relevant local scales.

Castelain, Mickaël; Pignon, Frédéric; Piau, Jean-Michel; Magnin, Albert; Mercier-Bonin, Muriel; Schmitz, Philippe



Single-molecule kinetics under force: probing protein folding and enzymatic activity with optical tweezers  

NASA Astrophysics Data System (ADS)

Weak non-covalent bonds between and within single molecules govern many aspects of biological structure and function (e.g. DNA base-paring, receptor-ligand binding, protein folding, etc.) In living systems, these interactions are often subject to mechanical forces, which can greatly alter their kinetics and activity. My group develops and applies novel single-molecule manipulation techniques to explore and quantify these force-dependent kinetics. Using optical tweezers, we have quantified the force-dependent unfolding and refolding kinetics of different proteins, including the cytoskeletal protein spectrin in collaboration with E. Evans's group [1], and the A2 domain of the von Willebrand factor blood clotting protein in collaboration with T. Springer's group [2]. Furthermore, we have studied the kinetics of the ADAMTS13 enzyme acting on a single A2 domain, and have shown that physiolgical forces in the circulation can act as a cofactor for enzymatic cleavage, regulating hemostatic activity [2]. References: 1. E. Evans, K. Halvorsen, K. Kinoshita, and W.P. Wong, Handbook of Single Molecule Biophysics, P. Hinterdorfer, ed., Springer (2009). 2. X. Zhang, K. Halvorsen, C.-Z. Zhang, W.P. Wong, and T.A. Springer, Science 324 (5932), 1330-1334 (2009).

Wong, Wesley



Induction of sustained glycolytic oscillations in single yeast cells using microfluidics and optical tweezers  

NASA Astrophysics Data System (ADS)

Yeast glycolytic oscillations have been studied since the 1950s in cell free extracts and in intact cells. Until recently, sustained oscillations have only been observed in intact cells at the population level. The aim of this study was to investigate sustained glycolytic oscillations in single cells. Optical tweezers were used to position yeast cells in arrays with variable cell density in the junction of a microfluidic flow chamber. The microfluidic flow chambers were fabricated using soft lithography and the flow rates in the different inlet channels were individually controlled by syringe pumps. Due to the low Reynolds number, the solutions mixed by diffusion only. The environment in the junction of the chamber could thus be controlled by changing the flow rates in the inlet channels, with a complete change of environment within 2 s. The optimum position of the cell array was determined by simulations, to ensure complete coverage of the intended solution without any concentration gradients over the cell array. Using a DAPI filter set, the NADH auto fluorescence could be monitored in up to 100 cells simultaneously. Sustained oscillations were successfully induced in individual, isolated cells within specific flow rates and concentrations of glucose and cyanide. By changing the flow rates without changing the surrounding solution, it was found that the cell behavior was dependent on the concentration of chemicals in the medium rather than the flow rates in the range tested. Furthermore, by packing cells tightly, cell-to-cell interaction and synchronization could be studied.

Gustavsson, Anna-Karin; Adiels, Caroline B.; Goksör, Mattias



Horizontal Magnetic Tweezers for Micromanipulation of Single DNA-Protein Complexes  

NASA Astrophysics Data System (ADS)

We report on the development of a new magnetic force transducer or "tweezer" that can apply pico-Newton forces on single DNA molecules in the focus plane. Since the changes in DNA's end-to-end extension are coplanar with the pulling force, there is no need to continually refocus. The DNA constructs (?-DNA end labeled with a 3?m polystyrene bead and a 2.8?m paramagnetic sphere) and appropriate buffer are introduced to a custom built 400?L to 650?L closed cell. This closed cell isolates our sample and produces low-noise force and extension measurements. This chamber rests on a stage fixed to a three axis micromanipulator. Entering the flat chamber are two micropipettes, a 2.5?m id pipette for aspirating the polystyrene bead and a 20?m id pipette for injecting proteins of interest. The suction and the injection pipettes are rigidly mounted to a hydraulic, three-axis micromanipulator. DNA-bead constructs, once introduced to the chamber, can be located by moving the stage over the objective. We have shown that we can easily and reputably find, capture, and manipulate single molecules of DNA within a force range of 0.1pN to 100pN.

McAndrew, C.; Sarkar, A.; Mehl, P.



