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optical tweezers

Xi-Juan Lv, Yang Wang, Chen Cai, Shu-Feng Pang, Jia-Bi Ma, Yun-Hong Zhang
Hygroscopicity and volatility of single magnesium acetate (MgAc2 ) aerosol particles at various relative humidities (RHs) are studied by a single-beam optical tweezers, and refractive indices (RIs) and morphology are characterized by cavity enhanced Raman spectroscopy. Gel formation and volatilization of acetate acid (HAc) in MgAc2 droplets are observed. Due to the formation of amorphous gel structure, water transposition in droplets at RH < 50% is significantly impeded on a time scale of 140,000 s...
April 14, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Daniela Bauer, Sarah Meinhold, Roman P Jakob, Johannes Stigler, Ulrich Merkel, Timm Maier, Matthias Rief, Gabriel Žoldák
The folding pathways of large proteins are complex, with many of them requiring the aid of chaperones and others folding spontaneously. Along the folding pathways, partially folded intermediates are frequently populated; their role in the driving of the folding process is unclear. The structures of these intermediates are generally not amenable to high-resolution structural techniques because of their transient nature. Here we employed single-molecule force measurements to scrutinize the hierarchy of intermediate structures along the folding pathway of the nucleotide binding domain (NBD) of Escherichia coli Hsp70 DnaK...
April 18, 2018: Proceedings of the National Academy of Sciences of the United States of America
Neus Oliver, Christina Alpmann, Álvaro Barroso, Lena Dewenter, Mike Woerdemann, Cornelia Denz
Although synchronization is a well-known physical phenomenon, experimental studies of its emergence in living bacterial cells are still scarce. The difficulty in generating a controlled scenario to detect synchronization has limited the experimental outcomes so far. We present a realization based on holographic optical tweezers in which adhered pairs of self-propelled bacteria rotate in a plane. The separation distance between the bacteria determines the strength of the hydrodynamic coupling. Despite the noisy environment and autonomous dynamics of the living bacteria, we find evidence of phase locking and frequency entrainment in their rotation...
April 17, 2018: Soft Matter
Motoki Takeda, Satoru Hiroto, Hiroki Yokoi, Sangsu Lee, Dongho Kim, Hiroshi Shinokubo
We designed and synthesized molecular tweezers consisted of nitrogen-embedded buckybowl subunits. The judicious choice of the covalent linkers modulated their binding strength with C60 or C70 in solution. Titration studies by optical and 1 H NMR analysis revealed a 1:1 composition of the resulting complexes. X-Ray diffraction analysis elucidated their solid-state structures in which two azabuckybowl units surround one molecule of fullerenes. The large association constants stabilize the complexes under redox reactions and purification process on silica-gel column chromatography...
April 17, 2018: Journal of the American Chemical Society
Alexander Parobek, Jacob W Black, Maria Kamenetska, Ziad Ganim
Measuring absorption spectra of single molecules presents a fundamental challenge for standard transmission-based instruments because of the inherently low signal relative to the large background of the excitation source. Here we demonstrate a new approach for performing absorption spectroscopy in solution using a force measurement to read out optical excitation at the nanoscale. The photoinduced force between model chromophores and an optically trapped gold nanoshell has been measured in water at room temperature...
April 14, 2018: Journal of Chemical Physics
Airong Zhao, Aline Pham, Nessim Jebali, Aurélien Drezet
Based on the spin-dependent directional coupling of surface plasmons (SPs) by ∧-shaped antennas, ring-shaped structures built with such antennas have potential applications for optical tweezers and optical switch technology. In this Letter, we introduce an optical method for realizing a complete polarization tomography of coupled SP fields by such a chiral-planar structure. We use a far-field optical approach, namely leakage radiation microscopy (LRM), to map the SPs propagation and polarization. Here, we fully analyze the polarization state of the generated SPs inside the vortex lens structure...
April 15, 2018: Optics Letters
L R Liu, J D Hood, Y Yu, J T Zhang, N R Hutzler, T Rosenband, K-K Ni
Chemical reactions typically proceed via stochastic encounters between reactants. Going beyond this paradigm, we combine exactly two atoms into a single, controlled reaction. The experimental apparatus traps two individual laser-cooled atoms (one sodium and one cesium) in separate optical tweezers and then merges them into one optical dipole trap. Subsequently, photo-association forms an excited-state NaCs molecule. The discovery of previously unseen resonances near the molecular dissociation threshold and measurement of collision rates are enabled by the tightly trapped ultracold sample of atoms...
