Note: This page contains sample records for the topic zn-porphyrin tweezer host-guest from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Host-guest interactions of phosphorescent molecular tweezers based on an alkynylplatinum(II) terpyridine system with polyaromatic hydrocarbons.  

PubMed

Host-guest interactions of a molecular tweezer complex 1 with various planar organic molecules including polyaromatic hydrocarbons (PAHs) were investigated by 1D and 2D (1)H?NMR spectroscopy, UV/Vis absorption and emission titration studies. 2D and DOSY NMR spectroscopies support the sandwiched binding mode based on 1:1 host-guest interactions. The binding constants (K(S)) of complex 1 for various PAHs were determined by NMR titration studies and the values were found to span up to an order of 10(4) ?M(-1) for coronene to no observable interaction for benzene, indicating that the ?-surface area is important for such host-guest interactions. The substituent effect on the host-guest interaction based on the guest series of 9-substituted anthracenes was also studied. In general, a stronger interaction was observed for the anthracene guest with electron-donating groups, although steric and ?-conjugation factors cannot be completely excluded. The photophysical responses of complex 1 upon addition of various PAHs were measured by UV/Vis and emission titration studies. The UV/Vis absorption spectra were found to show a drop in absorbance of the metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) admixture band upon addition of various guest molecules to 1, whereas the emission behavior was found to change differently depending on the guest molecules, showing emission enhancement and/or quenching. It was found that emission quenching occurred either via energy transfer or electron transfer pathway or both, while emission enhancement was caused by the increase in rigidity of complex 1 as a result of host-guest interaction. PMID:23180576

Tanaka, Yuya; Wong, Keith Man-Chung; Yam, Vivian Wing-Wah

2013-01-01

2

Switchable host-guest systems on surfaces.  

PubMed

Conspectus For device miniaturization, nanotechnology follows either the "top-down" approach scaling down existing larger-scale devices or the "bottom-up' approach assembling the smallest possible building blocks to functional nanoscale entities. For synthetic nanodevices, self-assembly on surfaces is a superb method to achieve useful functions and enable their interactions with the surrounding world. Consequently, adaptability and responsiveness to external stimuli are other prerequisites for their successful operation. Mechanically interlocked molecules such as rotaxanes and catenanes, and their precursors, that is, molecular switches and supramolecular switches including pseudorotaxanes, are molecular machines or prototypes of machines capable of mechanical motion induced by chemical signals, biological inputs, light or redox processes as the external stimuli. Switching of these functional host-guest systems on surfaces becomes a fundamental requirement for artificial molecular machines to work, mimicking the molecular machines in nature, such as proteins and their assemblies operating at dynamic interfaces such as the surfaces of cell membranes. Current research endeavors in material science and technology are focused on developing either a new class of materials or materials with novel/multiple functionalities by shifting host-guest chemistry from solution phase to surfaces. In this Account, we present our most recent attempts of building monolayers of rotaxanes/pseudorotaxanes on surfaces, providing stimuli-induced macroscopic effects and further understanding on the switchable host-guest systems at interfaces. Biocompatible versions of molecular machines based on synthetic macrocycles, such as cucurbiturils, pillararenes, calixarenes, and cyclodextrins, have been employed to form self-assembled monolayers of gates on the surfaces of mesoporous silica nanoparticles to regulate the controlled release of cargo/drug molecules under a range of external stimuli, such as light, pH variations, competitive binding, and enzyme. Rotaxanes have also been assembled onto the surfaces of gold nanodisks and microcantilevers to realize active molecular plasmonics and synthetic molecular actuators for device fabrication and function. Pillararenes have been successfully used to control and aid the synthesis of gold nanoparticles, semiconducting quantum dots, and magnetic nanoparticles. The resulting organic-inorganic hydrid nanomaterials have been successfully used for controlled self-assembly, herbicide sensing and detection, pesticide removal, and so forth, taking advantage of the selective binding of pillarenes toward target molecules. Cyclodextrins have also been successfully functionalized onto the surface of gold nanoparticles to serve as recycling extractors for C60. Many interesting prototypes of nanodevices based on synthetic macrocycles and their host-guest chemistry have been constructed and served for different potential applications. This Account will be a summary of the efforts made mainly by us, and others, on the host-guest chemistry of synthetic macrocyclic compounds on the surfaces of different solid supports. PMID:24635353

Yang, Ying-Wei; Sun, Yu-Long; Song, Nan

2014-07-15

3

Aromatic amide and hydrazide foldamer-based responsive host-guest systems.  

PubMed

Conspectus In host-guest chemistry, a larger host molecule selectively and noncovalently binds to a smaller guest molecule or ion. Early studies of host-guest chemistry focused on the recognition of spherical metal or ammonium ions by macrocyclic hosts, such as cyclic crown ethers. In these systems, preorganization enables their binding sites to cooperatively contact and attract a guest. Although some open-chain crown ether analogues possess similar, but generally lower, binding affinities, the design of acyclic molecular recognition hosts has remained challenging. One of the most successful examples was rigid molecular tweezers, acyclic covalently bonded preorganized host molecules with open cavities that bind tightly as they stiffen. Depending on the length of the atomic backbones, hydrogen bonding-driven aromatic amide foldamers can form open or closed cavities. Through rational design of the backbones and the introduction of added functional groups, researchers can regulate the shape and size of the cavity. The directionality of hydrogen bonding and the inherent rigidity of aromatic amide units allow researchers to predict both the shape and size of the cavity of an aromatic amide foldamer. Therefore, researchers can then design guest molecules with structure that matches the cavity shape, size, and binding sites of the foldamer host. In addition, because hydrogen bonds are dynamic, researchers can design structures that can adapt to outside stimuli to produce responsive supramolecular architectures. In this Account, we discuss how aromatic amide and hydrazide foldamers induced by hydrogen bonding can produce responsive host-guest systems, based on research by our group and others. First we highlight the helical chirality induced as binding occurs in solution, which includes the induction of helicity by chiral guests in oligomeric and polymeric foldamers, the formation of diastereomeric complexes between chiral foldamer hosts and guests, and the induction of helical chirality by chiral guests into inherently flexible backbones. In addition, molecular or ion-pair guests can produce supramolecular helical chirality in the organogel state. Such structures exhibit remarkable time-dependence and a "Sergeants and Soldiers" effect that are not observed for other two-component organogels that have been reported. We further illustrate that the reversible folding behavior of an aromatic amide foldamer segment can modulate the switching behavior of donor-acceptor interaction-based [2]rotaxanes. Finally we show that a folded oligomer can induce folding in one or two attached intrinsically flexible oligomers, an example of a solvent-responsive intramolecular host-guest system. PMID:24673152

Zhang, Dan-Wei; Zhao, Xin; Li, Zhan-Ting

2014-07-15

4

Molecular structures of recognition system host + guest and DNA complex  

NASA Astrophysics Data System (ADS)

Investigations were carried out to look into the system of host + guest as a ligand targeted to the duplex DNA. The possible structures of host RhB-?-CDen were studied by minimization and molecular dynamics simulation. In the association state of host + guest (1:1) system, the guest molecule of 1-borneol could insert into the cyclodextrin cavity of the host molecule RhB-?-CDen. The interactive sites of the RhB-?-CDen + borneol system as a ligand targeting to the duplex DNA d(C)8·d(G)8 were obtained by docking interaction. It was found that the ligand was probably bound to the duplex DNA in the minor groove. The conformations of DNA varies noticeably to accommodate the binding groups of the ligand. Water molecules bridge between the bases of duplex DNA and/or ligand by hydrogen bonds to make the entire system more stable.

Yang, Linjing; Feng, Xizeng; Lee, Imshik; Bai, Chunli

1998-03-01

5

The Host Guest Co-Crystal Approach to Supramolecular Structure  

Microsoft Academic Search

A host-guest co-crystal approach to supramolecular structure has been developed. Molecular functionalities have been identified that will self assemble via hydrogen bonds to give one dimensional ?-networks with defined intermolecular distances. Host molecules based on these functionalites can be co-crystallized with guest molecules, the characteristic distance defined by the host is thus imposed on the guest. Using this strategy, functional

John J. Kane; Tam Nguyen; Jun Xiao; Frank W. Fowler; Joseph W. Lauher

2001-01-01

6

Thermodynamic integration to predict host-guest binding affinities  

PubMed Central

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 R2 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.

Wereszczynski, Jeff; Ortiz-Sanchez, Juan Manuel; Nichols, Sara E.; McCammon, J. Andrew

2014-01-01

7

An order-disorder ferroelectric host-guest inclusion compound.  

PubMed

The host-guest complex [(DIPA)([18]crown-6)](ClO4) (1; DIPA=2,6-diisopropylanilinium) was constructed and found to undergo a sequence of phase transitions (Ibam-Pbcn-Pna21) at T1=278?K and T2=132?K, respectively. Systematic characterizations, such as differential scanning calorimetry, heat capacity, temperature-dependent dielectric constant, and P-E hysteresis loop, reveal that the centrosymmetric-to-polar phase transition at T2 is a paraelectric-to-ferroelectric transition. The symmetry breaking was also confirmed by temperature-dependent second-harmonic generation effect and X-ray powder diffraction. The ferroelectric mechanism is attributable to the linear motion of the perchlorate counterions accompanied by the order-disorder transition of the [18]crown-6 molecules and the anions. PMID:24497326

Zhang, Yi; Ye, Heng-Yun; Fu, Da-Wei; Xiong, Ren-Gen

2014-02-17

8

A new topological parameter for monitoring subtle aggregation events in host-guest inclusion processes  

NASA Astrophysics Data System (ADS)

Supramolecular complexes with cyclodextrin (CD) have been the subject of considerable research in the material and life sciences. The dynamics of systems are difficult to characterise, therefore, knowledge of the molecular features governing the host-guest equilibrium might aid in the design and practical application of the resulting inclusion complexes. In this Letter, we present a new topological parameter based on simple trigonometric considerations to be used to monitor subtle host-guest inclusion events along the molecular dynamics trajectory. The new topological descriptor, called vector- ?, was applied to amphetamine@?/?-CD inclusion complexes, providing interesting insights on the host-guest equilibrium.

Novato, Willian T. G.; De Almeida, Wagner B.; Dos Santos, Hélio F.

2012-02-01

9

Theoretical studies of host-guest interaction in gas hydrates.  

PubMed

Ab initio calculations and atoms-in-molecules (AIM) analysis have been used to investigate the host-guest interaction in dodecahedral water cages using a variety of guest species that include monatomic (He, Ne, Ar, Kr, and Xe), diatomic (CO, H(2), N(2), O(2), and NO), triatomic (CO(2), NO(2), and O(3)), and polyatomic (CH(4) and NH(3)) molecules. Geometry optimization for the guest species, host cage, and their complexes was carried out using the second order Møller-Plesset perturbation method with the 6-31G** basis set. Single point energy calculations using the same method but different basis sets (6-31++G**, 6-311++G**, aug-cc-pVDZ, and aug-cc-pVTZ) were carried out for the MP2/6-31G** optimized geometries. The interaction energy between the guest species and the host cage has been obtained in the complete basis set limit by basis set extrapolation. PMID:22044163

Kumar, Pradeep; Sathyamurthy, N

2011-12-22

10

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.

2013-01-01

11

Metallocenes@COF-102: organometallic host-guest chemistry of porous crystalline organic frameworks.  

PubMed

The organometallic host-guest chemistry of porous covalent organic frameworks is explored by vapour phase infiltration of volatile organometallic precursors; namely, [Fe(?(5)-C(5)H(5))(2)], [Co(?(5)-C(5)H(5))(2)], and [Ru(cod)(cot)]. The unique arrangement of ferrocene molecules inside COF-102 is driven by ?-? (host-guest) interactions and replicates the framework symmetry. PMID:21503349

Kalidindi, Suresh Babu; Yusenko, Kirill; Fischer, Roland A

2011-08-14

12

Supramolecular chemistry at interfaces: host-guest interactions for fabricating multifunctional biointerfaces.  

PubMed

Conspectus Host-guest chemistry can greatly improve the selectivity of biomolecule-ligand binding on account of recognition-directed interactions. In addition, functional structures and the actuation of supramolecular assemblies in molecular systems can be controlled efficiently through various host-guest chemistry. Together, these highly selective, strong yet dynamic interactions can be exploited as an alternative methodology for applications in the field of programmable and controllable engineering of supramolecular soft materials through the reversible binding between complementary components. Many processes in living systems such as biotransformation, transportation of matter, and energy transduction begin with interfacial molecular recognition, which is greatly influenced by various external stimuli at biointerfaces. Detailed investigations about the molecular recognition at interfaces can result in a better understanding of life science, and further guide us in developing new biomaterials and medicines. In order to mimic complicated molecular-recognition systems observed in nature that adapt to changes in their environment, combining host-guest chemistry and surface science is critical for fabricating the next generation of multifunctional biointerfaces with efficient stimuli-responsiveness and good biocompatibility. In this Account, we will summarize some recent progress on multifunctional stimuli-responsive biointerfaces and biosurfaces fabricated by cyclodextrin- or cucurbituril-based host-guest chemistry and highlight their potential applications including drug delivery, bioelectrocatalysis, and reversible adsorption and resistance of peptides, proteins, and cells. In addition, these biointerfaces and biosurfaces demonstrate efficient response toward various external stimuli, such as UV light, pH, redox chemistry, and competitive guests. All of these external stimuli can aid in mimicking the biological stimuli evident in complex biological environments. We begin by reviewing the current state of stimuli-responsive supramolecular assemblies formed by host-guest interactions, discussing how to transfer host-guest chemistry from solution onto surfaces required for fabricating multifunctional biosurfaces and biointerfaces. Then, we present different stimuli-responsive biosurfaces and biointerfaces, which have been prepared through a combination of cyclodextrin- or cucurbituril-based host-guest chemistry and various surface technologies such as self-assembled monolayers or layer-by-layer assembly. Moreover, we discuss the applications of these biointerfaces and biosurfaces in the fields of drug release, reversible adsorption and release of some organic molecules, peptides, proteins, and cells, and photoswitchable bioelectrocatalysis. In addition, we summarize the merits and current limitations of these methods for fabricating multifunctional stimuli-responsive biointerfaces in a dynamic noncovalent manner. Finally, we present possible strategies for future designs of stimuli-responsive multifunctional biointerfaces and biosurfaces by combining host-guest chemistry with surface science, which will lead to further critical development of supramolecular chemistry at interfaces. PMID:24766328

Yang, Hui; Yuan, Bin; Zhang, Xi; Scherman, Oren A

2014-07-15

13

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.

2011-01-01

14

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

2010-01-01

15

Axial binding and host-guest interactions of a phthalocyanine resorcinarene cavitand hybrid.  

PubMed

A Zn phthalocyanine-resorcinarene cavitand hybrid was prepared. The axial binding and host-guest interactions of this hybrid with a pyridinyl-pyrene were investigated by UV-vis and fluorescence spectroscopic means, revealing the encapsulation of the guest maintained by axial coordination to the Zn phthalocyanine. Energy transfer between the pyrene and the phthalocyanine was evidenced. PMID:24276488

Topkaya, Derya; Dumoulin, Fabienne; Ahsen, Vefa; I?ci, Ümit

2014-02-01

16

Engineering responsive polymer building blocks with host-guest molecular recognition for functional applications.  

PubMed

Conspectus All living organisms and soft matter are intrinsically responsive and adaptive to external stimuli. Inspired by this fact, tremendous effort aiming to emulate subtle responsive features exhibited by nature has spurred the invention of a diverse range of responsive polymeric materials. Conventional stimuli-responsive polymers are constructed via covalent bonds and can undergo reversible or irreversible changes in chemical structures, physicochemical properties, or both in response to a variety of external stimuli. They have been imparted with a variety of emerging applications including drug and gene delivery, optical sensing and imaging, diagnostics and therapies, smart coatings and textiles, and tissue engineering. On the other hand, in comparison with molecular chemistry held by covalent bonds, supramolecular chemistry built on weak and reversible noncovalent interactions has emerged as a powerful and versatile strategy for materials fabrication due to its facile accessibility, extraordinary reversibility and adaptivity, and potent applications in diverse fields. Typically involving more than one type of noncovalent interactions (e.g., hydrogen bonding, metal coordination, hydrophobic association, electrostatic interactions, van der Waals forces, and ?-? stacking), host-guest recognition refers to the formation of supramolecular inclusion complexes between two or more entities connected together in a highly controlled and cooperative manner. The inherently reversible and adaptive nature of host-guest molecular recognition chemistry, stemming from multiple noncovalent interactions, has opened up a new platform to construct novel types of stimuli-responsive materials. The introduction of host-guest chemistry not only enriches the realm of responsive materials but also confers them with promising new applications. Most intriguingly, the integration of responsive polymer building blocks with host-guest recognition motifs will endow the former with further broadened responsiveness to external stimuli and accordingly more sophisticated functions. In this Account, we summarize recent progress in the field of responsive polymeric materials containing host-guest recognition motifs with selected examples and highlight their versatile functional applications, whereas small molecule-oriented host-guest supramolecular systems are excluded. We demonstrate how the introduction of host-guest chemistry into conventional polymer systems can modulate their responsive modes to external stimuli. Moreover, the responsive specificity and selectivity of polymeric systems can also be inherited from the host-guest recognition motifs, and these features provide extra advantages in terms of function integration. The following discussions are categorized in terms of design and functions, namely, host-guest chemistry toward the fabrication of responsive polymers and assemblies, optical sensing and imaging, drug and gene delivery, and self-healing materials. A concluding remark on future developments is also presented. We wish this prosperous field would incur more original and evolutionary ideas and benefit fundamental research and our daily life in a more convenient way. PMID:24742049

Hu, Jinming; Liu, Shiyong

2014-07-15

17

Cyclodextrin-based host-guest supramolecular nanoparticles for delivery: from design to applications.  

PubMed

Conspectus Efficient assembly in host-guest interactions is crucial to supramolecular nanotechnology. Cyclodextrins (CDs), which possess a hydrophilic exterior surface and hydrophobic interior cavity on the truncated cone, improve the biocompatibility of nanodelivery systems, and hence, supramolecular approaches utilizing CDs can improve and expand the design and applications of functional delivery systems. Owing to good inclusion ability, ?CD and ?CD are commonly used in the design and construction of supramolecular structures. In this Account, we describe the design strategies to adopt CDs in host-guest delivery systems. Modification of CDs with polymers is popular in current research due to the potential benefits rendered by cationic protection and improved capability. While the process has only minor influence on the host characteristics of the CD cavity, the interaction between the CD and the guest moiety imparts new attributes to the nanosystems with guest-decorated functional groups such as adamantyl poly(ethylene glycol) (PEG) for coating protection, hybrid guests for conformational flexibility, and adamantyl prodrugs for drug delivery. Some specific agents form inclusion complexes with the polymerized ?CDs directly and core-shell nanoparticles with hydrophobic cores and are usually created to carry insoluble drugs while the hydrophilic shells offer protection. These unique designs provide the means to practically adapt special characteristics for additional functions or co-delivery. In order to be accepted clinically, delivery systems need to possess extra functions such as controlled particle size, biodegradability, controlled release, and targeted delivery to overcome the hurdles in delivery. These features can be added to biomaterials by self-assembly of functional groups facilitated by the host-guest interactions. Size control by hybridization of switchable polymer compartments in supramolecular structures contributes to the biodistribution utility and biodegradability by incorporating the moieties with hydrolyzable connections and enhancing intracellular degradation and clearance. Controlled release by application of responsive structures like molecular gatings eased by the host-guest interaction can be triggered by the tumor microenvironment at extreme pH and temperature or by external stimuli such as light. Along with the binding selectivity and controlled release, the host-guest nanoparticles show enhanced efficacy in delivery especially to tumors. Recent developments in supramolecular co-delivery systems are described in this Account. Nanoparticles can be designed to carry adamantyl prodrugs and therapeutic nucleotides to tumors so that the released drugs and gene expression synergistically inhibit malignant tissue growth. Optimization of nanoparticle delivery systems by multifunctional transitions yields better biocompatibility and controlled response, and such novel designs will expedite in vivo applications. Hence, multifunctional CD-based host-guest supramolecular nanoparticles with co-delivery ability are expected to have many potential clinical applications. PMID:24873201

Hu, Qi-Da; Tang, Gu-Ping; Chu, Paul K

2014-07-15

18

Stimuli-responsive host-guest systems based on the recognition of cryptands by organic guests.  

PubMed

Conspectus As the star compounds in host-guest chemistry, the syntheses of crown ethers proclaimed the birth of supramolecular chemistry. Crown ether-based host-guest systems have attracted great attention in self-assembly processes because of their good selectivity, high efficiency, and convenient responsiveness, enabling their facile application to the "bottom-up" approach for construction of functional molecular aggregates, such as artificial molecular machines, drug delivery materials, and supramolecular polymers. Cryptands, as preorganized derivatives of crown ethers, not only possess the above-mentioned properties but also have three-dimensional spatial structures and higher association constants compared with crown ethers. More importantly, the introduction of the additional arms makes cryptand-based host-guest systems responsive to more stimuli, which is crucial for the construction of adaptive or smart materials. In the past decade, we designed and synthesized crown ether-based cryptands as a new type of host for small organic guests with the purpose of greatly increasing the stabilities of the host-guest complexes and preparing mechanically interlocked structures and large supramolecular systems more efficiently while retaining or increasing their stimuli-responsiveness. Organic molecules such as paraquat derivatives and secondary ammonium salts have been widely used in the fabrication of functional supramolecular aggregates. Many host molecules including crown ethers, cyclodextrins, calixarenes, cucurbiturils, pillararenes, and cryptands have been used in the preparation of self-assembled structures with these guest molecules, but among them cryptands exhibit the best stabilities with paraquat derivatives in organic solvents due to their preorganization and additional and optimized binding sites. They enable the construction of sophisticated molecules or supramolecules in high yields, affording a very efficient way to fabricate stimuli-responsive functional supramolecular systems. This Account mainly focuses on the application of cryptands in the construction of mechanically interlocked molecules such as rotaxanes and catenanes, and stimuli-responsive host-guest systems such as molecular switches and supramolecular polymers due to their good host-guest properties. These cryptands are bicyclic derivatives of crown ethers, including dibenzo-24-crown-8, bis(m-phenylene)-26-crown-8, dibenzo-30-crown-10, and bis(m-phenylene)-32-crown-10. The length of the third arm has a very important influence on the binding strength of these cryptands with organic guests, because it affects not only the size fit between the host and the guest but also the distances and angles that govern the strengths of the noncovalent interactions between the host and the guest. For example, for bis(m-phenylene)-32-crown-10-based cryptands, a third arm of nine atoms is the best. The environmental responsiveness of these cryptand-based host-guest systems arises from either the crown ether units or the third arms. For example, a dibenzo-24-crown-8 unit introduces potassium cation responsiveness and an azobenzene group on the third arm imbues photoresponsiveness. We believe that studies on stimuli-responsive host-guest systems based on cryptands and organic guests will contribute significantly to future research on molecular devices, supramolecular polymers, and other functional supramolecular materials. PMID:24804805

Zhang, Mingming; Yan, Xuzhou; Huang, Feihe; Niu, Zhenbin; Gibson, Harry W

2014-07-15

19

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

2011-01-01

20

Spectroscopic and Thermal Characterization of the Host-Guest Interactions between ?-, ?-, and ?-cyclodextrins and vanadocene dichloride  

PubMed Central

Host-guest interactions between ?-, ?-, and ?-cyclodextrins and vanadocene dichloride (Cp2VCl2) have been investigated by a combination of thermogravimetric analysis, differential scanning calorimeters, PXRD and solid state and solution EPR spectroscopy. The solid state results demonstrated that only ?- and ?-cyclodextrins form 1:1 inclusion complexes, while ?-cyclodextrin does not form an inclusion complex with Cp2VCl2. The ?- and ?-CD-Cp2VCl2 inclusion complexes exhibited anisotropic electron-51V (I = 7/2) hyperfine coupling constants whereas the ?-CD- Cp2VCl2 system showed only an asymmetric peak with no anisotropic hyperfine constant. On the other hand, solution EPR spectroscopy showed that ?-CD may be involved in weak host-guest interactions in equilibrium with free vanadocene species.

Morales, Alexis; Weber, Ralph T.; Melendez, Enrique

2009-01-01

21

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.

2013-01-01

22

The SAMPL4 host-guest blind prediction challenge: an overview.  

PubMed

Prospective validation of methods for computing binding affinities can help assess their predictive power and thus set reasonable expectations for their performance in drug design applications. Supramolecular host-guest systems are excellent model systems for testing such affinity prediction methods, because their small size and limited conformational flexibility, relative to proteins, allows higher throughput and better numerical convergence. The SAMPL4 prediction challenge therefore included a series of host-guest systems, based on two hosts, cucurbit[7]uril and octa-acid. Binding affinities in aqueous solution were measured experimentally for a total of 23 guest molecules. Participants submitted 35 sets of computational predictions for these host-guest systems, based on methods ranging from simple docking, to extensive free energy simulations, to quantum mechanical calculations. Over half of the predictions provided better correlations with experiment than two simple null models, but most methods underperformed the null models in terms of root mean squared error and linear regression slope. Interestingly, the overall performance across all SAMPL4 submissions was similar to that for the prior SAMPL3 host-guest challenge, although the experimentalists took steps to simplify the current challenge. While some methods performed fairly consistently across both hosts, no single approach emerged as consistent top performer, and the nonsystematic nature of the various submissions made it impossible to draw definitive conclusions regarding the best choices of energy models or sampling algorithms. Salt effects emerged as an issue in the calculation of absolute binding affinities of cucurbit[7]uril-guest systems, but were not expected to affect the relative affinities significantly. Useful directions for future rounds of the challenge might involve encouraging participants to carry out some calculations that replicate each others' studies, and to systematically explore parameter options. PMID:24599514

Muddana, Hari S; Fenley, Andrew T; Mobley, David L; Gilson, Michael K

2014-04-01

23

Reversible single-chain selective point folding via cyclodextrin driven host-guest chemistry in water.  

PubMed

In the present communication we introduce a new platform technology for the reversible folding of single polymer chains in aqueous environment on the basis of cyclodextrin (CD) host-guest chemistry and controlled radical polymerization protocols. The single-chain folding of adamantyl-?-CD ?-?-functionalized poly(N,N-dimethylacrylamide) and its reversion at elevated temperatures were monitored by DLS and nuclear Overhauser enhancement spectroscopy (NOESY). PMID:24850295

Willenbacher, Johannes; Schmidt, Bernhard V K J; Schulze-Suenninghausen, David; Altintas, Ozcan; Luy, Burkhard; Delaittre, Guillaume; Barner-Kowollik, Christopher

2014-06-01

24

Probing conformational changes of ubiquitin by host-guest chemistry using electrospray ionization mass spectrometry.  

PubMed

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 Lys(6) or Lys(11) 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 Lys(48) and Lys(63) in low charge state (+7) complex. MD simulation studies reveal that the high charge state complexes are attributed to the CB[6] bound to Lys(11). The complexation prohibits salt bridge formation between Lys(11) and Glu(34) 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. PMID:23247966

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

2013-01-01

25

Blind prediction of host-guest binding affinities: A new SAMPL3 challenge  

PubMed Central

The computational prediction of protein-ligand binding affinities is of central interest in early-stage drug-discovery, and there is a widely recognized need for improved methods. Low molecular weight receptors and their ligands—i.e. host-guest systems – represent valuable test-beds for such affinity prediction methods, because their small size makes for fast calculations and relatively facile numerical convergence. The SAMPL3 community exercise included the first ever blind prediction challenge for host-guest binding affinities, through the incorporation of 11 new host-guest complexes. Ten participating research groups addressed this challenge with a variety of approaches. Statistical assessment indicates that, although most methods performed well at predicting some general trends in binding affinity, overall accuracy was not high, as all the methods suffered from either poor correlation or high RMS errors or both. There was no clear advantage in using explicit vs. implicit solvent models, any particular force field, or any particular approach to conformational sampling. In a few cases, predictions using very similar energy models but different sampling and/or free-energy methods resulted in significantly different results. The protonation states of one host and some guest molecules emerged as key uncertainties beyond the choice of computational approach. The present results have implications for methods development and future blind prediction exercises.

Muddana, Hari S.; Varnado, C. Daniel; Bielawski, Christopher W.; Urbach, Adam R.; Isaacs, Lyle; Geballe, Matthew T.; Gilson, Michael K.

2012-01-01

26

A responsive supramolecular polymer formed by orthogonal metal-coordination and cryptand-based host-guest interaction.  

PubMed

Herein, a cation responsive linear supramolecular polymer was constructed in an orthogonal fashion by unifying the themes of coordination-driven self-assembly and cryptand-based host-guest interaction. PMID:24609282

Wei, Peifa; Xia, Binyuan; Zhang, Yanyan; Yu, Yihua; Yan, Xuzhou

2014-04-18

27

Supramolecular polymers constructed from macrocycle-based host-guest molecular recognition motifs.  

PubMed

Conspectus Supramolecular polymers, fabricated via the combination of supramolecular chemistry and polymer science, are polymeric arrays of repeating units held together by reversible, relatively weak noncovalent interactions. The introduction of noncovalent interactions, such as hydrogen bonding, aromatic stacking interactions, metal coordination, and host-guest interactions, endows supramolecular polymers with unique stimuli responsiveness and self-adjusting abilities. As a result, diverse monomer structures have been designed and synthesized to construct various types of supramolecular polymers. By changing the noncovalent interaction types, numbers, or chemical structures of functional groups in these monomers, supramolecular polymeric materials can be prepared with tailored chemical and physical properties. In recent years, the interest in supramolecular polymers has been extended from the preparation of intriguing topological structures to the discoveries of potential applications as functional materials. Compared with traditional polymers, supramolecular polymers show some advantages in the fabrication of reversible or responsive materials. The development of supramolecular polymers also offers a platform to construct complex and sophisticated materials with a bottom-up approach. Macrocylic hosts, including crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, are the most commonly used building blocks in the fabrication of host-guest interaction-based supramolecular polymers. With the introduction of complementary guest molecules, macrocylic hosts demonstrate selective and stimuli-responsive host-guest complexation behaviors. By elaborate molecular design, the resultant supramolecular polymers can exhibit diverse structures based on the self-selectivity of host-guest interactions. The introduction of reversible host-guest interactions can further endow these supramolecular polymers with interesting and fascinating chemical/physical properties, including stimuli responsiveness, self-healing, and environmental adaptation. It has been reported that macrocycle-based supramolecular polymers can respond to pH change, photoirradition, anions, cations, temperature, and solvent. Macrocycle-based supramolecular polymers have been prepared in solution, in gel, and in the solid state. Furthermore, the solvent has a very important influence on the formation of these supramolecular polymers. Crown ether- and pillararene-based supramolecular polymers have mainly formed in organic solvents, such as chloroform, acetone, and acetonitrile, while cyclodextrin- and cucurbituril-based supramolecular polymerizations have been usually observed in aqueous solutions. For calixarenes, both organic solvents and water have been used as suitable media for supramolecular polymerization. With the development of supramolecular chemistry and polymer science, various methods, such as nuclear magnetic resonance spectroscopy, X-ray techniques, electron microscopies, and theoretical calculation and computer simulation, have been applied for characterizing supramolecular polymers. The fabrication of macrocycle-based supramolecular polymers has become a currently hot research topic. In this Account, we summarize recent results in the investigation of supramolecular polymers constructed from macrocycle-based host-guest molecular recognition motifs. These supramolecular polymers are classified based on the different macrocycles used in them. Their monomer design, structure control, stimuli-responsiveness, and applications in various areas are discussed, and future research directions are proposed. It is expected that the development of supramolecular polymers will not only change the way we live and work but also exert significant influence on scientific research. PMID:24684594

Dong, Shengyi; Zheng, Bo; Wang, Feng; Huang, Feihe

2014-07-15

28

Proton Transfer in Host-Guest Complexation between a Difunctional Pillar[5]arene and Alkyldiamines.  

PubMed

Host-guest complexation between a novel difunctional pillar[5]arene-based host H and alkyldiamines was fully investigated in both solution and the solid state. Proton transfer from the carboxylic acid groups to the amine units occurred in the principle by undergoing an acid-base reaction. Driven by the cooperativity of electrostatic interactions, multiple C-H···? interactions, and H-bonds, the guests penetrated into the cavity of H to form pseudorotaxane-type inclusion complexes with relatively high binding affinities. PMID:24735090

Yu, Guocan; Hua, Bin; Han, Chengyou

2014-05-01

29

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

PubMed Central

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

2013-01-01

30

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

PubMed

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

2013-01-01

31

Host-guest interaction between cyclen based macrotricyclic ligands and phosphate anions. A potentiometric investigation.  

PubMed

The host-guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen based macrotricyclic ligands possessing ortho- (TOC), meta- (TMC) and para-xylenyl (TPC) linkers was investigated by potentiometric measurements. The ternary species present in solution and their stability constants have been determined. The different behaviours are explained in terms of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed the importance of the distance between the two cyclen cores and emphasized the increasing of the triphosphate species selectivity together with the cavity size of the ligand. A comparison of the present results with those obtained with their mono-bridged homologues is also discussed. PMID:16832490

Develay, Stéphanie; Tripier, Raphaël; Le Baccon, Michel; Patinec, Véronique; Serratrice, Guy; Handel, Henri

2006-07-28

32

Temperature-Sensitive Transitions Below LCST in Amphiphilic Dendritic Assemblies - Host-Guest Implications  

PubMed Central

Oligoethylene glycol decorated supramolecular assemblies have been of great interest due to their charge-neutral character and thus the propensity to avoid non-specific 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 oligoethylene 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.

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

2013-01-01

33

Host-guest interactions between a nonmicellized amphiphilic invertible polymer and insoluble cyclohexasilane in acetonitrile.  

PubMed

Host-guest interactions between cyclohexasilane (Si(6)H(12)) and amphiphilic invertible macromolecules based on PEG and sebacic acid in acetonitrile (neither a solvent for cyclohexasilane nor a support for the micellization of amphiphilic invertible macromolecules) have been investigated. Despite the extended conformation of the macromolecules and the absence of self-assembled polymeric domains, a macromolecular amphiphilicity itself contributes to localizing Si(6)H(12) by AIP and thus enables Lewis acid-base interactions between Si(6)H(12) and the AIP carbonyl groups. The obtained results demonstrate an interesting phenomenon in that insoluble Si(6)H(12) can be localized by AIP macromolecules in a medium that does not support the formation of polymeric domains. PMID:21797281

Kohut, Ananiy; Kudina, Olena; Dai, Xuliang; Schulz, Douglas L; Voronov, Andriy

2011-09-01

34

Dual pH-triggered multistage drug delivery systems based on host-guest interaction-associated polymeric nanogels.  

PubMed

The polymeric nanogels were constructed via host-guest interactions for dual pH-triggered multistage drug delivery, which showed tumor acidity-triggered nanogel reorganization into smaller nanoparticles for deep tissue penetration, high-efficiency cellular uptake, and intracellular endo-lysosomal pH-responsive drug release. PMID:24909859

Zan, Minghui; Li, Junjie; Luo, Shizhong; Ge, Zhishen

2014-06-24

35

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

PubMed

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, (1)H 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. PMID:23872014

Siva, S; Thulasidhasan, J; Rajendiran, N

2013-11-01

36

Cyclodextrin-modified zeolites: host-guest surface chemistry for the construction of multifunctional nanocontainers.  

PubMed

The functionalization of nanoporous zeolite?L crystals with ?-cyclodextrin (CD) has been demonstrated. The zeolite surface was first modified with amino groups by using two different aminoalkoxysilanes. Then, 1,4-phenylene diisothiocyanate was reacted with the amino monolayer and used to bind CD heptamine by using its remaining isothiocyanate groups. The use of the different aminoalkoxysilanes, 3-aminopropyl dimethylethoxysilane (APDMES) and 3-aminopropyl triethoxysilane (APTES), led to drastic differences in uptake and release properties. Thionine was found to be absorbed and released from amino- and CD-functionalized zeolites when APDMES was used, whereas functionalization by APTES led to complete blockage of the zeolite channels. Fluorescence microscopy showed that the CD groups covalently attached to the zeolite crystals could bind adamantyl-modified dyes in a specific and reversible manner. This strategy allowed the specific immobilization of His-tagged proteins by using combined host-guest and His-tag-Ni-nitrilotriacetic acid (NTA) coordination chemistry. Such multifunctional systems have the potential for encapsulation of drug molecules inside the zeolite pores and non-covalent attachment of other (for example, targeting) ligand molecules on its surface. PMID:24038376

Szarpak-Jankowska, Anna; Burgess, Christine; De Cola, Luisa; Huskens, Jurriaan

2013-10-25

37

Predicting binding affinities of host-guest systems in the SAMPL3 blind challenge  

PubMed Central

Relative free energy calculations based on molecular dynamics simulations were combined with available experimental binding free energies to predict unknown binding affinities of acyclic Cucurbituril complexes in the blind SAMPL3 competition. The predictions showed good agreement with experimental results, yielding root mean square errors of about 2.6 kcal/mol for seven host-guest systems. However, the standard deviations found in our simulations were ranging up to 2.4 kcal/mol, which indicates the need for better sampling. We compare the performance of three different approaches: Bennett’s Acceptance Ratio Method and Thermodynamic Integration based on both the trapezoidal and Simpson’s rule. Surprisingly, both Bennett’s Acceptance Ratio Method and Thermodynamic Integration with trapezoidal rule lead to the same root mean square error. We also evaluate the influence of the protonation states of the amine groups of the guest molecules, showing that the deprotonated forms exhibit a poorer correspondence to experimental results with a root mean square error of 5.2 kcal/mol. In addition, we demonstrate that a decrease of the buffer concentration by about 20mM in our simulations can raise the root mean square error to 3.8 kcal/mol.

Konig, Gerhard; Brooks, Bernard R.

2013-01-01

38

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.

2009-06-23

39

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

2013-01-01

40

Vesicular gold assemblies based on host-guest inclusion and its controllable release of doxorubicin  

NASA Astrophysics Data System (ADS)

We have developed a kind of gold nanoparticle (AuNP) in which polyethylene glycol (PEG) and poly(N-isopropylacrylamide) (PNIPAM) are attached on the surface of a gold nanocrystal through the host-guest inclusion between adamantane groups (ADA) and ?-cyclodextrin (?-CD). The resulting AuNPs become amphiphilic in water above body temperature and self-assemble into vesicles. It is found that these vesicles can load doxorubicin (Dox) effectively. With a decrease in temperature, the PNIPAM shifted from hydrophobic to hydrophilic, causing Au vesicles to disassemble into stable small AuNPs, triggering the release of Dox. These hybrid vesicles, combining polymer functionality with the intriguing properties of AuNPs, can first release free Dox and AuNP/Dox at a site of a tumor through the application of either simple ice packs or deeply penetrating cryoprobes, then the AuNP/Dox can be taken in by tumor cells and destroy them like miniature munitions. Furthermore, these vesicles showed other therapeutic possibilities due to the presence of gold. We believe that the development of such multi-functional vesicles will provide new and therapeutically useful means for medical applications.

Ha, Wei; Kang, Yang; Peng, Shu-Lin; Ding, Li-Sheng; Zhang, Sheng; Li, Bang-Jing

2013-12-01

41

Host-guest complex of cypermethrin with ?-cyclodextrin: A spectroscopy and theoretical investigation  

NASA Astrophysics Data System (ADS)

An inclusion complex of ?-CD with cypermethrin was synthesized. To reveal the host-guest interaction, UV-vis and Raman spectroscopic analysis in combination with DFT calculations at B3LYP/6-31G(d) level were performed on cypermethrin and its ?-CD inclusion complex. Upon examining the optimized geometry of inclusion complex, we find that the cypermethrin molecule inserts into the cavity of ?-CD from the larger opening, and the phenyl moiety is staying inside the cavity. Partial density of states spectra (PDOS) and natural bond orbital (NBO) analysis reveals that intermolecular hydrogen bond is main driving force of formation of inclusion complex. DFT calculations reproduce well the experimental spectra and the deviation is within 20 cm -1. Comparing the same vibrational modes of inclusion complex with those of free cypermethrin and ?-CD, we note that most of characteristic bands of free molecules present in the Raman spectrum of inclusion complex, but a small Raman shift of 2-13 cm -1 has been observed on the same mode. The presence of characteristic bands and the small Raman shifts affirm the weak interaction between cypermethrin and ?-CD. Calculated thermodynamic analysis reveals that the formation of ?-CD cypermethrin inclusion complex is a spontaneous and enthalpy-driven process.

