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optical tweezers

Jin Hyun Lim, Jun Young Kim, Dong Woo Kang, Kyu Hwan Choi, Seong Jae Lee, Sang Hyuk Im, Bum Jun Park
Heterogeneous capillary interactions between ellipsoid particles at the oil-water interface were measured via optical laser tweezers. Two trapped particles were aligned in either tip-to-tip (tt) or side-to-side (ss) configurations via the double-trap method and were released from the optical traps, leading to particle-particle attractions due to the capillary forces caused by quadrupolar interface deformation. Based on image analysis and calculations of the Stokes drag force, the capillary interactions between two ellipsoid particles with the same aspect ratio (E) were found to vary with the particle pairs that were measured, indicating that the interactions were non-deterministic or heterogeneous...
December 12, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Shu Zhang, Lachlan J Gibson, Alexander B Stilgoe, Timo A Nieminen, Halina Rubinsztein-Dunlop
The characterisation of physical properties in biologically relevant processes and the development of novel microfluidic devices for this purpose are experiencing a great resurgence at present. In many of measurements of this type where a probe in a fluid is used, the strong influence of the boundaries of the volume used is a serious problem. In these geometries the proximity of a probe to a wall can severely influence the measurement. However, although much knowledge has been gained about flat walls, to date, the effect of non-planar surfaces at microscopic scale on rotational motion of micro-objects has not been studied...
December 11, 2017: Lab on a Chip
Lin Wang, Yongyin Cao, Tongtong Zhu, Rei Feng, Fangkui Sun, Weiqiang Ding
Optical trapping of nano-objects (i.e., the nano-tweezers) has been investigated intensively. Most of those nano-tweezers, however, were focused on the trapping of a single nanoparticle, while the interactions between them were seldom considered. In this work, we propose a nano-tweezers in a slot photonic crystal cavity supporting multiple modes, where the relative positions of two trapped nanoparticles can be tuned by selective excitation of different resonant mode. Results show that both the nanoparticles are trapped at the center of the cavity when the first order mode is excited...
November 27, 2017: Optics Express
Francesca Burgos-Bravo, Nataniel L Figueroa, Nathalie Casanova-Morales, Andrew F G Quest, Christian A M Wilson, Lisette Leyton
Thy-1 and αvβ3 integrin mediate bidirectional cell-to-cell communication between neurons and astrocytes. Thy-1/αvβ3 interactions stimulate astrocyte migration and the retraction of neuronal prolongations, both processes in which internal forces are generated affecting the bimolecular interactions that maintain cell-cell adhesion. Nonetheless, how the Thy-1/αvβ3 interactions respond to mechanical cues is an unresolved issue. In this study, optical tweezers were used as a single-molecule force transducer, and the Dudko-Hummer-Szabo Model was applied to calculate the kinetic parameters of Thy-1/αvβ3 dissociation...
December 6, 2017: Molecular Biology of the Cell
M Edward Quach, Matthew A Dragovich, Wenchun Chen, Anum K Syed, Wenpeng Cao, Xin Liang, Wei Deng, Simon F De Meyer, Guangheng Zhu, Jun Peng, Heyu Ni, Carolyn M Bennett, Ming Hou, Jerry Ware, Hans Deckmyn, X Frank Zhang, Renhao Li
Immune thrombocytopenia (ITP) is a prevalent autoimmune disease characterized by autoantibody-induced platelet clearance. Some ITP patients are refractory to standard immunosuppressive treatments such as intravenous immunoglobulin (IVIG). These patients often have autoantibodies targeting the ligand-binding domain (LBD) of glycoprotein (GP)Ibα, a major subunit of the platelet mechanoreceptor complex GPIb-IX. However, the molecular mechanism of this Fc-independent platelet clearance is not clear. Here, we report that many anti-LBD monoclonal antibodies such as 6B4, but not AK2, activated GPIb-IX in a shear-dependent manner and induced IVIG-resistant platelet clearance in mice...
December 4, 2017: Blood
Hao Yan, Jessica F Johnston, Sidney B Cahn, Megan C King, Simon G J Mochrie
In order to apply optical tweezers-based force measurements within an uncharacterized viscoelastic medium such as the cytoplasm of a living cell, a quantitative calibration method that may be applied in this complex environment is needed. We describe an improved version of the fluctuation-dissipation-theorem calibration method, which has been developed to perform in situ calibration in viscoelastic media without prior knowledge of the trapped object. Using this calibration procedure, it is possible to extract values of the medium's viscoelastic moduli as well as the force constant describing the optical trap...