April 12, 2018: Science
Yu Long Han, Pierre Ronceray, Guoqiang Xu, Andrea Malandrino, Roger D Kamm, Martin Lenz, Chase P Broedersz, Ming Guo
Animal cells in tissues are supported by biopolymer matrices, which typically exhibit highly nonlinear mechanical properties. While the linear elasticity of the matrix can significantly impact cell mechanics and functionality, it remains largely unknown how cells, in turn, affect the nonlinear mechanics of their surrounding matrix. Here, we show that living contractile cells are able to generate a massive stiffness gradient in three distinct 3D extracellular matrix model systems: collagen, fibrin, and Matrigel...
April 4, 2018: Proceedings of the National Academy of Sciences of the United States of America
M Rico-Pasto, I Pastor, F Ritort
Single-molecule experiments with optical tweezers have become an important tool to study the properties and mechanisms of biological systems, such as cells and nucleic acids. In particular, force unzipping experiments have been used to extract the thermodynamics and kinetics of folding and unfolding reactions. In hopping experiments, a molecule executes transitions between the unfolded and folded states at a preset value of the force [constant force mode (CFM) under force feedback] or trap position [passive mode (PM) without feedback] and the force-dependent kinetic rates extracted from the lifetime of each state (CFM) and the rupture force distributions (PM) using the Bell-Evans model...
March 28, 2018: Journal of Chemical Physics
Joost van Mameren, Karen Vermeulen, Gijs J L Wuite, Erwin J G Peterman
In the past decades, sensitive fluorescence microscopy techniques have contributed significantly to our understanding of the dynamics of DNA. The specific labeling of DNA using intercalating dyes has allowed for quantitative measurement of the thermal fluctuations the polymers undergo. On the other hand, recent advances in single-molecule manipulation techniques have unraveled the mechanical and elastic properties of this intricate polymer. Here, we have combined these two approaches to study the conformational dynamics of DNA under a wide range of tensions...
March 28, 2018: Journal of Chemical Physics
Richard Zeltner, Riccardo Pennetta, Shangran Xie, Philip St J Russell
Whispering-gallery mode (WGM) resonators combine small optical mode volumes with narrow resonance linewidths, making them exciting platforms for a variety of applications. Here we report a flying WGM microlaser, realized by optically trapping a dye-doped microparticle within a liquid-filled hollow-core photonic crystal fiber (HC-PCF) using a CW laser and then pumping it with a pulsed excitation laser whose wavelength matches the absorption band of the dye. The laser emits into core-guided modes that can be detected at the endfaces of the HC-PCF...
April 1, 2018: Optics Letters
Masaki Mizutani, Isil Tulum, Yoshiaki Kinosita, Takayuki Nishizaka, Makoto Miyata
Mycoplasma mobile is a bacterium that uses a unique mechanism to glide on solid surfaces at a velocity of up to 4.5 μm/s. Its gliding machinery comprises hundreds of units that generate the force for gliding based on the energy derived from ATP; the units catch and pull sialylated oligosaccharides fixed to solid surfaces. In this study, we measured the stall force of wild-type and mutant strains of M. mobile carrying a bead manipulated using optical tweezers. The strains that had been enhanced for binding exhibited weaker stall forces than the wild-type strain, indicating that stall force is related to force generation rather than to binding...
March 27, 2018: Biophysical Journal
Di Chang, Shinya Sakuma, Kota Kera, Nobuyuki Uozumi, Fumihito Arai
Synechocystis sp. strain PCC6803 (Synechocystis) is a model microorganism and its mechanosensitive (MS) channels play important roles in its osmoadaptation mechanism. When the osmotic concentration of the culture environment changes, the inner pressure of the cell also changes due to the transportation of water through ion channels. Because the tension in the cell membrane relates to the inner pressure, we expect that the response of the MS channels to an osmotic concentration change could be evaluated by measuring their mechanical properties...
March 23, 2018: Lab on a Chip
Tal Aharoni, Shy Shoham
Holographic speckle is a major impediment to computer-generated holographic (CGH) projections in applications ranging from display, optical tweezers, and machining to optogenetic neural control. We present an iterative phase retrieval algorithm that allows the projection of amplitude-controlled speckle-free one-dimensional patterns with a high degree of pattern uniformity. The algorithm, termed the weighted Gerchberg-Saxton with phase-control (GSW-PC), is shown to have the ability to simultaneously control both the phase and amplitude of projected patterns with high diffraction efficiencies...