Li, Wei; Lu, Bitai; Chen, Feifei; Yang, Feng; Wang, Zhendong

2011-03-01

42

Selective Organic and Organometallic Reactions in Water-Soluble Host-Guest Supramolecular Systems  

SciTech Connect

Inspired by the efficiency and selectivity of enzymes, synthetic chemists have designed and prepared a wide range of host molecules that can bind smaller molecules with their cavities; this area has become known as 'supramolecular' or 'host-guest' chemistry. Pioneered by Lehn, Cram, Pedersen, and Breslow, and followed up by a large number of more recent investigators, it has been found that the chemical environment in each assembly - defined by the size, shape, charge, and functional group availability - greatly influences the guest-binding characteristics of these compounds. In contrast to the large number of binding studies that have been carried out in this area, the exploration of chemistry - especially catalytic chemistry - that can take place inside supramolecular host cavities is still in its infancy. For example, until the work described here was carried out, very few examples of organometallic reactivity inside supramolecular hosts were known, especially in water solution. For that reason, our group and the group directed by Kenneth Raymond decided to take advantage of our complementary expertise and attempt to carry out metal-mediated C-H bond activation reactions in water-soluble supramolecular systems. This article begins by providing background from the Raymond group in supramolecular coordination chemistry and the Bergman group in C-H bond activation. It goes on to report the results of our combined efforts in supramolecular C-H activation reactions, followed by extensions of this work into a wider range of intracavity transformations.

Pluth, Michael D.; Raymond, Kenneth N.; Bergman, Robert G.

2008-02-16

43

Transparent, conducting Nb:SnO2 for host-guest photoelectrochemistry.  

PubMed

Many candidate materials for photoelectrochemical water splitting will be better employed by decoupling optical absorption from carrier transport. A promising strategy is to use multiple thin absorber layers supported on transparent, conducting materials; however there are limited such materials that are both pH stable and depositable on arbitrary high surface area substrates. Here we present the first 3D porous niobium doped tin oxide (NTO) electrodes fabricated by atomic layer deposition. After high temperature crystallization the NTO is transparent, conductive, and stable over a wide range of pH. The optimized films have high electrical conductivity up to 37 S/cm concomitant with a low optical attenuation coefficient of 0.99 ?m(-1) at 550 nm. NTO was deposited onto high surface area templates that were subsequently coated with hematite Fe(2)O(3) for the photoelectrochemical water splitting. This approach enabled near-record water splitting photocurrents for hematite electrodes employing a host-guest strategy. PMID:22974097

Stefik, Morgan; Cornuz, Maurin; Mathews, Nripan; Hisatomi, Takashi; Mhaisalkar, Subodh; Grätzel, Michael

2012-10-10

44

C60/corannulene on Cu(110): a surface-supported bistable buckybowl-buckyball host-guest system.  

PubMed

Corannulene (COR) buckybowls were proposed as near ideal hosts for fullerene C60, but direct complexation of C60 and COR has remained a challenge in supramolecular chemistry. We report the formation of surface-supported COR-C60 host-guest complexes by deposition of C60 onto a COR lattice on Cu(110). Variable-temperature scanning tunneling microscopy studies reveal two distinctly different states of C60 on the COR host lattice, with different binding energies and bowl-ball separations. The transition from a weakly bound precursor state to a strongly bound host-guest complex is found to be thermally activated. Simple model calculations show that this bistability originates from a subtle interplay between homo- and heteromolecular interactions. PMID:18338886

Xiao, Wende; Passerone, Daniele; Ruffieux, Pascal; Aït-Mansour, Kamel; Gröning, Oliver; Tosatti, Erio; Siegel, Jay S; Fasel, Roman

2008-04-01

45

Host-guest interactions mediated nano-assemblies using cyclodextrin-containing hydrophilic polymers and their biomedical applications  

PubMed Central

Summary Supramolecular nanostructures assembled by polymeric amphiphiles have been intensively studied during the last two decades. Such nanocarriers may be engineered to possess on-demand bio-responsitivity for the prevention, diagnosis, and treatment of human diseases. The successful development of several nanoassembly-based polymer therapeutics further encouraged scientists to develop nano-vehicles to achieve controlled release, enhanced efficacy, improved specificity and reduced toxicity. Different from the abundant existing literatures on the hydrophobically or electrostatically driven self-assemblies and their therapeutic applications, this article reviews host-guest interaction mediated nanoassemblies, especially those constructed using cyclodextrins as the host entities. The excellent biocompatibility, complexation capacity, and chemical-sensitivity of cyclodextrin make cyclodextrin-containing polymers attractive to construct host-guest nanoassemblies. Such nanocarriers may be advantageous also because of the broad availability of cyclodextrins, their flexibility for structure/property modulation and their chemical-responsive characteristics.

Zhang, Jianxiang; Ma, Peter X

2010-01-01

46

per-Hydroxylated pillar[6]arene: synthesis, X-ray crystal structure, and host-guest complexation.  

PubMed

A per-hydroxylated pillar[6]arene was prepared. Single-crystal X-ray analysis demonstrated that its molecules are arranged in an up-to-down manner to form infinite channels in the solid state. Its host-guest complexation with a series of bispyridinium salts in solution was further investigated. It was found that the per-hydroxylated pillar[6]arene could form a 1:1 complex with paraquat in acetone with an association constant of 2.2 × 10(2) M(-1). This complex is a [2]pseudorotaxane as shown by its crystal structure, which is the first pillar[6]arene-based host-guest complex crystal structure. PMID:22401142

Ma, Yingjie; Chi, Xiaodong; Yan, Xuzhou; Liu, Jiyong; Yao, Yong; Chen, Weixiang; Huang, Feihe; Hou, Jun-Li

2012-03-16

47

Tunable nonlinear optical properties of PDA/Ag composite vesicles based on reversible host-guest interaction  

NASA Astrophysics Data System (ADS)

We develop a novel photo-responsive supramolecular system in which the aggregation and disaggregation of polydiacetylene/silver (PDA/Ag) composite vesicles is mediated by a reversible photo-responsive molecular recognition process. The PDA/Ag composite vesicles provide necessary nonlinear optical (NLO) properties, the host-guest interaction between azobenzene and ?-cyclodextrin get PDA/Ag composite vesicles sufficiently close to each other for providing the enhanced surface plasmon resonance and a corresponding NLO effect. NLO switching of PDA/Ag composite vesicles based on reversible host-guest interactions is realized by alternating visible and UV light irradiation, which may introduce a new way for preparation of smart NLO materials.

Rao, Jinan; Jiang, Hao; Wang, Jin; Zou, Gang; Zhang, Qijin

2012-06-01

48

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.

49

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

2004-01-01

50

Water soluble octa-functionalized POSS: all-click chemistry synthesis and efficient host-guest encapsulation.  

PubMed

A series of water soluble octa-functionalized POSSs were facilely synthesized via thiol-ene and Menschutkin click chemistry. Among them, octa-alkynyl POSS further reacted with azide-terminal alkyl long chains, resulting in a well-defined, amphiphilic octopus-like POSS. For the first time it was used for host-guest encapsulation and it exhibited an ultrahigh loading capability. PMID:24964315

Han, Jin; Zheng, Yaochen; Zheng, Shuai; Li, Sipei; Hu, Tiannan; Tang, Aijin; Gao, Chao

2014-08-14

51

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

PubMed

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

2013-11-01

52

Host-Guest Interactions between Calixarenes and Cp2NbCl2  

PubMed Central

The possible inclusion complexes of Cp2NbCl2 into calixarenes hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed by a combination of NMR, ab-initio calculations, thermogravimetric analysis, FTIR, Raman and PXRD. Ab-initio calculations, 1H NMR solution and solid state 13C CP MAS NMR results demonstrated that p-sulfonic calix[6]arene does form an inclusion complex with Cp2NbCl2. Raman spectroscopy showed, for the inclusion compound of p-sulfonic calix[6]arene-Cp2NbCl2, a band between 500–850 cm?1 characteristic of Nb-O vibration. This result suggests that Nb(V) may engage in coordination with the oxygen of the sulfonate group, as part of the host-guest interaction. However, it is important to mention that the niobocene dichloride (Cp2NbCl2) dissolves in water and undergoes oxidation and hydrolysis processes to yield Cp2NbCl2(OH) species. For that reason this band does not exclude that the Nb-O band belongs to Cp2NbCl2(OH). Solid State 13C CP MAS NMR and solution 1H NMR spectroscopies together with ab-initio results showed that Cp2NbCl2 is included in the p-sulfonic calix[6]arene cavity, with both Cp rings inside the cavity. In contrast, the solution 1H NMR results demonstrated that calix[6]arene does not form inclusion complex with Cp2NbCl2 in CDCl3 solution. Cp2NbCl2 is not included in the calix[6]arene cavity, possibly due to the lack of sulfonate heads which promote Nb-O interactions and assist the inclusion of Cp2NbCl2 into the cavity.

Morales, Alexis; Santana, Alberto; Althoff, Gerhard; Melendez, Enrique

2011-01-01

53

Examination of cucurbit[7]uril and its host-guest complexes by diffusion nuclear magnetic resonance.  

PubMed

The self-diffusion of cucurbit[7]uril (CB[7]) and its host-guest complexes in D2O has been examined using pulsed gradient spin-echo nuclear magnetic resonance spectroscopy. CB[7] diffuses freely at a concentration of 2 mM with a diffusion coefficient (D) of 3.07 x 10(-10) m(2) s(-1). At saturation (3.7 mM), CB[7] diffuses more slowly (D = 2.82 x 10(-10) m(2) s(-1)) indicating that it partially self-associates. At concentrations between 2 and 200 mM, CsCl has no effect on the diffusion coefficient of CB[7] (1 mM). Conversely, CB[7] (2 mM) significantly affects the diffusion of 133Cs+ (1 mM), decreasing its diffusion coefficient from 1.86 to 0.83 x 10(-9) m(2) s(-1). Similar changes in the rate of diffusion of other alkali earth metal cations are observed upon the addition of CB[7]. The diffusion coefficient of 23Na+ changes from 1.26 to 0.90 x 10(-9) m(2) s(-1) and 7Li+ changes from 3.40 to 3.07 x 10(-9) m(2) s(-1). In most cases, encapsulation of a variety of inorganic and organic guests within CB[7] decreases their rates of diffusion in D2O. For instance, the diffusion coefficient of the dinuclear platinum complex trans-[[PtCl(NH3)2}2mu-dpzm](2+) (where dpzm is 4,4'-dipyrazolylmethane) decreases from 4.88 to 2.95 x 10(-10) m(2) s(-1) upon encapsulation with an equimolar concentration of CB[7]. PMID:18247599

Wheate, Nial J; Kumar, P G Anil; Torres, Allan M; Aldrich-Wright, Janice R; Price, William S

2008-02-28

54

Versatile host-guest chemistry and networking ability of the cyclic tungstophosphate {P 8W 48}: Two further manganese derivatives  

NASA Astrophysics Data System (ADS)

Two new manganese derivatives of the cyclic polyoxotungstate [H 7P 8W 48O 184] 33- are reported, providing further illustration of its versatile host-guest chemistry. Relatively small changes in the synthetic conditions result in different crystalline compounds 1 and 2 with respectively eight and six manganese(II) ions per {P 8W 48} unit. The cyclic cavity of the polyanion accommodates respectively six and four manganese(II) in 1 and 2. In addition, extra tungsten groups are grafted onto the inside of the cavity in 2. The cyclic subunits are differently linked into chains by manganese(II) ions in 1 and 2.

Chen, Su-Wen; Boubekeur, Kamal; Gouzerh, Pierre; Proust, Anna

2011-05-01

55

Tunable two-color luminescence and host-guest energy transfer of fluorescent chromophores encapsulated in metal-organic frameworks.  

PubMed

Co-assembly of chromophore guests with host matrices can afford materials which have photofunctionalities different from those of individual components. Compared with clay and zeolite materials, the use of metal-organic frameworks (MOFs) as a host structure for fabricating luminescent host-guest materials is still at an early stage. Herein, we report the incorporation of a laser dye, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), into stilbene-based and naphthalene-based MOF systems. The resulting materials exhibit blue/red two-color emission, and the intensity ratio of blue to red fluorescence varies in different planes within the MOF crystal as detected by 3D confocal fluorescence microscopy. The observed changes in ratiometric fluorescence suggest the occurrence of energy transfer from MOF host to DCM molecules, which can be further confirmed by periodic density functional theoretical (DFT) calculations. Moreover, selective changes in luminescence behavior are observed on treating the guest@MOF samples with volatile organic compounds (methanol, acetone and toluene), indicating that these host-guest systems have potential applications as fluorescence sensors. It can be expected that by rational selection of MOF hosts and guest chromophores with suitable emissive colors and energy levels, a wide variety of multi-color luminescent and energy-transfer systems can readily be prepared in a similar manner. PMID:24614015

Yan, Dongpeng; Tang, Yanqun; Lin, Heyang; Wang, Dan

2014-01-01

56

Supramolecular host-guest interactions of oxazine-1 dye with ?- and ?-cyclodextrins: a photophysical and quantum chemical study.  

PubMed

Supramolecular host-guest interactions of oxazine-1 dye with ?- and ?-cyclodextrins (?CD and ?CD, respectively) have been investigated in neutral aqueous solution (pH ? 7) at ambient temperature (?25 °C) following absorption, fluorescence, and circular dichroism measurements. The dye forms inclusion complexes with both CDs, causing significant changes in its photophysical properties. Whereas fluorescence titration data for lower dye concentrations fit well with 1:1 stoichiometric complexes, the time-resolved fluorescence results indicate formation of a small extent of 1:2 (dye-host) complexes as well, especially at higher CD concentrations. The moderate range of the binding constant values for the present systems indicates the weaker hydrophobic interaction as responsible for the inclusion complex formation in these systems. It has also been observed that ?CD facilitates dimerization of the dye, prominently indicated at the higher dye concentrations. On the contrary, ?CD always assists deaggregation of the dye, even at very high dye concentrations. Time-resolved fluorescence anisotropy results qualitatively support the inclusion complex formation in the present systems. Results from quantum chemical calculations also nicely corroborate with the inferences drawn from photophysical studies. Observed results demonstrate that the size compatibility of the guest and the host cavity mainly determines the host-guest interaction in the present systems, much similar to the substrate-catalyst binding in many biological systems. PMID:22998344

Shaikh, Mhejabeen; Mohanty, Jyotirmayee; Sundararajan, Mahesh; Bhasikuttan, Achikanath C; Pal, Haridas

2012-10-18

57

Tunable Two-color Luminescence and Host-guest Energy Transfer of Fluorescent Chromophores Encapsulated in Metal-Organic Frameworks  

NASA Astrophysics Data System (ADS)

Co-assembly of chromophore guests with host matrices can afford materials which have photofunctionalities different from those of individual components. Compared with clay and zeolite materials, the use of metal-organic frameworks (MOFs) as a host structure for fabricating luminescent host-guest materials is still at an early stage. Herein, we report the incorporation of a laser dye, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), into stilbene-based and naphthalene-based MOF systems. The resulting materials exhibit blue/red two-color emission, and the intensity ratio of blue to red fluorescence varies in different planes within the MOF crystal as detected by 3D confocal fluorescence microscopy. The observed changes in ratiometric fluorescence suggest the occurrence of energy transfer from MOF host to DCM molecules, which can be further confirmed by periodic density functional theoretical (DFT) calculations. Moreover, selective changes in luminescence behavior are observed on treating the guest@MOF samples with volatile organic compounds (methanol, acetone and toluene), indicating that these host-guest systems have potential applications as fluorescence sensors. It can be expected that by rational selection of MOF hosts and guest chromophores with suitable emissive colors and energy levels, a wide variety of multi-color luminescent and energy-transfer systems can readily be prepared in a similar manner.

Yan, Dongpeng; Tang, Yanqun; Lin, Heyang; Wang, Dan

2014-03-01

58

Pillar[5]- and pillar[6]arene-based supramolecular assemblies built by using their cavity-size-dependent host-guest interactions.  

PubMed

Pillar[n]arenes, which we first synthesized and named in 2008, are new pillar-shaped macrocyclic hosts. Pillar[n]arene homologues with n = 5-10 have already been synthesized, but the cyclic pentamers, i.e., pillar[5]arenes, and cyclic hexamers, i.e., pillar[6]arenes, have been most widely used because these can be obtained in good yields. To date, nearly all pillar[n]arene-based supramolecular assemblies have been constructed using pillar[5]- and pillar[6]arene scaffolds. In this feature article, we describe supramolecular assemblies built using host-guest interactions depending on the cavity sizes of pillar[5]- and pillar[6]arenes. We first discuss the effects of the type of substituents on the rims of pillar[5]- and pillar[6]arenes on their solubilities, functionalities and host-guest properties. We then discuss supramolecular assemblies based on their host-guest properties and pillar-shaped architectures. PMID:24643742

Ogoshi, T; Yamagishi, T

2014-04-10

59

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.

2012-01-18

60

Photoelectrochemical properties of alternating multilayer films composed of titania nanosheets and Zn porphyrin.  

PubMed

Alternating multilayer films composed of titania nanosheets and Zn porphyrins were prepared by use of a previously reported Langmuir-Blodgett film-transfer method in order to fabricate photoelectrochemical devices. Closely packed titania nanosheet monolayers on indium tin oxide (ITO), mica, and quartz surfaces strongly adsorbed cationic [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrinatozinc]4+ (ZnTMPyP4+) by electrostatic interactions. The alternating deposition process afforded nanometer-scale multilayer films with the following structure: solid surface/(titania nanosheet/ZnTMPyP4+)n (n is the number of layers). The multilayer films were characterized by various physical measurements, including AFM, XRD, and UV-visible spectra. The visible-light irradiation of this multilayer film on an ITO electrode in the presence of triethanolamine as an electron donor yielded an anodic photocurrent. The action spectrum was consistent with the absorption spectrum of ZnTMPyP4+, which indicates that the photoexcitation of ZnTMPyP4+ is responsible for the photocurrent generation. However, the photocurrent density decreased with an increasing number of layers, which indicates that the harvesting of photoexcited electrons vertically through the titania nanosheets in the ITO/(titania nanosheet/ZnTMPyP4+)n structure was not efficient. To overcome this problem, the use of a lateral interlayer connection to all of the titania nanosheets with Ag paste was examined. As a result, a dramatic improvement in the photocurrent density was obtained. Thus, for efficient photocurrent generation with the titania nanosheet-ZnTMPyP4+ composite material, the lateral connection to all of the titania nanosheet layers is effective. PMID:17472401

Akatsuka, Kosho; Ebina, Yasuo; Muramatsu, Masaru; Sato, Toshiyuki; Hester, Heidi; Kumaresan, Duraisamy; Schmehl, Russell H; Sasaki, Takayoshi; Haga, Masa-aki

2007-06-01

61

CO2 Captured in Zeolitic Imidazolate Frameworks: Raman Spectroscopic Analysis of Uptake and Host-Guest Interactions.  

PubMed

Zeolitic imidazolate frameworks (ZIFs) exhibit enhanced selectivity and increased CO2 uptake due to the incorporation of functional imidazolate units in their structure as well as their extensive porosity and ring flexibility. In?situ Raman investigation of a representative host compound, ZIF-69, in practical CO2 pressure and temperature regimes (0-10?bar and 0-64?°C) correlates well with corresponding macroscopic CO2 sorption data and shows clear clear spectroscopic evidence of CO2 uptake. Significant positive shift of the 159?cm(-1) phenyl bending mode of the benzimidazole moiety indicates weak hydrogen bonding with CO2 in the larger cavities of the ZIF matrix. Raman spectroscopy is shown to be an easy and sensitive tool for quantifying CO2 uptake, identifying weak host-guest interactions and elucidating CO2 sorption mechanism in ZIFs. PMID:24687911

Kontos, Athanassios G; Likodimos, Vlassis; Veziri, Charitomeni M; Kouvelos, Evangelos; Moustakas, Nikolaos; Karanikolos, Georgios N; Romanos, George Em; Falaras, Polycarpos

2014-06-01

62

Luminescent hybrid materials based on zeolite L crystals and lanthanide complexes: Host-guest assembly and ultraviolet-visible excitation.  

PubMed

Several kinds of host-guest hybrid materials have been synthesized employing a ship in a bottle method by loading 9-hydroxy-2-methylphenalenone (MHPO) or 9-hydroxyphenalen (HPNP) from gas phase into the nanochannels of Ln(3+)-exchanged zeolite L (ZL) crystals (Ln=Gd or Eu). The resulting hybrids without lanthanide ions, MHPO-ZL, HPNP-ZL and the hybrids with lanthanide ions Ln-MHPO-ZL and Ln-HPNP-ZL are characterized with FT-IR, UV-vis DRS and photoluminescence spectroscopy. The photoluminescence properties of these hybrid materials have been analyzed and discussed, exhibiting the luminescence of Eu(3+) and ligands under the excitation at ultraviolet-visible region. These results provide useful data and can be expected to have potential application in the practical fields. PMID:24815195

Chen, Lei; Yan, Bing

2014-10-15

63

Synthesis and Small Molecule Exchange Studies of a Magnesium Bisformate Metal-Organic Framework: An Experiment in Host-Guest Chemistry for the Undergraduate Laboratory  

ERIC Educational Resources Information Center

concepts of host-guest chemistry and size exclusion in porous metal-organic frameworks (MOFs). The experiment has been successfully carried out in both introductory and advanced-level inorganic chemistry laboratories. Students synthesized the porous MOF, alpha-Mg[subscript…

Rood, Jeffrey A.; Henderson, Kenneth W.

2013-01-01

64

Control of the stoichiometry in host-guest complexation by redox chemistry of guests: inclusion of methylviologen in cucurbit[8]uril.  

PubMed

The binding stoichiometry of a host-guest complex can be effectively controlled by the redox chemistry of the guest: a 1:1 inclusion complex of methylviologen dication (MV2+) in cucurbit[8]uril (CB[8]) converts completely and reversibly to a 2:1 inclusion complex of cation radical (MV+.) in CB[8] upon the reduction of the guest. PMID:12271629

Jeon, Woo Sung; Kim, Hee-Joon; Lee, Chongmok; Kim, Kimoon

2002-09-01

65

Study of the Counter Anions in the Host-Guest Chemistry of Cucurbit[8]uril and 1-Ethyl-1?-benzyl-4,4?-bipyridinium  

PubMed Central

A series of 1-ethyl-1?-benzyl-4,4?-bipyridinium compounds with different counter anions (BEV-X2, where the X is Cl, Br, I, PF6, ClO4) were synthesized. By using of NMR, MS, electrochemistry, Na2S2O4-induced redox chemistry, and UV-Vis, the role of the different counter anions in the host-guest chemistry of cucurbit[8]uril (CB[8]) was studied for the first time. The result demonstrated that BEV-X2 can form a 1?:?1 host-guest complex with CB[8] in water. Theoretical calculation further suggested that the viologen region was threaded through the cavity of CB[8], while the corresponding counter anions were located outside the cavity. Some difference can be observed on UV-Vis titration and Na2S2O4-induced redox chemistry, which showed that the counter anions have some effect on the host-guest chemistry. All these provide new insights into CB[8] host-guest system.

Ji, Hailong; Liu, Fengyu; Sun, Shiguo

2013-01-01

66

Predicting paramagnetic 1H NMR chemical shifts and state-energy separations in spin-crossover host-guest systems.  

PubMed

The behaviour of metal-organic cages upon guest encapsulation can be difficult to elucidate in solution. Paramagnetic metal centres introduce additional dispersion of signals that is useful for characterisation of host-guest complexes in solution using nuclear magnetic resonance (NMR). However, paramagnetic centres also complicate spectral assignment due to line broadening, signal integration error, and large changes in chemical shifts, which can be difficult to assign even for known compounds. Quantum chemical predictions can provide information that greatly facilitates the assignment of NMR signals and identification of species present. Here we explore how the prediction of paramagnetic NMR spectra may be used to gain insight into the spin crossover (SCO) properties of iron(II)-based metal organic coordination cages, specifically examining how the structure of the local metal coordination environment affects SCO. To represent the tetrahedral metal-organic cage, a model system is generated by considering an isolated metal-ion vertex: fac-ML3(2+) (M = Fe(II), Co(II); L = N-phenyl-2-pyridinaldimine). The sensitivity of the (1)H paramagnetic chemical shifts to local coordination environments is assessed and utilised to shed light on spin crossover behaviour in iron complexes. Our data indicate that expansion of the metal coordination sphere must precede any thermal SCO. An attempt to correlate experimental enthalpies of SCO with static properties of bound guests shows that no simple relationship exists, and that effects are likely due to nuanced dynamic response to encapsulation. PMID:24752730

Isley, William C; Zarra, Salvatore; Carlson, Rebecca K; Bilbeisi, Rana A; Ronson, Tanya K; Nitschke, Jonathan R; Gagliardi, Laura; Cramer, Christopher J

2014-06-14

67

Variational Implicit-Solvent Modeling of Host-Guest Binding: A Case Study on Cucurbit[7]uril|  

PubMed Central

The synthetic host cucurbit[7]uril (CB[7]) binds aromatic guests or metal complexes with ultrahigh affinity compared with that typically displayed in protein–ligand binding. Due to its small size, CB[7] serves as an ideal receptor–ligand system for developing computational methods for molecular recognition. Here, we apply the recently developed variational implicit-solvent model (VISM), numerically evaluated by the level-set method, to study hydration effects in the high-affinity binding of the B2 bicyclo[2.2.2]octane derivative to CB[7]. For the unbound host, we find that the host cavity favors the hydrated state over the dry state due to electrostatic effects. For the guest binding, we find reasonable agreement to experimental binding affinities. Dissection of the individual VISM free-energy contributions shows that the major driving forces are water-mediated hydrophobic interactions and the intrinsic (vacuum) host–guest van der Waals interactions. These findings are in line with recent experiments and molecular dynamics simulations with explicit solvent. It is expected that the level-set VISM, with further refinement on the electrostatic descriptions, can efficiently predict molecular binding and recognition in a wide range of future applications.

2013-01-01

68

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.

2010-01-01

69

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

PubMed

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

2010-06-15

70

A surprising host-guest relationship between 1,2-dichloroethane and the cesium complex of tetrabenzo-24-crown-8  

SciTech Connect

The structure of the complex [Cs(tetrabenzo-24-crown-8)(1,2-dichloroethane){sub 2}](NO{sub 3}){sm{underscore}bullet}H{sub 2}O was shown by X-ray crystallography to involve an unprecedented bidentate coordination of two 1,2-dichloroethane solvent molecules to the Cs{sup +} cation via the four chlorine atoms. The coordination of the solvent molecules occurs within two clefts between facing benzo groups, one pair of benzo groups related to the other pair by an improper noncrystallographic 90{degree} rotation. Resembling the seam on a tennis ball, the crown ether envelops the metal cation within a cagelike arrangement of eight crown ether oxygen atoms. Good geometric and electronic complimentarily characterizes the apparent host-guest relationship between the cleft environment and the solvent molecules. The complete encapsulation of the cation by the crown ether and two solvent molecules explains well the speciation behavior observed in liquid-liquid extraction of CsNO{sub 3} or CsClO{sub 4} from aqueous solution to 1,2-dichloroethane solutions of the alkylated analogues 4,4{double{underscore}prime}- or 4,5{double{underscore}prime}-bis(tert-octylbenzo)dibenzo-24-crown-8. In the extraction process studied at 25 C, simple 1:1 metal/crown complexes form in the solvent phase, as modeled by the program SXLSQI. The complex cation and counteranion are present both as ion-pairs, postulated to be ligand-separated ion-pairs as suggested by the crystal structure, and as dissociated ions. In agreement with a theoretical treatment of ion-pairing, the ion-pairs possess unusually low stability and exhibit no discrimination between the anions, largely ascribed to the large effective radius of the complex metal cation. Values of log K{sub f} corresponding to the formation of the complex cations Cs[bis(tert-octylbenzo)-dibenzo-24-crown-8]{sup +} in 1,2-dichloroethane at 25 C average 10.5 {+-} 0.2 for both positional isomers of the crown ether and for their 3:2 mixture. Overall, these results provide insight into the role of clefts as host environments for inclusion of neutral molecules and show how even solvent molecules with exceptionally weak donor-acceptor properties may participate in supramolecular assemblies. In addition, the results are unique in enabling a clear assessment of the effect of the encapsulation of the metal cation on the ion-pairing tendency of the metal complex and implications for anion selectivity.

Levitskaia, T.G.; Bryan, J.C.; Sachleben, R.A.; Lamb, J.D.; Moyer, B.A.

2000-02-02

71

Supramolecular Side-Chain Poly[2]pseudorotaxanes Formed by Orthogonal Coordination-Driven Self-Assembly and Crown-Ether-Based Host-Guest Interactions.  

PubMed

The themes of coordination-driven self-assembly, host-guest interactions, and supramolecular polymerization are unified in an orthogonal noninterfering fashion to deliver side-chain poly[2]pseudorotaxanes. Specifically, a bis(p-phenylene)-34-crown-10 derivative 1 bearing two pyridyl groups polymerizes into a side-chain poly[2]pseudorotaxane upon the addition of di-Pt(II) acceptor 4 in the presence of paraquat. Interestingly, by adding a competitive guest 3, the poly[2]pseudorotaxane can realize a conversion in one pot. PMID:24819441

Xing, Hao; Wei, Peifa; Yan, Xuzhou

2014-06-01

72

Tunable spin-crossover behavior of the Hofmann-like network {Fe(bpac)[Pt(CN)4]} through host-guest chemistry.  

PubMed

A study of the spin-crossover (SCO) behavior of the tridimensional porous coordination polymer {Fe(bpac)[Pt(CN)4]} (bpac=bis(4-pyridyl)acetylene) on adsorption of different mono- and polyhalobenzene guest molecules is presented. The resolution of the crystal structure of {Fe(bpac)[Pt(CN)4]}?G (G=1,2,4-trichlorobenzene) shows preferential guest sites establishing ????? stacking interactions with the host framework. These host-guest interactions may explain the relationship between the modification of the SCO behavior and both the chemical nature of the guest molecule (electronic factors) and the number of adsorbed molecules (steric factors). PMID:24105972

Bartual-Murgui, Carlos; Akou, Amal; Shepherd, Helena J; Molnár, Gábor; Real, J Antonio; Salmon, Lionel; Bousseksou, Azzedine

2013-10-25

73

A direct stereoselective preparation of a fish pheromone and application of the zinc porphyrin tweezer chiroptical protocol in its stereochemical assignment.  

PubMed

A two-step stereoselective preparation of a goldfish pheromone, 17?,20?-dihydroxy-4-pregnen-3-one, is reported from the readily available cortexolone in 64% overall yield. The (20S)-epimer was also synthesized in three steps from cortexolone with an overall yield of 47%. A microscale chiroptical technique based on a host/guest complexation mechanism between the substrate and a dimeric metalloporphyrin host (tweezer) was used to confirm the stereochemical assignment, while Density Functional Theory (DFT) calculations were employed to explain the high stereoselectivity induced by the 17?-hydroxyl and C18-methyl groups. PMID:23801425

Ouedraogo, Yannick P; Huang, Longchuan; Torrente, Mariana P; Proni, Gloria; Chadwick, Ekaterina; Wehmschulte, Rudolf J; Nesnas, Nasri

2013-09-01

74

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

2000-01-01

75

Host-guest chemistry of dendrimer-drug complexes. 4. An in-depth look into the binding/encapsulation of guanosine monophosphate by dendrimers.  

PubMed

In the present study, we investigated the host-guest chemistry of dendrimer/guanosine monophosphate (GMP) and present an in-depth look into the binding/encapsulation of GMP by dendrimers using NMR studies. (1)H NMR spectra showed a significant downfield shift of methylene protons in the outmost layer of the G5 dendrimer, indicating the formation of ion pairs between cationic amine groups of dendrimer and anionic phosphate groups of GMP. Chemical shift titration results showed that the binding constant between G5 dendrimer and GMP is 17,400 M(-1) and each G5 dendrimer has 107 binding sites. The binding of GMP to dendrimers prevents its aggregation in aqueous solutions and thereby enhances its stability. Nuclear Overhauser effect measurements indicated that a GMP binding and encapsulation balance occurs on the surface and in the interior of dendrimer. The binding/encapsulation transitions can be easily tailored by altering the surface and interior charge densities of the dendrimer. All these findings provide a new insight into the host-guest chemistry of dendrimer/guest complexes and may play important roles in the study of dendrimer/DNA aggregates by a "bottom-up" strategy. PMID:20446745

Hu, Jingjing; Fang, Min; Cheng, Yiyun; Zhang, Jiahai; Wu, Qinglin; Xu, Tongwen

2010-06-01

76

Removal of sulfamethoxazole sulfonamide antibiotic from water by high silica zeolites: a study of the involved host-guest interactions by a combined structural, spectroscopic, and computational approach.  

PubMed

Sulfonamide antibiotics are persistent pollutants present in surface and subsurface waters in both agricultural and urban environments. Sulfonamides are of particular concern in the environment because they are known to induce high levels of bacterial resistance. Adsorption of sulfamethoxazole sulfonamide antibiotic into three high silica zeolites (Y, mordenite, and ZSM-5) with pore opening sizes comparable to sulfamethoxazole dimensions is reported. Sulfamethoxazole was almost completely removed from water by zeolite Y and MOR in a few minutes. Adsorption onto ZSM-5 showed an increased kinetics with increasing temperature. Antibiotic sorption was largely irreversible with little antibiotic desorbed. Sulfamethoxazole incorporation and localization into the pore of each zeolite system was defined along with medium-weak and cooperative host-guest interactions in which water molecules play a certain role only in zeolite Y and mordenite. PMID:24491342

Blasioli, Sonia; Martucci, Annalisa; Paul, Geo; Gigli, Lara; Cossi, Maurizio; Johnston, Cliff T; Marchese, Leonardo; Braschi, Ilaria

2014-04-01

77

Tetrarhena-heterocycle from the palladium-catalyzed dimerization of Re2(CO)8(?-SbPh2)(?-H) exhibits an unusual host-guest behavior.  

PubMed

The six-membered heavy atom heterocycles [Re(2)(CO)(8)(?-SbPh(2))(?-H)](2), 5, and Pd[Re(2)(CO)(8)(?-SbPh(2))(?-H)](2), 7, have been prepared by the palladium-catalyzed ring-opening cyclo-dimerization of the three-membered heterocycle Re(2)(CO)(8)(?-SbPh(2))(?-H), 3. The palladium atom that lies in the center of the heterocycle 7 was removed to yield 5. The palladium removal was found to be partially reversible leading to an unusual example of host-guest behavior. A related dipalladium complex Pd(2)Re(4)(CO)(16)(?(4)-SbPh)(?(3)-SbPh(2))(?-Ph)(?-H)(2), 6, was also formed in these reactions of palladium with 3. PMID:21786819

Adams, Richard D; Pearl, William C; Wong, Yuen Onn; Zhang, Qiang; Hall, Michael B; Walensky, Justin R

2011-08-24

78

Self-assembled vehicle construction via boronic acid coupling and host-guest interaction for serum-tolerant DNA transport and pH-responsive drug delivery.  

PubMed

By exploiting boronic acid coupling and host-guest chemistry, a pH-responsive drug/gene co-delivery nanoplatform is designed for cancer treatments with the excellently serum-tolerant transfection activity and the capability to load and release hydrophobic drugs in an acidity-accelerated manner. Via boronate linkage, ?-CD is allowed to spontaneously attach onto phenylboronic-acid-modified oligoethylenimine (PEI1.8K-PB2.9 ) at neutral condition. The formed vehicle/DNA nanoformulation is thus surrounded densely by ?-CD moieties to biomimic the carbohydrate-rich cell surface, providing a novel approach to overcome serum-susceptible drawbacks frequently associated with synthetic gene carriers. PEI1.8K-PB2.9 -?-CD conjugates demonstrate significantly improved cell-biocompatibility and transfection activity over PEI1.8K-PB2.9 . Noticeably, serum-associated inhibition effect is negligible for PEI1.8K-PB2.9 -?-CD-mediated transfection whereas marked transfection reduction occurs for PEI25K and PEI1.8K-PB2.9 upon serum exposure. Consequently, PEI1.8K-PB2.9 -?-CDs afford much higher transfection efficiency, that is, 25-fold higher luciferase expression over PEI25K in presence of 30% serum. An anticancer drug of doxorubicin (DOX) is shown to be readily accommodated into the nanoformulation via host-guest chemistry and intracellularly co-delivered together with plasmid DNA. Due to the acidity-labile feature of boronate linkage, DOX/?-CD inclusion complexes would be mostly detached from the nanoformulation triggered by acidity, leading to faster drug release. Furthermore, drug inclusion does not alter the serum-compatible transfection efficiency of PEI1.8K-PB2.9 -?-CD. PMID:23983152

Yang, Bin; Jia, Huizhen; Wang, Xuli; Chen, Si; Zhang, Xianzheng; Zhuo, Renxi; Feng, Jun

2014-04-01

79

Photoinduced charge carrier dynamics of Zn-porphyrin-TiO2 electrodes: the key role of charge recombination for solar cell performance.  

PubMed

Time resolved absorption spectroscopy has been used to study photoinduced electron injection and charge recombination in Zn-porphyrin sensitized nanostructured TiO(2) electrodes. The electron transfer dynamics is correlated to the performance of dye sensitized solar cells based on the same electrodes. We find that the dye/semiconductor binding can be described with a heterogeneous geometry where the Zn-porphyrin molecules are attached to the TiO(2) surface with a distribution of tilt angles. The binding angle determines the porphyrin-semiconductor electron transfer distance and charge transfer occurs through space, rather than through the bridge connecting the porphyrin to the surface. For short sensitization times (1 h), there is a direct correlation between solar cell efficiency and amplitude of the kinetic component due to long-lived conduction band electrons, once variations in light harvesting (surface coverage) have been taken into account. Long sensitization time (12 h) results in decreased solar cell efficiency because of decreased efficiency of electron injection. PMID:20961148

Imahori, Hiroshi; Kang, Soonchul; Hayashi, Hironobu; Haruta, Mitsutaka; Kurata, Hiroki; Isoda, Seiji; Canton, Sophie E; Infahsaeng, Yingyot; Kathiravan, Arunkumar; Pascher, Torbjörn; Chábera, Pavel; Yartsev, Arkady P; Sundström, Villy

2011-04-28

80

Femtosecond Optical Tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers has drawn much attention of people since recent years, which shows great advantages on biological applications due to quite straightforward ideas and simple configurations. Optical tweezers rely upon the extremely high gradient in the electric field produced near the beam waist of a tightly focused laser beam, which creates a force sufficient to trap micron-sized dielectric particles in three dimensions.(J.E. Molloy and M.J. Padgett, Light, Action: Optical Tweezers, Contemporary P)hysics, 43 241 (2002). We applied a femtosecond laser on optical tweezers as light source and got successfully ``optical trapping'' and ``optical tweezers.'' Further, due to the characters of short pulse width and extremely high intensity of laser, femtosecond optical tweezers may direct us to new optics field. Under such strong intensity many non-linear optical phenomena could be observable, such like optical Kerr effect, stimulated Raman effect and so on. Our work will shows that it may be applied into the recently proposed FAST CAR (Femtosecond Adaptive Spectroscopic Techniques for Coherent Anti-Stokes Raman Spectroscopy) by M. Scully et. al.(M. O. Scully, G. W. Kattawar, R. P. Lucht, T. Opatrny, H. Pilloff, A. Rebane, A. V. Sokolov, and M. S. Zubairy, ``FAST CARS: Engineering a Laser Spectroscopic Technique for Rapid Identification of Bacterial Spores,'' Proceedings of NASE (2002).)

Peng, Jiahui; Wang, Lei; Sokolov, Alexei

2004-10-01

81

Optical tweezers-based immunosensor  

Microsoft Academic Search

The authors have developed an extremely sensitive immunoassay that uses optical tweezers to detect antigen-antibody bonds. An optical tweezers is used to manipulate a microscopic object with respect to a surface. The adjustable force applied by the tweezers is used to sense adhesion between the objects, which can either naturally or artificially present binding partners. This measurement can be used

B. J. Davies; R. Kishore; M.-N. Sinou; K. Helmerson; W. D. Phillips; H. H. Weetall

1998-01-01

82

Host-guest interactions between 2,4-dichlorophenol and humic substances as evaluated by 1H NMR relaxation and diffusion ordered spectroscopy.  