November 2017: Review of Scientific Instruments
Pranjal Nautiyal, Fahad Alam, Kantesh Balani, Arvind Agarwal
Nanomechanics has played a vital role in pushing our capability to detect, probe, and manipulate the biological species, such as proteins, cells, and tissues, paving way to a deeper knowledge and superior strategies for healthcare. Nanomechanical characterization techniques, such as atomic force microscopy, nanoindentation, nanotribology, optical tweezers, and other hybrid techniques have been utilized to understand the mechanics and kinetics of biospecies. Investigation of the mechanics of cells and tissues has provided critical information about mechanical characteristics of host body environments...
November 29, 2017: Advanced Healthcare Materials
Avijit Barik, Yao Zhang, Roberto Grassi, Binoy Paulose Nadappuram, Joshua B Edel, Tony Low, Steven J Koester, Sang-Hyun Oh
The many unique properties of graphene, such as the tunable optical, electrical, and plasmonic response make it ideally suited for applications such as biosensing. As with other surface-based biosensors, however, the performance is limited by the diffusive transport of target molecules to the surface. Here we show that atomically sharp edges of monolayer graphene can generate singular electrical field gradients for trapping biomolecules via dielectrophoresis. Graphene-edge dielectrophoresis pushes the physical limit of gradient-force-based trapping by creating atomically sharp tweezers...
November 30, 2017: Nature Communications
Supratik Sen Mojumdar, Zackary N Scholl, Derek R Dee, Logan Rouleau, Uttam Anand, Craig Garen, Michael T Woodside
Prion-like misfolding of superoxide dismutase 1 (SOD1) is associated with the disease ALS, but the mechanism of misfolding remains unclear, partly because misfolding is difficult to observe directly. Here we study the most misfolding-prone form of SOD1, reduced un-metallated monomers, using optical tweezers to measure unfolding and refolding of single molecules. We find that the folding is more complex than suspected, resolving numerous previously undetected intermediate states consistent with the formation of individual β-strands in the native structure...
December 1, 2017: Nature Communications
Avinash Dhamija, Bapan Saha, Sankar Prasad Rath
An apparently rigid dibenzothiophene-bridged zinc(II)/magnesium(II) bisporphyrin host (1M) has been explored for an accurate determination of the absolute configuration of a large series of amino alcohols. At lower substrate concentration, a 1:1 sandwich complex is formed which, upon addition of excess of substrate, converts to the 1:2 host-guest complex with complete inversion of the CD exciton couplet. The intensities of the couplet vary widely just by changing the metal ion (Zn vs Mg) and also vary between 1:1 and 1:2 host-guest complexes...
November 30, 2017: Inorganic Chemistry
Ye Yuan, Angel Martinez, Bohdan Senyuk, Mykola Tasinkevych, Ivan I Smalyukh
Colloidal particles disturb the alignment of rod-like molecules of liquid crystals, giving rise to long-range interactions that minimize the free energy of distorted regions. Particle shape and topology are known to guide this self-assembly process. However, how chirality of colloidal inclusions affects these long-range interactions is unclear. Here we study the effects of distortions caused by chiral springs and helices on the colloidal self-organization in a nematic liquid crystal using laser tweezers, particle tracking and optical imaging...
November 27, 2017: Nature Materials
Frederic Català, Ferran Marsà, Mario Montes-Usategui, Arnau Farré, Estela Martín-Badosa
In optical tweezers, heating of the sample due to absorption of the laser light is a major concern as temperature plays an important role at microscopic scale. A popular rule of thumb is to consider that, at the typical wavelength of 1064 nm, the focused laser induces a heating rate of B = 1 °C/100 mW. We analysed this effect under different routine experimental conditions and found a remarkable variability in the temperature increase. Importantly, we determined that temperature can easily rise by as much as 4 °C at a relatively low power of 100 mW, for dielectric, non-absorbing particles with certain sets of specific, but common, parameters...
November 22, 2017: Scientific Reports
Devina Jaiswal, Norah Cowley, Zichao Bian, Guoan Zheng, Kevin P Claffey, Kazunori Hoshino
We describe a novel mechanical characterization method that has directly measured the stiffness of cancer spheroids for the first time to our knowledge. Stiffness is known to be a key parameter that characterizes cancerous and normal cells. Atomic force microscopy or optical tweezers have been typically used for characterization of single cells with the measurable forces ranging from sub pN to a few hundred nN, which are not suitable for measurement of larger 3D cellular structures such as spheroids, whose mechanical characteristics have not been fully studied...