DNA Micromanipulation Using Novel High-Force, In-Plane Magnetic Tweezer  

NASA Astrophysics Data System (ADS)

We report the development of a magnetic force transducer that can apply piconewton forces on single DNA molecules in the focus plane allowing continuous high precision tethered-bead tracking. The DNA constructs, proteins, and buffer are introduced into a 200?L closed cell created using two glass slides separated by rigid spacers interspersed within a thin viscoelastic perimeter wall. This closed cell configuration isolates our sample and produces low-noise force-extension measurements. Specially-drawn micropipettes are used for capturing the polystyrene bead, pulling on the magnetic sphere, introducing proteins of interest, and maintaining flow. Various high-precision micromanipulators allow us to move pipettes and stage as required. The polystyrene bead is first grabbed, and held using suction; then the magnetic particle at the other end of the DNA is pulled by a force created by either two small (1mm x 2mm x 4mm) bar magnets or a micro magnet-tipped pipette. Changes in the end-to-end length of the DNA are observable in real time. We will present force extension data obtained using the magnetic tweezer.

McAndrew, Christopher; Mehl, Patrick; Sarkar, Abhijit



The history and evolution of surgical instruments. VII. Spring forceps (tweezers), hooks and simple retractors.  

PubMed Central

Instruments manufactured by bending a basic metal strip or rod, either about its middle to create spring forceps (tweezers), or towards one extremity to create hooks and retractors are related structures. Spring forceps depend on tension mediated at the bend (hoop) or fixed end which is transmitted as dynamic 'spring' to the jaws, whereas the bend of hooks and retractors remains fixed and static. If such instruments refine the digital postures of pinch, pincer and retraction during surgery, they have not supplanted these manual actions entirely. After a brief historical introduction, the structure, modifications, functions and controls of spring forceps are analysed. Importantly, this instrument enjoys both right and left-handed functions, some of which are ancient, some transient as haemostats and needle-holders, and some, including left-handed dissection, surprisingly recent. Hooks are sharp or blunt and, among other functions, pre-date the left-handed spring forceps for dissection; in general hooks function as retractors. Hand-held retractors are enlarged blunt hooks, the wide retracting contact surface reducing trauma to wound margins and viscera. The physical effort of employing these retractors deep in body cavities is abated by applying them autostatically around a square or circular frame. Images Figure 1

Kirkup, J.



Multiple trap Laguerre-Gaussian holographic optical tweezers using a multiplexed ferroelectric SLM  

NASA Astrophysics Data System (ADS)

A holographic optical tweezers system is constructed using time-shared multiplexing to generate multiple optical traps. Computer generated Fresnel zone plates are used to produce the required laser focuses for standard optical traps while helical zone plates are used to generate Laguerre-Gaussian (LG) laser modes that produce doughnut shaped focuses. Standard Fresnel zone plates are used for trapping non-biological matter whereas LG modes are used in trapping delicate biological matter that is susceptible to damage from excessive laser radiation. A reflective high speed ferroelectric spatial light modulator (SLM), which is used to display the zone plate images, is capable of multiplexing a maximum of 24 binary images at a refresh rate of up to 1440Hz. By programming the SLM to display one binary hologram per bit plane, a commercial 24 bit colour SLM is used to provide 24 multiplexed traps. The ferroelectric holographic system enables multiple independently movable traps using time-shared multiplexing without the need for mechanical movement within the system. The software developed to display the zone plates uses Open GL acceleration to allow fast smooth movement in real time. Open GL utilises the graphics processing unit (GPU) common on many computers today which greatly increases the frame rate of the images displayed on the SLM. Use of the apparatus is demonstrated by the trapping and manipulation of colloidal particles and yeast cells. Preliminary results indicate that the use of LG zone plates for trapping biological cells results in significantly less damage than standard Fresnel zone plates.

Lafong, A.; Hossack, W. J.; Arlt, J.; Nowakowski, T. J.; Read, N. D.



Attractive-repulsive dynamics on light-responsive chiral microparticles induced by polarized tweezers.  