PubMed

1H NMR measurements of spin-lattice (T1) and spin-spin (T2) relaxation times and diffusion ordered spectroscopy (DOSY) were applied to investigate the association of 2,4-dichlorophenol (DCP) with a soil fulvic (FA-VICO) and humic acid (HA(-)-VICO), and a lignite humic acid (HA-LIG). The 1H T1 and T2 values of DCP were found to decrease with increasing humic concentration, indicating reduction in molecular mobility due to formation of noncovalent interactions. The increased shortening of relaxation times observed upon addition of HA suggested more extensive association of DCP with HA than with FA. The extent of binding was inferred from diffusion coefficients (D) which showed slower diffusion for bound DCP. At 1 mg mL(-1) DCP was completely bound by 4.1 and 5.8 mg mL(-1) of HA-VICO and HA-LIG, respectively, while full DCP association was not observed even up to 20 mg mL(-1) of FA. This was reflected by association constants (Ka): 3.1 +/- 0.3 M(-1) for FA-DCP, and 15.5 +/- 3.1 M(-1) and 11.0 +/- 1.2 M(-1) for HA-VICO and HA-LIG DCP complexes, respectively. The stronger binding to HA is attributed to their larger hydrophobic character enabling formation of stable hydrophobic domains to which DCP becomes associated in host-guest complexes. DCP complexation within humic hydrophobic domains was confirmed by upfield chemical shifts and signal line broadenings observed in 1H NMR spectra. Similar chemical shift variations for the three DCP aromatic protons further indicated pi-pi interactions, rather than H-bonding, as the main driving force for noncovalent association between DCP and dissolved humic substances. Relaxation and diffusion 1H NMR techniques provide rapid and accurate measurements of binding constants and thermodynamic parameters for host-guest complexes between environmental contaminants and natural organic matter. PMID:19086345

Smejkalová, Daniela; Piccolo, Alessandro

2008-11-15

83

Host-guest complexation: a convenient route for the electroreduction of diazonium salts in aqueous media and the formation of composite materials.  

PubMed

Electrochemical grafting of a water-insoluble diazonium salt in aqueous media onto an electrode surface was achieved by host-guest complexation. 1-(2-Bisthienyl)-4-aminobenzene (BTAB) was solubilized in a water/beta-cyclodextrin solution (beta-CD). The corresponding diazonium salt was generated in situ then electroreduced. This process leads to the attachment of bithiophene or short oligothiophene groups to the electrode surface. The modified surfaces were analyzed by cyclic voltammetry (CV), scanning electrochemical microscopy (SECM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS), and atomic force microscopy (AFM). The electrochemical investigations show that the water-based modified surface is similar to one generated in acetonitrile without beta-CD. Thus, the attached organic layer behaves like an electrochemical switch (above some threshold potential, a soluble external probe is oxidized, but the oxidized form cannot be reduced). The modified surfaces consist of grafted bisthienylbenzene (BTB) and cyclodextrins that can be removed from the surface. This procedure may be considered as a new means of creating a surface made of submicrometric holes in an organic semiconducting layer. PMID:20070078

Santos, Luís; Ghilane, Jalal; Martin, Pascal; Lacaze, Pierre-Camille; Randriamahazaka, Hyacinthe; Lacroix, Jean-Christophe

2010-02-10

84

Converging free energies of binding in cucurbit[7]uril and octa-acid host-guest systems from SAMPL4 using expanded ensemble simulations.  

PubMed

Molecular containers such as cucurbit[7]uril (CB7) and the octa-acid (OA) host are ideal simplified model test systems for optimizing and analyzing methods for computing free energies of binding intended for use with biologically relevant protein-ligand complexes. To this end, we have performed initially blind free energy calculations to determine the free energies of binding for ligands of both the CB7 and OA hosts. A subset of the selected guest molecules were those included in the SAMPL4 prediction challenge. Using expanded ensemble simulations in the dimension of coupling host-guest intermolecular interactions, we are able to show that our estimates in most cases can be demonstrated to fully converge and that the errors in our estimates are due almost entirely to the assigned force field parameters and the choice of environmental conditions used to model experiment. We confirm the convergence through the use of alternative simulation methodologies and thermodynamic pathways, analyzing sampled conformations, and directly observing changes of the free energy with respect to simulation time. Our results demonstrate the benefits of enhanced sampling of multiple local free energy minima made possible by the use of expanded ensemble molecular dynamics and may indicate the presence of significant problems with current transferable force fields for organic molecules when used for calculating binding affinities, especially in non-protein chemistries. PMID:24610238

Monroe, Jacob I; Shirts, Michael R

2014-04-01

85

Core-shell structured nanoassemblies based on ?-cyclodextrin containing block copolymer and poly(?-benzyl L-aspartate) via host-guest complexation  

PubMed Central

Double hydrophilic copolymers (PEG-b-PCDs) with one PEG block and another block containing ?-cyclodextrin (?-CD) units were synthesized by macromolecular substitution reaction. Via a dialysis procedure, complex assemblies with a core-shell structure were prepared using PEG-b-PCDs in the presence of a hydrophobic homopolymer poly(?-benzyl L-aspartate) (PBLA). The hydrophobic PBLA resided preferably in the cores of assemblies, while the extending PEG chains acted as the outer shell. Host-guest interaction between ?-CD and hydrophobic benzyl group was found to mediate the formation of the assemblies, where PEG-b-PCD and PBLA served as the host and guest macromolecules, respectively. The particle size of the assemblies could be modulated by the composition of the host PEG-b-PCD copolymer. The molecular weight of the guest polymer also had a significant effect on the size of the assemblies. The assemblies prepared from the host and guest polymer pair were stable during a long-term storage. These assemblies could also be successfully reconstituted after freeze-drying. The assemblies may therefore be used as novel nanocarriers for the delivery of hydrophobic drugs.

Zhang, Jianxiang; Ma, Peter X

2011-01-01

86

Host-guest chemistry of dendrimer-cyclodextrin conjugates: selective encapsulations of guests within dendrimer or cyclodextrin cavities revealed by NOE NMR techniques.  

PubMed

In this study, G5 PAMAM dendrimer and ?-, ?-, ?-cyclodextrin (CD) conjugates were synthesized. Host-guest behaviors of the conjugates toward five guest molecules including sodium methotrexate (MTX), amantadine hydrochloride (ADH), sulfamethoxazole (SMZ), sodium deoxycholate (SDC), and sodium dodecyl sulfate (SDS) were analyzed by NOE NMR techniques. Among the five guest molecules, ADH only binds with ?-CD in G5-?-CD, SDC shows higher priority to localize within the cavity of ?-CD in G5-?-CD, while MTX exhibits selective encapsulation within the cavities of G5 dendrimer in G5-?-CD. SDS has high binding affinity with ?-CD in G5-?-CD but forms a precipitate in the complex solution. SMZ shows simultaneous encapsulation within CDs (?-, ?-, and ?-CD) or G5 in the presence of the three conjugates. The host behavior of G5-CD conjugates depends on CD cavity size, guest size, and hydrophobicity. The results obtained in this study are helpful in the optimization of dendrimer-CD conjugate-based drug delivery systems. PMID:22934608

Wang, Hui; Shao, Naimin; Qiao, Shengnan; Cheng, Yiyun

2012-09-13

87

Fluorescent and colorimetric magnetic microspheres as nanosensors for Hg2+ in aqueous solution prepared by a sol-gel grafting reaction and host-guest interaction.  

PubMed

Fluorescent sensing TSRh6G-?-cyclodextrin fluorophore/adamantane-modified inclusion complex magnetic nanoparticles (TFIC MNPs) have been synthesized via the cooperation of a host-guest interaction and sol-gel grafting reaction. Powder X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and UV-visible absorption and emission spectroscopy have been employed to characterize the material. Fluorescence and UV-visible spectra have shown that the resultant multifunctional nanoparticle sensors exhibit selective 'turn-on' type fluorescent enhancements and a clear color change from light brown to pink with Hg(2+). Owing to a larger surface area and high permeability, TFIC MNPs exhibit remarkable selectivity and sensitivity for Hg(2+), and its detection limit measures up to the micromolar level in aqueous solution. Most importantly, magnetic measurements have shown that TFIC magnetic nanoparticles are superparamagnetic and they can be separated and collected easily using a commercial magnet. These results not only solve the limitations in practical sensing applications of nanosensors, but also enable the fabrication of other multifunctional nanostructure-based hybrid nanomaterials. PMID:23632769

Wang, Wei; Zhang, Yue; Yang, Qingbiao; Sun, Mingda; Fei, Xiaoliang; Song, Yan; Zhang, Yingmu; Li, Yaoxian

2013-06-01

88

Host-guest chemistry and light driven molecular lock of Ru(bpy)(3)-viologen with cucurbit[7-8]urils.  

PubMed

Host-guest chemistry and photoinduced electron-transfer processes have been studied in the systems containing Ru(bpy)3 complex covalently linked to viologen as a guest molecule and cucurbit[n]urils (n = 7, 8) as host molecules in aqueous solution. The Ru(bpy)3-viologen complex, [Ru(2,2'-bipyridine)2(4-(4-(1'-methyl-4,4'-bipyridinediium-1-yl)butyl)-4'-methyl-2,2'-bipyridine)]Cl4 (denoted as Ru2+-MV2+, 1) was shown to form stable 1:1 inclusion complexes with cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]). The binding modes are slightly different with CB[7] and CB[8]. CB[7] preferentially binds to part of the viologen residue in 1 together with the butyl chain, whereas CB[8] preferentially encloses the whole viologen residue. Photoinduced intramolecular electron transfer from the excited-state of the Ru moiety to MV2(+) which is inserted into the cavity of the CBs occurred. Long-lived charge-separated states Ru3(+)-MV(+*) were generated with the lifetimes of 280 ns with CB[7] and 2060 ns with CB[8]. This shows that CBs can slow down the charge recombination within supramolecular systems, and the difference in lifetimes seems to be due to the difference in binding modes. In the presence of a sacrificial electron donor triethanolamine, light-driven formation of a dimer of MV(+*) inside the CB[8] cavity was observed. This "locked" molecular dimer can be "unlocked" by molecular oxygen to give back the original form of the molecular dyad 1 with the MV2(+) moiety inserted in the cavity of CB[8]. The processes could be repeated several times and showed nice reversibility. PMID:17960929

Sun, Shiguo; Zhang, Rong; Andersson, Samir; Pan, Jingxi; Zou, Dapeng; Akermark, Björn; Sun, Licheng

2007-11-29

89

A study on the versatility of metallacycles in host-guest chemistry: Interactions in halide-centered hexanuclear copper(ii) pyrazolate complexes.  

PubMed

Hexanuclear copper(ii) pyrazolate complexes have shown the ability to encapsulate different halide ions, leading to [trans-Cu6{?-3,5-(CF3)2pz}6(?-OH)6X](-) (X = F, Cl, Br, I). They offer an interesting case study for variation in local properties at host binding sites, due to the presence of a six membered ring involving Cu(ii) centers considered as the borderline Lewis acid according to the Pearson Hard and Soft Acids and Bases (HSAB) principle. Here, we describe the host-guest interactions via relativistic density functional calculations, involving the graphical description of local dipole and quadrupole moments, energy decomposition analysis, non-covalent indices, and magnetic behavior. The observed variation in the copper local dipole and quadrupole moments suggests that a metallacycle host offers great advantages in comparison to their organic counterparts, prompted by the versatility of the metallic centers to modulate the surrounding electron density accordingly. According to our results, the contribution of ion-dipole forces in the halide-centered series decreases from 95.0% to 77.0% from the fluoride to the iodide complex, whereas the contribution of higher order interactions such as quadrupole-dipole and quadrupole-quadrupole, goes from 5.0% to 23.0% towards a softer guest. In addition, the through-the-space magnetic response of trans-Cu6{?-3,5-(CF3)2pz}6(?-OH)6, reveals a noteworthy aromatic structure, which is driven by the superexchange through the ligands leading to a singlet ground state. PMID:24866754

Ponce-Vargas, Miguel; Muñoz-Castro, Alvaro

2014-06-11

90

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

2002-01-01

91

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.

2007-07-18

92

Interferometer Control of Optical Tweezers  

NASA Technical Reports Server (NTRS)

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 and to use a combination of the SLM and interferometry to control the intensity profile. The objective is to perform fine and calculable control of the moments and forces on a tip or tool to be used to manipulate and interrogate nanostructures. The performance of the SLM in generating multiple and independently controllable tweezers beams is also reported. Concurrent supporting research projects are mentioned and include tweezers beam scattering and neural-net processing of the interference patterns for control of the tweezers beams.

Decker, Arthur J.

2002-01-01

93

Host-guest chemistry of dendrimer-drug complexes. 5. Insights into the design of formulations for noninvasive delivery of heparin revealed by isothermal titration calorimetry and NMR studies.  

PubMed

The host-guest chemistry of dendrimer-biomacromolecule complexes is of great significance to both design and optimization of dendrimer-based drug delivery and host-guest systems. Here, we characterized the interactions between dendrimer and heparin by isothermal titration calorimetry (ITC), (1)H nuclear magnetic resonance ((1)H NMR), pulsed-field gradient (PFG) NMR, nuclear Overhauser effect spectroscopy (NOESY), and atomic force microscopy (AFM) studies. The calorimetric results suggest that miscellaneous aggregates are formed at different stages when heparin was titrated into a dendrimer solution: dendrimer-heparin "necklace" structures, followed by the formation of larger and more stable aggregates, and then macroscopic complexes which precipitate from the solution. The binding process is significantly influenced by dendrimer generation, surface functionality, and ion strength, indicating that the formation of dendrimer-heparin aggregates is predominantly driven by electrostatic interactions. The NMR results confirm the dendrimer-heparin binding models established by calorimetric measurement and present a new type of dendrimer-heparin aggregates at higher heparin/dendrimer molar ratios. Formulations containing generation 5 (G5) PAMAM dendrimers with a heparin/G5 molar ratio of 0.5-1.2 are proposed as effective ones for the treatment of thrombosis in noninvasive delivery routes such as nasal, pulmonary, transdermal, and oral routes. The combination of ITC and NMR in this study provides new insight into the interactions between globular and linear polymers and the delivery of macromolecular therapeutics such as heparin by dendrimers. PMID:20695473

Feng, Xueyan; Cheng, Yiyun; Yang, Kun; Zhang, Jiahai; Wu, Qinglin; Xu, Tongwen

2010-09-01

94

On chip shapeable optical tweezers  

PubMed Central

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.

2013-01-01

95

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.

2013-07-01

96

On chip shapeable optical tweezers.  

PubMed

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. PMID:23887310

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

2013-01-01

97

Plasmon nano-optical tweezers  

Microsoft Academic Search

Conventional optical tweezers, formed at the diffraction-limited focus of a laser beam, have become a powerful and flexible tool for manipulating micrometre-sized objects. Extending optical trapping down to the nanometre scale would open unprecedented opportunities in many fields of science, where such nano-optical tweezers would allow the ultra-accurate positioning of single nano-objects. Among the possible strategies, the ability of metallic

Mathieu L. Juan; Maurizio Righini; Romain Quidant

2011-01-01

98

Optical Tweezer Assembly and Calibration  

NASA Technical Reports Server (NTRS)

An Optical Tweezer, as the name implies, is a useful tool for precision manipulation of micro and nano scale objects. Using the principle of electromagnetic radiation pressure, an optical tweezer employs a tightly focused laser beam to trap and position objects of various shapes and sizes. These devices can trap micrometer and nanometer sized objects. An exciting possibility for optical tweezers is its future potential to manipulate and assemble micro and nano sized sensors. A typical optical tweezer makes use of the following components: laser, mirrors, lenses, a high quality microscope, stage, Charge Coupled Device (CCD) camera, TV monitor and Position Sensitive Detectors (PSDs). The laser wavelength employed is typically in the visible or infrared spectrum. The laser beam is directed via mirrors and lenses into the microscope. It is then tightly focused by a high magnification, high numerical aperture microscope objective into the sample slide, which is mounted on a translating stage. The sample slide contains a sealed, small volume of fluid that the objects are suspended in. The most common objects trapped by optical tweezers are dielectric spheres. When trapped, a sphere will literally snap into and center itself in the laser beam. The PSD s are mounted in such a way to receive the backscatter after the beam has passed through the trap. PSD s used with the Differential Interference Contrast (DIC) technique provide highly precise data. Most optical tweezers employ lasers with power levels ranging from 10 to 100 miliwatts. Typical forces exerted on trapped objects are in the pico-newton range. When PSDs are employed, object movement can be resolved on a nanometer scale in a time range of milliseconds. Such accuracy, however, can only by utilized by calibrating the optical tweezer. Fortunately, an optical tweezer can be modeled accurately as a simple spring. This allows Hook s Law to be used. My goal this summer at NASA Glenn Research Center is the assembly and calibration of an optical tweezer setup in the Instrumentation and Controls Division (5520). I am utilizing a custom LabVIEW Virtual Instrument program for data collection and microscope stage control. Helping me in my assignment are the following people: Mentor Susan Wrbanek (5520), Dr. Baha Jassemnejad (UCO) and Technicians Ken Weiland (7650) and James Williams (7650). Without their help, my task would not be possible.

Collins, Timothy M.

2004-01-01

99

Host-guest supramolecular interactions in the coordination compounds of 4,4'-azobis(pyridine) with MnX2 (X = NCS–, NCNCN–, and PF6(–)): structural analyses and theoretical study.  

PubMed

Three new Mn(II) coordination compounds {[Mn(NCNCN)(2)(azpy)]·0.5azpy}(n) (1), {[Mn(NCS)(2)(azpy)(CH(3)OH)(2)]·azpy}(n) (2), and [Mn(azpy)(2)(H(2)O)(4)][Mn(azpy)(H(2)O)(5)]·4PF(6)·H(2)O·5.5azpy (3) (where azpy = 4,4'-azobis(pyridine)) have been synthesized by self-assembly of the primary ligands, dicyanamide, thiocyanate, and hexafluorophosphate, respectively, together with azpy as the secondary spacer. All three complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, and single crystal X-ray crystallography. The structural analyses reveal that complex 1 forms a two-dimensional (2D) grid sheet motif. These sheets assemble to form a microporous framework that incorporates coordination-free azpy by host-guest ?···? and C-H···N hydrogen bonding interactions. Complex 2 features azpy bridged one-dimensional (1D) chains of centrosymmetric [Mn(NCS)(2)(CH (3)OH)(2)] units which form a 2D porous sheet via a CH(3)···? supramolecular interaction. A guest azpy molecule is incorporated within the pores by strong H-bonding interactions. Complex 3 affords a 0-D motif with two monomeric Mn(II) units in the asymmetric unit. There exist ?···?, anion···?, and strong hydrogen bonding interactions between the azpy, water, and the anions. Density functional theory (DFT) calculations, at the M06/6-31+G* level of theory, are used to characterize a great variety of interactions that explicitly show the importance of host-guest supramolecular interactions for the stabilization of coordination compounds and creation of the fascinating three-dimensional (3D) architecture of the title compounds. PMID:22272694

Kar, Paramita; Biswas, Rituparna; Drew, Michael G B; Frontera, Antonio; Ghosh, Ashutosh

2012-02-01

100

Quantum noise in optical tweezers  

NASA Astrophysics Data System (ADS)

Quantum enhanced sensitivity in optical tweezers based particle tracking was recently demonstrated. This has provided the necessary tool for quantum metrology to play an important role in biological measurements. Here we introduce the basic theory relevant to such optical tweezers experiments, and overview the significance of sub-shot noise limited sensitivity to practical experiments. In particular, biophysical experiments are subject to optical power constraints, which therefore limits the absolute sensitivity which is classically achievable. Quantum enhanced particle tracking can overcome this limit, and is therefore likely to play an important role in such biophysical experiments in the near future.

Taylor, Michael A.; Bowen, Warwick P.

2013-12-01

101

Optical tweezers for confocal microscopy  

NASA Astrophysics Data System (ADS)

In confocal laser scanning microscopes (CLSMs), lasers can be used for image formation as well as tools for the manipulation of microscopic objects. In the latter case, in addition to the imaging lasers, the light of an extra laser has to be focused into the object plane of the CLSM, for example as optical tweezers. Imaging as well as trapping by optical tweezers can be done using the same objective lens. In this case, z-sectioning for 3D imaging shifts the optical tweezers with the focal plane of the objective along the optical axis, so that a trapped object remains positioned in the focal plane. Consequently, 3D imaging of trapped objects is impossible without further measures. We present an experimental set-up keeping the axial trapping position of the optical tweezers at its intended position whilst the focal plane can be axially shifted over a distance of about 15 ?m. It is based on fast-moving correctional optics synchronized with the objective movement. First examples of application are the 3D imaging of chloroplasts of Elodea densa (Canadian waterweed) in a vigorous cytoplasmic streaming and the displacement of zymogen granules in pancreatic cancer cells (AR42 J).

Hoffmann, A.; Meyer zu Hörste, G.; Pilarczyk, G.; Monajembashi, S.; Uhl, V.; Greulich, K. O.

2000-11-01

102

Optical tweezers technique and its applications  

NASA Astrophysics Data System (ADS)

Since their advent in the 1980s, optical tweezers have attracted more and more attention due to their unique non-contact and non-invasion characteristics and their wide applications in physics, biology, chemistry, medical science and nanoscience. In this paper, we introduce the basic principle, the history and typical applications of optical tweezers and review our recent experimental works on the development and application of optical tweezers technique. We will discuss in detail several technological issues, including high precision displacement and force measurement in single-trap and dual-trap optical tweezers, multi-trap optical tweezers with each trap independently and freely controlled by means of space light modulator, and incorporation of cylindrical vector optical beams to build diversified optical tweezers beyond the conventional Gaussian-beam optical tweezers. We will address the application of these optical tweezers techniques to study biophysical problems such as mechanical deformation of cell membrane and binding energy between plant microtubule and microtubule associated proteins. Finally we present application of the optical tweezers technique for trapping, transporting, and patterning of metallic nanoparticles, which can be harnessed to manipulate surface plasmon resonance properties of these nanoparticles.

Guo, HongLian; Li, ZhiYuan

2013-12-01

103

Phase and glass transitions observed by adiabatic calorimetry of host p-tert-butylcalix[4]arene and guest toluene inclusion crystal, suggesting the progress of the combined order-disorder process of the host-guest molecules.  

PubMed

Heat capacities of crystalline p-tert-butylcalix[4]arene·toluene host-guest compound were measured in a temperature range between 3 K and 345 K by adiabatic calorimetry. The crystal showed one second-order phase transition at 256.4 K accompanied by wide heat-capacity tails on both the high and low temperature sides and two first-order phase transitions with heat-capacity peaks at 127 K and 139 K. The total entropy of a sequence of the phase transitions was assessed experimentally to be 47 J K(-1) mol(-1), indicating that the number of allowed distinguishable molecular configurations is over 100 in the high-temperature disordered state. Many such distinguishable configurations are understood to be produced by a special intermolecular interaction of C-H···(?-electron) bonds formed between p-tert-butylcalix[4]arene and toluene molecules, and the transitions were interpreted as originating from orientational order-disorder of both the guest toluene molecule and the tert-butyl groups of host arene in their combination. PMID:23992523

Ueda, Kouhei; Oguni, Masaharu

2013-10-01

104

Fluorescence support in optical tweezers  

NASA Astrophysics Data System (ADS)

This paper presents the development of an installation for proves for characterization by fluorescence of micrometer and nanometer particles supported on the trapping and manipulation by optical trapping technique (optical tweezers). The system features an laser operating at 480 nm, CCD camera for image acquisition, Thor Labs micrometric table X, Y, Z for the movement of the sample and the trap in the visual field. The design includes the use of intensity modulated optical trap, with the option of being used in pulsed, opening up possibilities for the use of resonant phenomena optomechanical type for particle capture.

Animas, J. G.; Arronte, M.; Flores, T.; Ponce, L.

2013-11-01

105

Optoelectronic tweezers for medical diagnostics  

NASA Astrophysics Data System (ADS)

Optoelectronic tweezers (OET) allows the spatial patterning of electric fields through selected illumination of a photoconductive surface. This enables the manipulation of micro particles and cells by creating non-uniform electrical fields that then produce dielectrophoretic (DEP) forces. The DEP responses of cells differ and can produce negative or positive (repelled or attracted to areas of high electric field) forces. Therefore OET can be used to manipulate individual cells and separate different cell types from each other. Thus OET has many applications for medical diagnostics, demonstrated here with work towards diagnosing Human African Trypanosomiasis, also known as sleeping sickness.

Kremer, Clemens; Neale, Steven; Menachery, Anoop; Barrett, Mike; Cooper, Jonathan M.

2012-02-01

106

Formation of heterotopic metallacalix[n]arenes (n=3, 4, 6) containing ethylenediaminepalladium(II) metal fragments and 4,7-phenanthroline and 2-pyrimidinolate bridges. Synthesis, structure and host-guest chemistry.  

PubMed

A multicomponent reaction involving ethylenediaminepalladium(II), 2-pyrimidinol derivatives (L) [L=2-pyrimidinol (a); 4-methyl-2-pyrimidinol (b); 4,6-dimethyl-2-pyrimidinol (c)] and 4,7-phenanthroline (4,7-phen) leads to the formation of heterotopic cyclic metallamacrocycles of the type [Pdn(en)n(mu-N,N'-L)m(mu-N,N'-4,7-phen)n-m](2n-m)+ [n=3, m=1 (3); n=4, m=2 (4); n=6, m=4 (5)]. These species can be obtained by different reaction pathways, including: (i) reaction of ethylenediaminepalladium(ii), L and 4,7-phen building blocks and (ii) reaction of the homotopic species [Pd4(en)4(mu-N,N'-L)4]4+ (1) and [Pd3(en)3(mu-N,N'-4,7-phen)3]6+ (2). The resulting heterotopic metallamacrocycles have been characterised by 1D and 2D 1H NMR spectroscopy. Additionally, species 3c and 4a have been studied by X-ray crystallography. The former one contains almost isosceles triangles of [Pd3(en)3(mu-N,N'-4,6-dimethyl-2-pyrimidinolate)(mu-N,N[prime or minute]-4,7-phen)2]5+ formulation, exhibiting a pinched-cone conformation. 4a contains a tetranuclear parallelogram [Pd4(en)4(mu-N,N'-2-pyrimidinolate)2(mu-N,N'-4,7-phenanthroline)2]6+, exhibiting a 1,3-alternate conformation. The host-guest properties of the here reported species have been studied, showing that they are able to interact with cationic as well as with anionic species. PMID:15514766

Galindo, Miguel A; Galli, Simona; Navarro, Jorge A R; Romero, M Angustias

2004-09-01

107

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)

2009-12-15

108

Steerable optical tweezers for ultracold atom studies  

NASA Astrophysics Data System (ADS)

We report on the implementation of an optical tweezer system for controlled transport of ultracold atoms along a narrow, static confinement channel. The tweezer system is based on high-efficiency acousto-optical deflectors and offers two-dimensional control over beam position. This opens up the possibility for tracking the transport channel when shuttling atomic clouds along the guide, forestalling atom spilling. Multiple clouds can be tracked independently by time-shared tweezer beams addressing individual sites in the channel. The deflectors are controlled using a multichannel direct digital synthesizer, which receives instructions on a sub-microsecond time scale from a field-programmable gate array. Using the tweezer system, we demonstrate sequential binary splitting of an ultracold $\\rm^{87}Rb$ cloud into $2^5$ clouds.

Roberts, K. O.; McKellar, T.; Fekete, J.; Rakonjac, A.; Deb, A. B.; Kjærgaard, N.

2014-04-01

109

Steerable optical tweezers for ultracold atom studies.  

PubMed

We report on the implementation of an optical tweezer system for controlled transport of ultracold atoms along a narrow, static confinement channel. The tweezer system is based on high-efficiency acousto-optic deflectors and offers two-dimensional control over beam position. This opens up the possibility for tracking the transport channel when shuttling atomic clouds along it, forestalling atom spilling. Multiple clouds can be tracked independently by time-shared tweezer beams addressing individual sites in the channel. The deflectors are controlled using a multichannel direct digital synthesizer, which receives instructions on a submicrosecond time scale from a field-programmable gate array. Using the tweezer system, we demonstrate sequential binary splitting of an ultracold 87Rb cloud into 2(5) clouds. PMID:24686662

Roberts, K O; McKellar, T; Fekete, J; Rakonjac, A; Deb, A B; Kjærgaard, N

2014-04-01

110

A DNA tweezer-actuated enzyme nanoreactor.  

PubMed

The functions of regulatory enzymes are essential to modulating cellular pathways. Here we report a tweezer-like DNA nanodevice to actuate the activity of an enzyme/cofactor pair. A dehydrogenase and NAD(+) cofactor are attached to different arms of the DNA tweezer structure and actuation of enzymatic function is achieved by switching the tweezers between open and closed states. The enzyme/cofactor pair is spatially separated in the open state with inhibited enzyme function, whereas in the closed state, enzyme is activated by the close proximity of the two molecules. The conformational state of the DNA tweezer is controlled by the addition of specific oligonucleotides that serve as the thermodynamic driver (fuel) to trigger the change. Using this approach, several cycles of externally controlled enzyme inhibition and activation are successfully demonstrated. This principle of responsive enzyme nanodevices may be used to regulate other types of enzymes and to introduce feedback or feed-forward control loops. PMID:23820332

Liu, Minghui; Fu, Jinglin; Hejesen, Christian; Yang, Yuhe; Woodbury, Neal W; Gothelf, Kurt; Liu, Yan; Yan, Hao

2013-01-01

111

Dielectrophoresis tweezers for single cell manipulation  

Microsoft Academic Search

Positioning single cells is of utmost importance in areas of biomedical research as diverse as in vitro fertilization, cell-cell\\u000a interaction, cell adhesion, embryology, microbiology, stem cell research, and single cell transfection. Here we describe dielectrophoretic\\u000a tweezers, a sharp glass tip with electrodes on either side, capable of trapping single cells with electric fields. Mounted\\u000a on a micromanipulator, dielectrophoresis tweezers can

T. P. Hunt; R. M. Westervelt

2006-01-01

112

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

113

Potential-well model in acoustic tweezers  

Microsoft Academic Search

Standing-wave acoustic tweezers are popularly used for non-invasive and non-contact particle manipulation. Because of their good penetration in biological tissue, they also show promising prospects for in vivo applications. According to the concept of an optical vortex, we propose an acoustics-vortex- based trapping model of acoustic tweezers. A four-element 1-MHz planar transducer was used to generate 1-MHz sine waves at

Shih-Tsung Kang; Chih-Kuang Yeh

2010-01-01

114

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

2009-03-01

115

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

2008-01-01

116

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

PubMed Central

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. These techniques are described and illustrated with examples highlighting current capabilities and limitations.

Neuman, Keir C.; Nagy, Attila

2012-01-01

117

Comparison between radiation forces upon nanoparticles in continuous laser tweezers and in pulsed laser tweezers  

Microsoft Academic Search

It is easier to obtain high energy in very short period through pulse laser than through continuous laser. And in the field of biology, especially in researching the active cells by optical tweezers, the traditional continuous laser employed in the tweezers are inclined to hurt even kill the cells. So, substituting the traditional continuous laser by pulsed laser is one

XiaoYu Liu; Feng Wang

2010-01-01

118

Synergetic effect of host-guest chemistry and spin crossover in 3D Hofmann-like metal-organic frameworks [Fe(bpac)M(CN)4] (M=Pt, Pd, Ni).  

PubMed

The synthesis and characterization of a series of three-dimensional (3D) Hofmann-like clathrate porous metal-organic framework (MOF) materials [Fe(bpac)M(CN)(4)] (M=Pt, Pd, and Ni; bpac=bis(4-pyridyl)acetylene) that exhibit spin-crossover behavior is reported. The rigid bpac ligand is longer than the previously used azopyridine and pyrazine and has been selected with the aim to improve both the spin-crossover properties and the porosity of the corresponding porous coordination polymers (PCPs). The 3D network is composed of successive {Fe[M(CN)(4)]}(n) planar layers bridged by the bis-monodentate bpac ligand linked in the apical positions of the iron center. The large void between the layers, which represents 41.7% of the unit cell, can accommodate solvent molecules or free bpac ligand. Different synthetic strategies were used to obtain a range of spin-crossover behaviors with hysteresis loops around room temperature; the samples were characterized by magnetic susceptibility, calorimetric, Mössbauer, and Raman measurements. The complete physical study reveals a clear relationship between the quantity of included bpac molecules and the completeness of the spin transition, thereby underlining the key role of the ?-? stacking interactions operating between the host and guest bpac molecules within the network. Although the inclusion of the bpac molecules tends to increase the amount of active iron centers, no variation of the transition temperature was measured. We have also investigated the ability of the network to accommodate the inclusion of molecules other than water and bpac and studied the synergy between the host-guest interaction and the spin-crossover behavior. In fact, the clathration of various aromatic molecules revealed specific modifications of the transition temperature. Finally, the transition temperature and the completeness of the transition are related to the nature of the metal associated with the iron center (Ni, Pt, or Pd) and also to the nature and the amount of guest molecules in the lattice. PMID:22147670

Bartual-Murgui, Carlos; Salmon, Lionel; Akou, Amal; Ortega-Villar, Norma A; Shepherd, Helena J; Muñoz, M Carmen; Molnár, Gábor; Real, José Antonio; Bousseksou, Azzedine

2012-01-01

119

Magnetic tweezers for the measurement of twist and torque.  

PubMed

Single-molecule techniques make it possible to investigate the behavior of individual biological molecules in solution in real time. These techniques include so-called force spectroscopy approaches such as atomic force microscopy, optical tweezers, flow stretching, and magnetic tweezers. Amongst these approaches, magnetic tweezers have distinguished themselves by their ability to apply torque while maintaining a constant stretching force. Here, it is illustrated how such a "conventional" magnetic tweezers experimental configuration can, through a straightforward modification of its field configuration to minimize the magnitude of the transverse field, be adapted to measure the degree of twist in a biological molecule. The resulting configuration is termed the freely-orbiting magnetic tweezers. Additionally, it is shown how further modification of the field configuration can yield a transverse field with a magnitude intermediate between that of the "conventional" magnetic tweezers and the freely-orbiting magnetic tweezers, which makes it possible to directly measure the torque stored in a biological molecule. This configuration is termed the magnetic torque tweezers. The accompanying video explains in detail how the conversion of conventional magnetic tweezers into freely-orbiting magnetic tweezers and magnetic torque tweezers can be accomplished, and demonstrates the use of these techniques. These adaptations maintain all the strengths of conventional magnetic tweezers while greatly expanding the versatility of this powerful instrument. PMID:24894412

Lipfert, Jan; Lee, Mina; Ordu, Orkide; Kerssemakers, Jacob W J; Dekker, Nynke H

2014-01-01

120

Optical tweezers: light for manipulating microscopic world  

NASA Astrophysics Data System (ADS)

Optical tweezers make use of a tightly focused laser beam to trap, move, guide, rotate and even sort microscopic objects solely with light. Although the basic laser tweezers, making use of a TEM00 laser beam to create a single trap point, have proved to be useful for any applications in areas ranging from physics to biology, a major breakthrough in this field came as the use of computer generated holograms enabled researchers to create multiple trap sites from single laser source (holographic optical tweezers). Coupled with microfluidic techniques, holographic optical tweezers have promised development of optical techniques for high throughput sorting of different cell types under a single micro-chip platform. The holographic methods have also helped the use of specialized laser beams like Laguerre-Gaussian beams instead of the conventional laser beam for interesting applications like orienting/rotating the trapped objects or trapping cells with minimum photodamage. Further, combining optical tweezers with Raman spectroscopy is becoming increasingly popular for studying single cell biochemistry as use of optical forces to immobilize the cells under investigations not only avoids the negative effects of fixing the cells onto substrate but also improve the quality of the recorded spectra. These advanced optical trapping techniques as outlined above along with some illustrative biophotonics applications have been explored.

Dasgupta, Raktim

2012-05-01

121

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

2013-05-01

122

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)

2011-09-15

123

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

2003-01-01

124

Molecular tweezers targeting transthyretin amyloidosis.  

PubMed

Transthyretin (TTR) amyloidoses comprise a wide spectrum of acquired and hereditary diseases triggered by extracellular deposition of toxic TTR aggregates in various organs. Despite recent advances regarding the elucidation of the molecular mechanisms underlying TTR misfolding and pathogenic self-assembly, there is still no effective therapy for treatment of these fatal disorders. Recently, the "molecular tweezers", CLR01, has been reported to inhibit self-assembly and toxicity of different amyloidogenic proteins in vitro, including TTR, by interfering with hydrophobic and electrostatic interactions known to play an important role in the aggregation process. In addition, CLR01 showed therapeutic effects in animal models of Alzheimer's disease and Parkinson's disease. Here, we assessed the ability of CLR01 to modulate TTR misfolding and aggregation in cell culture and in an animal model. In cell culture assays we found that CLR01 inhibited TTR oligomerization in the conditioned medium and alleviated TTR-induced neurotoxicity by redirecting TTR aggregation into the formation of innocuous assemblies. To determine whether CLR01 was effective in vivo, we tested the compound in mice expressing TTR V30M, a model of familial amyloidotic polyneuropathy, which recapitulates the main pathological features of the human disease. Immunohistochemical and Western blot analyses showed a significant decrease in TTR burden in the gastrointestinal tract and the peripheral nervous system in mice treated with CLR01, with a concomitant reduction in aggregate-induced endoplasmic reticulum stress response, protein oxidation, and apoptosis. Taken together, our preclinical data suggest that CLR01 is a promising lead compound for development of innovative, disease-modifying therapy for TTR amyloidosis. PMID:24459092

Ferreira, Nelson; Pereira-Henriques, Alda; Attar, Aida; Klärner, Frank-Gerrit; Schrader, Thomas; Bitan, Gal; Gales, Luís; Saraiva, Maria João; Almeida, Maria Rosário

2014-04-01

125

Twin-core fiber optical tweezers.  

PubMed

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

2008-03-31

126

Optical tweezers study life under tension  

PubMed Central

Optical tweezers have become one of the primary weapons in the arsenal of biophysicists, and have revolutionized the new field of single-molecule biophysics. Today’s techniques allow high-resolution experiments on biological macromolecules that were mere pipe dreams only a decade ago.

Fazal, Furqan M.; Block, Steven M.

2011-01-01

127

Independent trapping and manipulation of microparticles using dexterous acoustic tweezers  

NASA Astrophysics Data System (ADS)

An electronically controlled acoustic tweezer was used to demonstrate two acoustic manipulation phenomena: superposition of Bessel functions to allow independent manipulation of multiple particles and the use of higher-order Bessel functions to trap particles in larger regions than is possible with first-order traps. The acoustic tweezers consist of a circular 64-element ultrasonic array operating at 2.35 MHz which generates ultrasonic pressure fields in a millimeter-scale fluid-filled chamber. The manipulation capabilities were demonstrated experimentally with 45 and 90-?m-diameter polystyrene spheres. These capabilities bring the dexterity of acoustic tweezers substantially closer to that of optical tweezers.

Courtney, Charles R. P.; Demore, Christine E. M.; Wu, Hongxiao; Grinenko, Alon; Wilcox, Paul D.; Cochran, Sandy; Drinkwater, Bruce W.

2014-04-01

128

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

2008-01-01

129

Magnetic tweezers microscope for cellular manipulation  

Microsoft Academic Search

We present the design of a magnetic tweezers microscope for cellular manipulation. Our design allows versatile and significant 3D stress application over a large sample region. For linear force application, forces up to 250 pN per 4.5 micrometers magnetic bead can be applied. Finite element analysis shows that variance in force level is around 10 percent within an area of

Chen-Yuan Dong; Hayden Huang; Jason D. Sutin; H. S. Kwon; George Cragg; R. Gilbert; Richard T. Lee; Enrico Gratton; Roger D. Kamm; Douglas A. Lauffenburger; Peter T. So

2000-01-01

130

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

2006-02-10

131

Interactive approach to optical tweezers control.  