2017: PloS One
Omri Malik, Hadeel Khamis, Sergei Rudnizky, Ariel Kaplan
Retroviral reverse transcriptase catalyses the synthesis of an integration-competent dsDNA molecule, using as a substrate the viral RNA. Using optical tweezers, we follow the Murine Leukemia Virus reverse transcriptase as it performs strand-displacement polymerization on a template under mechanical force. Our results indicate that reverse transcriptase functions as a Brownian ratchet, with dNTP binding as the rectifying reaction of the ratchet. We also found that reverse transcriptase is a relatively passive enzyme, able to polymerize on structured templates by exploiting their thermal breathing...
November 20, 2017: Nucleic Acids Research
H Moysés Nussenzveig
Membrane elastic properties play important roles in regulating cell shape, motility, division and differentiation. Here I review optical tweezer (OT) investigations of membrane surface tension and bending modulus, emphasizing didactic aspects and insights provided for cell biology. OT measurements employ membrane-attached microspheres to extract long cylindrical nanotubes named tethers. The Helfrich-Canham theory yields elastic parameters in terms of tether radius and equilibrium extraction force. It assumes initial point-like microsphere attachment and no cytoskeleton content within tethers...
November 21, 2017: European Biophysics Journal: EBJ
Yang Liu, Kornelia Galior, Victor Pui-Yan Ma, Khalid Salaita
Mechanical forces are essential for a variety of biological processes ranging from transcription and translation to cell adhesion, migration, and differentiation. Through the activation of mechanosensitive signaling pathways, cells sense and respond to physical stimuli from the surrounding environment, a process widely known as mechanotransduction. At the cell membrane, many signaling receptors, such as integrins, cadherins and T- or B-cell receptors, bind to their ligands on the surface of adjacent cells or the extracellular matrix (ECM) to mediate mechanotransduction...
November 21, 2017: Accounts of Chemical Research
Praneet Prakash, Manoj Varma
Suspensions of micro/nano particles made of Polystyrene, Poly(methyl methacrylate), Silicon dioxide etc. have been a standard model system to understand colloidal physics. These systems have proved useful insights into phenomena such as self-assembly. Colloidal model systems are also extensively used to simulate many condensed matter phenomena such as dynamics in a quenched disordered system and glass transition. A precise control of particles using optical or holographic tweezers is essential for such studies...
November 16, 2017: Scientific Reports
Andrés Bustamante, Juan Sotelo-Campos, Daniel G Guerra, Martin Floor, Christian M A Wilson, Carlos Bustamante, Mauricio Báez
Knots are natural topologies of chains. Yet, little is known about spontaneous knot formation in a polypeptide chain-an event that can potentially impair its folding-and about the effect of a knot on the stability and folding kinetics of a protein. Here we used optical tweezers to show that the free energy cost to form a trefoil knot in the denatured state of a polypeptide chain of 120 residues is 5.8 ± 1 kcal mol(-1). Monte Carlo dynamics of random chains predict this value, indicating that the free energy cost of knot formation is of entropic origin...
November 17, 2017: Nature Communications
Zdeněk Pilát, Alexandr Jonáš, Jan Ježek, Pavel Zemánek
Baker's yeast (Saccharomyces cerevisiae) represents a very popular single-celled eukaryotic model organism which has been studied extensively by various methods and whose genome has been completely sequenced. It was also among the first living organisms that were manipulated by optical tweezers and it is currently a frequent subject of optical micromanipulation experiments. We built a microfluidic system for optical trapping experiments with individual cells and used it for the assessment of cell tolerance to phototoxic stress...
November 16, 2017: Sensors
Kaja Fraczkowska, Marcin Bacia, Magda Przybyło, Dominik Drabik, Aleksandra Kaczorowska, Justyna Rybka, Ewa Stefanko, Slawomir Drobczynski, Jan Masajada, Halina Podbielska, Tomasz Wrobel, Marta Kopaczynska
Mechanical properties of biological structures play an important role in regulating cellular activities and are critical for understanding metabolic processes in cancerous cells and the effects of drugs. For some cancers, such as acute myeloid leukaemia, chemotherapy is one of preferential methods. However, due to the lack of selectivity to cancer cells, cytostatic agents cause toxicity to normal tissues. Here, we study the effect of doxorubicin (DOX) on the mechanical properties of DNA molecules, leukemic blast cells and erythrocytes, using optical tweezers...
November 10, 2017: Biomedicine & Pharmacotherapy, Biomédecine & Pharmacothérapie
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