Multifunctional colloidal micro and nano-particles with controlled architectures have very promising properties for applications in bio and nanotechnologies. Here we report on the unique dichotomous dynamical behaviour of chiral spherical microparticles, either fluid or solid, manipulated by polarized optical tweezers. The particles are created using a reactive mesogen mixed with a chiral dopant to form cholesteric liquid crystal droplets in water emulsion. The photopolymerization enables the chiral supramolecular configurations to be frozen in solid particles. Different internal architectures in the supramolecular structures, guided by the interfacial chemistry, enable optically isotropic or anisotropic spherical objects to be obtained. For particles having radial configuration of the cholesteric helices, we show that light can exert either a repulsive or attractive force depending on the handedness of its circular polarization, due to the unique selective reflection property of the cholesteric phase. On the other hand, very exotic dynamics is observed in the case of anisotropic chiral particles. Depending on the light handedness, they behave like Janus spherical particles with dissimilar optical properties, meaning that the surface of the dielectric particles is partly transparent and partly reflecting. We foresee interesting potential applications in micro and optofluidics, microphotonics and materials science. PMID:23235908

Hernández, Raúl Josué; Mazzulla, Alfredo; Pane, Alfredo; Volke-Sepúlveda, Karen; Cipparrone, Gabriella



Analysis of RBC damage using laser tweezers Raman spectroscopy (LTRS) during femtosecond laser optical trapping  

NASA Astrophysics Data System (ADS)

We monitored cell viability and damage under femtosecond laser irradiation using aser weezers Raman pectroscopy (LTRS) which is becoming a powerful tool for the analysis of biological materials. Femtosecond lasers are more frequently used as a light source for optical tweezers since they enable nonlinear optical phenomena such as two-photon absorption or second harmonic generation trapping. Femtosecond laser optical trapping similar to thee CW laser optical trapping except that optical damage can be easily induced due to extremely high peak power of femtosecond pulses. We monitored the Raman signal changes as a marker for optical damage. We used red blood cell (RBC) as a target sample and first used the CW laser beams to trap the RBC from the bottom of the chamber. After the trapped RBC is moved to a desired depth, we switched the laser mode to mode-locked mode and monitored the Raman signals as a function of the laser irradiation time. It was observed that the Raman shift at 1543 cm-1 may be a good marker for optical damage both for CW and femtosecond laser trapping.

Ju, Sung-bin; Pyo, Jin-woo; Jang, Jae-young; Lee, Seungduk; Kim, Beop-Min



Thermal processes in red blood cells exposed to infrared laser tweezers (? = 1064 nm).  


Continuous-wave laser micro-beams are generally used as diagnostic tools in laser scanning microscopes or in the case of near-infrared (NIR) micro-beams, as optical traps for cell manipulation and force characterization. Because single beam traps are created with objectives of high numerical aperture, typical trapping intensities and photon flux densities are in the order of 10(6) W/cm(2) and 10(3) cm(-2) s(-1), respectively. The main idea of our theoretical study was to investigate the thermal reaction of RBCs irradiated by laser micro-beam. The study is supported by the fact that many experiments have been carried out with RBCs in laser NIR tweezers. In the present work it has been identified that the laser affects a RBC with a density of absorbed energy at approximately 10(7) J/cm(3), which causes a temperature rise in the cell of about 7-12 °C. PMID:20680975

Krasnikov, Ilya; Seteikin, Alexey; Bernhardt, Ingolf



Optical tweezers reveal relationship between microstructure and nanoparticle penetration of pulmonary mucus  

PubMed Central

In this study, the mobility of nanoparticles in mucus and similar hydrogels as model systems was assessed to elucidate the link between microscopic diffusion behavior and macroscopic penetration of such gels. Differences in particle adhesion to mucus components were strongly dependent on particle coating. Particles coated with 2 kDa PEG exhibited a decreased adhesion to mucus components, whereas chitosan strongly increased the adhesion. Despite such mucoinert properties of PEG, magnetic nanoparticles of both coatings did not penetrate through native respiratory mucus, resisting high magnetic forces (even for several hours). However, model hydrogels were, indeed, penetrated by both particles in dependency of particle coating, obeying the theory of particle mobility in an external force field. Comparison of penetration data with cryogenic scanning EM images of mucus and the applied model systems suggested particularly high rigidity of the mucin scaffold and a broad pore size distribution in mucus as reasons for the observed particle immobilization. Active probing of the rigidity of mucus and model gels with optical tweezers was used in this context to confirm such properties of mucus on the microscale, thus presenting the missing link between micro- and macroscopical observations. Because of high heterogeneity in the size of the voids and pores in mucus, on small scales, particle mobility will depend on adhesive or inert properties. However, particle translocation over distances larger than a few micrometers is restricted by highly rigid structures within the mucus mesh.