PubMed

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. PMID:16512531

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

2006-02-10

132

Nanoprobes with optical tweezers for biological applications  

NASA Astrophysics Data System (ADS)

We explore the use of sub-micron sized particles in optical tweezer traps as nanoprobes in microfluidic devices and biological cells. For applications that require high spatial resolution, the ability to suppress the particle's natural Brownian motion down to the nanometer or sub-nanometer scales is essential. However, the optical tweezer force scales with the volume of the particle making it difficult to confine and manipulate nanometer sized particles with high precision. To overcome this difficulty, we explore the possibility of using optically resonant particles as nanoprobes. The resonant particles should experience an increase in the optical tweezer force at wavelengths on the red side of the absorption resonance, resulting in a tighter confinement. We explore this phenomenon by measuring the trapping force acting on resonant particles (dye-filled polymeric and metallic particles) as a function of trapping laser wavelength and discuss the feasibility of using them as a high spatial resolution probe. In addition, we use similar particles as optically trapped nanoprobes to monitor temporal and spatial differences in an inhomogeneous environment; for example, we have developed pH-sensitive fluorescent nanoprobes for biological applications.

Kendrick, Mark; McIntyre, David; Ostroverkhova, Oksana; Bychkova, Valeriya; Shvarev, Alexey

2010-03-01

133

Optical tweezers applied to a microfluidic system.  

PubMed

We will demonstrate how optical tweezers can be combined with a microfluidic system to create a versatile microlaboratory. Cells are moved between reservoirs filled with different media by means of optical tweezers. We show that the cells, on a timescale of a few seconds, can be moved from one reservoir to another without the media being dragged along with them. The system is demonstrated with an experiment where we expose E. coli bacteria to different fluorescent markers. We will also discuss how the system can be used as an advanced cell sorter. It can favorably be used to sort out a small fraction of cells from a large population, in particular when advanced microscopic techniques are required to distinguish various cells. Patterns of channels and reservoirs were generated in a computer and transferred to a mask using either a sophisticated electron beam technique or a standard laser printer. Lithographic methods were applied to create microchannels in rubber silicon (PDMS). Media were transported in the channels using electroosmotic flow. The optical system consisted of a combined confocal and epi-fluorescence microscope, dual optical tweezers and a laser scalpel. PMID:15159778

Enger, Jonas; Goksör, Mattias; Ramser, Kerstin; Hagberg, Petter; Hanstorp, Dag

2004-06-01

134

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

NASA Technical Reports Server (NTRS)

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 carbide (SiC) nanotubes. The tweezers uses one or more focused laser beams to hold micrometer-sized particles called tools (sometimes called tips in atomic-force-microscope terminology). A strongly focused laser beam has an associated light-pressure gradient that is strong enough to pull small particles to the focus, in spite of the oppositely directed scattering force; "optical tweezers" is the common term for this effect. The objective is to use the tools to create carefully shaped secondary traps to hold and assemble nanostructures that may contain from tens to hundreds of atoms. The interaction between a tool and the nanostructures is to be monitored optically as is done with scanning probe microscopes. One of the initial efforts has been to create, shape, and control multiple tweezers beams. To this end, a programmable spatial-light modulator (SLM) has been used to modify the phase of a laser beam at up to 480 by 480 points. One program creates multiple, independently controllable tweezer beams whose shapes can be tailored by making the SLM an adaptive mirror in an interferometer (ref. 1). The beams leave the SLM at different angles, and an optical Fourier transform maps these beams to different positions in the focal plane of a microscope objective. The following figure shows two arrays of multiple beams created in this manner. The patterns displayed above the beam array control the intensity-to-phase transformation required in programming the SLM. Three of the seven beams displayed can be used as independently controllable beams.

Decker, Arthur J.; Jassemnejad, Baha; Seibel, Robin E.; Weiland, Kenneth E.

2003-01-01

135

Calibrating optical tweezers with Bayesian inference.  

PubMed

We present a new method for calibrating an optical-tweezer setup that does not depend on input parameters and is less affected by systematic errors like drift of the setup. It is based on an inference approach that uses Bayesian probability to infer the diffusion coefficient and the potential felt by a bead trapped in an optical or magnetic trap. It exploits a much larger amount of the information stored in the recorded bead trajectory than standard calibration approaches. We demonstrate that this method outperforms the equipartition method and the power-spectrum method in input information required (bead radius and trajectory length) and in output accuracy. PMID:24514731

Richly, Maximilian U; Türkcan, Silvan; Le Gall, Antoine; Fiszman, Nicolas; Masson, Jean-Baptiste; Westbrook, Nathalie; Perronet, Karen; Alexandrou, Antigoni

2013-12-16

136

Micromechanics of Dipolar Chains Using Optical Tweezers  

NASA Technical Reports Server (NTRS)

Here we present our initial study of the micromechanical properties of dipolar chains and columns in a magnetorheological (MR) suspension. Using dual-trap optical tweezers, we are able to directly measure the deformation of the dipolar chains parallel and perpendicular to the applied magnetic field. We observe the field dependence of the mechanical properties such as resistance to deformation, chain reorganization, and rupturing of the chains. These forms of energy dissipation are important for understanding and tuning the yield stress and rheological behavior of an MR suspension.

Furst, Eric M.; Gast, Alice P.

1999-01-01

137

Optical tweezers based on cylindrical vector beams  

NASA Astrophysics Data System (ADS)

Optical tweezers based on cylindrical vector beams are studied theoretically and experimentally. First, we present the basic concept of a cylindrical vector beam (CVB), whose polarization is axially symmetric to the optical axis. Second, two theoretical modes to analyze the interaction between the light beam and the particle are introduced, respectively, and some simulations have been shown. Then, the system structure and its operation principle are introduced in details, where a spatial light modulator (SLM) is used to flexibly generate the CVBs, and experimental results are also demonstrated, which show some advantages for optical manipulation of particles using CVBs.

Xu, Yongheng; Zhou, Zhehai; Zhang, Xiaolin; Zhao, Zhidan; Zhu, Lianqing

2013-10-01

138

Micro Magnetic Tweezers for Nanomanipulation Inside Live Cells  

PubMed Central

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 one direction; and II), tweezers that consist of multiple poles and allow exertion of forces in multiple directions but at very low forces. The magnetic tweezers described here combines both aspects in a single apparatus: high forces in a controllable direction. To this end, micron scale magnetic structures are fabricated using cleanroom technologies. With these tweezers, magnetic flux gradients of ?B = 8 × 103 T m?1 can be achieved over the dimensions of a single cell. This allows exertion of forces up to 12 pN on paramagnetic probes with a diameter of 350 nm, enabling us to maneuver them through the cytoplasm of a living cell. It is expected that with the current tweezers, picoNewton forces can be exerted on beads as small as 100 nm.

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

2005-01-01

139

Micro magnetic tweezers for nanomanipulation inside live cells.  

PubMed

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 one direction; and II), tweezers that consist of multiple poles and allow exertion of forces in multiple directions but at very low forces. The magnetic tweezers described here combines both aspects in a single apparatus: high forces in a controllable direction. To this end, micron scale magnetic structures are fabricated using cleanroom technologies. With these tweezers, magnetic flux gradients of nablaB = 8 x 10(3) T m(-1) can be achieved over the dimensions of a single cell. This allows exertion of forces up to 12 pN on paramagnetic probes with a diameter of 350 nm, enabling us to maneuver them through the cytoplasm of a living cell. It is expected that with the current tweezers, picoNewton forces can be exerted on beads as small as 100 nm. PMID:15556976

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

2005-03-01

140

Quantitative modeling of forces in electromagnetic tweezers  

NASA Astrophysics Data System (ADS)

This paper discusses numerical simulations of the magnetic field produced by an electromagnet for generation of forces on superparamagnetic microspheres used in manipulation of single molecules or cells. Single molecule force spectroscopy based on magnetic tweezers can be used in applications that require parallel readout of biopolymer stretching or biomolecular binding. The magnetic tweezers exert forces on the surface-immobilized macromolecule by pulling a magnetic bead attached to the free end of the molecule in the direction of the field gradient. In a typical force spectroscopy experiment, the pulling forces can range between subpiconewton to tens of piconewtons. In order to effectively provide such forces, an understanding of the source of the magnetic field is required as the first step in the design of force spectroscopy systems. In this study, we use a numerical technique, the method of auxiliary sources, to investigate the influence of electromagnet geometry and material parameters of the magnetic core on the magnetic forces pulling the target beads in the area of interest. The close proximity of the area of interest to the magnet body results in deviations from intuitive relations between magnet size and pulling force, as well as in the force decay with distance. We discuss the benefits and drawbacks of various geometric modifications affecting the magnitude and spatial distribution of forces achievable with an electromagnet.

Bijamov, Alex; Shubitidze, Fridon; Oliver, Piercen M.; Vezenov, Dmitri V.

2010-11-01

141

Quantitative modeling and optimization of magnetic tweezers.  

PubMed

Magnetic tweezers are a powerful tool to manipulate single DNA or RNA molecules and to study nucleic acid-protein interactions in real time. Here, we have modeled the magnetic fields of permanent magnets in magnetic tweezers and computed the forces exerted on superparamagnetic beads from first principles. For simple, symmetric geometries the magnetic fields can be calculated semianalytically using the Biot-Savart law. For complicated geometries and in the presence of an iron yoke, we employ a finite-element three-dimensional PDE solver to numerically solve the magnetostatic problem. The theoretical predictions are in quantitative agreement with direct Hall-probe measurements of the magnetic field and with measurements of the force exerted on DNA-tethered beads. Using these predictive theories, we systematically explore the effects of magnet alignment, magnet spacing, magnet size, and of adding an iron yoke to the magnets on the forces that can be exerted on tethered particles. We find that the optimal configuration for maximal stretching forces is a vertically aligned pair of magnets, with a minimal gap between the magnets and minimal flow cell thickness. Following these principles, we present a configuration that allows one to apply > or = 40 pN stretching forces on approximately 1-microm tethered beads. PMID:19527664

Lipfert, Jan; Hao, Xiaomin; Dekker, Nynke H

2009-06-17

142

Dielectrophoretic tweezer for isolating and manipulating target cells.  

PubMed

The ability to isolate and accurately position single cells in three dimensions is becoming increasingly important in many areas of biological research. The authors describe the design, theoretical modelling and testing of a novel dielectrophoretic (DEP) tweezer for picking out and relocating single target cells. The device is constructed using facilities available in most electrophysiology laboratories, without the requirement of sophisticated and expensive microfabrication technology, and offers improved practical features over previously reported DEP tweezer designs. The DEP tweezer has been tested using transfected HEI-193 human schwannoma cells, with visual identification of the target cells being aided by labelling the incorporated gene product with a green fluorescent protein. PMID:21241155

Menachery, A; Graham, D; Messerli, S M; Pethig, R; Smith, P J S

2011-03-01

143

Investigating the potential applications of a Raman tweezer system  

NASA Astrophysics Data System (ADS)

This thesis describes the construction of an Optical Tweezer apparatus to be used in conjunction with a confocal Raman spectrometer. The tweezer utilizes an infrared (e=1064 nm) laser directed into an inverted microscope with NA=1.4 oil immersion 100x objective lens that strongly focuses the laser light into a sample to function as a single-beam gradient force trap. The long term goal of this research program is to develop a single molecule Raman tweezers apparatus that allows one to control the position of a Raman nanoplasmonic amplifier. This thesis describes the construction of the Raman tweezer apparatus along with several Raman spectra obtained from optically trapped samples of polystyrene fluorescent orange, amine-modified latex beads. In addition, I explored the Raman spectra of bulk cytochrome c mixed with or injected onto Ag aggregates for SERs enhancement.

Wray, John Casey

144

Tunable Optical Tweezers for Wavelength-dependent Measurements.  

National Technical Information Service (NTIS)

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, simp...

B. Hester C. Lopez-Mariscal C. L. Filgueira G. K. Campbell R. Huschka

2012-01-01

145

21 CFR 878.5360 - Tweezer-type epilator.  

Code of Federal Regulations, 2013 CFR

... FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES GENERAL AND PLASTIC SURGERY DEVICES Therapeutic Devices § 878.5360 Tweezer-type epilator. (a) Identification. The...

2013-04-01

146

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

PubMed

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

2013-08-14

147

MatLab program for precision calibration of optical tweezers  

Microsoft Academic Search

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

Iva Marija Toli; Kirstine Berg-Sørensen; Henrik Flyvbjerg

148

A theoretical potential-well model of acoustic tweezers  

Microsoft Academic Search

Standing wave acoustic tweezers have been popularly used in non-invasive and non-contact particle manipulation. With better penetration ability in biological tissue, acoustic tweezers has the promising potential for in-vivo study. However, the dual-beam configuration has many limits on operation and system setup. A single-beam trapping model is thus preferable. According to the concept of optical vortex, we propose an acoustics-vortex

Shih-Tsung Kang; Chih-Kuang Yeh

2009-01-01

149

Optical tweezers for studying taxis in parasites  

NASA Astrophysics Data System (ADS)

In this work we present a methodology to measure force strengths and directions of living parasites with an optical tweezers setup. These measurements were used to study the parasites chemotaxis in real time. We observed behavior and measured the force of: (i) Leishmania amazonensis in the presence of two glucose gradients; (ii) Trypanosoma cruzi in the vicinity of the digestive system walls, and (iii) Trypanosoma rangeli in the vicinity of salivary glands as a function of distance. Our results clearly show a chemotactic behavior in every case. This methodology can be used to study any type of taxis, such as chemotaxis, osmotaxis, thermotaxis, phototaxis, of any kind of living microorganisms. These studies can help us to understand the microorganism sensory systems and their response function to these gradients.

de Thomaz, A. A.; Fontes, A.; Stahl, C. V.; Pozzo, L. Y.; Ayres, D. C.; Almeida, D. B.; Farias, P. M. A.; Santos, B. S.; Santos-Mallet, J.; Gomes, S. A. O.; Giorgio, S.; Feder, D.; Cesar, C. L.

2011-04-01

150

Subpiconewton Dynamic Force Spectroscopy Using Magnetic Tweezers  

PubMed Central

We introduce a simple method for dynamic force spectroscopy with magnetic tweezers. This method allows application of subpiconewton force and twist control by calibration of the applied force from the height of the magnets. Initial dynamic force spectroscopy experiments on DNA molecules revealed a large hysteresis that is caused by viscous drag on the magnetic bead and will conceal weak interactions. When smaller beads are used, this hysteresis is sufficiently reduced to reveal intramolecular interactions at subpiconewton forces. Compared with typical quasistatic force spectroscopy, a significant reduction of measurement time is achieved, allowing the real-time study of transient structures and reaction intermediates. As a proof of principle, nucleosome-nucleosome interactions on a subsaturated chromatin fiber were analyzed.

Kruithof, M.; Chien, F.; de Jager, M.; van Noort, J.

2008-01-01

151

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

2007-06-01

152

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

153

P6F-4 A Theoretical Time-Course Study of Acoustic Tweezers  

Microsoft Academic Search

Single beam based optical tweezers has been applied to many biomedical applications in trapping macromolecules and cells. Due to the finite penetration ability of laser in tissue and only utilization in opaque particles, these limitations reduce the potential of optical tweezers in-vivo performance. Consequently, some researchers theoretically demonstrated to manipulate micro-size particles by acoustic tweezers to avoid mentioned problems. To

Hsiao-Chun Ting; Chih-Kuang Yeh

2007-01-01

154

Transforming Mesoscopic (Bio)materials with Holographic Optical Tweezers  

NASA Astrophysics Data System (ADS)

An optical tweezer uses the forces exerted by a strongly focused beam of light to trap and move objects ranging in size from tens of nanometers to tens of micrometers. Since their introduction in 1986, optical tweezers have become a mainstay of research in biology, physical chemistry, and soft condensed matter physics. This talk highlights recent advances made possible by new classes of optical traps created with computer-designed holograms, a technique we call holographic optical trapping. Holographic optical tweezers can trap hundreds of mesoscopic objects simultaneously and move them independently in three dimensions. Arrays of optical traps can be used to continuously sort heterogeneous samples into selected fractions, a process we call optical fractionation. The same holograms can transform optical traps into optical scalpels and scissors that photochemically transform mesoscopic samples with exquisite spatial resolution. They also can impose arbitrary phase profiles onto the trapping beams, thereby creating optical vortices and related optical machines capable of actuating MEMS devices and driving mesoscale pumps and mixers. These new applications for laser light promise to take optical tweezers out of the laboratory and into real-world applications including manufacturing, diagnostics, and even consumer products. The unprecedented access to the mesoscopic world provided by holographic optical tweezers also offers revolutionary new opportunities for fundamental and applied research.

Grier, David

2004-03-01

155

How safe is gamete micromanipulation by laser tweezers?  

NASA Astrophysics Data System (ADS)

Laser tweezers, used as novel sterile micromanipulation tools of living cells, are employed in laser-assisted in vitro fertilization (IVF). For example, controlled spermatozoa transport with 1064 nm tweezers to human egg cells has been performed in European clinics in cases of male infertility. The interaction of approximately 100 mW near infrared (NIR) trapping beams at MW/cm2 intensity with human gametes results in low mean less than 2 K temperature increases and less than 100 pN trapping forces. Therefore, photothermal or photomechanical induced destructive effects appear unlikely. However, the high photon flux densities may induce simultaneous absorption of two NIR photons resulting in nonlinear interactions. These nonlinear interactions imply non-resonant two-photon excitation of endogenous cellular chromophores. In the case of less than 800 nm tweezers, UV- like damage effects may occur. The destructive effect is amplified when multimode cw lasers are used as tweezer sources due to longitudinal mode-beating effects and partial mode- locking. Spermatozoa damage within seconds using 760 nm traps due to formation of unstable ps pulses in a cw Ti:Sa ring laser is demonstrated. We recommend the use of greater than or equal to 800 nm traps for optical gamete micromanipulation. To our opinion, further basic studies on the influence of nonlinear effects of laser tweezers on human gamete are necessary.

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

1998-04-01

156

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

1997-07-01

157

Optical tweezers-assisted measurements of elastic light scattering  

NASA Astrophysics Data System (ADS)

Optical tweezers have been used in biophysical studies for over twenty years. Typical application areas are force measurements of subcellular structures and cell biomechanics. Optical tweezers can also be used to manipulate the orientation of objects. Moreover, using various beam shapes, optical tweezers allow measuring light scattering from single and multiple objects by keeping particles and cells in place during the measurement. At single cell level, light scattering yields important information about the object being studied, including its size, shape and refractive index. Also dependent scattering can be studied. In this paper, we review experimental work conducted in this area by our group and show new results relating to optical clearing phenomena at single microparticle level.

Kinnunen, M.; Tuorila, J.; Haapalainen, T.; Karmenyan, A.; Tuchin, V.; Myllylä, R.

2014-01-01

158

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

2012-01-01

159

Magnetic tweezers for manipulation of magnetic particles in single cells  

NASA Astrophysics Data System (ADS)

Magnetic tweezers gain increasing interest for applications in biology. Here, a setup of magnetic tweezers is introduced using micropatterned conducting lines on transparent glass slides. Magnetic particles of 1 ?m diameter were injected in barley cell vacuoles using a microinject system under microscopic control. Time dependent tracking of the particles after application of a magnetic field was used to determine the viscosity of vacuolar sap in vivo relative to water and isolated vacuolar fluid. The viscosity of vacuolar sap in cells was about 2-fold higher than that of extracted vacuolar fluid and 5 times higher than that of water.

Ebrahimian, H.; Giesguth, M.; Dietz, K.-J.; Reiss, G.; Herth, S.

2014-02-01

160

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.

2009-06-01

161

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

2013-11-01

162

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

2005-06-10

163

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.

2006-09-01

164

Host-guest supramolecular nanosystems for cancer diagnostics and therapeutics.  

PubMed

Extensive efforts have been devoted to the construction of functional supramolecular nanosystems for applications in catalysis, energy conversion, sensing and biomedicine. The applications of supramolecular nanosystems such as liposomes, micelles, inorganic nanoparticles, carbon materials for cancer diagnostics and therapeutics have been reviewed by other groups. Here, we will focus on the recent momentous advances in the implementation of typical supramolecular hosts (i.e., cyclodextrins, calixarenes, cucurbiturils and metallo-hosts) and their nanosystems in cancer diagnostics and therapeutics. We discuss the evolutive process of supramolecular nanosystems from the structural control and characterization to their diagnostic and therapeutic function exploitation and even the future potentials for clinical translation. PMID:24048975

Wang, Lei; Li, Li-li; Fan, Yun-shan; Wang, Hao

2013-07-26

165

Isotopic enrichment of tritium by using host-guest chemistry  

NASA Astrophysics Data System (ADS)

The isotopic enrichment of tritium in the liquid-liquid extraction system, butylammonium/crownether was investigated using water solution of butylammonium iodide and chloroform solution of dicyclohexyl-18-crown-6. Tritium was enriched in the ammonium-crown complex which was extracted into the organic phase. Both the enthalpy and entropy changes were positive for the direction of negative free energy change in the following equilibrium equation: R-NH 2T +(aq) + R-NH +3L (org) = R-NH 2T +L (org) + R-NH +3(aq) where L represents the ligand of dicyclohexyl-18-crown-6 and R-NH +3, butylammonium ion, respectively. The value of entropy effect (T?S) exceeded that of enthalpy change around room temperature. Single stage isotope separation factors obtained were 12 for n-butylammonium and 50 for tertbutylammonium as guest compounds at 55°C.

Nishizawa, Kazushige

1985-02-01

166

Host-Guest Self-assembly in Block Copolymer Blends  

NASA Astrophysics Data System (ADS)

Ultrafine, uniform nanostructures with excellent functionalities can be formed by self-assembly of block copolymer (BCP) thin films. However, extension of their geometric variability is not straightforward due to their limited thin film morphologies. Here, we report that unusual and spontaneous positioning between host and guest BCP microdomains, even in the absence of H-bond linkages, can create hybridized morphologies that cannot be formed from a neat BCP. Our self-consistent field theory (SCFT) simulation results theoretically support that the precise registration of a spherical BCP microdomain (guest, B-b-C) at the center of a perforated lamellar BCP nanostructure (host, A-b-B) can energetically stabilize the blended morphology. As an exemplary application of the hybrid nanotemplate, a nanoring-type Ge2Sb2Te5 (GST) phase-change memory device with an extremely low switching current is demonstrated. These results suggest the possibility of a new pathway to construct more diverse and complex nanostructures using controlled blending of various BCPs.

Park, Woon Ik; Kim, Yongjoo; Jeong, Jae Won; Kim, Kyungho; Yoo, Jung-Keun; Hur, Yoon Hyung; Kim, Jong Min; Thomas, Edwin L.; Alexander-Katz, Alfredo; Jung, Yeon Sik

2013-11-01

167

NMR method for simultaneous host-guest binding constant measurement.  

PubMed

An NMR-based relative binding affinity measurement method has been developed in which differences in the binding affinities of different hosts toward a particular guest (?logK(ass) values) are measured in the same solution. As an advancement, the method allows the simultaneous determination of several ?logK(ass) values in a single run. As a proof of principle, the method was used to measure binding affinity differences of a number of indolocarbazole- and urea-based synthetic receptors toward acetate ion in DMSO-d6/H2O (99.5%:0.5% m/m). As a result, a binding affinity scale containing 33 receptors and spanning 2.32 log units with excellent self-consistency (consistency standard deviation = 0.01 log unit) was created. Together with the very good agreement of the results with those obtained by UV-vis spectrophotometry, this demonstrates the high accuracy of the method and the fact that the NMR and UV-vis techniques can be used interchangeably (in spite of the very different concentrations used in these techniques). Additionally, it was found for symmetrical receptor molecules from the same compound family that there is a correlation between the acetate binding affinity of a receptor and the (15)N chemical shift of the nitrogen atoms of its binding centers. PMID:24533827

Kadam, Sandip A; Haav, Kristjan; Toom, Lauri; Haljasorg, Tõiv; Leito, Ivo

2014-03-21

168

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

2010-01-01

169

Mechanical Forces Impeding Exocytotic Surfactant Release Revealed by Optical Tweezers  

Microsoft Academic Search

The release of surfactant from alveolar type II cells is essential to lower the surface tension in the lung and to facilitate inspiration. However, the factors controlling dispersal and diffusion of this hydrophobic material are still poorly understood. Here we report that release of surfactant from the fused vesicle, termed lamellar body (LB), resisted mechanical forces applied by optical tweezers:

Wolfgang Singer; Manfred Frick; Thomas Haller; Stefan Bernet; Monika Ritsch-Marte; Paul Dietl

2003-01-01

170

Ultrahigh Frequency Lensless Ultrasonic Transducers for Acoustic Tweezers Application  

PubMed Central

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 ?m 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.

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

2014-01-01

171

Ultrahigh frequency lensless ultrasonic transducers for acoustic tweezers application.  

PubMed

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

2013-03-01

172

Effect of ultrasonic attenuation on the feasibility of acoustic tweezers  

Microsoft Academic Search

A modified mathematical formulation for the calculation of axial radiation force was developed to incorporate the effect of ultrasonic attenuation. Axial forces, Fresnel coefficients, average internal attenuation factors and effective internal reflection coefficients were calculated. Thermal and mechanical indices were also computed to address the safety issues in the implementation of acoustic tweezers and were found to be negligible. The

Jungwoo Lee; K. Kirk Shung

2006-01-01

173

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

2000-01-01

174

Host-guest chemistry of the chromium-wheel complex [Cr8F8(tBuCO2)16]: prediction of inclusion capabilities by using an electrostatic potential distribution determined by modeling synchrotron X-ray structure factors at 16 K.  

PubMed

The structure and detailed electron density distribution (EDD) of the large octanuclear chromium-wheel host complex [Cr8F8(tBuCO2)16] (1) has been determined from synchrotron X-ray structure factors collected at 16(5) K. The complex has a central cavity with a minimum entry distance between carbon atoms of the pivalate methyl groups (pivalic acid = tBuCO2H) of 4.027(4) A on one side of the molecule and 7.273(4) A on the other. The screened side of the molecule can be "opened" by rotation of methyl groups to create a strained host structure, which is compensated for by improved host-guest and host-solvent interaction. The EDD of the 272-atom complex (1144 e-) was determined by multipole modeling based on the experimental structure factors. 3d orbital populations on the Cr atoms and topological analysis of the EDD show that the covalent part of the metal-ligand interactions consists mainly of sigma donation from the ligands, but that overall the interactions are predominantly electrostatic. The electrostatic potential (EP) has been calculated from the experimental EDD. Knowledge of the geometry of the naked complex 1 as well as the EP in the central cavity of this molecule allows us to deduce which characteristic properties guest molecules must have to be accepted into the void. To probe these predictions, a series of complexes of 1 with different guest inclusions were synthesized (2 = 1 + N,N'-dimethylformamide (DMF), 3 = 1 + N,N'-dimethylacetamide (DMA), 4 = 1 + DMA + DMF, 5 = 1 + 2CH3CN), and their structures were examined by using X-ray diffraction data measured at 120(1) K. Results of these studies indicate that in the crystalline state, the optimal guest molecule should be linear and possess a permanent dipole. Attempts to crystallize the host complex with cations incorporated into the cavity were fruitless, although electrospray ionization mass spectrometry showed that a [1 + potassium]+ entity pre-exists in solution and can be transferred intact into the gas phase. PMID:12391657

Overgaard, Jacob; Iversen, Bo B; Palii, Sergiu P; Timco, Grigore A; Gerbeleu, Nicolae V; Larsen, Finn K

2002-06-17

175

Drug release by pH-responsive molecular tweezers: Atomistic details from molecular modeling.  

PubMed

pH-responsive molecular tweezers have been proposed as an approach for targeting drug-delivery to tumors, which tend to have a lower pH than normal cells. We performed a computational study of a pH-responsive molecular tweezer using ab initio quantum chemistry in the gas-phase and molecular dynamics (MD) simulations in solution. The binding free energy in solution was calculated using steered MD. We observe, in atomistic detail, the pH-induced conformational switch of the tweezer and the resulting release of the drug molecule. Even when the tweezer opens, the drug molecule remains near a hydrophobic arm of the molecular tweezer. Drug release cannot occur, it seems, unless the tweezer is in a hydrophobic environment with low pH. © 2014 Wiley Periodicals, Inc. PMID:24962869

Mohammed, Ahmed A K; Burger, Steven K; Ayers, Paul W

2014-08-01

176

Dual optical tweezers integrated in a four-core fiber: design and simulation  

NASA Astrophysics Data System (ADS)

We propose a novel dual optical fiber tweezers integrated in a four-core fiber which can trap, rotate and orient a micro particle immersed in a fluid medium. We design the structures and the functions of this dual optical fiber tweezers, and simulate the optical trapping forces, optical torques exerting on the micro particle. We also give out the experimental setup and the controlling method of this integrated dual optical fiber tweezers.

Zhang, Yu; Yuan, Libo; Liu, Zhihai; Yang, Jun

2013-09-01

177

Single-sided lateral-field and phototransistor-based optoelectronic tweezers  

NASA Technical Reports Server (NTRS)

Described herein are single-sided lateral-field optoelectronic tweezers (LOET) devices which use photosensitive electrode arrays to create optically-induced dielectrophoretic forces in an electric field that is parallel to the plane of the device. In addition, phototransistor-based optoelectronic tweezers (PhOET) devices are described that allow for optoelectronic tweezers (OET) operation in high-conductivity physiological buffer and cell culture media.

Ohta, Aaron (Inventor); Chiou, Pei-Yu (Inventor); Hsu, Hsan-Yin (Inventor); Jamshidi, Arash (Inventor); Wu, Ming-Chiang (Inventor); Neale, Steven L. (Inventor)

2011-01-01

178

Photoacoustic tweezers with a pulsed laser: theory and experiments  

NASA Astrophysics Data System (ADS)

A novel noninvasive optical technique for manipulating particles and cells is presented that utilizes laser-generated forces in an absorbing medium surrounding the particles or cells. In this technique, a laser pulse creates near-object acoustic waves, which during interaction with the objects lead to then being moved or trapped. The main optical schemes are considered, and a theory is presented for this new optical tool, namely photoacoustic (PA) tweezer with pulsed laser. The magnitudes of forces acting on polystyrene particles suspended in water were estimated as a function of the particles' properties for circular and ring geometries of the laser beam. Results of our preliminary experiments demonstrated proof that the manipulation, trapping and even rotation of cells is possible with PA tweezers.

Zharov, V. P.; Malinsky, T. V.; Kurten, R. C.

2005-08-01

179

Scanning probe microscopy installed with nanotube probes and nanotube tweezers.  

PubMed

We have developed well-controlled processes for the growth and manipulation of carbon nanotubes. The relatively thin multiwalled nanotubes were prepared with high purity by arc discharge with a high gas temperature. In the manipulation of nanotubes, the first crucial process is to prepare a nanotube array, so-called nanotube cartridge. We have found the alternated current electrophoresis of nanotubes by which nanotubes are aligned at the knife-edge of a disposal razor. The second important process is to transfer a nanotube from the nanotube cartridge onto a substrate in a scanning electron microscope. Using this method, we have developed nanotube probes and nanotube tweezers that operate in a scanning probe microscope (SPM). The nanotube probes have been applied for observation of biological samples and industrial samples to clarify their advantages. The nanotube tweezers have been demonstrated for their motion in scanning electron microscope and operated to carry a nanomaterial in a SPM. PMID:12211483

Nakayama, Yoshikazu

2002-05-01

180

Optical Tweezer Studies of Liquid Crystals Using Multiple Optical Traps  

NASA Astrophysics Data System (ADS)

We have constructed an acousto-optically scanned CW YAG laser system to generate dynamically controllable multiple optical traps. This multiple optical tweezer is being employed to probe the static and dynamic interactions of defects and textures in two and three dimensional liquid crystal (LC) systems. Results will be presented on 2D systems, where interactions between islands, thicker circular regions on few-layer thick freely suspended liquid crystal (LC) films, have been studied in the smectic C phase, in which the islands interact via the c-director orientation field. In the Smectic A phase, it has been found that the elastic interactions between islands are much smaller than in the Smectic C, and it is easy to induce coalescence using the optical tweezers. Studies of motion of suspended particles in 3D nematics and smectics will also be presented. *This research is supported by NASA Grant NAG3-2457, and NSF MRSEC Grant DMR 0213918

Pattanaporkratana, Apichart

2005-03-01

181

Active-passive calibration of optical tweezers in viscoelastic media  

NASA Astrophysics Data System (ADS)

In order to use optical tweezers as a force measuring tool inside a viscoelastic medium such as the cytoplasm of a living cell, it is crucial to perform an exact force calibration within the complex medium. This is a nontrivial task, as many of the physical characteristics of the medium and probe, e.g., viscosity, elasticity, shape, and density, are often unknown. Here, we suggest how to calibrate single beam optical tweezers in a complex viscoelastic environment. At the same time, we determine viscoelastic characteristics such as friction retardation spectrum and elastic moduli of the medium. We apply and test a method suggested [M. Fischer and K. Berg-Sørensen, J. Opt. A, Pure Appl. Opt. 9, S239 (2007)], a method which combines passive and active measurements. The method is demonstrated in a simple viscous medium, water, and in a solution of entangled F-actin without cross-linkers.

Fischer, Mario; Richardson, Andrew C.; Reihani, S. Nader S.; Oddershede, Lene B.; Berg-Sørensen, Kirstine

2010-01-01

182

A novel optoelectronic tweezer using light induced dielectrophoresis  

Microsoft Academic Search

We demonstrate a novel optoelectronic tweezer using light induced dielectrophoresis mechanism to optically trap and transport micro particles with optical power in the ?W range. This device consists of two pattern-less surfaces: a bottom glass substrate coated with photoconductive material and a top transparent indium-tin-oxide (ITO) glass. To achieve optical trapping, we sandwich the liquid-immersed micro particles between these two

Pei Yu Chiou; Zehao Chang; M. C. Wu

2003-01-01

183

Single-molecule magnetic tweezers studies of type IB topoisomerases.  

PubMed

The past few years have seen the application of single-molecule force spectroscopy techniques to the study of topoisomerases. Magnetic tweezers are particularly suited to the study of topoisomerases due to their unique ability to exert precise and straightforward control of the supercoiled state of DNA. Here, we illustrate in a stepwise fashion how the dynamic properties of type IB topoisomerases can be monitored using this technique. PMID:19763943

Lipfert, Jan; Koster, Daniel A; Vilfan, Igor D; Hage, Susanne; Dekker, Nynke H

2009-01-01

184

Optical tweezers for vortex rings in Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

We study generation and stabilization of vortex rings in atomic Bose-Einstein condensates. We suggest an approach for generating vortex rings by optical tweezers—two blue-detuned optical beams forming a toroidal void in a magnetically or optically confined condensate cloud. We demonstrate that matter-wave vortex rings trapped within the void are energetically and dynamically stable. Our theoretical findings suggest a possibility for the generation, stabilization, and nondestructive manipulation of quantized vortex rings in experimentally feasible trapping configurations.

Yakimenko, A. I.; Bidasyuk, Yu. M.; Prikhodko, O. O.; Vilchinskii, S. I.; Ostrovskaya, E. A.; Kivshar, Yu. S.

2013-10-01

185

Cluster formation in ferrofluids induced by holographic optical tweezers.  

PubMed

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

2013-10-01

186

A GSO tweezers-type coincidence detector for tumor detection.  

PubMed

A Gd2SiO5 (GSO) tweezers-type coincidence detector was developed and tested for tumor detection in procedures such as (18)F-fluorodeoxyglucose (FDG)-guided surgery. The detector consists of a pair of GSO scintillators, a pair of metal-packaged small-sized photomultiplier tubes (PMTs), and a coincidence circuit. Because the GSO scintillators are located on the tips of tweezers, a target organ such as a lymph node or the colon can be easily positioned between them. The size of a single GSO was 8 × 14 × 14 mm. The results show that the energy resolution was 30 % full-width at half-maximum (FWHM) and the timing resolution was 6 ns FWHM for 511-keV gamma photons. The point-spread function perpendicular to the detector was 4.5 mm FWHM, and the point-spread function parallel to the detector was 7.5 mm FWHM. The absolute sensitivity of the coincidence detector was 0.6% at the center of the detector when the two GSOs were 5 mm apart. Background counts due to the accidental and scatter coincidence were 2 cps up to 48 MBq from the positron source contained in a 20-cm-diameter, 20-cm-high cylindrical phantom. From these results, we conclude that the proposed tweezers-type coincidence detector is useful for tumor detection by the use of FDG, such as that in radio-guided surgery. PMID:23283753

Yamamoto, Seiichi; Higashi, Tatsuya; Senda, Michio

2013-07-01

187

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

2000-01-01

188

A theoretical time-course model of acoustic tweezers: Pulse-wave mode  

Microsoft Academic Search

The optical tweezers has been a very useful tool in biological research. However, due to finite penetration depth in optics, it is only utilized for transparent particle. This limitation reduces its potential of in-vivo manipulation. The idea of acoustic tweezers with better penetration ability than optics was recently proposed. In this paper, a novel pulse-wave mode is theoretically demonstrated to

Shih-Tsung Kang; Chih-Kuang Yeh

2008-01-01

189

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)

1995-05-01

190

Interferometer-Controlled Optical Tweezers Constructed for Nanotechnology and Biotechnology  

NASA Technical Reports Server (NTRS)

A new method to control microparticles was developed in-house at the NASA Glenn Research Center in support of the nanotechnology project under NASA's Aerospace Propulsion and Power Base Research Program. A prototype interferometer-controlled optical tweezers was constructed to manipulate scanning probe microscope (SPM) tips. A laser beam passed through a Mach-Zehnder interferometer, and a microscope objective then produced an optical trap from the coaxial beams. The trap levitated and generated the coarse motion of a 10-mm polystyrene sphere used to simulate a SPM tip. The interference between the beams provided fine control of the forces and moments on the sphere. The interferometer included a piezoelectric-scanned mirror to modulate the interference pattern. The 10-mm sphere was observed to oscillate about 1 mm as the mirror and fringe pattern oscillated. The prototype tweezers proved the feasibility of constructing a more sophisticated interferometer tweezers to hold and manipulate SPM tips. The SPM tips are intended to interrogate and manipulate nanostructures. A more powerful laser will be used to generate multiple traps to hold nanostructures and SPM tips. The vibrating mirror in the interferometer will be replaced with a spatial light modulator. The modulator will allow the optical phase distribution in one leg of the interferometer to be programmed independently at 640 by 480 points for detailed control of the forces and moments. The interference patterns will be monitored to measure the motion of the SPM tips. Neuralnetwork technology will provide fast analysis of the interference patterns for diagnostic purposes and for local or remote feedback control of the tips. This effort also requires theoretical and modeling support in the form of scattering calculations for twin coherent beams from nonspherical particles.

Decker, Arthur J.

2002-01-01

191

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

2008-05-01

192

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

2011-08-01

193

Planar optical tweezers using tapered-waveguide junctions.  

PubMed

We demonstrate planar optical tweezers using the evanescent field of a silicon nitride tapered-waveguide junction between a singlemode waveguide and a multimode waveguide. Our experiments show that the junction embedded in a fluidic channel holds up to one and two polystyrene particles of sizes of 2.2 ?m and 1 ?m, respectively. The trapped particles are successively substituted by the incoming particles. Our experiments and numerical modeling reveal that the junction particle trapping depends on particle size and number. PMID:22825205

Cai, Hong; Poon, Andrew W

2012-07-15

194

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)

2007-01-19

195

pH microprobe manipulated in microchannels using optical tweezers  

NASA Astrophysics Data System (ADS)

SNARF-1 fluorochrome was used to functionalize 3?m diameter latex spheres making them sensitive to the pH of their environment, manifested as a change in their fluorescence. The fluorescence emission at 580nm was excited using a filtered xenon arc lamp at 515nm. A solution of functionalized latex spheres was placed between gold microelectrodes in a microfluidic channel. Optical tweezers were used to trap and manipulate the spheres in the vicinity of the microelectrodes, to map out the pH profile in the electrolyte solution, induced by passing 20 microsecond transient current pulses through the microelectrodes.

Sinclair, Gavin S.; Klauke, Norbert; Monaghan, Paul; Padgett, Miles J.; Cooper, Jon

2005-03-01

196

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

2009-09-01

197

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.