April 2018: Neurophotonics
Peifeng Jing, Yannan Liu, Ethan G Keeler, Nelly M Cruz, Benjamin S Freedman, Lih Y Lin
Cell manipulation is one of the most impactful applications for optical tweezers, and derived from this promise, we demonstrate a new optical tweezers system for the study of cell adhesion and organization. This method utilizes photonic-crystal-enhanced optical tweezers to manipulate cells with low laser intensities. By doing so, it enables effective cell patterning and culturing within the conditions necessary for successful differentiation and colony formation of human pluripotent stem cells. To this end, the biocompatibility of plasma-treated parylene-C for cell culturing was studied, and a thorough characterization of cellular interactive forces was performed using this system...
February 1, 2018: Biomedical Optics Express
Jannis Köhler, Jegor Ruschke, Katja Bettina Ferenz, Cemal Esen, Michael Kirsch, Andreas Ostendorf
Albumin-derived perfluorocarbon-based capsules are promising as artificial oxygen carriers with high solubility. However, these capsules have to be studied further to allow initial human clinical tests. The aim of this paper is to provide and characterize a holographic optical tweezer to enable contactless trapping and moving of individual capsules in an environment that mimics physiological (in vivo) conditions most effectively in order to learn more about the artificial oxygen carrier behavior in blood plasma without recourse to animal experiments...
February 1, 2018: Biomedical Optics Express
Timothée Menais
DNA translocation through nanopores is one of the most promising strategies for next-generation sequencing technologies. Most experimental and numerical works have focused on polymer translocation biased by electrophoresis, where a pulling force acts on the polymer within the nanopore. An alternative strategy, however, is emerging, which uses optical or magnetic tweezers. In this case, the pulling force is exerted directly at one end of the polymer, which strongly modifies the translocation process. In this paper, we report numerical simulations of both linear and structured (mimicking DNA) polymer models, simple enough to allow for a statistical treatment of the pore structure effects on the translocation time probability distributions...
February 2018: Physical Review. E
Vahid Sheikh-Hasani, Mehrad Babaei, Ali Azadbakht, Hamidreza Pazoki-Toroudi, Alireza Mashaghi, Ali Akbar Moosavi-Movahedi, Seyed Nader Seyed Reihani
Optical tweezers are proven indispensable single-cell micro-manipulation and mechanical phenotyping tools. In this study, we have used optical tweezers for measuring the viscoelastic properties of human red blood cells (RBCs). Comparison of the viscoelastic features of the healthy fresh and atorvastatin treated cells revealed that the drug softens the cells. Using a simple modeling approach, we proposed a molecular model that explains the drug-induced softening of the RBC membrane. Our results suggest that direct interactions between the drug and cytoskeletal components underlie the drug-induced softening of the cells...
March 1, 2018: Biomedical Optics Express
Wen-Hao Huang, Shun-Feng Li, Hai-Tao Xu, Zheng-Xun Xiang, Yong-Bing Long, Hai-Dong Deng
The optomechanical interaction between a plasmonic nanocavity and a gold nanorod through optical forces is demonstrated. It is revealed that strong localized plasmon resonance mode hybridization induced by a gold nanorod results in the resonance mode of the nanocavity splitting into two different plasmon resonance modes (bonding plasmon resonance mode and antibonding plasmon resonance mode). When the whole system (gold nanorod and gold nanocavity) is excited at the antibonding plasmon mode, the gold nanorod can receive an optical pushing force and be pushed away from the gold nanocavity...
March 5, 2018: Optics Express
Micah J McCauley, Leah Furman, Catherine A Dietrich, Ioulia Rouzina, Megan E Núñez, Mark C Williams
One of the most common DNA lesions is created when reactive oxygen alters guanine. 8-oxo-guanine may bind in the anti-conformation with an opposing cytosine or in the syn-conformation with an opposing adenine paired by transversion, and both conformations may alter DNA stability. Here we use optical tweezers to measure the stability of DNA hairpins containing 8-oxoguanine (8oxoG) lesions, comparing the results to predictive models of base-pair energies in the absence of the lesion. Contrasted with either a canonical guanine-cytosine or adenine-thymine pair, an 8oxoG-cytosine base pair shows significant destabilization of several kBT...
March 7, 2018: Nucleic Acids Research
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