Kirch, Julian; Schneider, Andreas; Abou, Berengere; Hopf, Alexander; Schaefer, Ulrich F.; Schneider, Marc; Schall, Christian; Wagner, Christian; Lehr, Claus-Michael



Combined optical tweezers and laser dissector for controlled ablation of functional connections in neural networks  

NASA Astrophysics Data System (ADS)

Regeneration of functional connectivity within a neural network after different degrees of lesion is of utmost clinical importance. To test pharmacological approaches aimed at recovering from a total or partial damage of neuronal connections within a circuit, it is necessary to develop a precise method for controlled ablation of neuronal processes. We combined a UV laser microdissector to ablate neural processes in vitro at single neuron and neural network level with infrared holographic optical tweezers to carry out force spectroscopy measurements. Simultaneous force spectroscopy, down to the sub-pico-Newton range, was performed during laser dissection to quantify the tension release in a partially ablated neurite. Therefore, we could control and measure the damage inflicted to an individual neuronal process. To characterize the effect of the inflicted injury on network level, changes in activity of neural subpopulations were monitored with subcellular resolution and overall network activity with high temporal resolution by concurrent calcium imaging and microelectrode array recording. Neuronal connections have been sequentially ablated and the correlated changes in network activity traced and mapped. With this unique combination of electrophysiological and optical tools, neural activity can be studied and quantified in response to controlled injury at the subcellular, cellular, and network level.

Difato, Francesco; Dal Maschio, Marco; Marconi, Emanuele; Ronzitti, Giuseppe; Maccione, Alessandro; Fellin, Tommasso; Berdondini, Luca; Chieregatti, Evelina; Benfenati, Fabio; Blau, Axel



Thermodynamic DNA Looping by a Two-Site Restriction Endonuclease Studied using Optical Tweezers  

NASA Astrophysics Data System (ADS)

Many enzyme-DNA interactions involve multimeric protein complexes that bind at two distant sites such that the DNA is looped. An example is the type IIe restriction enzyme Sau3AI, which requires two recognition sites to cleave the DNA. Here we study this process at the single DNA level using force measuring optical tweezers. We characterize cleavage rates of single DNA molecules in the presence of Sau3AI as a function of enzyme concentration, incubation time, and the fractional extension of the DNA molecule. Activity is completely inhibited by tensions of a few picoNewtons. By replacing Mg^2+ with Ca^2+, the Sau3AI dimers form but do not cleave the DNA, thus trapping DNA loops. We are able to pull apart these loops, measuring the force needed and the length of DNA released for each. We also characterize the number and length distributions of these loops as a function of incubation time and DNA fractional extension. The results of these studies are discussed in the context of a Brownian dynamics model of DNA looping.

Gemmen, Gregory J.



Biomechanics and dynamics of red blood cells probed by optical tweezers and digital holographic microscopy  

NASA Astrophysics Data System (ADS)

Red blood cells (RBC), with their unique viscoelastic properties, can undergo large deformations during interaction with fluid flow and migration through narrow capillaries. Both local and overall viscoelastic property is important for cellular function and change in these properties indicate diseased condition. Though biomechanics of the cells have been studied using variety of physical techniques (AFM, optically-trapped anchoring beads and microcapilary aspiration) in force regime > 10pN, little is studied at low force regime <1pN. Such perturbations are not only hard to exercise on the cell membrane, but quantification of such deformations becomes extremely difficult. By application of low power optical tweezers directly on cell membrane, we could locally perturb discotic RBC along the axial direction, which was monitored dynamically by digital holographic microscopy-a real time, wide-field imaging method having nm axial resolution. The viscoelastic property of the RBC at low force regime was found to be significantly different from that of high-force regime. The results were found to be in good agreement with the simulation results obtained using finite element model of the axially-stretched RBC. The simulations and results of viscoelestic measurements will be presented.

Cardenas, Nelson; Thomas, Pattrick; Yu, Lingfeng; Mohanty, Samarendra



CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Manipulation of Nanoparticles Using Dark-Field-Illumination Optical Tweezers with Compensating Spherical Aberration  

NASA Astrophysics Data System (ADS)

Based on our previous investigation of optical tweezers with dark field illumination [Chin. Phys. Lett. 25(2008)329], nanoparticles at large trap depth are better viewed in wide field and real time for a long time, but with poor forces. Here we present the mismatched tube length to compensate for spherical aberration of an oil-immersion objective in a glass-water interface in an optical tweezers system for manipulating nanoparticles. In this way, the critical power of stable trapping particles is measured at different trap depths. It is found that trap depth is enlarged for trapping nanoparticles and trapping forces are enhanced at large trap depth. According to the measurement, 70-nm particles are manipulated in three dimensions and observed clearly at large appropriate depth. This will expand applications of optical tweezers in a nanometre-scale colloidal system.