2013-09-01

198

Algorithm for computing holographic optical tweezers at video rates  

NASA Astrophysics Data System (ADS)

Digital holography enables the creation of multiple optical traps at arbitrary three-dimensional locations and spatial light modulators permit updating those holograms at video rates. However, the time required for computing the holograms makes interactive optical manipulation of several samples difficult to achieve. We introduce an algorithm for computing holographic optical tweezers that is both easy to implement and capable of speeds in excess of 10 Hz when running on a Pentium IV computer. A discussion of the pros and cons of the algorithm, a mathematical analysis of the efficiency of the resulting traps, as well as results of the three-dimensional manipulation of polystyrene micro spheres are included.

Montes-Usategui, Mario; Pleguezuelos, Encarnación; Andilla, Jordi; Martín-Badosa, Estela; Juvells, Ignacio

2006-09-01

199

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.

2013-03-01

200

Advances in magnetic tweezers for single molecule and cell biophysics.  

PubMed

Magnetic tweezers (MTW) enable highly accurate forces to be transduced to molecules to study mechanotransduction at the molecular or cellular level. We review recent MTW studies in single molecule and cell biophysics that demonstrate the flexibility of this technique. We also discuss technical advances in the method on several fronts, i.e., from novel approaches for the measurement of torque to multiplexed biophysical assays. Finally, we describe multi-component nanorods with enhanced optical and magnetic properties and discuss their potential as future MTW probes. PMID:24263142

Kilinc, Devrim; Lee, Gil U

2014-01-01

201

Moving average process underlying the holographic-optical-tweezers experiments  

NASA Astrophysics Data System (ADS)

We study statistical properties of the recordings which contain time-dependent positions of a bead trapped in optical tweezers. Analysis of such a time series indicates that the commonly accepted model, i.e., the autoregressive process of first order, is not sufficient to fit the data. We show a presence of the first-order moving average part in the dynamical model of the system. We explain origin of this part as an influence of the high frequency CCD camera on the measurements. The proposed autoregressive moving average model appears to reflect perfectly all statistical features of the high-frequency recording data.

?lezak, Jakub; Drobczy?ski, S?awomir; Weron, Karina; Masajada, Jan

2013-12-01

202

Laser-tweezer-controlled solid immersion microscopy in microfluidic systems.  

PubMed

We describe the creation and implementation of a near-field scanning solid immersion microscope that is specifically tailored for use in microfluidic systems. The microscope comprises a newly fabricated Weierstrass solid immersion lens (SIL), which is detached from its substrate and is free floating in the fluid, and a laser optical tweezer, which serves both as a trapping beam for alignment and positioning of the SIL and as a near-field scanning beam that images the sample through the SIL. A discussion of the SIL's fabrication method is presented along with experimental results that demonstrate the effectiveness of our microscope design. PMID:16252750

Birkbeck, Aaron L; Zlatanovic, Sanja; Esener, Sadik C; Ozkan, Mihrimah

2005-10-15

203

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

PubMed

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

2013-09-15

204

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

2013-08-01

205

All-optical constant-force laser tweezers.  

PubMed

Optical tweezers are a powerful tool for the study of single biomolecules. Many applications require that a molecule be held under constant tension while its extension is measured. We present two schemes based on scanning-line optical tweezers to accomplish this, providing all-optical alternatives to force-clamp traps that rely on electronic feedback to maintain constant-force conditions for the molecule. In these schemes, a laser beam is rapidly scanned along a line in the focal plane of the microscope objective, effectively creating an extended one-dimensional optical potential over distances of up to 8 microm. A position-independent lateral force acting on a trapped particle is created by either modulating the laser beam intensity during the scan or by using an asymmetric beam profile in the back focal plane of the microscope objective. With these techniques, forces of up to 2.69 pN have been applied over distances of up to 3.4 microm with residual spring constants of <26.6 fN/microm. We used these techniques in conjunction with a fast position measurement scheme to study the relaxation of lambda-DNA molecules against a constant external force with submillisecond time resolution. We compare the results to predictions from the wormlike chain model. PMID:15345573

Nambiar, Rajalakshmi; Gajraj, Arivalagan; Meiners, Jens-Christian

2004-09-01

206

Process limitations in microassembling using holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Microassembling with holographic optical tweezers (HOT) is a flexible manufacturing technology for the precise fabrication of complex microstructures. In contrast to classical direct writing techniques, here, microparticles are transported within a fluid to appropriate positions, where they are finally bound. Therefore, optical forces act against the inner friction of the fluid. This effect limits the microassembling process in the meaning of process speed. In this work we investigate these limitations depending on the applied laser power and particle size. Additionally, different to conventional optical tweezers, HOTs use spatial light modulators (SLM) to control the laser beam and the object's position. This is performed at discrete step sizes caused by successively imaging respective kinoforms on the SLM at specific refresh rates. An optimization of the step size and the applied update rate are crucial to reach maximum velocities in particle movement. Therefore, the performance of dynamic particle manipulation is investigated in individual experiments. Stable manipulation velocities of up to 114 ?m/s have been reported in our work using 6 ?m polystyrene particles and an applied laser power of 445 mW.

Ghadiri, R.; Guo, Q.; Yeoh, I.; Esen, C.; Ostendorf, A.

2012-02-01

207

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

2009-06-01

208

Radiation forces exerted on arbitrarily located sphere by acoustic tweezer.  

PubMed

In a previous paper acoustic radiation force on a lipid sphere in a 100-MHz focused Gaussian field was calculated to demonstrate the acoustic tweezer effect near the focus. The theoretical formulation was based on the situation where the sphere is centered along the beam axis. Given intensity distribution independent of the x axis, it was then approximated by a cylindrical model for the sake of simplicity. Only the axial forces were considered because no lateral forces exist due to an object's symmetry. However, it was difficult to employ the same technique to the more general case when it is off the beam axis. To overcome the limitation, in this paper the previous model is modified to compute two additional lateral forces by carrying out the projection over arbitrary incident planes to restrict the integration limits. For different sizes of the sphere, the magnitudes of the net forces in three orthogonal directions are computed. The results show that the acoustic tweezer can be realized more easily in the lateral directions than in the axial directions. Differing from the axisymmetric case, the spheres of small sizes tend to be more strongly attracted than the larger ones in the lateral directions. PMID:16938994

Lee, Jungwoo; Shung, K Kirk

2006-08-01

209

Use of optical tweezers to probe epithelial mechanosensation  

NASA Astrophysics Data System (ADS)

Cellular mechanosensation mechanisms have been implicated in a variety of disease states. Specifically in renal tubules, the primary cilium and associated mechanosensitive ion channels are hypothesized to play a role in water and salt homeostasis, with relevant disease states including polycystic kidney disease and hypertension. Previous experiments investigating ciliary-mediated cellular mechanosensation have used either fluid flow chambers or micropipetting to elicit a biological response. The interpretation of these experiments in terms of the ``ciliary hypothesis'' has been difficult due the spatially distributed nature of the mechanical disturbance-several competing hypotheses regarding possible roles of primary cilium, glycocalyx, microvilli, cell junctions, and actin cytoskeleton exist. I report initial data using optical tweezers to manipulate individual primary cilia in an attempt to elicit a mechanotransduction response-specifically, the release of intracellular calcium. The advantage of using laser tweezers over previous work is that the applied disturbance is highly localized. I find that stimulation of a primary cilium elicits a response, while stimulation of the apical surface membrane does not. These results lend support to the hypothesis that the primary cilium mediates transduction of mechanical strain into a biochemical response in renal epithelia.

Resnick, Andrew

2010-01-01

210

Molecular basis for preventing ?-synuclein aggregation by a molecular tweezer.  

PubMed

Recent work on ?-synuclein has shown that aggregation is controlled kinetically by the rate of reconfiguration of the unstructured chain, such that the faster the reconfiguration, the slower the aggregation. In this work we investigate this relationship by examining ?-synuclein in the presence of a small molecular tweezer, CLR01, which binds selectively to Lys side chains. We find strong binding to multiple Lys within the chain as measured by fluorescence and mass-spectrometry and a linear increase in the reconfiguration rate with concentration of the inhibitor. Top-down mass-spectrometric analysis shows that the main binding of CLR01 to ?-synuclein occurs at the N-terminal Lys-10/Lys-12. Photo-induced cross-linking of unmodified proteins (PICUP) analysis shows that under the conditions used for the fluorescence analysis, ?-synuclein is predominantly monomeric. The results can be successfully modeled using a kinetic scheme in which two aggregation-prone monomers can form an encounter complex that leads to further oligomerization but can also dissociate back to monomers if the reconfiguration rate is sufficiently high. Taken together, the data provide important insights into the preferred binding site of CLR01 on ?-synuclein and the mechanism by which the molecular tweezer prevents self-assembly into neurotoxic aggregates by ?-synuclein and presumably other amyloidogenic proteins. PMID:24567327

Acharya, Srabasti; Safaie, Brian M; Wongkongkathep, Piriya; Ivanova, Magdalena I; Attar, Aida; Klärner, Frank-Gerrit; Schrader, Thomas; Loo, Joseph A; Bitan, Gal; Lapidus, Lisa J

2014-04-11

211

A simple method for evaluating the trapping performance of acoustic tweezers  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to present a rapid and simple method to evaluate the trapping performance of high frequency focused ultrasonic transducers for acoustic tweezer applications. The method takes into consideration the friction between the particle to be trapped and the surface that it resides on. As a result it should be more reliable and accurate than the methods proposed previously. The trapping force produced by a 70-MHz press-focused transducer was measured to evaluate the performance of this approach. This method demonstrates its potential in optimizing the excitation conditions for acoustic tweezer applications and the design of acoustic tweezers.

Li, Ying; Lee, Changyang; Ho Lam, Kwok; Kirk Shung, K.

2013-02-01

212

A simple method for evaluating the trapping performance of acoustic tweezers.  

PubMed

The purpose of this paper is to present a rapid and simple method to evaluate the trapping performance of high frequency focused ultrasonic transducers for acoustic tweezer applications. The method takes into consideration the friction between the particle to be trapped and the surface that it resides on. As a result it should be more reliable and accurate than the methods proposed previously. The trapping force produced by a 70-MHz press-focused transducer was measured to evaluate the performance of this approach. This method demonstrates its potential in optimizing the excitation conditions for acoustic tweezer applications and the design of acoustic tweezers. PMID:23526834

Li, Ying; Lee, Changyang; Ho Lam, Kwok; Kirk Shung, K

2013-02-25

213

A simple method for evaluating the trapping performance of acoustic tweezers  

PubMed Central

The purpose of this paper is to present a rapid and simple method to evaluate the trapping performance of high frequency focused ultrasonic transducers for acoustic tweezer applications. The method takes into consideration the friction between the particle to be trapped and the surface that it resides on. As a result it should be more reliable and accurate than the methods proposed previously. The trapping force produced by a 70-MHz press-focused transducer was measured to evaluate the performance of this approach. This method demonstrates its potential in optimizing the excitation conditions for acoustic tweezer applications and the design of acoustic tweezers.

Li, Ying; Lee, Changyang; Ho Lam, Kwok; Kirk Shung, K.

2013-01-01

214

Design and construction of a space-borne optical tweezer apparatus  

NASA Astrophysics Data System (ADS)

A compact optical tweezer package has been developed for use on a microscope to be flown on the International Space Station as part of a series of experiments in colloid crystallization. A brief introduction to the principles of single-beam optical tweezer operation will be presented, after which a detailed system layout will be shown. Special design requirements due to the spaceflight nature of the hardware will also be discussed. The tweezer apparatus is capable of trapping many particles through use of a two-axis acousto-optical deflector. The trap strength is sufficient to perform the required science (50 pN at ?n=0.2). The trap beam behaves approximately as a diffraction limited single mode Gaussian beam of numerical aperture, NA=1.4, as shown through spot size measurements and confocal-type images of the focal region. This is the first time optical tweezers will be deployed in a microgravity environment.

Resnick, Andrew

2001-11-01

215

Cooling a Single Atom in an Optical Tweezer to Its Quantum Ground State  

NASA Astrophysics Data System (ADS)

We report cooling of a single neutral atom to its three-dimensional vibrational ground state in an optical tweezer. After employing Raman sideband cooling for tens of milliseconds, we measure via sideband spectroscopy a three-dimensional ground-state occupation of about 90%. We further observe coherent control of the spin and motional state of the trapped atom. Our demonstration shows that an optical tweezer, formed simply by a tightly focused beam of light, creates sufficient confinement for efficient sideband cooling. This source of ground-state neutral atoms will be instrumental in numerous quantum simulation and logic applications that require a versatile platform for storing and manipulating ultracold single neutral atoms. For example, these results will improve current optical-tweezer experiments studying atom-photon coupling and Rydberg quantum logic gates, and could provide new opportunities such as rapid production of single dipolar molecules or quantum simulation in tweezer arrays.

Kaufman, A. M.; Lester, B. J.; Regal, C. A.

2012-10-01

216

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

SciTech Connect

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; Kisun Li

2012-06-30

217

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

Microsoft Academic Search

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.

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

2007-01-01

218

Investigation of inclined dual-fiber optical tweezers for 3D manipulation and force sensing.  

PubMed

Optical tweezers provide a versatile tool in biological and physical researches. Optical tweezers based on optical fibers are more flexible and ready to be integrated when compared with those based on microscope objectives. In this paper, the three-dimensional (3D) trapping ability of an inclined dual-fiber optical tweezers is demonstrated. The trapping efficiency with respect to displacement is experimentally calibrated along two dimensions. The system is studied numerically using a modified ray-optics model. The spring constants obtained in the experiment are predicted by simulations. It is found both experimentally and numerically that there is a critical value for the fiber inclination angle to retain the 3D trapping ability. The inclined dual-fiber optical tweezers are demonstrated to be more robust to z-axis misalignment than the counter-propagating fiber optical tweezers, which is a special case of th former when the fiber inclination angle is 90 masculine. This inclined dual-fiber optical tweezers can serve as both a manipulator and a force sensor in integrated systems, such as microfluidic systems and lab-on-a-chip systems. PMID:19654770

Liu, Yuxiang; Yu, Miao

2009-08-01

219

Optimization of holographic optical tweezers for multiplexed fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

We are developing a multiplexed spectroscopy technique that employs holographic optical tweezers to trap and excite multiple sensor particles. Our goal is to develop a lab-on-a-chip measurement platform for monitoring pH and other ion concentrations with high spatial resolution in a microfluidic device or within biological cells. To ensure efficient use of the available laser power required to trap multiple particles, we address three aspects of the spatial light modulator (SLM) used in the holographic technique. We measure and optimize the input and output polarizations used before and after the birefringent SLM. We reduce optical aberrations by adding appropriate Zernike polynomials to the computed hologram. We optimize the diffraction efficiency of the SLM by adjusting the gray scale input-to-output table to account for the nonlinear phase response of the SLM.

Cibula, Matthew; McIntyre, David

2012-10-01

220

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.

2010-02-01

221

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.

2010-04-01

222

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.

2008-01-01

223

Spatial measurement of spurious forces with optical tweezers  

NASA Astrophysics Data System (ADS)

The study of diffusion in a crowded and complex environment, such as inside a cell or within a porous medium, is of fundamental importance for science and technology. Combining blinking holographic optical tweezers and sub-pixel video microscopy permits one to study Brownian motion in confined geometries. In this work, in particular, we have studied the Brownian motion of two colloidal particles interacting hydrodynamically with each other. The proximity between the two microspheres induces a space-dependence in the particles diffusion coefficient and, therefore, a spurious drift. We measure this drift and evaluate the magnitude of the spurious force associated with it. We present the optoelectronic tools employed in the experiment and we discuss the experimental results.

Bordeu, Ignacio; Volpe, Giovanni; Staforelli, Juan Pablo

2013-11-01

224

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

1996-01-01

225

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

2008-03-01

226

Microrheology Using Optical Tweezers at the Air-Water Interface  

NASA Astrophysics Data System (ADS)

Microrheological techniques have been used successfully to determine mechanical properties of materials important in cellular structure. Also critical to cellular mechanical functions are biological membranes. Many aspects of biological membranes can be modeled using Langmuir monolayers, which are single layers surfactants at the air-water interface. The macroscopic mechanical properties of Langmuir monolayers have been extensively characterized. In contrast to macroscopic measurements, we report on experimental methods for studying the rheological properties of Langmuir monolayers on the micron scale. A water immersion optical tweezers system is used to trap ˜1 micron diameter beads in a monolayer. The passive motion of the trapped beads is recorded at high frequency and the complex shear modulus is calculated. Preliminary microrheological data of a fatty acid monolayer showing dependence on surface pressure will be presented. Experimental obstacles will also be discussed.

Boatwright, Thomas; Levine, Alex; Dennin, Michael

2010-11-01

227

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)

2009-08-15

228

Moving average process underlying the holographic-optical-tweezers experiments.  

PubMed

We study the statistical properties of recordings that contain time-dependent positions of a bead trapped in optical tweezers. Analysis of such a time series indicates that the commonly accepted model, i.e., the autoregressive process of first-order, is not sufficient to fit the data. We show the presence of a first-order moving average part in the dynamical model of the system. We explain the origin of this part as an influence of the high-frequency CCD camera on the measurements. We show that this influence evidently depends on the applied exposure time. The proposed autoregressive moving average model appears to reflect perfectly all statistical features of the high-frequency recording data. PMID:24787213

?l?zak, Jakub; Drobczy?ski, S?awomir; Weron, Karina; Masajada, Jan

2014-04-01

229

Optical tweezers formed by pure phase pupil filter  

NASA Astrophysics Data System (ADS)

The focusing properties of vector beams have attracted great attention and quickly became the subject of extensive worldwide research due to their applications in lithography, optical storage, microscopy, material processing, and optical trapping. Focusing properties of the radially polarized beam and generalized cylindrical vector beams in high numerical aperture system with designed pure phase filter are analyzed in detail by using vector Debye diffraction theory. By utilizing diffractive optical element to partly change the polarization of vector beams, the energy density of light field in the vicinity of focus is studied by the numerical analysis. Numerical simulation result shows that optical bubbles can be obtained by changing the composition and polarization of the incident beams. At last, optical tweezers are constituted by two optical bubbles around the focus.

Lv, Wei; You, Chenglong; Wang, Mei; Yun, Maojin

2013-09-01

230

A tunable line optical tweezers instrument with nanometer spatial resolution.  

PubMed

We describe a simple scanning-line optical tweezers instrument for measuring pair interactions between micrometer-sized colloidal particles. Our instrument combines a resonant scanning mirror and an acousto-optic modulator. The resonant scanning mirror creates a time-averaged line trap whose effective one-dimensional intensity profile, and corresponding trapping potential energy landscape can be programmed using the acousto-optic modulator. We demonstrate control over the confining potential by designing and measuring a family of one-dimensional harmonic traps. By adjusting the spring constant, we balance scattering-induced repulsive forces between a pair of trapped particles, creating a flat potential near contact that facilitates interaction measurements. We also develop a simple method for extracting the out-of-plane motion of trapped particles from their relative brightness, allowing us to resolve their relative separation to roughly 1 nm. PMID:24784615

Rogers, W Benjamin; Crocker, John C

2014-04-01

231

Probing multiscale mechanics of collagen with optical tweezers  

NASA Astrophysics Data System (ADS)

How the molecular structure of the structural, extracellular matrix protein collagen correlates with its mechanical properties at different hierarchical structural levels is not known. We demonstrate the utility of optical tweezers to probe collagen's mechanical response throughout its assembly hierarchy, from single molecule force-extension measurements through microrheology measurements on solutions of collagen molecules, collagen fibrillar gels and gelatin. These experiments enable the determination of collagen's flexibility, mechanics, and timescales and strengths of interaction at different levels of hierarchy, information critical to developing models of how collagen's physiological function and stability are influenced by its chemical composition. By investigating how the viscoelastic properties of collagen are affected by the presence of telopeptides, protein domains that strongly influence fibril formation, we demonstrate that these play a role in conferring transient elasticity to collagen solutions.

Shayegan, Marjan; Rezaei, Naghmeh; Lam, Norman H.; Altindal, Tuba; Wieczorek, Andrew; Forde, Nancy R.

2013-09-01

232

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

1998-01-01

233

Aromatic interactions by molecular tweezers and clips in chemical and biological systems.  

PubMed

Noncovalent interactions involving aromatic rings, such as ?-stacking and CH-?, occur throughout a range of fundamental processes including self-assembly and (bio)catalysis. Molecular clips and tweezers possess a central parallel or torus-shaped cavity with a surrounding belt of convergent aromatic rings; hence these structures exploit multiple aromatic interactions in a positively cooperative manner. Both clips and tweezers demonstrate selective binding of cationic or neutral guests that bear acceptor groups. The electrostatic surface potentials (ESP) explain this unexpected behavior: calculated ESPs were highly negative inside the tweezer or clip cavity, providing complementary profiles to the positive ESP plots of their preferred guest molecules. This Account presents more complex systems that use aromatic clips and tweezers to alter the reactivities of included guest species, to distinguish between guest enantiomers, and to interfere with biological processes such as enzymatic activity and protein aggregation. Napthalene tweezers show potential applications in organocatalysis. When pyridinium moieties are bound within the spacious cavity of naphthyl-spaced tweezers, the resulting complex significantly influences the first step of single-electron reductions of (bi)pyridinium salts. In addition, the environment within the tweezer cavity strongly accelerates the Menshutkin reaction (the alkylation of pyridine derivatives). Introduction of phosphonate, phosphate, or sulfate anions into the central aromatic bridge renders clips and tweezers water-soluble. Larger systems form extremely tight intertwined dimers that rely on the nonclassical hydrophobic effect for their stability. Smaller clips and tweezers with a simple benzene bridge remain monomeric in buffered aqueous solution and display a complementary binding profile. While the clips with parallel sidewalls prefer flat aromatic cations such as pyridinium salts, the torus-shaped tweezers bind to basic amino acids lysine and arginine via a threading process. These mutually exclusive binding modes make water-soluble clips and tweezers valuable tools for probing critical biological interactions with positively charged amino acid side chains and cofactors. Molecular clips and tweezers can be employed for the complete inhibition of dehydrogenases. The clip extracts NAD(+) from its Rossman fold, while the tweezer complexes access strategic lysine residues around the active site. Our new enzyme inhibitors recognize the protein surface and thus offer additional targets for medicinal chemistry. Finally, the ability of molecular tweezers to cap critical lysine residues can be used to interfere with the pathology of protein misfolding diseases such as Alzheimer's disease, because many of them involve noncovalent interactions with these critical residues during their early stages. When the key protein produces a ?-sheet-rich nucleus, this structure undergoes spontaneous polymerization into highly toxic oligomers, ultimately leading to mature fibrils. The benzene-spaced phosphate tweezer forms a specific complex with lysine residues 16 and 28 in A?42 and thus prevents the formation of misfolded oligomers rich in ?-sheets. This entirely new process-specific mechanism that prevents pathologic protein aggregation also operates in many other related amyloidogenic proteins. PMID:22725723

Klärner, Frank-Gerrit; Schrader, Thomas

2013-04-16

234

Pyrene-Appended Fluorescent Tweezers Generated via the Weak-Link Approach and Their Halide Recognition Properties  

PubMed Central

Through the Weak-Link Approach, fluorescent condensed and open Cu(I) tweezer complexes were prepared and characterized. These complexes exhibit fluorescence-sensitive binding properties for halide anions. The solid-state structure of a non-fluorescent Rh(I) tweezer analogue, determined by X-ray crystallography, shows that the counter anion, Cl?, is trapped in between the two amide groups of the tweezer arms through hydrogen bonds. Although the tweezer binds Cl?, the open complex also binds Cl?, showing that the main role of the metal is to increase the local concentration of the pyrenyl amide moieties so that 2:1 binding can take place.

Jeon, You-Moon; Kim, Dongwoo; Mirkin, Chad A.; Golen, James A.; Rheingold, Arnold L.

2011-01-01

235

Computer-automated program for calibration of optical tweezers  

NASA Astrophysics Data System (ADS)

An optical tweezers (OT) system uses focused laser light to contain and manipulate nano-scale to micro-scale particles. Trap stiffness is the quantitative measurement of the ability to trap a particle. For some techniques, this measurement depends on an accurate knowledge of the particle's position in time. A position sensing detector (PSD) is used to track particle motion by detecting laser light from the trapping region. The PSD outputs voltages corresponding to the x- and y-coordinates of particle motion, providing a means of knowing the location of the particle in time. An OT system requires a calibration to convert the measured voltages into accurate distances. This process is time-consuming and frequently needs to be repeated, however, with the growing availability of computer-aided data acquisition and control, the complete process can now be automated, reducing time spent by researchers and increasing level of accuracy of future measurements. We have developed a program written in LabVIEW that will, after initialization, 1) via image processing, calibrate the pixel size of the camera, 2) calibrate the optical tweezer position detector by controlling a motorized mirror to move a trapped bead through a detection laser with simultaneous position detector signal measurements, 3) re-align the trap beam and the detection beam by motorized mirror control, 4) measure position data for the same trapped particle being illuminated by the detection beam, and 5) analyze the position signal via the power spectrum method and equipartition method to give two trap stiffness values for comparison. Previous automated calibration methods require additional and sometimes costly equipment as well as some precalibration of stage motion or pixel size. Here, the user only needs to input the known size of the bead (provided by the manufacturer) into the program, insert their prepared slide into their microscope, input some parameters and make selections, and click "start" in order to achieve experimental values of the camera and position detector calibrations, as well as trap stiffness. We intend to implement many other calibration techniques that require additional equipment, but have designed this initial system for use in a standard position-detection-capable OT setup as long as it has a digital camera and motorized mirror that can be controlled with LabVIEW.

Taylor, C. D.; Foley, T. W.; Chang, A. N.; Mowa, S.; Burris, J. L.; Hester, B. C.

2012-10-01

236

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

237

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

2011-03-01

238

P2I-2 Design of Steep Intensity Distribution for Acoustic Tweezer Using Multiple High Frequency Focused Transducers  

Microsoft Academic Search

Sharp intensity change around a focal point is one of the most essential elements for acoustic tweezers. This paper presents a method to create such intensity distribution by using multiple high frequency focused transducers. In addition to a 50 MHz tweezer transducer, 20 MHz holder transducers are needed for initial positioning of lipid particles into a water chamber. The results

Jungwoo Lee; K. Kirk Shung

2007-01-01

239

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)

2008-08-01

240

Grasping microscopic objects by multiple tools actuated by optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers is a promising manipulation tool for objects in the range of micrometers to nanometers. Although there are many reported works on manipulating objects made of different materials and objects of irregular shapes, it is more suitable for non-opaque materials and objects that are symmetrical. Furthermore, there are potential damages on the objects arising from immense heat that is produced by the laser beam. These problems can be alleviated by trapping objects (micro-handles) and using them collectively as a gripper to indirectly hold and manipulate a target object. Holding denotes equilibrium of forces exerted by the tools on a target object. However, there still is a problem with this approach. When the trapping volume is larger than the size of a tool, target objects get pulled towards the center of the trapping volume. This breaks the force equilibrium and gripping thus fails. In this paper, we report a new design of tools that can overcome this problem. The tool is a slender object with one end acting as a probe while the other end is spherical so that trapping is easy. The length of the tool is designed to be larger than the radius of the trapping volume. Thus the target object is never pulled towards the trapping center. A group of multiple identical tools will surround and push a target object at the probe tips resulting in a stable grasp.

Sung, Seung-Yong; Park, In-Yong; Lee, Jong-Hyun; Lee, Yong-Gu

2006-09-01

241

Membrane tether formation from outer hair cells with optical tweezers.  

PubMed Central

Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-microm 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 in the force required to pull tethers is consistent with an extensive cytoskeletal framework associated with the lateral wall known as the cortical lattice. The apparent plasma membrane stiffness, estimated under the static conditions by measuring tether force at different tether length, was 3.71 pN/microm for OHC lateral wall and 4.57 pN/microm for OHC basal end. The effective membrane viscosity was measured by pulling tethers at different rates while continuously recording the tether force, and estimated in the range of 2.39 to 5.25 pN x s/microm. The viscous force most likely results from the viscous interactions between plasma membrane lipids and the OHC cortical lattice and/or integral membrane proteins. The information these studies provide on the mechanical properties of the OHC lateral wall is important for understanding the mechanism of OHC electromotility.

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

2002-01-01

242

Application of laser tweezers to passive microrheology of collagen solutions  

NASA Astrophysics Data System (ADS)

Rheology is the field that can describe both viscous and elastic properties of a material in response to applied force or deformation. Passive microrheology (PMR) is a technique in which motion of a particle arising from thermal fluctuations is measured on nanometer length scales. One experimental approach to PMR uses optical tweezers, which trap and probe ?m-sized particles, located within the material, at a high bandwidth. In this study, viscoelastic properties of solutions of collagen are characterized. To do this, we have probed the power spectral density of fluctuations of 1-?m-diameter microspheres optically trapped in acidic solutions of varying concentration of collagen type I (0, 0.5, and 1 mg/ml). The results show evidence that the behaviour of the solutions becomes increasingly non-Newtonian at high protein concentration. We attribute this to the presence of the viscoelastic polymer. This introduces frequency dependence to the complex modulus of the solution which is used to characterize the elasticity and viscosity of these systems.

Shayegan, Marjan; Forde, Nancy R.

2009-05-01

243

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.

2010-01-01

244

Parallel lipoplex folding pathways revealed using magnetic tweezers  

PubMed Central

Lipid-coated DNA nanoparticles (lipoplexes) are a powerful gene delivery tool with promising therapeutic applications. The mechanism of lipoplex assembly remains poorly understood. We explored DNA packing by a cationic lipid DSTAP (distearoyl trimethylammonium-propane) using magnetic tweezers. DSTAP-induced DNA condensation occurred as a series of bursts with the mean step size of 60 nm to 80 nm. The pause time preceding the steps could be approximated as a bimodal distribution, which reveals at least two distinct condensation pathways. The rapidly condensed DNA was more resilient to force-induced decondensation. The proportion of the stable, fast-formed complexes decreased at high salt concentrations. A similar trend was observed in bulk experiments. Lipoplexes assembled at low salt concentration more efficiently shielded DNA from fluorescent dyes and DNase even after transfer to the high salt conditions. These data reveal that lipoplex folding occurs via two parallel pathways even at the single molecule level. The progress through the two pathways can be monitored in real time using single DNA manipulations. The relative efficiency of the two pathways can be varied by external conditions.

Sun, Zhiqiang; Tikhonova, Elena B.; Zgurskaya, Helen I.; Rybenkov, Valentin V.

2012-01-01

245

Triaxial Atomic Force Microscope Contact-Free Tweezers for Nanoassembly  

PubMed Central

We propose a Traixial Atomic Force Microscope (AFM) Contact-free Tweezer (TACT) for the controlled assembly of nanoparticles suspended in a liquid. The TACT overcomes four major challenges faced in nanoassembly: (1) The TACT can hold and position a single nanoparticle with spatial accuracy smaller than the nanoparticle size (~ 5 nm). (2) The nanoparticle is held away from the surface of the TACT by negative dielectrophoresis (nDEP) to prevent van der Waals forces from sticking it to the TACT. (3) The TACT holds nanoparticles in a trap that is size-matched to the particle and surrounded by a repulsive region so that it will only trap a single particle at a time. (4) The trap can hold a semiconductor nanoparticle in water with a trapping energy greater than thermal energy. For example, a 5 nm radius silicon nanoparticle is held with 10 kBT at room temperature. We propose methods for using the TACT as a nanoscale pick-and-place tool to assemble semiconductor quantum dots, biological molecules, semiconductor nanowires, and carbon nanotubes.

Brown, Keith A; Westervelt, Robert M

2010-01-01

246

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.

2012-10-01

247

Temperature-Dependent Conformations of a Membrane Supported 'Zinc Porphyrin Tweezer' by 2D Fluorescence Spectroscopy  

PubMed Central

We studied the equilibrium conformations of a ‘zinc porphyrin tweezer’ composed of two carboxylphenyl-functionalized zinc tetraphenyl porphyrin subunits connected by a 1,4 butyndiol spacer, which was suspended inside the amphiphilic regions of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) liposomes. By combining phase-modulation two-dimensional fluorescence spectroscopy (2D FS) with linear absorbance and fluorimetry, we determined that the zinc porphyrin tweezer adopts a mixture of ‘folded’ and ‘extended’ conformations in the membrane. By fitting an exciton-coupling model to a series of data sets recorded over a range of temperatures (17 – 85 °C) and at different laser center wavelengths, we determined that the folded form of the tweezer is stabilized by a favorable change in the entropy of the local membrane environment. Our results provide insights toward understanding the balance of thermodynamic factors that govern molecular assembly in membranes.

Widom, Julia R.; Lee, Wonbae; Perdomo-Ortiz, Alejandro; Rappoport, Dmitrij; Molinski, Tadeusz F.; Aspuru-Guzik, Alan; Marcus, Andrew H.

2013-01-01

248

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.

2013-08-01

249

Resolving stable axial trapping points of nanowires in an optical tweezers using photoluminescence mapping.  

PubMed

Axially resolved microphotoluminescence mapping of semiconductor nanowires held in an optical tweezers reveals important new experimental information regarding equilibrium trapping points and trapping stability of high aspect ratio nanostructures. In this study, holographic optical tweezers are used to scan trapped InP nanowires along the beam direction with respect to a fixed excitation source and the luminescent properties are recorded. It is observed that nanowires with lengths on the range of 3-15 ?m are stably trapped near the tip of the wire with the long segment positioned below the focus in an inverted trapping configuration. Through the use of trap multiplexing we investigate the possibility of improving the axial stability of the trapped nanowires. Our results have important implication for applications of optically assisted nanowire assembly and optical tweezers based scanning probes microscopy. PMID:23394286

Wang, Fan; Toe, Wen Jun; Lee, Woei Ming; McGloin, David; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati; Reece, Peter J

2013-03-13

250

A high-speed magnetic tweezer beyond 10,000 frames per second.  

PubMed

The magnetic tweezer is a single-molecule instrument that can apply a constant force to a biomolecule over a range of extensions, and is therefore an ideal tool to study biomolecules and their interactions. However, the video-based tracking inherent to most magnetic single-molecule instruments has traditionally limited the instrumental resolution to a few nanometers, above the length scale of single DNA base-pairs. Here we have introduced superluminescent diode illumination and high-speed camera detection to the magnetic tweezer, with graphics processing unit-accelerated particle tracking for high-speed analysis of video files. We have demonstrated the ability of the high-speed magnetic tweezer to resolve particle position to within 1 A? at 100 Hz, and to measure the extension of a 1566 bp DNA with 1 nm precision at 100 Hz in the presence of thermal noise. PMID:23635212

Lansdorp, Bob M; Tabrizi, Shawn J; Dittmore, Andrew; Saleh, Omar A

2013-04-01

251

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

2006-09-01

252

Single and dual fiber nano-tip optical tweezers: trapping and analysis  

NASA Astrophysics Data System (ADS)

An original optical tweezers using one or two chemically etched fiber nano-tips is developed. We demonstrate optical trapping of 1 micrometer polystyrene spheres at optical powers down to 2 mW. Harmonic trap potentials were found in the case of dual fiber tweezers by analyzing the trapped particle position fluctuations. The trap stiffness was deduced using three different models. Consistent values of up to 1 fN/nm were found. The stiffness linearly decreases with decreasing light intensity and increasing fiber tip-to-tip distance.

Decombe, Jean-Baptiste; Huant, Serge; Fick, Jochen

2013-12-01

253

Single and dual fiber nano-tip optical tweezers: trapping and analysis.  

PubMed

An original optical tweezers using one or two chemically etched fiber nano-tips is developed. We demonstrate optical trapping of 1 micrometer polystyrene spheres at optical powers down to 2 mW. Harmonic trap potentials were found in the case of dual fiber tweezers by analyzing the trapped particle position fluctuations. The trap stiffness was deduced using three different models. Consistent values of up to 1 fN/nm were found. The stiffness linearly decreases with decreasing light intensity and increasing fiber tip-to-tip distance. PMID:24514629

Decombe, Jean-Baptiste; Huant, Serge; Fick, Jochen

2013-12-16

254

Two-particle quantum interference in tunnel-coupled optical tweezers.  

PubMed

The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles. Here, we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled (87)Rb atoms trapped in two optical tweezers. This controllability allows us to observe signatures of indistinguishability via two-particle interference. Our work establishes laser-cooled atoms in optical tweezers as a promising route to bottom-up engineering of scalable, low-entropy quantum systems. PMID:24968938

Kaufman, A M; Lester, B J; Reynolds, C M; Wall, M L; Foss-Feig, M; Hazzard, K R A; Rey, A M; Regal, C A

2014-07-18

255

Advanced optical tweezers for the study of cellular and molecular biomechanics.  

PubMed

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, fluorescence microscopy, etc.). Acousto-optic deflectors (AODs) steer each beam and can create multiple time-shared traps. Position detection, force calibrations and AOD performance are presented. The system can detect subnanometer displacements and forces below 0.1 pN. PMID:12617534

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

2003-01-01

256

Dynamic properties of bacterial pili measured by optical tweezers  

NASA Astrophysics Data System (ADS)

The ability of uropathogenic Escherichia coli (UPEC) to cause urinary tract infections is dependent on their ability to colonize the uroepithelium. Infecting bacteria ascend the urethra to the bladder and then kidneys by attaching to the uroepithelial cells via the differential expression of adhesins. P pili are associated with pyelonephritis, the more severe infection of the kidneys. In order to find means to treat pyelonephritis, it is therefore of interest to investigate the properties P pili. The mechanical behavior of individual P pili of uropathogenic Escherichia coli has recently been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of ~1000 PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. We have earlier studied P pili regarding its stretching/elongation properties where we have found and characterized three different elongation regions, of which one constitute an unfolding of the quaternary (helical) structure of the PapA rod. It was shown that this unfolding takes place at an elongation independent force of 27 +/- 2 pN. We have also recently performed studies on its folding properties and shown that the unfolding/folding of the PapA rod is completely reversible. Here we present a study of the dynamical properties of the PapA rod. We show, among other things, that the unfolding force increases and that the folding force decreases with the speed of unfolding and folding respectively. Moreover, the PapA rod can be folded-unfolded a significant number of times without loosing its characteristics, a phenomenon that is believed to be important for the bacterium to keep close contact to the host tissue and consequently helps the bacterium to colonize the host tissue.

Fallman, Erik G.; Andersson, Magnus J.; Schedin, Staffan S.; Jass, Jana; Uhlin, Bernt Eric; Axner, Ove

2004-10-01

257

The use of optical tweezers to study sperm competition and motility in primates  

Microsoft Academic Search

Optical trapping is a non-invasive biophysical tool which has been widely applied to study physiological and biomechanical properties of cells. Using laser 'tweezers' in combination with custom-designed computer tracking algorithms, the swimming speeds and the relative swimming forces of individual sperm can be measured in real time. This combination of physical and engineering tools has been used to examine the

Jaclyn M. Nascimento; Linda Z. Shi; Stuart Meyers; Pascal Gagneux; Naida M. Loskutoff; Elliot L. Botvinick; Michael W. Berns

2008-01-01

258

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

Microsoft Academic Search

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

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

2011-01-01

259

Construction and actuation of a microscopic gear assembly formed using optical tweezers  

NASA Astrophysics Data System (ADS)

The assembly of micrometer-sized parts is an important manufacturing process; any development in it could potentially change the current manufacturing practices for micrometer-scale devices. Due to the lack of reliable microassembly techniques, these devices are often manufactured using silicon, which includes etching and depositions with little use of assembly processes. The result is the requirement of specialized manufacturing conditions with hazardous byproducts and limited applications where only simple mechanisms are allowed. Optical tweezers are non-contact type manipulators that are very suitable for assembling microparts and solve one of the most difficult problems for microassembly, which is the sticking of the physical manipulator to the micropart. Although contact type manipulators can be surface modified to be non-sticky, this involves extra preprocessing—optical tweezers do not require such additional efforts. The weakness of using optical tweezers is that the permanent assembly of parts is not possible as only very small forces can be applied. We introduce an advanced microassembly environment with the combined use of optical tweezers and a motorized microtip, where the former is used to position two parts and the latter is used to introduce deformation in the parts so that they form a strongly fitted assembly.

Kim, Jung-Dae; Lee, Yong-Gu

2013-06-01

260

Noncontact microsurgery and micromanipulation of living cells with combined system femtosecond laser scalpel-optical tweezers  

NASA Astrophysics Data System (ADS)

We report on the results of using self-developed combined laser system consisting of a femtosecond laser scalpel (Cr:Forsterite seed oscillator and a regenerative amplifier, 620 nm, 100 fs, 10 Hz) and optical tweezers (cw laser, 1064 nm) for performing noncontact laser-mediated polar body (PB) and trophectoderm (TE) biopsy of early mammalian embryos. To perform PB biopsy the femtosecond laser scalpel was initially used to drill an opening in the zona pellucida, and then the PB was extracted out of the zygote with the optical tweezers. Unlike PB biopsy, TE biopsy allows diagnosing maternally-derived as well as paternally-derived defects. Moreover, as multiple TE cells can be taken from the embryo, more reliable diagnosis can be done. TE biopsy was performed by applying laser pulses to dissect the desired amount of TE cells that had just left the zona pellucida during the hatching. Optical tweezers were then used to trap and move the dissected TE cells in a prescribed way. Laser power in optical tweezers and energy of femtosecond laser pulses were thoroughly optimized to prevent cell damage and obtain high viability rates. In conclusion, the proposed techniques of laser-based embryo biopsy enable accurate, contamination-free, simple and quick microprocessing of living cells.

Il'ina, Inna V.; Sitnikov, Dmitry S.; Ovchinnikov, Andrey V.; Agranat, Mikhail B.; Khramova, Yulia V.; Semenova, Maria L.

2012-05-01

261

Robot-assisted automatic cell sorting with combined optical tweezer and microfluidic chip technologies  

Microsoft Academic Search

This paper presents a robot-assisted methodology that integrates optical tweezer and microfluidic chip technologies to realize automatic cell sorting from small sample population. The microfluidic chip used for cell sorter is designed and fabricated, and the flow environment within the microfluidic channel is investigated with simulation. Two image processing methods, depending on size and fluorescence label respectively, are used to

Xiaolin Wang; Shuxun Chen; Dong Sun

2011-01-01

262

Nanomanipulation of single influenza virus using optical tweezers and dielectrophoretic force on a microfluidic chip  

Microsoft Academic Search

A major problem for analysis of bio-nanoparticles such as the influenza viruses (size is about 100 nm) is that sample concentration is low. We developed manipulation of the single virus using optical tweezers supported by dielectrophoretic concentration of the viruses in a microfluidic chip. The microfluidic chip made of poly (dimethyl siloxane) (PDMS) is useful to achieve stable manipulation of

Hisataka Maruyama; Kyosuke Kotani; Ayae Honda; Tatsuro Takahata; Fumihito Arai

2010-01-01

263

Inversion of product selectivity in an enzyme-inspired metallosupramolecular tweezer catalyzed epoxidation reaction†  

PubMed Central

This study describes a heteroligated, hemilabile PtII–P,S tweezer coordination complex that combines a chiral Jacobsen–Katsuki MnIII-salen epoxidation catalyst with an amidopyridine receptor, which leads to an inversion of the major epoxide product compared to catalysts without a recognition group.

Ulmann, Pirmin A.; Braunschweig, Adam B.; Lee, One-Sun; Wiester, Michael J.

2014-01-01

264

A microfluidic system for studies of stress response in single cells using optical tweezers  

Microsoft Academic Search

In recent years there has been a growing interest in the use of optical manipulation techniques, such as optical tweezers, in biological research as the full potential of such applications are being realized. Biological research is developing towards the study of single entities to reveal new behaviors that cannot be discovered with more traditional ensemble techniques. To be able to

Annette Granéli; Emma Eriksson; Jonas Enger; Kerstin Ramser; Mattias Goksör; Stefan Hohmann; Dag Hanstorp

2006-01-01

265

A microfluidic system for studies of stress response in single cells using optical tweezers  

NASA Astrophysics Data System (ADS)

In recent years there has been a growing interest in the use of optical manipulation techniques, such as optical tweezers, in biological research as the full potential of such applications are being realized. Biological research is developing towards the study of single entities to reveal new behaviors that cannot be discovered with more traditional ensemble techniques. To be able to study single cells we have developed a new method where a combination of micro-fluidics and optical tweezers was used. Micro-fluidic channels were fabricated using soft lithography. The channels consisted of a Y-shaped junction were two channels merged into one. By flowing different media in the two channels in laminar flow we were able to create a sharp concentration gradient at the junction. Single cells were trapped by the tweezers and the micro-fluidic system allowed fast environmental changes to be made for the cell in a reversible manner. The time required to change the surroundings of the cell was limited to how sharp mixing region the system could create, thus how far the cells had to be moved using the optical tweezers. With this new technique cellular response in single cells upon fast environmental changes could be investigated in real time. The cellular response was detected by monitoring variations in the cell by following the localization of fluorescently tagged proteins within the cell.

Granéli, Annette; Eriksson, Emma; Enger, Jonas; Ramser, Kerstin; Goksör, Mattias; Hohmann, Stefan; Hanstorp, Dag

2006-09-01

266

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.

2004-12-01

267

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

2005-01-01

268

Micro bubble fluidics by EWOD and ultrasonic excitation for micro bubble tweezers  

Microsoft Academic Search

Recently, we envisioned so called micro bubble tweezers where EWOD (electrowetting-on-dielectric) actuated bubbles can manipulate micro objects such as biological cells by pushing or pulling them. Besides, oscillating (shrinking and expanding) bubbles in the presence of ultrasonic wave act as a to deliver drugs and molecules into the cells. In this paper, as a great stride in our quest for

Sang Kug Chung; Yuejun Zhao; Ui-Chong Yi; Sung Kwon Cho

2007-01-01

269

Analysis of RBC damage using laser tweezers Raman spectroscopy (LTRS) during femtosecond laser optical trapping  

Microsoft Academic Search

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

Sung-bin Ju; Jin-woo Pyo; Jae-young Jang; Seungduk Lee; Beop-Min Kim

2008-01-01

270

Stress response in Caenorhabditis elegans caused by optical tweezers: wavelength, power, and time dependence.  

PubMed Central

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 heat-shock-responsive reporter gene, has been exposed to laser light under a variety of illumination conditions. It was found that gene expression was most often induced by light of 760 nm, and least by 810 nm. The stress response increased with laser power and irradiation time. At 810 nm, significant gene expression could be observed at 360 mW of illumination, which is more than one order of magnitude above that normally used in optical tweezers. In the 700-760-nm range, the results show that the stress response is caused by photochemical processes, whereas at 810 nm, it mainly has a photothermal origin. These results give further evidence that the 700-760-nm wavelength region is unsuitable for optical tweezers and suggest that work at 810 nm at normal laser powers does not cause stress at the cellular level.

Leitz, Guenther; Fallman, Erik; Tuck, Simon; Axner, Ove

2002-01-01

271

Development of high frequency focused transducers for single beam acoustic tweezers  

NASA Astrophysics Data System (ADS)

Contactless particle trapping and manipulation have found many potential applications in diverse fields, especially in biological and medical research. Among the various methods, optical tweezers is the most well-known and extensively investigated technique. However, there are some limitations for particle manipulation based on optical tweezers. Due to the conceptual similarity with the optical tweezers and recent advances in high frequency ultrasonic transducer, a single beam acoustic tweezer using high frequency (? 20 MHz) focused transducer has recently been considered, and its feasibility was theoretically and experimentally investigated. This dissertation mainly describes the development of high frequency focused ultrasonic transducers for single beam acoustic tweezers applications. Three different types of transducers were fabricated. First, a 60 MHz miniature focused transducer (<1 mm) was made using press-focusing technique. The single beam acoustic trapping experiment was performed to manipulate 15 microm polystyrene microspheres using this transducer. In vitro ultrasonic biomicroscopy imaging on the rabbit eye was also obtained with this device. Second approach is to build a 200 MHz self-focused ZnO transducer by sputtering ZnO film on a curved surface of the aluminum backing material. An individual 10 microm microsphere was effectively manipulated in two dimensions by this type of transducer. Another ultrahigh frequency focused transducer based on silicon lens design has also been developed, where a 330 MHz silicon lens transducer was fabricated and evaluated. Microparticle trapping experiment was carried out to demonstrate that silicon lens transducer can manipulate a single microsphere as small as 5 microm. The realization of single beam acoustic tweezers using high frequency focused transducers can offer wide range of applications in biomedical and chemical sciences including intercellular kinetics studies and cell stimulation. Additionally, we propose a simple and efficient approach to prepare xPMN-PT-(1-x)PZT (where x is 0.1, 0.3, 0.5, 0.7 and 0.9) composite films with controllable dielectric constant that offers better performance for high frequency ultrasonic transducer applications. A 200 MHz single element transducer utilizing 0.9PMN-PT-0.1PZT thin film was built. This type of xPMN-PT-(1-x)PZT film transducers may satisfy current needs of very high frequency biomedical applications, such as ultrasonic biomicroscopy or acoustic tweezers.

Hsu, Hsiu-Sheng

272

The supramolecular design of low-dimensional carbon nano-hybrids encoding a polyoxometalate-bis-pyrene tweezer.  

PubMed

A novel bis-pyrene tweezer anchored on a rigid polyoxometalate scaffold fosters a unique interplay of hydrophobic and electrostatic supramolecular interactions, to shape carbon nanostructures (CNSs)-based extended architectures. PMID:24595872

Modugno, Gloria; Syrgiannis, Zois; Bonasera, Aurelio; Carraro, Mauro; Giancane, Gabriele; Valli, Ludovico; Bonchio, Marcella; Prato, Maurizio

2014-05-18

273

Laser Raman Tweezer Spectroscopy for the Molecular and Functional Characterization of Single Live Mouse Mammary Tumor-Initiating Cells.  

National Technical Information Service (NTIS)

The purpose of this research is to utilize Raman Spectroscopy (RS) combined with optical tweezer technology (RTS) to isolate and characterize the intracellular molecular profiles of live tumor initiating cells derived from p53 null mouse mammary tumors. T...

F. Behbod

2012-01-01

274

Monitoring of germination dynamics of multiple individual bacterial spores by multiple-trap Raman tweezers and differential interference contrast microscopy  

Microsoft Academic Search

Multiple-trap Raman tweezers and differential interference contrast microscopy were used for simultaneously monitoring the germination dynamics of multiple individual bacterial spores.codes: (350.4855) Optical tweezers or optical manipulation, (170.5660) Raman spectroscopy, 170.0180 Microscopy Optical monitoring of biological dynamics of individual living cells under physiological condition is essential to understand various events and heterogeneity among genetically identical cells. Germination is the process

Pengfei Zhang; Lingbo Kong; Peter Setlow; Yong-qing Li

2011-01-01

275

Influence of multiple particles in optical tweezers on the trapping efficiency  

NASA Astrophysics Data System (ADS)

Since the early times of Arthur Ashkins groundbreaking experiments on optical tweezers, a great number of theoretical works was dedicated to this subject. Most of them treated the optical trapping of single spherical or elliptical particles. In the last years optical tweezers have become more and more a tool for assembling three dimensional structures using single microspheres as building blocks. Since all structures and particles inside the light beams influence the properties of the traps, we investigated theoretically the influence of additional single particles and particle arrays on the properties of optical traps. For this reason a geometrical optics based model is used with the inherent flexibility to be applied for various shapes and particle numbers.

Weigel, Thomas; Ghadiri, Reza; Esen, Cemal; Schweiger, Gustav; Ostendorf, Andreas

2014-02-01

276

Optoelectronic tweezers system for single cell manipulation and fluorescence imaging of live immune cells.  

PubMed

A compact optoelectronic tweezers system for combined cell manipulation and analysis is presented. CMOS-controlled gallium nitride micro-LED arrays are used to provide simultaneous spatio-temporal control of dielectrophoresis traps within an optoelectronic tweezers device and fluorescence imaging of contrasting dye labelled cells. This capability provides direct identification, selection and controlled interaction of single T-lymphocytes and dendritic cells. The trap strength and profile for two emission wavelengths of micro-LED array have been measured and a maximum trapping force of 13.1 and 7.6 pN was achieved for projected micro-LED devices emitting at ?max 520 and 450 nm, respectively. A potential application in biological research is demonstrated through the controlled interaction of live immune cells where there is potential for this method of OET to be implemented as a compact device. PMID:24515144

Jeorrett, Abigail H; Neale, Steven L; Massoubre, David; Gu, Erdan; Henderson, Robert K; Millington, Owain; Mathieson, Keith; Dawson, Martin D

2014-01-27

277

Neural Network for Image-to-Image Control of Optical Tweezers  

NASA Technical Reports Server (NTRS)

A method is discussed for using neural networks to control optical tweezers. Neural-net outputs are combined with scaling and tiling to generate 480 by 480-pixel control patterns for a spatial light modulator (SLM). The SLM can be combined in various ways with a microscope to create movable tweezers traps with controllable profiles. The neural nets are intended to respond to scattered light from carbon and silicon carbide nanotube sensors. The nanotube sensors are to be held by the traps for manipulation and calibration. Scaling and tiling allow the 100 by 100-pixel maximum resolution of the neural-net software to be applied in stages to exploit the full 480 by 480-pixel resolution of the SLM. One of these stages is intended to create sensitive null detectors for detecting variations in the scattered light from the nanotube sensors.

Decker, Arthur J.; Anderson, Robert C.; Weiland, Kenneth E.; Wrbanek, Susan Y.

2004-01-01

278

An improved optical tweezers assay for measuring the force generation of single kinesin molecules.  

PubMed

Numerous microtubule-associated molecular motors, including several kinesins and cytoplasmic dynein, produce opposing forces that regulate spindle and chromosome positioning during mitosis. The motility and force generation of these motors are therefore critical to normal cell division, and dysfunction of these processes may contribute to human disease. Optical tweezers provide a powerful method for studying the nanometer motility and piconewton force generation of single motor proteins in vitro. Using kinesin-1 as a prototype, we present a set of step-by-step, optimized protocols for expressing a kinesin construct (K560-GFP) in Escherichia coli, purifying it, and studying its force generation in an optical tweezers microscope. We also provide detailed instructions on proper alignment and calibration of an optical trapping microscope. These methods provide a foundation for a variety of similar experiments. PMID:24633799

Nicholas, Matthew P; Rao, Lu; Gennerich, Arne

2014-01-01

279

Optical tweezers for precise control of micro-bubble arrays: in situ temperature measurement  

NASA Astrophysics Data System (ADS)

We use highly a focused laser beam incident on a carbon coated coverslip to create microcavitation. Full optical control of the radii of the bubbles is attained. Multiple bubbles can also be created and their size changed independently. The dynamics of such multi-bubble systems are studied. These bubble systems generate strong flows such as Marangoni convection and also large thermal gradients. Since the size of the micro-bubbles is highly dependent on the temperature, we anticipate that these systems can be used for precise temperature control of samples. These methods are of use when the knowledge of exact and local temperature profiles are of importance. Furthermore, since bubble expansion can generate orders of magnitude more force than conventional optical tweezers, systems have application in manipulation of particles where large forces are required. We present methods based on optical tweezers for using the generated bubbles as thermal sensors and as opto-mechanical transducers.

Burns, Tristan M.; Preece, Daryl; Niemenen, Timo A.; Rubinsztein-Dunlop, Haliina

2013-09-01

280

Multiple Optical Traps with a Single-Beam Optical Tweezer Utilizing Surface Micromachined Planar Curved Grating  

NASA Astrophysics Data System (ADS)

In this paper, we present a single-beam optical tweezer integrated with a planar curved diffraction grating for microbead manipulation. Various curvatures of the surface micromachined planar curved grating are systematically investigated. The planar curved grating was fabricated using multiuser micro-electro-mechanical-system (MEMS) processes (MUMPs). The angular separation and the number of diffracted orders were determined. Experimental results indicate that the diffraction patterns and curvature of the planar curved grating are closely related. As the curvature of the planar curved grating increases, the vertical diffraction angle increases, resulting in the strip patterns of the planar curved grating. A single-beam optical tweezer integrated with a planar curved diffraction grating was developed. We demonstrate a technique for creating multiple optical traps from a single laser beam using the developed planar curved grating. The strip patterns of the planar curved grating that resulted from diffraction were used to trap one row of polystyrene beads.

Kuo, Ju-Nan; Chen, Kuan-Yu

2010-11-01

281

NOTE: Manufacturing micro-scale structures by an optical tweezers system controlled by five finger tips  

NASA Astrophysics Data System (ADS)

Because of the compelling need for manufacturing micro- to nano-scale structures, researchers are actively investigating new methods that are applicable for small scale manufacturing. Among them, optical tweezers that can manipulate microscopic objects using a laser are receiving key attention. Optical tweezers have been used actively in the field of science. For example, they were used for measuring mechanical characteristics on the scale of piconewtons or for manipulating and sorting large numbers of particles. However, little work has been reported on 'manufacturing' objects. In this paper, we present a new method for manufacturing micro-scale structures using micro-scale polystyrene particles. Particles will be controlled with a user interface that utilizes a human hand and glued together by the bonding force between biotin and streptavidin.

Park, In-Yong; Sung, Seung-Yong; Lee, Jong-Hyun; Lee, Yong-Gu

2007-10-01

282

Optical tweezers and non-ratiometric fluorescent-dye-based studies of respiration in sperm mitochondria  

Microsoft Academic Search

The purpose of this study is to investigate how the mitochondrial membrane potential affects sperm motility using laser tweezers and a non-ratiometric fluorescent probe, DiOC6(3). A 1064 nm Nd:YVO4 continuous wave laser was used to trap motile sperm at a power of 450 mW in the trap spot. Using customized tracking software, the curvilinear velocity (VCL) and the escape force

Timothy Chen; Linda Z. Shi; Qingyuan Zhu; Charlie Chandsawangbhuwana; Michael W. Berns

2011-01-01

283

Three Powerful Research Tools from Single Cells into Single Molecules: AFM, Laser Tweezers, and Raman Spectroscopy  

Microsoft Academic Search

By using three physical techniques (atomic force microscopy (AFM), laser tweezers, and Raman spectroscopy), many excellent\\u000a works in single-cell\\/molecule research have been accomplished. In this review, we present a brief introduction to the principles\\u000a of these three techniques, and their capabilities toward single-cell\\/molecule research are highlighted. Afterward, the advances\\u000a in single-cell\\/molecule research that have been facilitated by these three techniques

Yongkuan Wu; Kun Liu; Kedong Song; Shi Pan

284

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

PubMed

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 axial and transverse, are also given. PMID:19529686

Liu, Zhihai; Guo, Chengkai; Yang, Jun; Yuan, Libo

2006-12-11

285

Optical Trapping of Thermo-responsive Microgel Particles by Holographic Optical Tweezers  

Microsoft Academic Search

Holographic Optical Tweezers (HOT) is a technique in which the phase of trapping laser is modulated for generating steerable, multiple optical traps in a sample chamber. An indigenously developed HOT set-up at Raja Ramanna Centre for Advanced Technology, Indore has been used to trap thermo-responsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-co-AAc) spherical particles of 1.6 mum diameter suspended in aqueous medium. The videos

M. R. Rajesh Kannan; B. V. R. Tata; R. Dasgupta; S. Ahlawat; P. K. Gupta

2011-01-01

286

Optical Trapping of Thermo-responsive Microgel Particles by Holographic Optical Tweezers  

Microsoft Academic Search

Holographic Optical Tweezers (HOT) is a technique in which the phase of trapping laser is modulated for generating steerable, multiple optical traps in a sample chamber. An indigenously developed HOT set-up at Raja Ramanna Centre for Advanced Technology, Indore has been used to trap thermo-responsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-co-AAc) spherical particles of 1.6 ?m diameter suspended in aqueous medium. The videos

M. R. Rajesh Kannan; B. V. R. Tata; R. Dasgupta; S. Ahlawat; P. K. Gupta

2011-01-01

287

Practical lab tool for living cells based on microstereolithography and multiple dynamic holographic optical tweezers  

Microsoft Academic Search

Recent studies have shown that the cell is mechanically differentiated both spatially and temporally, leading to a regional approach in cell behaviour essays. Most experiments are based on spatially-controlled contacts between microbeads and cells. We here propose an apparatus based on holographic optical tweezers to put on a target cell a two- or three-dimensional custom-built pattern of beads, with respect

Serge Monneret; Federico Belloni; Didier Marguet

2006-01-01

288

Floating electrode optoelectronic tweezers: Light-driven dielectrophoretic droplet manipulation in electrically insulating oil medium  

Microsoft Academic Search

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 mum de-ionized water droplet immersed in corn oil medium is actuated by a 3.21 muW laser beam with an average intensity as

Chenlu Pan; Ting-Hsiang Wu; Christoph Kloss; Sheraz Kalim; Caitlin E. Callahan; Michael Teitell; Eric P. Y. Chiou

2008-01-01

289

Acoustic radiation force of high-order Bessel beam standing wave tweezers on a rigid sphere  

Microsoft Academic Search

Background and objectiveParticle manipulation using the acoustic radiation force of Bessel beams is an active field of research. In a previous investigation, [F.G. Mitri, Acoustic radiation force on a sphere in standing and quasi-standing zero-order Bessel beam tweezers, Annals of Physics 323 (2008) 1604–1620] an expression for the radiation force of a zero-order Bessel beam standing wave experienced by a

F. G. Mitri

2009-01-01

290

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

NASA Astrophysics Data System (ADS)

The 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 acoustically trap particles near the focal point where most of the acoustic energy is concentrated if certain conditions are met. Acoustic force exerted on a fluid particle in ultrasonic fields is analyzed in a ray acoustics regime where the wavelength of acoustic beam is much smaller than the size of the particle. In order to apply the acoustical tweezer to manipulating macromolecules and cells whose size is in the order of a few microns or less, a prerequisite is that the ultrasound wavelength has to be much smaller than a few microns. In this paper, the analysis is therefore based on the field pattern produced by a strongly focused 100 MHz ultrasonic transducer with Gaussian intensity distribution. For the realization of acoustic trapping, negative axial radiation force has to be generated to pull a particle towards a focus. The fat particle considered for acoustic trapping in this paper has an acoustic impedance of 1.4 MRayls. The magnitude of the acoustic axial radiation force that has been calculated as the size of the fat particle is varied from 8? to 14?. In addition, both Fresnel coefficients at various positions are also calculated to assess the interaction of reflection and refraction and their relative contribution to the effect of the acoustical tweezer. The simulation results show that the feasibility of the acoustical tweezer depends on both the degree of acoustic impedance mismatch and the degree of focusing relative to the particle size. .

Lee, Jungwoo; Ha, Kanglyeol; Shung, K. Kirk

2005-05-01

291

Time-resolved nanoseconds dynamics of ultrasound contrast agent microbubbles manipulated and controlled by optical tweezers  

Microsoft Academic Search

Optical tweezers enable non-destructive, contact-free manipulation of ultrasound contrast agent (UCA) microbubbles, which are used in medical imaging for enhancing the echogenicity of the blood pool and to quantify organ perfusion. The understanding of the fundamental dynamics of ultrasound-driven contrast agent microbubbles is a first step for exploiting their acoustical properties and to develop new diagnostic and therapeutic applications. In

Valeria Garbin; Dan Cojoc; Enrico Ferrari; Enzo Di Fabrizio; Marlies Overvelde; Michel Versluis; Sander van der Meer; Nico de Jong; Detlef Lohse; Kishan Dholakia; Gabriel C. Spalding

2006-01-01

292

A theoretical study of the feasibility of acoustical tweezers: ray acoustics approach.  

PubMed

The 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 acoustically trap particles near the focal point where most of the acoustic energy is concentrated if certain conditions are met. Acoustic force exerted on a fluid particle in ultrasonic fields is analyzed in a ray acoustics regime where the wavelength of acoustic beam is much smaller than the size of the particle. In order to apply the acoustical tweezer to manipulating macromolecules and cells whose size is in the order of a few microns or less, a prerequisite is that the ultrasound wavelength has to be much smaller than a few microns. In this paper, the analysis is therefore based on the field pattern produced by a strongly focused 100 MHz ultrasonic transducer with Gaussian intensity distribution. For the realization of acoustic trapping, negative axial radiation force has to be generated to pull a particle towards a focus. The fat particle considered for acoustic trapping in this paper has an acoustic impedance of 1.4 MRayls. The magnitude of the acoustic axial radiation force that has been calculated as the size of the fat particle is varied from 8lambda to 14lambda. In addition, both Fresnel coefficients at various positions are also calculated to assess the interaction of reflection and refraction and their relative contribution to the effect of the acoustical tweezer. The simulation results show that the feasibility of the acoustical tweezer depends on both the degree of acoustic impedance mismatch and the degree of focusing relative to the particle size. PMID:15957793

Lee, Jungwoo; Ha, Kanglyeol; Shung, K Kirk

2005-05-01

293

Computational characterization and modeling of buckyball tweezers: density functional study of concave–convex ?•••? interactions  

SciTech Connect

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The geometries and binding energies of a recent buckyball tweezers (C60H28) and its supramolecular complexes are investigated using recently developed density functionals (M06-L and M06-2X) that include an accurate treatment of medium-range correlation energy. The pincer part of the tweezers, corannulene, has a strong attractive interaction with C60. However, due to the entropy penalty, the calculated gas-phase free energy of association of the C60@corannulene supramolecule is positive 3.5 kcal mol-1; and this entropy penalty explains why it is difficult to observe C60@corannulene supramolecule experimentally. By using a p-extended tetrathiafulvalene (TTF), in particular 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (TTFAQ or C20H10S4), as the pincer part, we modeled a new buckyball tweezers. The geometries and binding energies of the new buckyball tweezers and its supramolecular complexes are also calculated. Due to fact that the attractive interaction between TTFAQ and C60 is weaker than that between corannulene and C60, the gas-phase binding free energy in the C60@C60H 32S8 supramolecular complex is smaller than that in the C60@C60H28 supramolecule. We also discuss solvent effects.

Zhao, Yan; Truhlar, Donald G.

2008-02-18

294

Use of laser tweezers to analyze sperm motility and mitochondrial membrane potential.  

PubMed

We combine laser tweezers with custom computer tracking software and robotics to analyze the motility [swimming speed, VCL (curvilinear velocity), and swimming force in terms of escape laser power (Pesc)] and energetics [mitochondrial membrane potential (MP)] of individual sperm. Domestic dog sperm are labeled with a cationic fluorescent probe, DiOC2(3), that reports the MP across the inner membrane of the mitochondria located in the sperm's midpiece. Individual sperm are tracked to calculate VCL. Pesc is measured by reducing the laser power after the sperm is trapped using laser tweezers until the sperm is capable of escaping the trap. The MP is measured every second over a 5-s interval during the tracking phase (sperm is swimming freely) and continuously during the trapping phase. The effect of the fluorescent probe on sperm motility is addressed. The sensitivity of the probe is measured by assessing the effects of a mitochondrial uncoupling agent (CCCP) on MP of free swimming sperm. The effects of prolonged exposed to the laser tweezers on VCL and MP are analyzed. The system's capabilities are demonstrated by measuring VCL, Pesc, and MP simultaneously for individual sperm. This combination of imaging tools is useful to quantitatively assess sperm quality and viability. PMID:18315360

Nascimento, Jaclyn M; Shi, Linda Z; Chandsawangbhuwana, Charlie; Tam, James; Durrant, Barbara; Botvinick, Elliot L; Berns, Michael W

2008-01-01

295

Raman Tweezers as a Diagnostic Tool of Hemoglobin-Related Blood Disorders  

PubMed Central

This review presents the development of a Raman Tweezers system for detecting hemoglobin-related blood disorders at a single cell level. The study demonstrates that the molecular fingerprint insight provided by Raman analysis holds great promise for distinguishing between healthy and diseased cells in the field of biomedicine. Herein a Raman Tweezers system has been applied to investigate the effects of thalassemia, a blood disease quite diffuse in the Mediterranean Sea region. By resonant excitation of hemoglobin Raman bands, we examined the oxygenation capability of normal, alpha- and beta-thalassemic erythrocytes. A reduction of this fundamental red blood cell function, particularly severe for beta-thalassemia, has been found. Raman spectroscopy was also used to draw hemoglobin distribution inside single erythrocytes; the results confirmed the characteristic anomaly (target shape), occurring in thalassemia and some other blood disorders. The success of resonance Raman spectroscopy for thalassemia detection reported in this review provide an interesting starting point to explore the application of a Raman Tweezers system in the analysis of several blood disorders.

Rusciano, Giulia; De Luca, Anna C.; Pesce, Giuseppe; Sasso, Antonio

2008-01-01

296

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.

1996-05-01

297

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.

2006-06-01

298

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

2012-05-01

299

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

2012-01-01

300

Scanning a DNA Molecule for Bound Proteins Using Hybrid Magnetic and Optical Tweezers  

PubMed Central

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/. 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.

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

2013-01-01

301

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

PubMed Central

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.

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

2013-01-01

302

Calibration of trapping force and response function of optical tweezers in viscoelastic media  

NASA Astrophysics Data System (ADS)

At present, a major obstacle to the quantitative application of optical tweezers as a force spectrometer in living cells is the lack of a method to calibrate the tweezers. Calibration with approved methods such as the power spectrum method (Berg-Sørensen and Flyvbjerg 2004 Rev. Sci. Instrum. 75 594; Berg-Sørensen et al 2006 Rev. Sci. Instrum. 77 063106) is not possible as the viscoelastic properties of the bio-active medium are a priori unknown. Here, we present an approach that neither requires explicit assumptions about the size of the trapped particle nor about the viscoelastic properties of the medium. Instead, the interaction between the medium and the trapped particle is described in a general manner, through velocity and acceleration memory. Our method is applicable to general, at least locally homogeneous, viscoelastic media. The procedure combines active and passive approaches by the application of Onsager's regression hypothesis. It allows extraction of the trapping stiffness ? of the optical tweezers and of the response function ?(?), which is the frequency-dependent effective inverse spring constant of the system. Finally, information about the viscoelastic properties of the medium may also be found. To test the method, we have performed simulations in which the system is driven sinusoidally. These simulations serve as an example of how to deal with real experimental data. For realistic parameters, we calibrate the trap stiffness ? with ~1% stochastic error.

Fischer, Mario; Berg-Sørensen, Kirstine

2007-08-01

303

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

PubMed

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

2012-06-01

304

Measurements of host-guest interaction energies in a calixarene supramolecular complex  

Microsoft Academic Search

We report the results of NMR relaxometry measurements on the p-tert-butyl-calix[4]arene and the p-tert-butyl-calix[4]arene(1:1)toluene supramolecular systems in the solid state. Relevant information on the dynamics of the p-tert-butyl groups of the host cage is obtained, and the variation produced by the toluene guest molecule in the activation energy characterizing the reorientation of the methyl groups is determined. This variation provides

R. Caciuffo; R. Galeazzi; A. J. Horsewill; A. Ikram; F. Ugozzoli

1999-01-01

305

Photoresponsive hybrid raspberry-like colloids based on cucurbit[8]uril host-guest interactions.  

PubMed

Hybrid raspberry-like colloids (HRCs) were prepared by employing cucurbit[8]uril (CB[8]) as a supramolecular linker to assemble functional polymeric nanoparticles onto a silica core. The formed HRCs are photoresponsive and can be reversibly disassembled upon light irradiation. This facile supramolecular approach provides a platform for the synthesis of colloids with sophisticated structures and properties. PMID:24446350

Lan, Yang; Wu, Yuchao; Karas, Athan; Scherman, Oren A

2014-02-17

306

Fluorescence detecting of paraquat using host-guest chemistry with cucurbit[8]uril.  

PubMed

Paraquat (PQ) is one of the most widely used herbicides in the world, which has a good occupational safety record when used properly. While, it presents high mortality index after intentional exposure. Accidental deaths and suicides from PQ ingestion are relatively common in developing countries with an estimated 300,000 deaths occurring in the Asia-Pacific region alone each year, and there are no specific antidotes. Good predictors of outcome and prognosis may be plasma and urine testing within the first 24 h of intoxication. A fluorescence enhancement of approximately 30 times was seen following addition of PQ to a solution of the supramolecular compound 2MB@CB[8], which comprised two methylene blue (MB) molecules within one cucurbit[8]uril (CB[8]) host molecule. The fluorescence intensity was linearly proportional to the amount of PQ added over the concentration range 2.4 × 10(-10) M-2.5 × 10(-4) M. The reaction also occurred in living cells and within live mice. PMID:24389647

Sun, Shiguo; Li, Fusheng; Liu, Fengyu; Wang, Jitao; Peng, Xiaojun

2014-01-01

307

Fluorescence detecting of paraquat using host-guest chemistry with cucurbit[8]uril  

NASA Astrophysics Data System (ADS)

Paraquat (PQ) is one of the most widely used herbicides in the world, which has a good occupational safety record when used properly. While, it presents high mortality index after intentional exposure. Accidental deaths and suicides from PQ ingestion are relatively common in developing countries with an estimated 300,000 deaths occurring in the Asia-Pacific region alone each year, and there are no specific antidotes. Good predictors of outcome and prognosis may be plasma and urine testing within the first 24 h of intoxication. A fluorescence enhancement of approximately 30 times was seen following addition of PQ to a solution of the supramolecular compound 2MB@CB[8], which comprised two methylene blue (MB) molecules within one cucurbit[8]uril (CB[8]) host molecule. The fluorescence intensity was linearly proportional to the amount of PQ added over the concentration range 2.4 × 10-10 M-2.5 × 10-4 M. The reaction also occurred in living cells and within live mice.

Sun, Shiguo; Li, Fusheng; Liu, Fengyu; Wang, Jitao; Peng, Xiaojun

2014-01-01

308

Tailoring the optical and rheological properties of an epoxy acrylate based host-guest system  

NASA Astrophysics Data System (ADS)

Polymers with individually adjusted optical and rheological properties are gaining more and more importance in industrial applications like in information technology. To modify the refractive index n, an electron-rich organic dopant is added to a commercially available polymer based resin. Changes in viscosity for applications like ink-jet printing can be achieved by using a comonomer with suitable properties. Therefore we used a commercially available epoxy acrylate based UV-curable polymer matrix to investigate the influence of ethylene glycol dimethacrylate (EGDMA) on viscosity and phenanthrene on refractive index. Refractive index was measured at a wavelength of 589 nm and 20 °C using an Abbe refractometer. As a result the change in viscosity decreased linearly from 47 Pa·s to 4 mPa·s which is a more suitable region for inkjet printing. However, the refractive index decreased at the same time from 1.548 to 1.514. Adding phenanthrene the refractive index increased linearly from 1.548 up to 1.561. It was shown that both, viscosity and refractive index can be successfully adjusted in a wide range depending on desired properties.

Gleißner, Uwe; Hanemann, Thomas

2014-05-01

309

Host-Guest Interactions in Fe(III)-Trimesate MOF Nanoparticles Loaded with Doxorubicin.  

PubMed

Doxorubicin (DOX) entrapment in porous Fe(III)-trimesate metal organic frameworks (MIL-100(Fe)) nanoparticles was investigated in neutral Tris buffer via UV-vis absorption, circular dichroism (CD), and fluorescence. The binding constants and the absolute spectra of the DOX-MIL-100(Fe) complexes were determined via absorption and fluorescence titrations. A binding model where DOX associates as monomer to the dehydrated Fe3O (OH)(H2O)2 [(C6H3)(CO2)3]2 structural unit in 1:1 stoichiometry, with apparent association constant of (1.1 to 1.8) × 10(4) M(-1), was found to reasonably fit the experimental data. Spectroscopic data indicate that DOX binding occurs via the formation of highly stable coordination bonds between one or both deprotonated hydroxyl groups of the aglycone moiety and coordinatively unsaturated Fe(III) centers. Complete quenching of the DOX fluorescence and remarkable thermal and photochemical stability were observed for DOX incorporated in the MIL-100(Fe) framework. PMID:24960194

Anand, Resmi; Borghi, Francesco; Manoli, Francesco; Manet, Ilse; Agostoni, Valentina; Reschiglian, Pierluigi; Gref, Ruxandra; Monti, Sandra

2014-07-24

310

Solubility enhancement of kinetin through host–guest interactions with cucurbiturils  

Microsoft Academic Search

We explored the use of cucurbiturils to form inclusion complexes to overcome the solubility problems of kinetin, a plant cytokinin.\\u000a Inclusion complexes between kinetin and Q[7], TMeQ[6] and HMeQ[6] in aqueous solution and in solid state were investigated\\u000a by phase solubility studies, 1H NMR and IR. The effects of pH and temperature on complex stability were also investigated. Phase solubility

Ying Huang; Sai-Feng Xue; Zhu Tao; Qian-Jiang Zhu; Hong Zhang; Jing-Xiang Lin; Da-Hai Yu

2008-01-01

311

Host-guest Interaction Mediated Polymeric Assemblies: Multifunctional Nanoparticles for Drug and Gene Delivery  

PubMed Central

Novel core-shell structured nano-assemblies are assembled by a ?-cyclodextrin containing positively charged host polymer and a hydrophobic guest polymer. The hydrophobic core of this type of assemblies serves as a nano-container to load and release the hydrophobic drugs, while the positively charged hydrophilic shell is able to condense the plasmid DNA and achieve its transfection/expression in osteoblast cells. These assemblies may be used as a new generation of multi-functional nano-carriers for simultaneous drug delivery and gene therapy.

Zhang, Jianxiang; Sun, Hongli; Ma, Peter X

2010-01-01

312

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

2013-04-01

313

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.

1999-01-11

314

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

PubMed

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, Ángel; Da Silva, José P; García-Río, Luis

2013-09-20

315

Uniaxial negative thermal expansion facilitated by weak host-guest interactions.  

PubMed

A nitromethane solvate of 18-crown-6 was investigated by means of variable-temperature single-crystal X-ray diffraction in response to a report of abnormal unit cell contraction. Exceptionally large positive thermal expansion in two axial directions and negative thermal expansion along the third was confirmed. The underlying mechanism relies exclusively on weak electrostatic interactions to yield a linear thermal expansion coefficient of -129 × 10(-6) K(-1), the largest negative value yet observed for an organic inclusion compound. PMID:24633431

Engel, Emile R; Smith, Vincent J; Bezuidenhout, Charl X; Barbour, Leonard J

2014-04-25

316

Supramolecular fishing for plasma membrane proteins using an ultrastable synthetic host-guest binding pair  

Microsoft Academic Search

Membrane proteomics, the large-scale global analysis of membrane proteins, is often constrained by the efficiency of separating and extracting membrane proteins. Recent approaches involve conjugating membrane proteins with the small molecule biotin and using the receptor streptavidin to extract the labelled proteins. Despite the many advantages of this method, several shortcomings remain, including potential contamination by endogenously biotinylated molecules and

Don-Wook Lee; Kyeng Min Park; Mainak Banerjee; Sang Hoon Ha; Taehoon Lee; Kyungwon Suh; Somak Paul; Hyuntae Jung; Jaeyoon Kim; Narayanan Selvapalam; Sung Ho Ryu; Kimoon Kim

2011-01-01

317

Efficient host-guest energy transfer in polycationic cyclophane-perylene diimide complexes in water.  

PubMed

We report the self-assembly of a series of highly charged supramolecular complexes in aqueous media composed of cyclobis(4,4'-(1,4-phenylene)bispyridine-p-phenylene)tetrakis(chloride) (ExBox) and three dicationic perylene diimides (PDIs). Efficient energy transfer (ET) is observed between the host and guests. Additionally, we show that our hexacationic complexes are capable of further complexation with neutral cucurbit[7]uril (CB[7]), producing a 3-polypseudorotaxane via the self-assembly of orthogonal recognition moieties. ExBox serves as the central ring, complexing to the PDI core, while two CB[7]s behave as supramolecular stoppers, binding to the two outer quaternary ammonium motifs. The formation of the 3-polypseudorotaxane results in far superior photophysical properties of the central PDI unit relative to the binary complexes at stoichiometric ratios. Lastly, we also demonstrate the ability of our binary complexes to act as a highly selective chemosensing ensemble for the neurotransmitter melatonin. PMID:24893200

Ryan, Seán T J; Del Barrio, Jesús; Ghosh, Indrajit; Biedermann, Frank; Lazar, Alexandra I; Lan, Yang; Coulston, Roger J; Nau, Werner M; Scherman, Oren A

2014-06-25

318

Enhanced imine synthesis in water: from surfactant-mediated catalysis to host-guest mechanisms.  