Zhou, Jin-Hua; Tao, Run-Zhe; Hu, Zhi-Bin; Zhong, Min-Cheng; Wang, Zi-Qiang; Cai, Jun; Li, Yin-Mei



Three-dimensional light-scattering and deformation of individual biconcave human blood cells in optical tweezers.  


For studying the elastic properties of a biconcave red blood cell using the dual-trap optical tweezers without attaching microbeads to the cell, we implemented a three-dimensional finite element simulation of the light scattering and cell's deformation using the coupled electromagnetic and continuum mechanics modules. We built the vector field of the trapping beams, the cell structure layout, the hyperelastic and viscoelastic cell materials, and we reinforced the constraints on the cell constant volume in the simulation. This computation model can be useful for studying the scattering and the other mechanical properties of the biological cells. PMID:23736438

Yu, Lingyao; Sheng, Yunlong; Chiou, Arthur



Modeling highly focused laser beam in optical tweezers with the vector Gaussian beam in the T-matrix method.  


The vector Gaussian beam with high-order corrections is used to describe accurately the laser beam up to numerical aperture NA=1.20 in the optical tweezers for trapping nanoparticles. The beam is then expanded in the T-matrix method into the vector spherical wave function (VSWF) series using the point matching method with a new selection of the matching points. The errors in the beam description and in the VSWF expansion are much lower than those that occur in the paraxial Gaussian beam model. PMID:23455996

Bareil, Paul B; Sheng, Yunlong



Video-based analysis of the rotational behaviour of rod-shaped, self-propelled bacteria in holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Utilising the versatility of holographic optical tweezers and high speed video analysis, we present a scheme for the analysis of the rotational properties of multiple rod-shaped bacteria directly from video microscopy data. The bacterial body and flagella rotation frequency of Bacillus subtilis are determined by temporally resolved monitoring of the position of the bacterial body. In contrast to established methods, the video-based approach can be extended to the simultaneous analysis of several bacteria within the field of view. Monitoring multiple bacteria simultaneously will allow resolving the role of hydrodynamic interactions of multiple flagella motors on their mutual dynamics.

Dewenter, Lena; Alpmann, Christina; Woerdemann, Mike; Denz, Cornelia



Force mapping during the formation and maturation of cell adhesion sites with multiple optical tweezers.  


Focal contacts act as mechanosensors allowing cells to respond to their biomechanical environment. Force transmission through newly formed contact sites is a highly dynamic process requiring a stable link between the intracellular cytoskeleton and the extracellular environment. To simultaneously investigate cellular traction forces in several individual maturing adhesion sites within the same cell, we established a custom-built multiple trap optical tweezers setup. Beads functionalized with fibronectin or RGD-peptides were placed onto the apical surface of a cell and trapped with a maximum force of 160 pN. Cells form adhesion contacts around the beads as demonstrated by vinculin accumulation and start to apply traction forces after 30 seconds. Force transmission was found to strongly depend on bead size, surface density of integrin ligands and bead location on the cell surface. Highest traction forces were measured for beads positioned on the leading edge. For mouse embryonic fibroblasts, traction forces acting on single beads are in the range of 80 pN after 5 minutes. If two beads were positioned parallel to the leading edge and with a center-to-center distance less than 10 µm, traction forces acting on single beads were reduced by 40%. This indicates a spatial and temporal coordination of force development in closely related adhesion sites. We also used our setup to compare traction forces, retrograde transport velocities, and migration velocities between two cell lines (mouse melanoma and fibroblasts) and primary chick fibroblasts. We find that maximal force development differs considerably between the three cell types with the primary cells being the strongest. In addition, we observe a linear relation between force and retrograde transport velocity: a high retrograde transport velocity is associated with strong cellular traction forces. In contrast, migration velocity is inversely related to traction forces and retrograde transport velocity. PMID:23372781

Schwingel, Melanie; Bastmeyer, Martin



Effect of salicylate on outer hair cell plasma membrane viscoelasticity: studies using optical tweezers  

NASA Astrophysics Data System (ADS)

The plasma membrane (PM) of mammalian outer hair cells (OHCs) generates mechanical forces in response to changes in the transmembrane electrical potential. The resulting change in the cell length is known as electromotility. Salicylate (Sal), the anionic, amphipathic derivative of aspirin induces reversible hearing loss and decreases electromotile response of the OHCs. Sal may change the local curvature and mechanical properties of the PM, eventually resulting in reduced electromotility or it may compete with intracellular monovalent anions, particularly Cl-, which are essential for electromotility. In this work we have used optical tweezers to study the effects of Sal on viscoelastic properties of the OHC PM when separated from the underlying composite structures of the cell wall. In this procedure, an optically trapped microsphere is brought in contact with PM and subsequently pulled away to form a tether. We measured the force exerted on the tether as a function of time during the process of tether growth at different pulling rates. Effective tether viscosity, steady-state tethering force extrapolated to zero pulling rate, and the time constant for tether growth were estimated from the measurements of the instantaneous tethering force. The time constant for the tether growth measured for the OHC basal end decreased 1.65 times after addition of 10 mM Sal, which may result from an interaction between Sal and cholesterol, which is more prevalent in the PM of OHC basal end. The time constants for the tether growth calculated for the OHC lateral wall and control human embryonic kidney cells as well as the other calculated viscoelastic parameters remained the same after Sal perfusion, favoring the hypothesis of competitive inhibition of electromotility by salicylate.

Ermilov, Sergey A.; Brownell, William E.; Anvari, Bahman



Nonequilibrium thermodynamics of single DNA hairpins in a dual-trap optical tweezers setup  

NASA Astrophysics Data System (ADS)

We use two counter propagating laser beams to create a dual trap optical tweezers setup which is free from cross interference between the beams and provides great instrumental stability. This setup works by direct measurement of light momentum, separately for each trap, and is based on the Minitweezers design [1]. The dual trap setup has many applications: it can be used to study the force-dependent unfolding kinetics of single molecules and to address fundamental problems in nonequilibrium thermodynamics of small systems [2]. Recent progress in statistical physics has shown the importance of considering large energy deviations in the beahvior of systems that are driven out-of-equilibrium by time-dependent forces. Prominent examples are nonequilibrium work relations (e.g. the Jarzynski equality [3]) and fluctuation theorems. By repeated measurement of the irreversible work the Jarzynski equality allows us to recover the free energy difference between two thermodynamic states, AF, by taking exponential averages of the work W done by the external agent on the system, e-??F =

Crivellari, M. Ribezzi; Huguet, J. M.; Ritort, F.



Femtosecond single optical fiber tweezers enabled two-photon fluorescence excitation of trapped microscopic objects  

NASA Astrophysics Data System (ADS)

Analysis of trapped microscopic objects using fluorescence and Raman spectroscopy is gaining considerable interest. We report on the development of single fiber femto second optical tweezers and its use in two-photon fluorescence (TPF) excitation of trapped fluorescent particles. Trapping of the floating objects led to stable fluorescence emission intensity over a long period of time, suitable for spectroscopic measurements. Trapping depth of few cm was achieved inside colloidal sample with TPF from the trapped particle being visible to the naked eye. Furthermore, the fiber optic trapping was so stable that the trapped particle could be moved in 3D even by holding the fiber in hand and slow maneuvering of the same. Owing to the propagation distance of the Bessel-like beam emerging from the axicon-fiber tip, a relatively longer streak of fluorescence was observed along the microsphere length. The cone angle of axicon was engineered so as to provide better trapping stability and high axial confinement of TPF. The theoretical simulation of fiber optical microbeam profiles emerging from the axicon tip and trapping force estimations was found to be in good agreement with the experimentally observed stiffness and TPF patterns. Apart from miniaturization capability into lab-on- a-chip micro-fluidic devices, the proposed non-invasive micro axicon tipped optical fiber can be used in multifunctional mode for in-depth trapping, rotation, sorting and ablation as well as for two-photon fluorescence excitation of motile sample which will revolutionize biophysics and research in material science.

Mishra, Yogeshwar N.; Pinto, Mervyn; Ingle, Ninad; Mohanty, Samarendra K.