PubMed

An environment-responsive and fluorogenic reaction is reported and used as a model system to demonstrate experimentally three mechanisms of enhanced imine synthesis in water using either surfactants (below and above their CMC) or double-stranded DNA (acting as a reaction host). PMID:24162811

Meguellati, Kamel; Fallah-Araghi, Ali; Baret, Jean-Christophe; El Harrak, Abdeslam; Mangeat, Thomas; Marques, Carlos M; Griffiths, Andrew D; Ladame, Sylvain

2013-12-14

319

Host-guest chemistry of Cu2+\\/Histidine complexes in molecular sieves  

Microsoft Academic Search

The high activity and selectivity of enzymes have inspired many scientists to study the structure and working mechanism of bio-molecular complexes. Also in the catalysis community this subject is of topical interest, as it may provide inspiration for the development of a new generation of bio-inspired catalyst materials. Functionalization of inorganic substrates, such as zeolites, with transition metal ion (TMI)

Jan Gijsbert Mesu

2005-01-01

320

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

2006-05-01

321

Host-guest interactions in fluorinated polymer electrolytes: A 7Li-13C NMR study  

NASA Astrophysics Data System (ADS)

Gel-type electrolytes based on fluorinated polymers are of interest for electrochemical devices. We present a 7Li-13C solid-state NMR and modulated differential scanning calorimetry (MDSC) study of gel electrolytes based on a copolymer poly(vinylidene fluoride) (PVdF)-hexafluoropropylene (HFP) activated with a nonaqueous solution ethylene carbonate (EC)-propylene carbonate (PC)-LiN(CF3SO2)2. We show that the narrowing of the Li lineshape is decoupled from the glass transition. The behavior of the longitudinal relaxation times, T1, confirms that the host polymer matrix simply behaves like a quasiinert cage for the solution. These results are confirmed by 13C NMR at the magic angle (MAS) data, which show that the presence of the polymer does not significantly affect the chemical shift changes induced in the EC/PC carbons by the imide salt.

Mustarelli, P.; Quartarone, E.; Capiglia, C.; Tomasi, C.; Ferloni, P.; Magistris, A.

1999-08-01

322

Theoretical Calculation of Relative Binding Affinity in Host--Guest Systems  

NASA Astrophysics Data System (ADS)

The relative free energy of binding the anions Cl- and Br- to the macrotricyclic receptor SC24 in water has been computed by a computer simulation technique. This result and an incidental result for the relative free energy of hydration of the anions are in excellent agreement with experimental data. The simulation approach to ligand-receptor interactions that is described here has significant potential as a predictive tool in chemistry, biochemistry, and pharmacology.

Lybrand, Terry P.; McCammon, J. Andrew; Wipff, Georges

1986-02-01

323

A study of supramolecular host-guest interaction of dothiepin and doxepin drugs with cyclodextrin macrocycles  

NASA Astrophysics Data System (ADS)

Inclusion complexation behavior of dothiepin (DOT) and doxepin (DOX) with two cyclodextrins (?-CD and ?-CD) were studied by absorption, fluorescence, time resolved fluorescence, scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transformation infrared spectroscopy (FT-IR), differential scanning colorimetry (DSC), powder X-ray diffraction (PXRD), proton nuclear magnetic resonance (1H NMR) and molecular modeling methods. Absorption and fluorescence spectral studies reveal that both drugs form different types of inclusion complexes with ?-CD and ?-CD. DOT and DOX exhibit short life time in aqueous medium (DOT ? 2.29 ns, DOX ? 1.89 ns) and higher in CD medium (DOT:?-CD ? 3.45 ns, DOT:?-CD ? 4.84 ns, DOX:?-CD ? 3.55 ns and DOT:?-CD ? 4.33 ns). The supramolecular structure of the nano-sized sphere and agglomerate was established by TEM. Alkyl chain and aromatic ring protons of the drug molecule are entrapped in the CD nanocavities. The significant proton chemical shifts give evidence for expected inclusion complex formation. PM3 calculations suggest that the alkyl chain encapsulation is most energetically favored in ?-CD. The positive free energy and entropy changes indicated that both inclusion complexation processes are non-spontaneous and entropy driven.

Rajendiran, N.; Sankaranarayanan, R. K.; Saravanan, J.

2014-06-01

324

Experimental quantification of anion-? interactions in solution using neutral host-guest model systems.  

PubMed

Chemical intuition suggests that anions and ?-aromatic systems would repel each other. Typically, we think of cations as being attracted to electron-rich ?-systems of aromatic rings, and the cation-? interaction, a well-established noncovalent interaction, plays an important role in nature. Therefore the anion-? interaction can be considered the opposite of the cation-? interaction. Computational studies of simple models of anion-? interactions have provided estimates of the factors that govern the binding geometry and the binding energy, leading to a general consensus about the nature of these interactions. In order to attract an anion, the charge distribution of the aromatic system has to be reversed, usually through the decoration of the aromatic systems with strongly electron-withdrawing groups. Researchers have little doubt about the existence of attractive anion-? interactions in the gas phase and in the solid state. The bonding energies assigned to anion-? interactions from quantum chemical calculations and gas phase experiments are significant and compare well with the values obtained for cation-? interactions. In solution, however, there are few examples of attractive anion-? interactions. In this Account, I describe several examples of neutral molecular receptors that bind anions in solution either solely through anion-? interactions or as a combination of anion-? interactions and hydrogen bonding. In the latter cases, the strength of the anion-? interaction is indirectly detected as a modulation of the stronger hydrogen bonding interaction (enforced proximity). The dissection of the energy contribution of the anion-? interaction to the overall binding is complex, which requires the use of appropriate reference systems. This Account gives an overview the experimental efforts to determine the binding energies that can be expected from anion-? interactions in solution with examples that center around the recognition of halides. The studies show that anion-? interactions also exist in solution, and the free energy of binding estimated for these attractive interactions is less than 1 kcal/mol for each substituted phenyl groups. The quantification of anion-? interactions in solution relies on the use of molecular recognition model systems; therefore researchers need to consider how the structure of the model system can alter the magnitude of the observed energy values. In addition, the recognition of anions in solution requires the use of salts (ion pairs) as precursors, which complicates the analysis of the titration data and the corresponding estimate of the binding strength. In solution, the weak binding energies suggest that anion-? interactions are not as significant for the selective or enhanced binding of anions but offer potential applications in catalysis and transport within functional synthetic and biological systems. PMID:22621170

Ballester, Pablo

2013-04-16

325

New self-assembled nanogels based on host–guest interactions: Characterization and drug loading  

Microsoft Academic Search

We show here, for the first time, that two neutral polymers may completely associate together in water to spontaneously form supramolecular nanoassemblies (nanogels) of spherical shape. The cohesion of these stable structures of about 200 nm is based upon a “lock and key” mechanism: inclusion complexes are formed between the hydrophobic alkyl chains grafted on a polysaccharide (dextran) and the

Ruxandra Gref; Catherine Amiel; Karine Molinard; Samia Daoud-Mahammed; Bernard Sébille; Brigitte Gillet; Jean-Claude Beloeil; Catherine Ringard; Véronique Rosilio; Jaques Poupaert; Patrick Couvreur

2006-01-01

326

Three-dimensional parallel particle manipulation and tracking by integrating holographic optical tweezers and engineered point spread functions.  

PubMed

We demonstrate an integrated holographic optical tweezers system with double-helix point spread function (DH-PSF) imaging for high precision three-dimensional multi-particle tracking. The tweezers system allows for the creation and control of multiple optical traps in three-dimensions, while the DH-PSF allows for high precision, 3D, multiple-particle tracking in a wide field. The integrated system is suitable for particles emitting/scattering either coherent or incoherent light and is easily adaptable to existing holographic tweezers systems. We demonstrate simultaneous tracking of multiple micro-manipulated particles and perform quantitative estimation of the lateral and axial forces in an optical trap by measuring the fluid drag force exerted on the particles. The system is thus capable of unveiling complex 3D force landscapes that make it suitable for quantitative studies of interactions in colloidal systems, biological materials, and a variety of soft matter systems. PMID:21369208

Conkey, Donald B; Trivedi, Rahul P; Pavani, Sri Rama Prasanna; Smalyukh, Ivan I; Piestun, Rafael

2011-02-28

327

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

2013-02-01

328

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.

2006-09-01

329

Preliminary study for the development of a tweezers-type coincidence detector for tumor detection  

NASA Astrophysics Data System (ADS)

We have conducted a preliminary study for development of a tweezer-type coincidence detector for tumor detection in procedures such as FDG-guided surgery. The detector consists of a pair of LSO scintillators, optical fibers, a pair of photo-multiplier tubes (PMTs), and a coincidence circuit. Because the LSO scintillators are located on the tips of tweezers, a target organ such as a lymph node or the colon can be positioned between them. The size of a single LSO was 3.7 mm×3.7 mm×10 mm, and the scintillation photons are transferred to the PMTs via 2-mm-diameter, 1-m long optical fibers. The results show that the light loss due to the fiber was significant but there was sufficient light to observe the photo-peak of the 511-keV gamma photons. Sensitivity response function perpendicular to the detector has a full-width at half-maximum (FWHM) of 2.5 mm, while that parallel to the detector has a FWHM of 5.5 mm. Background counts due to the natural radioisotope in 176Lu can be observed when the distance between these two scintillators is small. Results also show that the absolute sensitivity was 0.057% at the center of the detector when the two LSOs were 10 mm apart and that the optical fiber was insensitive to bending up to a radius of 10 cm. From these results, we conclude that the proposed tweezers-type coincidence detector could be some interest for tumor detection using FDG, such as that in radio-guided surgery.

Yamamoto, Seiichi; Higashi, Tatsuya; Matsumoto, Keiichi; Senda, Michio

2005-08-01

330

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.

2012-09-01

331

Force increment of twin-core fiber optical tweezers using an optimum structure radius  

NASA Astrophysics Data System (ADS)

Far-field distribution at the tip of a twin-core fiber optical tweezers is studied by using the finite-difference time-domain beam-propagation method (FDTD-BPM). Based on the Poynting vector calculations and from this distribution, the operating force on a particle at the end tip was computed. It is found that, for thin and thick radius of the cladding layer, the trapping force on micro-particles became weak. So, there is an optimum value for this parameter to have maximum force.

Rahimi-Kazerooni, Ammar; Emami, Farzin

2012-09-01

332

Phase space tweezers for tailoring cavity fields by quantum Zeno dynamics.  

PubMed

We discuss an implementation of quantum Zeno dynamics in a cavity quantum electrodynamics experiment. By performing repeated unitary operations on atoms coupled to the field, we restrict the field evolution in chosen subspaces of the total Hilbert space. This procedure leads to promising methods for tailoring nonclassical states. We propose to realize "tweezers" picking a coherent field at a point in phase space and moving it towards an arbitrary final position without affecting other nonoverlapping coherent components. These effects could be observed with a state-of-the-art apparatus. PMID:21231304

Raimond, J M; Sayrin, C; Gleyzes, S; Dotsenko, I; Brune, M; Haroche, S; Facchi, P; Pascazio, S

2010-11-19

333

Surface-enhanced resonance Raman scattering in optical tweezers using co-axial second harmonic generation.  

PubMed

Silica particles were partially coated with silver, and a suitable chromophore, such that they could be simultaneously trapped within an optical tweezers system, and emit a surface-enhanced resonance Raman scattering (SERRS) response. A standard 1064 nm TEM00 mode laser was used to trap the bead whilst a frequency doubling crystal inserted into the beam gave several microwatts of 532 nm co-linear light to excite the SERRS emission. The con fi guration has clear applications in providing apparatus that can simultaneously manipulate a particle whilst obtaining surface sensitive sensory information. PMID:19495327

Jordan, Pamela; Cooper, Jon; McNay, Graeme; Docherty, Frances; Graham, Duncan; Smith, W; Sinclair, Gavin; Padgett, Miles

2005-05-30

334

Mechanical analysis of the optical tweezers in time-sharing regime.  

PubMed

Time-sharing optical tweezers is a versatile technique to realize multiple traps for manipulating biological cells and macromolecules. It has been based on an intuitive hypothesis that the trapped viscoelastic object does not "sense" blinking of the optical beam. We present a quantitative analysis using mechanical modeling and numerical simulation, showing that the local stress and strain are jumping all the time and at all locations with the jumping amplitude independent of the recovery time of the viscoelastic material and the jumping frequency. Effects of the stress and strain jumping on the object deformation and the internal energy dissipation are analyzed. PMID:24718171

Yu, Lingyao; Sheng, Yunlong

2014-04-01

335

A new determination of the shear modulus of the human erythrocyte membrane using optical tweezers.  

PubMed Central

Optical tweezers are used to apply calibrated forces to human erythrocytes, via small silica beads bound to their membrane. The shear modulus mu of the membrane is inferred from measurements of the cell deformation in the small strain linear regime. We find the same result mu = 2.5 +/- 0.4 microN/m for both discotic and nearly spherical swollen cells. This value is smaller than the one deduced from micropipettes experiments. However the two methods do not operate in the same deformation regime and are not expected to lead to the same result.

Henon, S; Lenormand, G; Richert, A; Gallet, F

1999-01-01

336

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

SciTech Connect

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; Wang Xiaolin; Sun Dong [Department of Mechanical and Biomedical Engineering, City University of Hong Kong (Hong Kong); Cheng Jinping; Han Cheng, Shuk [Department of Biology and Chemistry, City University of Hong Kong (Hong Kong); Kong, Chi-Wing [Stem Cell and Regenerative Medicine Consortium, and Departments of Medicine and Physiology, LKS Faculty of Medicine, University of Hong Kong (Hong Kong); Li, Ronald A. [Stem Cell and Regenerative Medicine Consortium, and Departments of Medicine and Physiology, LKS Faculty of Medicine, University of Hong Kong (Hong Kong); Center of Cardiovascular Research, Mount Sinai School of Medicine, New York, New York 10029 (United States)

2013-07-15

337

Manipulation and assembly of ZnO nanowires with single holographic optical tweezers system.  

PubMed

ZnO nanowires, characterized with high melting points, are hard to assemble together with laser fusion. In order to build micro-nano structures with ZnO nanowires, a polymer film with a low melting point and high optical transparency is introduced as a substrate for ZnO nanowires to be deposited. A holographic optical tweezers system is used not only to manipulate ZnO nanowires, but also to melt the polymer film for the fixation of ZnO nanowires. By this method, micro-nano structures composed of ZnO nanowires are produced, which can be utilized as subwavelength optical waveguides. PMID:24514119

Li, Jing; Du, Gang

2014-01-20

338

Adding functionalities to precomputed holograms with random mask multiplexing in holographic optical tweezers.  

PubMed

In this study, we present a method designed to generate dynamic holograms in holographic optical tweezers. The approach combines our random mask encoding method with iterative high-efficiency algorithms. This hybrid method can be used to dynamically modify precalculated holograms, giving them new functionalities-temporarily or permanently-with a low computational cost. This allows the easy addition or removal of a single trap or the independent control of groups of traps for manipulating a variety of rigid structures in real time. PMID:21460909

Mas, Josep; Roth, Michelle S; Martín-Badosa, Estela; Montes-Usategui, Mario

2011-04-01

339

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

PubMed

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

2013-09-21

340

Trapping and manipulation of microscopic bubbles with a scanning optical tweezer  

NASA Astrophysics Data System (ADS)

The authors have demonstrated three-dimensional trapping of ultrasound contrast agent microbubbles using a circularly scanning optical tweezers to confine the microbubble in a time-averaged optical potential. They have measured the maximum transverse drag force that may be applied to the trapped microbubble before it escapes and found that this decreases significantly at small trap radii. They explain this in terms of the relative volumes of the microbubble and the trap and anticipate that this feature will be important in experiments involving the insonation of optically trapped microbubbles.

Jones, P. H.; Stride, E.; Saffari, N.

2006-08-01

341

Optoelectronic Tweezers as a Tool for Parallel Single-Cell Manipulation and Stimulation  

PubMed Central

Optoelectronic tweezers (OET) is a promising approach for the parallel manipulation of single cells for a variety of biological applications. By combining the manipulation capabilities of OET with other relevant biological techniques (such as cell lysis and electroporation), one can realize a true parallel, single-cell diagnostic and stimulation tool. Here, we demonstrate the utility of the OET device by integrating it onto single-chip systems capable of performing in-situ, electrode-based electroporation/lysis, individual cell, light-induced lysis, and light-induced electroporation.

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

2010-01-01

342

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

2013-08-01

343

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

2013-07-01

344

Direct manipulation of malaria parasites with optical tweezers reveals distinct functions of Plasmodium surface proteins.  

PubMed

Plasmodium sporozoite motility is essential for establishing malaria infections. It depends on initial adhesion to a substrate as well as the continuous turnover of discrete adhesion sites. Adhesion and motility are mediated by a dynamic actin cytoskeleton and surface proteins. The mode of adhesion formation and the integration of adhesion forces into fast and continuous forward locomotion remain largely unknown. Here, we use optical tweezers to directly trap individual parasites and probe adhesion formation. We find that sporozoites lacking the surface proteins TRAP and S6 display distinct defects in initial adhesion; trap(-) sporozoites adhere preferentially with their front end, while s6(-) sporozoites show no such preference. The cohesive strength of the initial adhesion site is differently affected by actin filament depolymerization at distinct adhesion sites along the parasite for trap(-) and s6(-) sporozoites. These spatial differences between TRAP and S6 in their functional interaction with actin filaments show that these proteins have nonredundant roles during adhesion and motility. We suggest that complex protein-protein interactions and signaling events govern the regulation of parasite gliding at different sites along the parasite. Investigating how these events are coordinated will be essential for our understanding of sporozoite gliding motility, which is crucial for malaria infection. Laser tweezers will be a valuable part of the toolset. PMID:22568891

Hegge, Stephan; Uhrig, Kai; Streichfuss, Martin; Kynast-Wolf, Gisela; Matuschewski, Kai; Spatz, Joachim P; Frischknecht, Friedrich

2012-06-26

345

A combined double-tweezers and wavelength-tunable laser nanosurgery microscope  

NASA Astrophysics Data System (ADS)

In two previous studies we have conducted combined laser subcellular microsurgery and optical trapping on chromosomes in living cells1, 2. In the latter study we used two separate microscopes, one for the trap and one for the laser scissors, thus requiring that we move the cell specimen between microscopes and relocate the irradiated cells. In the former paper we combined the 1064 nm laser trap and the 532 nm laser scissors into one microscope. However, in neither study did we have multiple traps allowing for more flexibility in application of the trapping force. In the present paper we describe a combined laser scissors and tweezers microscope that (1) has two trapping beams (both moveable via rapid scanning mirrors (FSM- 300, Newport Corp.), (2) uses a short pulsed tunable 200 fs 710-990 nm Ti:Sapphire laser for laser microsurgery, and (3) also has the option to use a 337 nm 4 ns UV laser for subcellular surgery. The two laser tweezers and either of the laser ablation beams can be used in a cell surgery experiment. The system is integrated into the robotic-controlled RoboLase system3. Experiments on mitotic chromosomes of rat kangaroo PTK2 cells are described.

Zhu, Qingyuan; Parsa, Shahab; Shi, Linda Z.; Harsono, Marcellinus; Wakida, Nicole M.; Berns, Michael W.

2009-08-01

346

Crosstalk elimination in the detection of dual-beam optical tweezers by spatial filtering.  

PubMed

In dual-beam optical tweezers, the accuracy of position and force measurements is often compromised by crosstalk between the two detected signals, this crosstalk leading to systematic and significant errors on the measured forces and distances. This is true both for dual-beam optical traps where the splitting of the two traps is done by polarization optics and for dual optical traps constructed by other methods, e.g., holographic tweezers. If the two traps are orthogonally polarized, most often crosstalk is minimized by inserting polarization optics in front of the detector; however, this method is not perfect because of the de-polarization of the trapping beam introduced by the required high numerical aperture optics. Here we present a simple and easy-to-implement method to efficiently eliminate crosstalk. The method is based on spatial filtering by simply inserting a pinhole at the correct position and is highly compatible with standard back focal plane photodiode based detection of position and force. Our spatial filtering method reduces crosstalk up to five times better than polarization filtering alone. The effectiveness is dependent on pinhole size and distance between the traps and is here quantified experimentally and reproduced by theoretical modeling. The method here proposed will improve the accuracy of force-distance measurements, e.g., of single molecules, performed by dual-beam optical traps and hence give much more scientific value for the experimental efforts. PMID:24880354

Ott, Dino; Reihani, S Nader S; Oddershede, Lene B

2014-05-01

347

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

2013-04-01

348

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.

2009-01-01

349

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

2012-01-01

350

Auto- and cross-power spectral analysis of dual trap optical tweezer experiments using Bayesian inference  

NASA Astrophysics Data System (ADS)

The thermal fluctuations of micron-sized beads in dual trap optical tweezer experiments contain complete dynamic information about the viscoelastic properties of the embedding medium and--if present--macromolecular constructs connecting the two beads. To quantitatively interpret the spectral properties of the measured signals, a detailed understanding of the instrumental characteristics is required. To this end, we present a theoretical description of the signal processing in a typical dual trap optical tweezer experiment accounting for polarization crosstalk and instrumental noise and discuss the effect of finite statistics. To infer the unknown parameters from experimental data, a maximum likelihood method based on the statistical properties of the stochastic signals is derived. In a first step, the method can be used for calibration purposes: We propose a scheme involving three consecutive measurements (both traps empty, first one occupied and second empty, and vice versa), by which all instrumental and physical parameters of the setup are determined. We test our approach for a simple model system, namely a pair of unconnected, but hydrodynamically interacting spheres. The comparison to theoretical predictions based on instantaneous as well as retarded hydrodynamics emphasizes the importance of hydrodynamic retardation effects due to vorticity diffusion in the fluid. For more complex experimental scenarios, where macromolecular constructs are tethered between the two beads, the same maximum likelihood method in conjunction with dynamic deconvolution theory will in a second step allow one to determine the viscoelastic properties of the tethered element connecting the two beads.

von Hansen, Yann; Mehlich, Alexander; Pelz, Benjamin; Rief, Matthias; Netz, Roland R.

2012-09-01

351

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

NASA Astrophysics Data System (ADS)

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 acoustically trap particles near the focal point if certain conditions are met. Acoustic force exerted on fat tissue in ultrasonic fields is analyzed in ray acoustics regime where the wavelength of acoustic beam is much smaller than the size of the particle. In this paper, the analysis is therefore based on the field pattern produced by a strongly focused 100 MHz ultrasonic transducer with Gaussian intensity distribution. The magnitude of force and Fresnel coefficients at various positions are calculated. According to the simulation results, acoustical tweezer works particularly when the beam width at focus is one wavelength and the tolerance of acoustic impedance mismatch between two media lies within 6.7%. [Work supported by NIH Grant P41-EB2182.

Lee, Jungwoo; Shung, Kirk

2005-04-01

352

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.

2012-01-01

353

Analysis of cell mechanics in single vinculin-deficient cells using a magnetic tweezer  

NASA Technical Reports Server (NTRS)

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 the transmembrane integrin linkages to the cytoskeleton than previously reported using related techniques that measured average mechanical properties of large cell populations. The mechanical properties measured varied widely among cells, exhibiting an approximately log-normal distribution. The median lateral bead displacement was 2-fold larger in F9 Vin (-/-) cells compared to wild-type cells whereas the arithmetic mean displacement only increased by 37%. We conclude that vinculin serves a greater mechanical role in cells than previously reported and that this magnetic tweezer device may be useful for probing the molecular basis of cell mechanics within single cells. Copyright 2000 Academic Press.

Alenghat, F. J.; Fabry, B.; Tsai, K. Y.; Goldmann, W. H.; Ingber, D. E.

2000-01-01

354

Electrochemical detection of single microbeads manipulated by optical tweezers in the vicinity of ultramicroelectrodes.  

PubMed

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

2013-10-01

355

A modular system architecture for agile assembly of nanocomponents using optical tweezers  

NASA Astrophysics Data System (ADS)

In order to realize the flexibility optical trapping offers as a nanoassembly tool, we need to develop natural and intuitive interfaces to assemble large quantities of nanocomponents quickly and cheaply. We propose a system to create such an interface that is scalable, inter-changeable and modular. Several prototypes are described, starting with simple interfaces that control a single trap in the optical tweezers instrument using a 3-dimensional Phantom haptic device. A networkbased approach is adopted early on, and a modular prototype is then described in detail. In such a design, individual modules developed on different platforms work independently and communicate with each other through a common language interface using the Neutral Messaging Language (NML) communication protocol. A natural user interface is implemented that can be used to create and manipulate traps interactively like in a CAD program. Modules such as image processing and automatic assembly are also added to help simplify routine assembly tasks. Drawing on lessons learned from the prototypes, a new system specification is formulated to better integrate the modules. Finally, conclusions are drawn on the overall viability and future of network-based systems for nanoassembly using optical tweezers.

Balijepalli, Arvind; LeBrun, Thomas; Gagnon, Cedric; Lee, Yong-Gu; Dagalakis, Nicholas

2005-09-01

356

Optical properties of red blood cells: an optical tweezer based analysis  

NASA Astrophysics Data System (ADS)

A microscopic object finds an equilibrium orientation under a laser tweezer such that a maximum of its volume lies in the region of highest electric field. Furthermore, birefringent microscopic objects show no rotational diffusion after reorienting under a linearly polarized optical trap and also are seen to follow the plane of polarization when the latter is changed using a half wave plate. We observe that a healthy human Red Blood Cell (RBC) reproduces these observations in an optical tweezer, which confirms it to be birefringent. Polarization microscopy based measurements reveal that the birefringence is confined to the cell's dimple region and the mean value of retardation for polarized green light (? = 546nm) is 9 +/- 1.5nm. We provide a simple geometrical model that attributes the birefringence to the nature of arrangement of the phospholipid molecules of the bilayer. This predicts the observed variation in the measured birefringence, from the dimple to the rim of the cell which we further show, can serve to demarcate the extent of the dimple region. This points to the value of birefringence measurements in revealing cell membrane contours. . We extend this technique to understand the birefringence of a chicken RBC, an oblate shaped cell, wherein the slow axis is identified to be coincident with the long axis of the cell. Further, we observe the birefringence to be confined to the edges of the cell. Experiments to probe the optomechanical response of the chicken RBC are in progress.

Nagesh, B. V.; Lakkegowda, Yogesha; Pratibha, R.; Praveen, P.; Bhattacharya, Sarbari; Ananthamurthy, Sharath

2014-03-01

357

Computational characterization and modeling of buckyball tweezers: density functional study of concave convex pi...pi interactions  

Microsoft Academic Search

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The geometries and binding energies of a recent buckyball tweezers (C60H28) and its supramolecular complexes are investigated using recently developed

Yan Zhao; Donald G. Truhlar

2008-01-01

358

Development of a two-photon polymerization and optical tweezers microscope for fabrication and manipulation of microstructures  

NASA Astrophysics Data System (ADS)

We report development of a two-photon polymerization (TPP) microscope, for micro-fabrication of microstructures, which is capable of optical manipulation by use of optical tweezers. The system is based on an inverted Nikon microscope with a tunable Ti: Sapphire femto-second (fs) laser coupled to the upper back port. While in modelocked condition, nanoparticles and wires were fabricated in photo-polymerizable synthetic materials using TPP. By axial positioning of the focused TPP laser beam, 1D-structures (for use as wave guide) were fabricated at desired height above the surface of the substrate. In the mode lock-OFF condition the same tunable laser microbeam was employed as optical tweezers to the hold the nanostructures and manipulate them even in highly viscous medium before immobilizing. Size of the TPP induced structure was found to depend on the fs laser intensity and exposure. Further, by shaping the fs laser beam to line pattern, linear 1D structures could be fabricated without scanning the beam or stage, which remain aligned along the line intensity profile due to anisotropic trapping force of the line tweezers in X and Y-directions. Use of optical tweezers with two-photon polymerization not only allowed in-situ corrective positioning of the polymerized structures, but also the integration of fluorescent microspheres (resonator/detector) with polymerized waveguide.

Ingle, Ninad; Mohanty, Samarendra K.

2011-02-01

359

Computational characterization and modeling of buckyball tweezers: density functional study of concave-convex pi...pi interactions.  

PubMed

The geometries and binding energies of a recent buckyball tweezers (C(60)H(28)) and its supramolecular complexes are investigated using recently developed density functionals (M06-L and M06-2X) that include an accurate treatment of medium-range correlation energy. The pincer part of the tweezers, corannulene, has a strong attractive interaction with C(60). However, due to the entropy penalty, the calculated gas-phase free energy of association of the C(60)@corannulene supramolecule is positive 3.5 kcal mol(-1); and this entropy penalty explains why it is difficult to observe C(60)@corannulene supramolecule experimentally. By using a pi-extended tetrathiafulvalene (TTF), in particular 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (TTFAQ or C(20)H(10)S(4)), as the pincer part, we modeled a new buckyball tweezers. The geometries and binding energies of the new buckyball tweezers and its supramolecular complexes are also calculated. Due to fact that the attractive interaction between TTFAQ and C(60) is weaker than that between corannulene and C(60), the gas-phase binding free energy in the C(60)@C(60)H (32)S(8) supramolecular complex is smaller than that in the C(60)@C(60)H(28) supramolecule. We also discuss solvent effects. PMID:18464998

Zhao, Yan; Truhlar, Donald G

2008-05-21

360

Responsive Supramolecular Polymers Based on the Bis[alkynylplatinum(II)] Terpyridine Molecular Tweezer/Arene Recognition Motif.  

PubMed

Supramolecular polymers are constructed based on the novel bis[alkynylplatinum(II)] terpyridine molecular tweezer/pyrene recognition motif. Successive addition of anthracene as the diene and cyano-functionalized dienophile triggers the reversible supramolecular polymerization process, thus advancing the concept of utilizing Diels-Alder chemistry to access stimuli-responsive materials in compartmentalized systems. PMID:24810864

Tian, Yu-Kui; Shi, Yong-Gang; Yang, Zhi-Shuai; Wang, Feng

2014-06-10

361

Dynamics analysis and closed-loop control of biological cells in transportation using robotic manipulation system with optical tweezers  

Microsoft Academic Search

Increasing demands for both accuracy and productivity in cell manipulation highlight the need for automated process that integrates robotics and micro manipulation technologies. Optical tweezers, which use low power laser beams to trap and manipulate particles at micro\\/nano scale, have provided a revolutionary solution to manipulate biological objects in a noninvasive way. In this paper, we propose to use a

Songyu Hu; Dong Sun; Gang Feng

2010-01-01

362

Light-matter Interactions: From the Photophysics of Organic Semiconductors to High Spatial Resolution Optical Tweezer-controlled Nanoprobes  

NASA Astrophysics Data System (ADS)

Studies of light-matter interactions in organic semiconductors and in optical tweezer trapping of nanoparticles are presented. In the research related to organic semiconductor materials, a variety of novel materials and their composites have been characterized, and physical mechanisms behind their optoelectronic properties have been established. Three novel functionalized hexacene derivatives were deemed sufficiently stable to enable characterization of these materials in devices. From dark current and photocurrent measurements of the hexacene thin-films, it was determined that all three derivatives are photoconductive in the near-infrared, and space charge limited mobility values were obtained. In addition, physical mechanisms behind charge transfer, charge carrier photogeneration, and charge transport in small-molecule donor/acceptor composite films have been systematically studied. In these studies, it was determined that the charge transfer from the donor to the acceptor molecule can result in either an emissive charge transfer exciton (exciplex) or a non-emissive charge transfer exciton formation, depending on the energy difference between LUMO of the donor and the acceptor. However, the most dramatic trends in photoluminescent and photoconductive properties of the donor/acceptor composites were correlated with the separation between the donor and acceptor molecules at the donor/acceptor interface. In particular, composite films with larger separations exhibited electric field-assisted charge transfer exciton dissociation, which contributed to nanosecond time-scale photocurrents under a 500 ps pulsed photoexciation. Large donor/acceptor separation also resulted in reduced charge carrier recombination, which led to a factor of 5-10 increase in continuous wave photocurrents in certain donor/acceptor composites, as compared to those in pristine donor films. In the optical tweezer based studies, work towards the development of high spatial resolution optical tweezer controlled nanoprobes is presented. In particular, the possibility of exploiting the optical resonance of a particle to increase the optical tweezer forces acting on it within the trap has been investigated. Such an increase in the force would improve the potential spatial resolution of an optical tweezer controlled probe. Experimental results and numerical simulations on micron sized resonant dielectric particles showed a small increase in the optical forces that confine such particles within the trap, when tweezer trapping is conducted at wavelengths on the red-side of the optical resonance. Preliminary work on optical tweezer controlled ion/pH sensitive probes and on surface charge measurements is also reported.

Kendrick, Mark J.

363

A bisphosphonate tweezers and clickable PEGylated PAMAM dendrons for the preparation of functional iron oxide nanoparticles displaying renal and hepatobiliary elimination.  

PubMed

The functionalization of superparamagnetic iron oxide nanoparticles (SPION) with PEGylated PAMAM dendrons through a bisphosphonate tweezers yielded 15 and 30 nm dendritic nano-objects stable in physiological media and showing both renal and hepatobiliary elimination. PMID:23991429

Ghobril, Cynthia; Popa, Gabriela; Parat, Audrey; Billotey, Claire; Taleb, Jacqueline; Bonazza, Pauline; Begin-Colin, Sylvie; Felder-Flesch, Delphine

2013-10-14

364

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

1998-01-01

365

Engineered Tumor Cell Apoptosis Monitoring Method Based on Dynamic Laser Tweezers  

PubMed Central

Monitoring the cells' apoptosis progression could provide a valuable insight into the temporal events that initiate cell death as well as the potential for rescue of apoptotic cells. In this paper, we engineered a novel and robust method for monitoring apoptosis of tumor cells based on dynamic laser tweezers, using A549 and HeLa cell line as typical samples. The entire experiment can be completed in a few hours with small amount of fluid sample, presenting great advantages of celerity, microscaled measurement, and label-free explorations without perturbing experimental conditions in combination with other probes. Validity and stability of this method are verified experimentally in terms of physical parameters of the system. The proposed technique has great potential in improving cancer treatment by monitoring the objective efficacy of tumor cell killing.

Zhang, Yuquan; Wu, Xiaojing; Min, Changjun; Zhu, Siwei; Urbach, H. Paul; Yuan, Xiaocong

2014-01-01

366

Two-photon fluorescence excitation in continuous-wave infrared optical tweezers  

NASA Astrophysics Data System (ADS)

We report the observation of two-photon fluorescence excitation 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 sample. In particular, a cw Nd:YAG (1064-nm) laser is used simultaneously to confine, and excite visible fluorescence from submicrometer regions of, cell specimens. Two-photon fluorescence emission spectra are presented for motile human sperm cells and immotile Chinese hamster ovary cells that have been labeled with nucleic acid (Propidium Iodide) and pH-sensitive (Snarf) fluorescent probes. The resulting spectra are correlated to light-induced changes in the physiological state experienced by the trapped cells. This spectral technique should prove extremely useful for monitoring cellular activity and the effects of confinement by optical tweezers.

Liu, Y.; Sonek, G. J.; Berns, M. W.; Konig, K.; Tromberg, B. J.

1995-11-01

367

Optimization of particle trapping and patterning via photovoltaic tweezers: role of light modulation and particle size  

NASA Astrophysics Data System (ADS)

The role of light modulation m and particle size on the morphology and spatial resolution of nano-particle patterns obtained by photovoltaic tweezers on Fe?:?LiNbO3 has been investigated. The impact of m when using spherical as well as non-spherical (anisotropic) nano-particles deposited on the sample surface has been elucidated. Light modulation is a key parameter determining the particle profile contrast that is optimum for spherical particles and high-m values (m ? 1). The minimum particle periodicities reachable are also investigated obtaining periodic patterns up to 3.5 µm. This is a value at least one order of magnitude shorter than those obtained in previous reported experiments. Results are successfully explained and discussed in light of the previous reported models for photorefraction including nonlinear carrier transport and dielectrophoretic trapping. From the results, a number of rules for particle patterning optimization are derived.

Matarrubia, J.; García-Cabañes, A.; Plaza, J. L.; Agulló-López, F.; Carrascosa, M.

2014-07-01

368

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

2004-06-01

369

Accurate measurement of force and displacement with optical tweezers using DNA molecules as metrology standards  

NASA Astrophysics Data System (ADS)

Optical tweezers facilitate measurement of piconewton-level forces and nanometer-level displacements and have broad applications in biophysics and soft matter physics research. We have shown previously that DNA molecules can be used as metrology standards to define such measurements. Force-extension measurements on two DNA molecules of different lengths can be used to determine four necessary measurement parameters. Here, we show that the accuracy of determining these parameters can be improved by more than 7-fold by incorporating measurements of the DNA overstretching transition and using a multi-step data analysis procedure. This method results in very robust and precise fitting of DNA force-extension measurements to the worm-like chain model. We verify the accuracy through independent measurements of DNA stretching, DNA unzipping, and microsphere contact forces.

delToro, Damian; Smith, Douglas E.

2014-04-01

370

Engineered tumor cell apoptosis monitoring method based on dynamic laser tweezers.  

PubMed

Monitoring the cells' apoptosis progression could provide a valuable insight into the temporal events that initiate cell death as well as the potential for rescue of apoptotic cells. In this paper, we engineered a novel and robust method for monitoring apoptosis of tumor cells based on dynamic laser tweezers, using A549 and HeLa cell line as typical samples. The entire experiment can be completed in a few hours with small amount of fluid sample, presenting great advantages of celerity, microscaled measurement, and label-free explorations without perturbing experimental conditions in combination with other probes. Validity and stability of this method are verified experimentally in terms of physical parameters of the system. The proposed technique has great potential in improving cancer treatment by monitoring the objective efficacy of tumor cell killing. PMID:24800217

Zhang, Yuquan; Wu, Xiaojing; Min, Changjun; Zhu, Siwei; Urbach, H Paul; Yuan, Xiaocong

2014-01-01

371

Amplitude-phase modulation for reducing the 0th order beam spot in holographic optical tweezers  

NASA Astrophysics Data System (ADS)

The 0-th order diffraction light in an intensity pattern produced by a hologram disturbs optical manipulation of micro-objects in dynamic holographic optical tweezers (HOT). The purpose of this study is to investigate polarization characteristics of amplitude and phase modulations in the HOT to reduce the influence of the 0-th order beam spot. Numerical simulations are conducted using a Jones matrix of the system, whose the validity is experimentally confirmed. The optimum conditions to reduce the influence of the 0-th order beam spot can be estimated on the bases of the numerical results and its effectiveness in performance of the HOT system is experimentally demonstrated by the optical manipulation of polystyrene particles.

Iwai, Toshiaki; Yamamoto, Johtaro; Doi, Yuki

2010-08-01

372

Double nanohole optical tweezers visualize protein p53 suppressing unzipping of single DNA-hairpins.  

PubMed

Here we report on the use of double-nanohole (DNH) optical tweezers as a label-free and free-solution single-molecule probe for protein-DNA interactions. Using this approach, we demonstrate the unzipping of individual 10 base pair DNA-hairpins, and quantify how tumor suppressor p53 protein delays the unzipping. From the Arrhenius behavior, we find the energy barrier to unzipping introduced by p53 to be 2 × 10(-20) J, whereas cys135ser mutant p53 does not show suppression of unzipping, which gives clues to its functional inability to suppress tumor growth. This transformative approach to single molecule analysis allows for ultra-sensitive detection and quantification of protein-DNA interactions to revolutionize the fight against genetic diseases. PMID:24940547

Kotnala, Abhay; Gordon, Reuven

2014-06-01

373

Constructing 3D crystal templates for photonic band gap materials using holographic optical tweezers.  

PubMed

A simple and robust method is presented for the construction of 3-dimensional crystals from silica and polystyrene microspheres. The crystals are suitable for use as templates in the production of three-dimensional photonic band gap (PBG) materials. Manipulation of the microspheres was achieved using a dynamic holographic assembler (DHA) consisting of computer controlled holographic optical tweezers. Attachment of the microspheres was achieved by adjusting their colloidal interactions during assembly. The method is demonstrated by constructing a variety of 3-dimensional crystals using spheres ranging in size from 3 microm down to 800 nm. A major advantage of the technique is that it may be used to build structures that cannot be made using self-assembly. This is illustrated through the construction of crystals in which line defects have been deliberately included, and by building simple cubic structures. PMID:18711539

Benito, D C; Carberry, D M; Simpson, S H; Gibson, G M; Padgett, M J; Rarity, J G; Miles, M J; Hanna, S

2008-08-18

374

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

2005-07-01

375

Raman tweezers provide the fingerprint of cells supporting the late stages of KSHV reactivation  

PubMed Central

Kaposi’s sarcoma-associated herpesvirus (KSHV) has both latent and lytic phases of replication. The molecular switch that triggers a reactivation is still unclear. Cells from S phase of cell cycle provide apt conditions for an active reactivation. In order to specifically delineate the Raman spectra of cells supporting KSHV reactivation, we followed a novel approach where cells were sorted based on the state of infection (latent Vs lytic) by a flow cytometer and then analyzed by the Raman tweezers. The Raman bands at 785, 813, 830, 1095, and 1128 cm?1 are specifically altered in cells supporting KSHV reactivation. These 5 peaks make up the Raman fingerprint of cells supporting KSHV reactivation. The physiological relevance of the changes in these peaks with respect to KSHV reactivation is discussed in the following report.

Dyson, Ossie F.; Ford, Patrick W.; Chen, De; Li, Yong-Qing; Akula, Shaw M.

2009-01-01

376

The use of optical tweezers to study sperm competition and motility in primates.  

PubMed

Optical trapping is a non-invasive biophysical tool which has been widely applied to study physiological and biomechanical properties of cells. Using laser 'tweezers' in combination with custom-designed computer tracking algorithms, the swimming speeds and the relative swimming forces of individual sperm can be measured in real time. This combination of physical and engineering tools has been used to examine the evolutionary effect of sperm competition in primates. The results demonstrate a correlation between mating type and sperm motility: sperm from polygamous (multi-partner) primate species swim faster and with greater force than sperm from polygynous (single partner) primate species. In addition, sperm swimming force linearly increases with swimming speed for each species, yet the regression relating the two parameters is species specific. These results demonstrate the feasibility of using these tools to study rapidly moving (microm s(-1)) biological cells. PMID:17650470

Nascimento, Jaclyn M; Shi, Linda Z; Meyers, Stuart; Gagneux, Pascal; Loskutoff, Naida M; Botvinick, Elliot L; Berns, Michael W

2008-03-01

377

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.

2006-01-01

378

Haptic guidance for improved task performance in steering microparticles with optical tweezers.  

PubMed

We report the manipulation of 4-5 mum diameter polymer microspheres floating in water using optical tweezers (OT) and a haptic device (i.e. force-reflecting robotic arm). Trapped microspheres are steered using the end-effector of a haptic device that is virtually coupled to an XYZ piezo-scanner controlling the movements of the fluid bed. To help with the manipulations, we first calculate a collision-free path for the particle and then display artificial guidance forces to the user through the haptic device to keep him/her on this path during steering. Experiments conducted with 8 subjects show almost two-fold improvements in the average path error and average speed under the guidance of haptic feedback. PMID:19547521

Basdogan, Cagatay; Kiraz, Alper; Bukusoglu, Ibrahim; Varol, Ayd?n; Do?anay, Sultan

2007-09-01

379

Characterizing the rotation of non symmetric objects in an optical tweezer  

NASA Astrophysics Data System (ADS)

We present an optical tweezer based study of the rotation of microscopic objects with shape asymmetry. Thermal fluctuations and rotations are simultaneously monitored through laser back scattering. The rotation causes a modulation in intensity of the back scattered light incident on a quadrant photo detector. The resulting power spectrum is a modified Lorentzian with additional peaks located at the fundamental rotational frequency of the object and at the integer harmonics. The manifestation of these peaks reveals that the rotations are periodic but with varying angular velocity. We model our experimental results to illustrate the hydrodynamic interplay between the rotor and the surrounding medium that results in the time dependence of the angular speed of the former. Further, we demonstrate the use of video microscopy for characterization of low reflectivity rotors, such as biological cells. We propose through these studies that an analysis of these rotations can provide insights into the role of hydrodynamics at micron levels.

Yogesha; Bhattacharya, Sarbari; Ananthamurthy, Sharath

2012-05-01

380

Double nanohole optical tweezers visualize protein p53 suppressing unzipping of single DNA-hairpins  

PubMed Central

Here we report on the use of double-nanohole (DNH) optical tweezers as a label-free and free-solution single-molecule probe for protein–DNA interactions. Using this approach, we demonstrate the unzipping of individual 10 base pair DNA-hairpins, and quantify how tumor suppressor p53 protein delays the unzipping. From the Arrhenius behavior, we find the energy barrier to unzipping introduced by p53 to be 2 × 10?20 J, whereas cys135ser mutant p53 does not show suppression of unzipping, which gives clues to its functional inability to suppress tumor growth. This transformative approach to single molecule analysis allows for ultra-sensitive detection and quantification of protein–DNA interactions to revolutionize the fight against genetic diseases.

Kotnala, Abhay; Gordon, Reuven

2014-01-01

381

New developments on the design and modeling of fiber optical tweezers  

NASA Astrophysics Data System (ADS)

The intensity profile of a focused beam of light can exert small drift forces on particles with a few microns and even smaller, which can be used to confine or manipulate them. Optical trapping has several applications, in particular it has been adopted as a powerful tool in biology, allowing, for instance to manipulate in vivo single cells. A wide variety of optical setups have been implemented to optically trap microscopic bodies, however, the single beam trap using a tightly focused Gaussian beam continues to be the most used. Recent developments introduced an alternative to bulk optical trapping systems based on lensed optical fibers. This work presents simulations showing new designs of fiber optic and 2D waveguide tweezers based on studies of the forces acting on dielectric particles immersed in media with a distinct refractive index, which take into account the refractive index and structure of the particles.

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

2013-11-01

382

Tuning the size and configuration of nanocarbon microcapsules: aqueous method using optical tweezers.  

PubMed

To date, optical manipulation techniques for aqueous dispersions have been developed that deposit and/or transport nanoparticles not only for fundamental studies of colloidal dynamics, but also for either creating photonic devices or allowing accurate control of liquids on micron scales. Here, we report that optical tweezers (OT) system is able to direct three-dimensional assembly of graphene, graphite, and carbon nanotubes (CNT) into microcapsules of hollow spheres. The OT technique facilitates both to visualize the elasticity of a CNT microcapsule and to arrange a triplet of identical graphene microcapsules in aqueous media. Furthermore, the similarity of swelling courses has been found over a range of experimental parameters such as nanocarbon species, the power of the incident light, and the suspension density. Thanks to the universality in evolutions of rescaled capsule size, we can precisely control the size of various nanocarbon microcapsules by adjusting the duration time of laser emission. PMID:24509866

Frusawa, Hiroshi; Matsumoto, Youei

2014-01-01

383

Measurement of the electrostatic interaction between polyelectrolyte brush surfaces by optical tweezers.  

PubMed

We demonstrated an optical tweezers method to measure the electrostatic interaction between the strong polyelectrolyte brushes, poly(2-(methacryloyloxy)ethyltrimethylammonium chloride) (PMTAC), grafted on silica particles in aqueous media. The weak electrostatic interaction was successfully detected with a resolution of less than 0.1 ?N m(-1). The apparent Debye length, including the charge distribution in the polymer brush and the surface potential, decreased as the salt concentration in the medium increased. The experimentally obtained surface charge density was much smaller than that estimated from the amount of polyelectrolyte on the surface. Furthermore, the dissociation of ionic groups was enhanced by decreasing the grafting density of the polyelectrolyte brush. The results suggest that the majority of chloride counterions was immobilized in the dense polyelectrolyte brush layer to neutralize the high charge density. PMID:24325298

Murakami, Daiki; Takenaka, Ai; Kobayashi, Motoyasu; Jinnai, Hiroshi; Takahara, Atsushi

2013-12-31

384

Correction of aberration in holographic optical tweezers using a Shack-Hartmann sensor.  

PubMed

Optical aberration due to the nonflatness of spatial light modulators used in holographic optical tweezers significantly deteriorates the quality of the trap and may easily prevent stable trapping of particles. We use a Shack-Hartmann sensor to measure the distorted wavefront at the modulator plane; the conjugate of this wavefront is then added to the holograms written into the display to counteract its own curvature and thus compensate the optical aberration of the system. For a Holoeye LC-R 2500 reflective device, flatness is improved from 0.8? to ?/16 (?=532 nm), leading to a diffraction-limited spot at the focal plane of the microscope objective, which makes stable trapping possible. This process could be fully automated in a closed-loop configuration and would eventually allow other sources of aberration in the optical setup to be corrected for. PMID:23567567

López-Quesada, Carol; Andilla, Jordi; Martín-Badosa, Estela

2009-02-20

385

Dynamic and programmable cell-sorting by using microfluidics and holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Cell sorting is important in quantitative analysis for cellular and molecular biology study. For this purpose, we develop an opto-electro-mechanical sorting system which integrates a holographic optical tweezers (HOT) system to a microfluidics device. This system is designed to manipulate and sort various micro objects of different sizes by an optical pattern which is dynamic and programmable. In this work, we fabricate a microchannel with a main channel and two branches with polydimethylsiloxane (PDMS) which is a biocompatible elastomer material by utilizing semiconductor micro-fabrication techniques. By using a HOT system, we also generate two linear optical traps for the manipulation of micro particles. As a result, we have demonstrated that the larger particles are guided to the second branch by the two linear optical traps while the smaller particles remain unaffected and flow into the first branch of the microchannel.

Lin, Ho-Chien; Hsu, Long

2005-08-01

386

Reverse DNA translocation through a solid-state nanopore by magnetic tweezers  

PubMed Central

Voltage-driven DNA translocation through nanopores has attracted wide interest for many potential applications in molecular biology and biotechnology. However, it is intrinsically difficult to control the DNA motion in standard DNA translocation processes in which a strong electric field is required in drawing DNA into the pore, but it also leads to uncontrollable fast DNA translocation. Here we explore a new type of DNA translocation. We dub it ‘reverse DNA translocation’, in which the DNA is pulled through a nanopore mechanically by a magnetic bead, driven by a magnetic-field gradient. This technique is compatible with simultaneous ionic current measurements and is suitable for multiple nanopores, paving the way for large scale applications. We report the first experiment of reverse DNA translocation through a solid-state nanopore using magnetic tweezers.

Peng, Hongbo; Ling, Xinsheng Sean

2009-01-01

387

Simultaneous detection of rotational and translational motion in optical tweezers by measurement of backscattered intensity.  

PubMed

We describe a simple yet powerful technique of simultaneously measuring both translational and rotational motion of mesoscopic particles in optical tweezers by measuring the backscattered intensity on a quadrant photodiode (QPD). While the measurement of translational motion by taking the difference of the backscattered intensity incident on adjacent quadrants of a QPD is well known, we demonstrate that rotational motion can be measured very precisely by taking the difference between the diagonal quadrants. The latter measurement eliminates the translational component entirely and leads to a detection sensitivity of around 50 mdeg at S/N of 2 for angular motion of a driven microrod. The technique is also able to resolve the translational and rotational Brownian motion components of the microrod in an unperturbed trap and can be very useful in measuring translation-rotation coupling of micro-objects induced by hydrodynamic interactions. PMID:24876042

Roy, Basudev; Bera, Sudipta K; Banerjee, Ayan

2014-06-01

388

Evaluating cell matrix mechanics using an integrated nonlinear optical tweezer-confocal imaging system  

NASA Astrophysics Data System (ADS)

Biomechanics plays a central role in breast epithelial morphogenesis. In this study we have used 3D cultures in which normal breast epithelial cells are able to organize into rounded acini and tubular ducts, the main structures found in the breast tissue. We have identified fiber organization as a main determinant of ductal organization. While bulk rheological properties of the matrix seem to play a negligible role in determining the proportion of acini versus ducts, local changes may be pivotal in shape determination. As such, the ability to make microscale rheology measurements coupled with simultaneous optical imaging in 3D cultures can be critical to assess the biomechanical factors underlying epithelial morphogenesis. This paper describes the inclusion of optical tweezers based microrheology in a microscope that had been designed for nonlinear optical imaging of collagen networks in ECM. We propose two microrheology methods and show preliminary results using a gelatin hydrogel and collagen/Matrigel 3D cultures containing mammary gland epithelial cells.

Peng, Berney; Alonzo, Carlo A. C.; Xia, Lawrence; Speroni, Lucia; Georgakoudi, Irene; Soto, Ana M.; Sonnenschein, Carlos; Cronin-Golomb, Mark

2013-09-01

389

Mechanism of termination of bacteriophage DNA packaging investigated with optical tweezers  

NASA Astrophysics Data System (ADS)

The genomes of many dsDNA viruses are replicated by a mechanism that produces a long concatemer of multiple genomes. These viruses utilize multifunctional molecular motor complexes referred to as "terminases" that can excise a unit genome length of DNA and package it into preformed viral shells. Remarkably, the terminase motor can initiate packaging at the appropriate start point, translocate DNA, sense when a sufficient length has been packaged, and then switch into a mode where it arrests and cleaves the DNA to release a filled virus particle. We have recently developed an improved method to measure single phage lambda DNA packaging using dual-trap optical tweezers and pre-stalled motor-DNA-procapsid complexes. We are applying this method to test proposed mechanisms for the sensor that triggers termination; specifically a velocity-monitor model vs. energy-monitor model vs. capsid-filling monitor model.

delToro, Damian J.; Smith, Douglas E.

2012-10-01

390

Dual-trap technique for reduction of low-frequency noise in force measuring optical tweezers.  

PubMed

High-resolution long-time force measurements by optical tweezers are often limited by low-frequency (1/f) noise. A dual-trap technique is presented that can reduce such noise in the force signal. It incorporates a second trap (a reference trap) that probes the noise in the system and it is based upon the assumption that the low-frequency parts of the noise from the two traps are correlated. A subtraction of the low-frequency signal from the reference trap from the signal from the force measuring trap will therefore yield a net signal that is significantly less influenced by noise. It is shown that this dual-trap technique can reduce the noise in the force signal up to 60% depending on detection bandwidth. PMID:17228388

Klein, Markus; Andersson, Magnus; Axner, Ove; Fällman, Erik

2007-01-20

391

Protection of primary neurons and mouse brain from Alzheimer's pathology by molecular tweezers  

PubMed Central

Alzheimer’s disease is a devastating cureless neurodegenerative disorder affecting >35 million people worldwide. The disease is caused by toxic oligomers and aggregates of amyloid ? protein and the microtubule-associated protein tau. Recently, the Lys-specific molecular tweezer CLR01 has been shown to inhibit aggregation and toxicity of multiple amyloidogenic proteins, including amyloid ? protein and tau, by disrupting key interactions involved in the assembly process. Following up on these encouraging findings, here, we asked whether CLR01 could protect primary neurons from Alzheimer’s disease-associated synaptotoxicity and reduce Alzheimer’s disease–like pathology in vivo. Using cell culture and brain slices, we found that CLR01 effectively inhibited synaptotoxicity induced by the 42-residue isoform of amyloid ? protein, including ?80% inhibition of changes in dendritic spines density and long-term potentiation and complete inhibition of changes in basal synaptic activity. Using a radiolabelled version of the compound, we found that CLR01 crossed the mouse blood–brain barrier at ?2% of blood levels. Treatment of 15-month-old triple-transgenic mice for 1 month with CLR01 resulted in a decrease in brain amyloid ? protein aggregates, hyperphosphorylated tau and microglia load as observed by immunohistochemistry. Importantly, no signs of toxicity were observed in the treated mice, and CLR01 treatment did not affect the amyloidogenic processing of amyloid ? protein precursor. Examining induction or inhibition of the cytochrome P450 metabolism system by CLR01 revealed minimal interaction. Together, these data suggest that CLR01 is safe for use at concentrations well above those showing efficacy in mice. The efficacy and toxicity results support a process-specific mechanism of action of molecular tweezers and suggest that these are promising compounds for developing disease-modifying therapy for Alzheimer’s disease and related disorders.

Attar, Aida; Ripoli, Cristian; Riccardi, Elisa; Maiti, Panchanan; Li Puma, Domenica D.; Liu, Tingyu; Hayes, Jane; Jones, Mychica R.; Lichti-Kaiser, Kristin; Yang, Fusheng; Gale, Greg D.; Tseng, Chi-hong; Tan, Miao; Xie, Cui-Wei; Straudinger, Jeffrey L.; Klarner, Frank-Gerrit; Schrader, Thomas; Frautschy, Sally A.; Grassi, Claudio

2012-01-01

392

An active one-particle microrheometer: incorporating magnetic tweezers to total internal reflection microscopy.  

PubMed

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. PMID:23556822

Gong, Xiangjun; Hua, Li; Wu, Chi; Ngai, To

2013-03-01

393

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

2013-03-01

394

Photoacoustic tweezers  

Microsoft Academic Search

The goal of this study was to develop a new approach to manipulating biological and nonbiological objects in liquid or gas, with a focus on living cells in liquid. This approach is based on laser-generated thermal and pressure gradients in the medium surrounding an object, which create forces of different origins acting on the object. In general, depending on the

Vladimir P. Zharov

2002-01-01

395

Surface charge measurements and (dis)charging dynamics of organic semiconductors in various media using optical tweezers  

NASA Astrophysics Data System (ADS)

An exciting application of optical tweezers is the measurement of the surface charge on a trapped particle, as well as its time evolution with a single charge resolution. We report on an optical tweezer-based method to measure the effective surface charge on an organic semiconductor film at microscopic scales, which offers opportunities for investigations of ion and electron transfer between organic molecules and surrounding medium. Effective charge densities of 13+/-5 elementary charges per ?m2 were observed in anthradithiophene-coated silica microspheres suspended in water, with a more than an order of magnitude reduction in charge densities upon replacing water with the 50% wt/wt glycerol/water mixture.

Grollman, Rebecca R.; Peters, Kyle; Ostroverkhova, Oksana

2014-03-01

396

Power spectrum analysis for optical tweezers. II: Laser wavelength dependence of parasitic filtering, and how to achieve high bandwidth  

NASA Astrophysics Data System (ADS)

In a typical optical tweezers detection system, the position of a trapped object is determined from laser light impinging on a quadrant photodiode. When the laser is infrared and the photodiode is of silicon, they can act together as an unintended low-pass filter. This parasitic effect is due to the high transparency of silicon to near-infrared light. A simple model that accounts for this phenomenon [Berg-Sørensen et al., J. Appl. Phys. 93, 3167 (2003)] is here solved for frequencies up to 100 kHz and for laser wavelengths between 750 and 1064 nm. The solution is applied to experimental data in the same range, and is demonstrated to give this detection system of optical tweezers a bandwidth, accuracy, and precision that are limited only by the data acquisition board's bandwidth and bandpass ripples, here 96.7 kHz and 0.005 dB, respectively.

Berg-Sørensen, Kirstine; Peterman, Erwin J. G.; Weber, Tom; Schmidt, Christoph F.; Flyvbjerg, Henrik

2006-06-01

397

The interaction of lipopolysaccharide-coated polystyrene particle with membrane receptor proteins on macrophage measured by optical tweezers  

Microsoft Academic Search

Lipopolysaccharide (LPS) is one of the cell wall components of Gram-positive bacteria recognized by and interacted with receptor proteins such as CD14 on macrophage cells. Such a process plays an important role in our innate immune system. In this paper, we report the application of optical tweezers (lambda = 1064nm Gaussian beam focused by a water-immersed objective lens with N.A.

Ming-Tzo Wei; Kuo-Feng Hua; Jowey Hsu; Artashes Karmenyan; Hsien-Yeh Hsu; Arthur Chiou

2006-01-01

398

3D manipulation and visualization of in-vitro cells by optical tweezers and digital holographic microscopy  

NASA Astrophysics Data System (ADS)

We present the possibility to trap cells (mouse fibroblasts, bovine spermatozoa and diatoms), to manage their position and to induce rotation, by using optical tweezers. The aim is to place them in desired positions, in order to record holographic images in a microscope configuration. Then we are able to recover the 3D shape and to calculate the biovolume of the cells starting from the reconstructed quantitative phase maps (QPMs).

Merola, F.; Miccio, L.; Memmolo, P.; Di Caprio, G.; Coppola, G.; Netti, P.; Ferraro, P.

2014-03-01

399

Normal and system lupus erythematosus red blood cell interactions studied by double trap optical tweezers: direct measurements of aggregation forces  

NASA Astrophysics Data System (ADS)

Direct measurements of aggregation forces in piconewton range between two red blood cells in pair rouleau are performed under physiological conditions using double trap optical tweezers. Aggregation and disaggregation properties of healthy and pathologic (system lupus erythematosis) blood samples are analyzed. Strong difference in aggregation speed and behavior is revealed using the offered method which is proposed to be a promising tool for SLE monitoring at single cell level.

Khokhlova, Maria D.; Lyubin, Eugeny V.; Zhdanov, Alexander G.; Rykova, Sophia Yu.; Sokolova, Irina A.; Fedyanin, Andrey A.

2012-02-01

400

Asymmetric electron transport and highest occupied molecular orbital assisted tunneling through Zn-porphyrin molecular junctions  

NASA Astrophysics Data System (ADS)

We report electron transport measurements from gold-zinc-porphyrin-gold molecular junctions formed in an electromigrated nanogap. Asymmetric current-voltage (I-V) behaviors about the zero bias voltage were observed at room temperature and 4.2 K. These observations are in contrast to measurements from a nanogap without any molecules, which are dominated by tunneling and display symmetric I-V characteristics. In addition, increasing the gate voltage suppressed the current through the junction at room temperature, indicating electron tunneling proceeded through the highest occupied molecular orbital. Density of states calculations were performed to explain these findings and understand the microscopic origins of the observations.

Saha, Swatilekha; Owens, Jonathan R.; Meunier, Vincent; Lewis, K. M.

2013-10-01

401

Spectrin-Level Modeling of the Cytoskeleton and Optical Tweezers Stretching of the Erythrocyte  

PubMed Central

We present a three-dimensional computational study of whole-cell equilibrium shape and deformation of human red blood cell (RBC) using spectrin-level energetics. Random network models consisting of degree-2, 3, …, 9 junction complexes and spectrin links are used to populate spherical and biconcave surfaces and intermediate shapes, and coarse-grained molecular dynamics simulations are then performed with spectrin connectivities fixed. A sphere is first filled with cytosol and gradually deflated while preserving its total surface area, until cytosol volume consistent with the real RBC is reached. The equilibrium shape is determined through energy minimization by assuming that the spectrin tetramer links satisfy the worm-like chain free-energy model. Subsequently, direct stretching by optical tweezers of the initial equilibrium shape is simulated to extract the variation of axial and transverse diameters with the stretch force. At persistence length p = 7.5 nm for the spectrin tetramer molecule and corresponding in-plane shear modulus ?0 ? 8.3 ?N/m, our models show reasonable agreement with recent experimental measurements on the large deformation of RBC with optical tweezers. We find that the choice of the reference state used for the in-plane elastic energy is critical for determining the equilibrium shape. If a position-independent material reference state such as a full sphere is used in defining the in-plane energy, then the bending modulus ? needs to be at least a decade larger than the widely accepted value of 2 × 10?19 J to stabilize the biconcave shape against the cup shape. We demonstrate through detailed computations that this paradox can be avoided by invoking the physical hypothesis that the spectrin network undergoes constant remodeling to always relax the in-plane shear elastic energy to zero at any macroscopic shape, at some slow characteristic timescale. We have devised and implemented a liquefied network structure evolution algorithm that relaxes shear stress everywhere in the network and generates cytoskeleton structures that mimic experimental observations.

Li, J.; Dao, M.; Lim, C. T.; Suresh, S.

2005-01-01

402

Probing the micro-rheological properties of aerosol particles using optical tweezers  

NASA Astrophysics Data System (ADS)

The use of optical trapping techniques to manipulate probe particles for performing micro-rheological measurements on a surrounding fluid is well-established. Here, we review recent advances made in the use of optical trapping to probe the rheological properties of trapped particles themselves. In particular, we review observations of the continuous transition from liquid to solid-like viscosity of sub-picolitre supersaturated solution aerosol droplets using optical trapping techniques. Direct measurements of the viscosity of the particle bulk are derived from the damped oscillations in shape following coalescence of two particles, a consequence of the interplay between viscous and surface forces and the capillary driven relaxation of the approximately spheroidal composite particle. Holographic optical tweezers provide a facile method for the manipulation of arrays of particles allowing coalescence to be controllably induced between two micron-sized aerosol particles. The optical forces, while sufficiently strong to confine the composite particle, are several orders of magnitude weaker than the capillary forces driving relaxation. Light, elastically back-scattered by the particle, is recorded with sub-100 ns resolution allowing measurements of fast relaxation (low viscosity) dynamics, while the brightfield image can be used to monitor the shape relaxation extending to times in excess of 1000 s. For the slowest relaxation dynamics studied (particles with the highest viscosity) the presence and line shape of whispering gallery modes in the cavity enhanced Raman spectrum can be used to infer the relaxation time while serving the dual purpose of allowing the droplet size and refractive index to be measured with accuracies of ±0.025% and ±0.1%, respectively. The time constant for the damped relaxation can be used to infer the bulk viscosity, spanning from the dilute solution limit to a value approaching that of a glass, typically considered to be >1012 Pa s, whilst the frequencies of the normal modes of the oscillations of the particle can be used to infer surface properties. We will review the use of optical tweezers for studying the viscosity of aerosol particles and discuss the potential use of this micro-rheological tool for probing the fundamental concepts of phase, thermodynamic equilibrium and metastability.

Power, Rory M.; Reid, Jonathan P.

2014-07-01

403

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.

2005-03-01

404

A survey of DNA looping and cleavage properties of different restriction enzymes using optical tweezers  

NASA Astrophysics Data System (ADS)

Of the more than 3500 known Type II REases, a small but growing number have been identified that require two copies of the enzyme's recognition site for activity. Each site is bound to one enzyme subunit, and the two subunits come together by thermodynamic DNA looping to form an active multimer that cleaves the DNA. When Ca^++ is replaced with Mg^++ however, the multimers usually ``staple'' the recognition sites together trapping the DNA loops. Using force measuring optical tweezers, we investigate the behavior of 16 different two-site REases from the Type IIe, Type IIf, and Type IIs subsets on single DNA molecules in the presence of Mg^++, Ca^++, and EDTA. We show that one-site and two-site REases may be rapidly discerned. By measuring the force needed to disrupt the loops in the presence of Ca^++, we elucidate various binding behaviors amongst the two-site REases, probing DNA-enzyme and/or enzymatic subunit-subunit affinity. For one enzyme, HpaII, the effect of [Ca^++] on activity is studied in detail.

Millin, Rachel

2005-03-01

405

Cell viability in optical tweezers: high power red laser diode versus Nd:YAG laser.  

PubMed

Viability of cultivated Chinese hamster ovary cells in optical tweezers was measured after exposure to various light doses of red high power laser diodes (lambda = 670-680 nm) and a Nd:yttrium-aluminum-garnet laser (lambda = 1064 nm). When using a radiant exposure of 2.4 GJ/cm2, a reduction of colony formation up to a factor 2 (670-680 nm) or 1.6 (1064 nm) as well as a delay of cell growth were detected in comparison with nonirradiated controls. In contrast, no cell damage was found at an exposure of 340 MJ/cm2 for both wavelengths, and virtually no lethal damage at 1 GJ/cm2 applied at 1064 nm. Cell viabilities were correlated with fluorescence excitation spectra and with literature data of wavelength dependent cloning efficiencies. Fluorescence excitation maxima of the coenzymes NAD(P)H and flavins were detected at 365 and 450 nm, respectively. This is half of the wavelengths of the maxima of cell inactivation, suggesting that two-photon absorption by these coenzymes may contribute to cellular damage. Two-photon excitation of NAD(P)H and flavins may also affect cell viability after exposure to 670-680 nm, whereas one-photon excitation of water molecules seems to limit cell viability at 1064 nm. PMID:10938764

Schneckenburger, H; Hendinger, A; Sailer, R; Gschwend, M H; Strauss, W S; Bauer, M; Schütze, K

2000-01-01

406

Guest encapsulation and coronene-C60 exchange in supramolecular zinc porphyrin tweezers, grids and prisms.  

PubMed

Using a variant of the HETPHEN concept, heteroleptic 2D and 3D metallosupramolecular structures, such as tweezer T, grid G and tetragonal prism P, were fabricated quantitatively and characterised by (1)H NMR, (13)C NMR, (1)H-(1)H COSY, DOSY as well as ESI-MS. All structures encapsulate C60, with P showing the highest binding affinity (Kassoc = 3.3 × 10(6) M(-1)). The association constant increases along the series T < G < P, most likely due to the enhanced structural rigidity and better coplanarity of the two zinc porphyrin units. In contrast to T and G, the tetragonal prism P shows notable encapsulation of coronene (Kassoc = 1.1 × 10(4) M(-1)). In T and G, on the other hand, complexation of coronene is kinetically inhibited by the bulky mesityl rings at the porphyrin periphery. As illustrated in the facile displacement of coronene by C60 in coronene@P to furnish C60@P, P behaves as a flexible and guest-adaptive host. PMID:23440088

Samanta, Soumen K; Schmittel, Michael

2013-05-21

407

Force measuring optical tweezers system for long time measurements of P pili stability  

NASA Astrophysics Data System (ADS)

A force-measuring optical tweezers instrumentation and long time measurements of the elongation and retraction of bacterial fimbriae from Uropathogenic E. coli (UPEC) under strain are presented. The instrumentation is presented in some detail. Special emphasis is given to measures taken to reduce the influence of noise and drifts in the system and from the surrounding, which makes long term force measurements possible. Individual P pili from UPEC bacteria were used as a biological model system for repetitive unfolding and refolding cycles of bacterial fimbriae under equilibrium conditions. P pili have evolved into a three-dimensional helix-like structure, the PapA rod, that can be successively and significantly elongated and/or unfolded when exposed to external forces. The instrumentation is used for characterization of the force-vs.-elongation response of the PapA rod of individual P pili, with emphasis on the long time stability of the forced unfolding and refolding of the helical structure of the PapA rod. The results show that the PapA rod is capable of withstanding extensive strain, leading to a complete unfolding of the helical structure, repetitive times during the life cycle of a bacterium without any noticeable alteration of the mechanical properties of the P pili. This function is believed to be importance for UPEC bacteria in vivo since it provides a close contact to a host cell (which is an initial step of invasion) despite urine cleaning attempts.

Andersson, Magnus; Fällman, Erik; Uhlin, Bernt Eric; Axner, Ove

2006-03-01

408

An Interactive Virtual Reality Simulation for Nanoparticle Manipulation for Nanoassembly using Optical Tweezers  

NSDL National Science Digital Library

Nanotechnology and nano devices is believed to be one of the most promising steps that science is taking to the future. This paper proposes virtual reality (VR) as a tool to simulate nano particle manipulation using optical tweezers towards achieving nano- assembly for effectively handling issues such as difficulty in viewing, perceiving and controlling the nano-scale objects. The nano simulation is modeled, using virtual reality, displaying all the forces acting on nano particle during the manipulation. The simulation is developed for particles that belong to Rayleigh region and, represents interactions of OT (a laser beam) with the nano particle. The laser beam aimed on to the nano particle traps the particle by applying optical forces. The trapped particle is then moved by moving the laser beam. The proposed VR based simulation tool with its capabilities can be easily extended and used for creating an open system framework by connecting it to a real OT setup to control nano particles manipulation. In addition, a feedback system can be build to increase of precision of movement.

Bhavaraju, Krishna; Choudhury, Alamgir A.; Dwivedi, Suren; Ikonomove, Pavel

2009-10-02

409

A model for inertial particle trapping locations in hydrodynamic tweezers arrays  

NASA Astrophysics Data System (ADS)

We present a model for the trapping of particles with finite inertia in the microscale viscous steady streaming flow of hydrodynamic tweezers. Devices containing a square array and an offset array of cylindrical posts of radius 25 µm were fabricated. As water is oscillated at small amplitude (s < 5 µm) and audible frequency (5000 Hz), highly symmetric microeddies form causing the fluid and particles suspended in the fluid to transport through the device. We image the flows by using 0.5 µm radius fluorescent polystyrene particles, and demonstrate trapping with larger 5 µm radius polystyrene particles. The streaming flow fields are simulated numerically using a fast analytic-numeric approach, and inertial particle motion is determined using the well-known Maxey–Riley equation for small Stokes number (St) particle motion. The St-dependent period-averaged particle velocity is used to describe the effects of inertia on particle trapping locations. We find the St-dependence of trapping location depends on the underlying symmetry of the flow. Only traps located near eddy centers are affected by particle inertia.

House, Tyler A.; Lieu, Valerie H.; Schwartz, Daniel T.

2014-04-01

410

Cell patterning with a heptagon acoustic tweezer - application in neurite guidance.  

PubMed

Accurate control over positioning of cells is a highly desirable feature in tissue engineering applications since it allows, for example, population of substrates in a controlled fashion, rather than relying on random seeding. Current methods to achieve a differential distribution of cells mostly use passive patterning methods to change chemical, mechanical or topographic properties of surfaces, making areas differentially permissive to the adhesion of cells. However, these methods have no ad hoc control over the actual deposition of cells. Direct patterning methods like bioprinting offer good control over cell position, but require sophisticated instrumentation and are often cost- and time-intensive. Here, we present a novel electronically controlled method of generating dynamic cell patterns by acoustic trapping of cells at a user-determined position, with a heptagonal acoustic tweezer device. We demonstrate the capability of the device to create complex patterns of cells using the device's ability to re-position acoustic traps by using a phase shift in the acoustic wave, and by switching the configuration of active piezoelectric transducers. Furthermore, we show that by arranging Schwann cells from neonatal rats in a linear pattern we are able to create Bands of Büngner-like structures on a non-structured surface and demonstrate that these features are able to guide neurite outgrowth from neonatal rat dorsal root ganglia. PMID:24817215

Gesellchen, F; Bernassau, A L; Déjardin, T; Cumming, D R S; Riehle, M O

2014-07-01

411

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

2012-10-01

412

On-chip pH measurement using functionalized gel-microbeads positioned by optical tweezers.  

PubMed

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

2008-02-01

413

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

2013-02-01

414

Microrheology of complex fluids using optical tweezers: a comparison with macrorheological measurements  

NASA Astrophysics Data System (ADS)

The increasing interest in the mechanical properties of complex systems at mesoscopic scale has recently fueled the development of new experimental techniques, collectively indicated as microrheology. Unlike bulk-based approaches (macrorheology), these new techniques make use of micrometric probes (usually microspheres) which explore the mechanical properties of the surrounding medium. In this paper we discuss the basic idea of microrheology and we will focus on one specific technique based on optical tweezers (OT). The discussion starts from Newtonian fluids to tackle the more general case of complex fluids, also showing results of these techniques on solutions of a relevant biomolecule: hyaluronic acid (HA). In particular, we study the viscoelastic properties of low molecular weight HA (155 kDa) at low ionic strength over an extended frequency range (0.1-1000 Hz) and in a wide range of concentrations (0.01-20 mg ml-1), which include both the dilute and semidilute regime. In the concentration range here explored and within the test frequencies covered by our techniques, samples prevalently exhibit a viscous behavior, the elastic contribution becoming significant at the highest concentrations. By comparing OT outcomes to those obtained by a traditional rheometer, we found that they were in good agreement in the overlapping frequency range of the two techniques, thus confirming the reliability of the microrheological approach.

Pesce, G.; DeLuca, A. C.; Rusciano, G.; Netti, P. A.; Fusco, S.; Sasso, A.

2009-03-01

415

The ?PIVOT: an integrated particle image velocimeter and optical tweezers instrument for microenvironment investigations  

PubMed Central

A novel instrument to manipulate and characterize the mechanical environment in and around microscale objects in a fluidic environment has been developed by integrating two laser-based techniques: micron-resolution particle image velocimetry (?PIV) and optical tweezers (OT). This instrument, the ?PIVOT, enables a new realm of microscale studies, yet still maintains the individual capabilities of each optical technique. This was demonstrated with individual measurements of optical trap stiffness (?70 pN ?m?1 for a 20 ?m polystyrene sphere and a linear relationship between trap stiffness and laser power) and fluid velocities within 436 nm of a microchannel wall. The integrated device was validated by comparing computational flow predictions to the measured velocity profile around a trapped particle in either a uniform flow or an imposed, gravity-driven microchannel flow (R2 = 0.988, RMS error = 13.04 ?m s?1). Interaction between both techniques is shown to be negligible for 15 ?m to 35 ?m diameter trapped particles subjected to fluid velocities from 50 ?m s?1 to 500 ?m s?1 even at the highest laser power (1.45 W). The integrated techniques will provide a unique perspective toward understanding microscale phenomena including single-cell biomechanics, non-Newtonian fluid mechanics and single particle or particle–particle hydrodynamics.

Neve, N; Lingwood, J K; Zimmerman, J; Kohles, S S; Tretheway, D C

2008-01-01

416

Spatially-sculpted aberrated optical tweezers for delivery of nanoparticles onto cells  

NASA Astrophysics Data System (ADS)

Nanoparticles (NP) are emerging as photochemical and photothermal agents for delivery of drugs and heat onto the targeted cells. Here, we report spatially-sculpting of transverse potential landscape by introducing aberration in the optical tweezers beam for delivery of therapeutic NP on to the prostate cancer PC3 cells. A tunable Ti-Sapphire laser beam was focused to a diffraction limited spot by use of a high numerical aperture microscope objective for optical trapping. A cylindrical lens was used to create the beam profile astigmatic, which led to spatially extended potential landscape. In order to facilitate transport of NP, Comatic potential was created by tilting of the astigmatic beam with respect to the optic axis. NPs were attracted towards the potential minima, transported along the major axis of the elliptic spot and ejected out along the direction having lower stiffness. The Carbon NPs as well as Poly Lactic-co-Glycolic Acid NPs were efficiently transported and concentrated near the PC3 cells in-vitro. The direction and the speed of transport of nano-particles could be reversed by change in tilt direction and angle. Further, by utilizing the scattering force with the asymmetric gradient force, three-dimensional transport of nanoparticles was achieved. The effect of laser beam power and size / refractive index of the nano-particles on the speed of transport will be presented.

Shivalingaiah, Shivaranjani; Chhajed, Suyash; Mohanty, Samarendra

2011-03-01

417

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

2011-03-01

418

Measuring the viscosity of embryonic epithelia in vivo by magnetic tweezers  

NASA Astrophysics Data System (ADS)

During early development, sheets of epithelial cells are reshaped by cellular forces. Several recent investigations in fruit fly (Drosophila) embryos have used laser microsurgery and video force microscopy to measure these forces; however, these measurements are actually limited to force/viscosity ratios because the effective viscosity of epithelial cells in a living embryo is largely unknown. This effective viscosity may vary spatially within the embryo and temporally as development progresses. To address this issue, we use microinjection, magnetic tweezers and confocal microscopy to measure the effective viscosity of epithelial cells in fruit fly embryos in vivo. We inject fluorescent magnetic beads (2-?m diameter) into GFP-labeled embryos at the multi-nuclear syncytial blastoderm stage. The beads are pulled to embryo's surface by a permanent magnet and become engulfed by individual epithelial cells during cellularization. During later stages of development, we supply current pulses to an electromagnet to apply force pulses to the beads with a magnitude of ˜100 pN. The effective viscosity is inferred from the movement of these beads as tracked by confocal microscopy. We will report initial results on amnioserosa cells during dorsal closure.

Ma, Xiaoyan; Angarita, M. Paula; Frierson, Mershard; Sheldon, Drew; Hutson, M. Shane

2011-03-01

419

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

2009-03-01

420

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

2010-03-01

421

Measurements of the force fields within an acoustic standing wave using holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Direct measurement of the forces experienced by micro-spheres in an acoustic standing wave device have been obtained using calibrated optical traps generated with holographic optical tweezers. A micro-sphere, which is optically trapped in three dimensions, can be moved through the acoustic device to measure forces acting upon it. When the micro-sphere is subjected to acoustic forces, it's equilibrium position is displaced to a position where the acoustic forces and optical forces are balanced. Once the optical trapping stiffness has been calibrated, observation of this displacement enables a direct measurement of the forces acting upon the micro-sphere. The measured forces are separated into a spatially oscillating component, attributed to the acoustic radiation force, and a constant force, attributed to fluid streaming. As the drive conditions of the acoustic device were varied, oscillating forces (>2.5 pNpp) and streaming forces (<0.2 pN) were measured. A 5 ?m silica micro-sphere was used to characterise a 6.8 MHz standing wave, ? = 220 ?m, to