Force Unfolding Kinetics of RNA Using Optical Tweezers. I. Effects of Experimental Variables on Measured Results  

PubMed Central

Experimental variables of optical tweezers instrumentation that affect RNA folding/unfolding kinetics were investigated. A model RNA hairpin, P5ab, was attached to two micron-sized beads through hybrid RNA/DNA handles; one bead was trapped by dual-beam lasers and the other was held by a micropipette. Several experimental variables were changed while measuring the unfolding/refolding kinetics, including handle lengths, trap stiffness, and modes of force applied to the molecule. In constant-force mode where the tension applied to the RNA was maintained through feedback control, the measured rate coefficients varied within 40% when the handle lengths were changed by 10-fold (1.1–10.2 Kbp); they increased by two- to threefold when the trap stiffness was lowered to one-third (from 0.1 to 0.035 pN/nm). In the passive mode, without feedback control and where the force applied to the RNA varied in response to the end-to-end distance change of the tether, the RNA hopped between a high-force folded-state and a low-force unfolded-state. In this mode, the rates increased up to twofold with longer handles or softer traps. Overall, the measured rates remained with the same order-of-magnitude over the wide range of conditions studied. In the companion article on pages 3010–3021, we analyze how the measured kinetics parameters differ from the intrinsic molecular rates of the RNA, and thus how to obtain the molecular rates.

Wen, Jin-Der; Manosas, Maria; Li, Pan T. X.; Smith, Steven B.; Bustamante, Carlos; Ritort, Felix; Tinoco, Ignacio



Novel single-cell functional analysis of red blood cells using laser tweezers Raman spectroscopy: application for sickle cell disease.  


Laser tweezers Raman spectroscopy was used to characterize the oxygenation response of single normal adult, sickle, and cord blood red blood cells (RBCs) to an applied mechanical force. Individual cells were subjected to different forces by varying the laser power of a single-beam optical trap, and the intensities of several oxygenation-specific Raman spectral peaks were monitored to determine the oxygenation state of the cells. For all three cell types, an increase in laser power (or mechanical force) induced a greater deoxygenation of the cell. However, sickle RBCs deoxygenated more readily than normal RBCs when subjected to the same optical forces. Conversely, cord blood RBCs were able to maintain their oxygenation better than normal RBCs. These results suggest that differences in the chemical or mechanical properties of fetal, normal, and sickle cells affect the degree to which applied mechanical forces can deoxygenate the cell. Populations of normal, sickle, and cord RBCs were identified and discriminated based on this mechanochemical phenomenon. This study demonstrates the potential application of laser tweezers Raman spectroscopy as a single-cell, label-free analytical tool to characterize the functional (e.g., mechanical deformability, oxygen binding) properties of normal and diseased RBCs. PMID:23537725

Liu, Rui; Mao, Ziliang; Matthews, Dennis L; Li, Chin-Shang; Chan, James W; Satake, Noriko



Optoacoustic tweezers: a programmable, localized cell concentrator based on opto-thermally generated, acoustically activated, surface bubbles.  


We present a programmable, biocompatible technique for dynamically concentrating and patterning particles and cells in a microfluidic device. Since our technique utilizes opto-thermally generated, acoustically activated, surface bubbles, we name it "optoacoustic tweezers". The optoacoustic tweezers are capable of concentrating particles/cells at any prescribed locations in a microfluidic chamber without the use of permanent structures, rendering it particularly useful for the formation of flexible, complex cell patterns. Additionally, this technique has demonstrated excellent biocompatibility and can be conveniently integrated with other microfluidic units. In our experiments, micro-bubbles were generated by focusing a 405 nm diode laser onto a gold-coated glass chamber. By properly tuning the laser, we demonstrate precise control over the position and size of the generated bubbles. Acoustic waves were then applied to activate the surface bubbles, causing them to oscillate at an optimized frequency. The resulting acoustic radiation force allowed us to locally trap particles/cells, including 15 ?m polystyrene beads and HeLa cells, around each bubble. Cell-adhesion tests were also conducted after cell concentrating to confirm the biocompatibility of this technique. PMID:23511348

Xie, Yuliang; Zhao, Chenglong; Zhao, Yanhui; Li, Sixing; Rufo, Joseph; Yang, Shikuan; Guo, Feng; Huang, Tony Jun



Single-cell adhesion probed in-situ using optical tweezers: A case study with Saccharomyces cerevisiae  

NASA Astrophysics Data System (ADS)

A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynam