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optical tweezers

Di Liu, Le Yu, Xiao Xiong, Lei Yang, Yan Li, Ming Li, Hai-Ou Li, Gang Cao, Ming Xiao, Bin Xiang, Chang-Jun Min, Guang-Can Guo, Xi-Feng Ren, Guo-Ping Guo
Monolayer transition-metal dichalcogenides (TMDs) have grown as fantastic building blocks for optoelectronic applications, owing to their direct band gap, transparency, and mechanical flexibility. Since the luminescence of monolayer TMDs suffers from low light absorption and emission, surface plasmons, which confine light at subwavelength and enhance the local electric field, are utilized to boost both excitation and emission fields of TMDs, enabling strong light-matter interaction at the nano-scale. Meanwhile, radially-polarized beams (RPBs) as new and attractive excitation source have found many applications in surface plasmon polaritons, optical tweezer and so on...
November 28, 2016: Optics Express
Shiyao Fu, Chunqing Gao, Tonglu Wang, Shikun Zhang, Yanwang Zhai
We demonstrate an approach to generate multiple perfect polarization vortices (PPVs) with selective spatial polarization distribution in various diffraction orders. The key is the design of a hologram with an anisotropic polarization diffraction grating. In the experiment, a setup consisting of two spatial light modulators is built. By encoding the specially designed holograms, PPVs with various states are obtained in different diffraction orders simultaneously, for instance, in radial and azimuthal polarized states...
December 1, 2016: Optics Letters
Jianfa Zhang, Wenbin Liu, Zhihong Zhu, Xiaodong Yuan, Shiqiao Qin
Graphene plasmons are rapidly emerging as a versatile platform for manipulating light at the deep subwavelength scale. Here we show numerically that strong optical near-field forces can be generated under the illumination of mid-IR light when dielectric nanoparticles are located in the vicinity of a nanostructured graphene film. These near-field forces are attributed to the excitation of the graphene's plasmonic mode. The optical forces can generate an efficient optical trapping potential for a 10-nm-diameter dielectric particle when the light intensity is only about about 4...
December 1, 2016: Scientific Reports
Kevin D Whitley, Matthew J Comstock, Yann R Chemla
Despite its fundamental importance in cellular processes and abundant use in biotechnology, we lack a detailed understanding of the kinetics of nucleic acid hybridization. In particular, the identity of the transition state, which determines the kinetics of the two-state reaction, remains poorly characterized. Here, we used optical tweezers with single-molecule fluorescence to observe directly the binding and unbinding of short oligonucleotides (7-12 nt) to a complementary strand held under constant force. Binding and unbinding rate constants measured across a wide range of forces (1...
November 29, 2016: Nucleic Acids Research
Jing Liu, Hong-Lian Guo, Zhi-Yuan Li
Controlled propulsion of microparticles and micromachines in fluids could revolutionize many aspects of technology, such as biomedicine, microfluidics, micro-mechanics, optomechanics, and cell biology. We report the self-propelled cyclic round-trip motion of metallo-dielectric Janus particles in static line optical tweezers (LOT). The Janus particle is a 5 μm-diameter polystyrene sphere half-coated with 3 nanometer thick gold film. Both experiment and theory show that this cyclic translational and rotational motion is a consequence of the collective and fine action of the gold-face orientation dependent propulsion optical force, the gradient optical force, and the spontaneous symmetry breaking induced optical torque in different regions of the LOT...
December 1, 2016: Nanoscale
Gang Chen, Zhi-Xiang Wu, An-Ping Yu, Zhi-Hai Zhang, Zhong-Quan Wen, Kun Zhang, Lu-Ru Dai, Sen-Lin Jiang, Yu-Yan Li, Li Chen, Chang-Tao Wang, Xian-Gang Luo
The generation of a sub-diffraction optical hollow ring is of great interest in various applications, such as optical microscopy, optical tweezers, and nanolithography. Azimuthally polarized light is a good candidate for creating an optical hollow ring structure. Various of methods have been proposed theoretically for generation of sub-wavelength hollow ring by focusing azimuthally polarized light, but without experimental demonstrations, especially for sub-diffraction focusing. Super-oscillation is a promising approach for shaping sub-diffraction optical focusing...
November 23, 2016: Scientific Reports
Kwok Ho Lam, Ying Li, Yang Li, Hae Gyun Lim, Qifa Zhou, Koping Kirk Shung
Non-contact precise manipulation of single microparticles, cells, and organisms has attracted considerable interest in biophysics and biomedical engineering. Similar to optical tweezers, acoustic tweezers have been proposed to be capable of manipulating microparticles and even cells. Although there have been concerted efforts to develop tools for non-contact manipulation, no alternative to complex, unifunctional tweezer has yet been found. Here we report a simple, low-cost, multifunctional single beam acoustic tweezer (SBAT) that is capable of manipulating an individual micrometer scale non-spherical cell at Rayleigh regime and even a single millimeter scale organism at Mie regime, and imaging tissue as well...
November 22, 2016: Scientific Reports
Emma Hodges, B M Cooke, E M Sevick, Debra J Searles, B Dünweg, J Ravi Prakash
Brownian dynamics simulations are used to study the detachment of a particle from a substrate. Although the model is simple and generic, we attempt to map its energy, length and time scales onto a specific experimental system, namely a bead that is weakly bound to a cell and then removed by an optical tweezer. The external driving force arises from the combined optical tweezer and substrate potentials, and thermal fluctuations are taken into account by a Brownian force. The Jarzynski equality and Crooks fluctuation theorem are applied to obtain the equilibrium free energy difference between the final and initial states...
November 18, 2016: Soft Matter
Robert Fickler, Geoff Campbell, Ben Buchler, Ping Koy Lam, Anton Zeilinger
Photons with a twisted phase front carry a quantized amount of orbital angular momentum (OAM) and have become important in various fields of optics, such as quantum and classical information science or optical tweezers. Because no upper limit on the OAM content per photon is known, they are also interesting systems to experimentally challenge quantum mechanical prediction for high quantum numbers. Here, we take advantage of a recently developed technique to imprint unprecedented high values of OAM, namely spiral phase mirrors, to generate photons with more than 10,000 quanta of OAM...
November 15, 2016: Proceedings of the National Academy of Sciences of the United States of America
Jiajie Chen, Hengji Cong, Fong-Chuen Loo, Zhiwen Kang, Minghui Tang, Haixi Zhang, Shu-Yuen Wu, Siu-Kai Kong, Ho-Pui Ho
Optical tweezers are a well-established tool for manipulating small objects. However, their integration with microfluidic devices often requires an objective lens. More importantly, trapping of non-transparent or optically sensitive targets is particularly challenging for optical tweezers. Here, for the first time, we present a photon-free trapping technique based on electro-thermally induced forces. We demonstrate that thermal-gradient-induced thermophoresis and thermal convection can lead to trapping of polystyrene spheres and live cells...
November 17, 2016: Scientific Reports
Yongli Zhang, Junyi Jiao, Aleksander A Rebane
Hidden Markov modeling (HMM) has revolutionized kinetic studies of macromolecules. However, results from HMM often violate detailed balance when applied to the transitions under thermodynamic equilibrium, and the consequence of such violation has not been well understood. Here, to our knowledge, we developed a new HMM method that satisfies detailed balance (HMM-DB) and optimizes model parameters by gradient search. We used free energy of stable and transition states as independent fitting parameters and considered both normal and skew normal distributions of the measurement noise...
November 15, 2016: Biophysical Journal
Philipp Rinklin, Hans-Joachim Krause, Bernhard Wolfrum
Emerging miniaturization technologies for biological and bioengineering applications require precise control over position and actuation of microparticles. While many of these applications call for high-throughput approaches, common tools for particle manipulation, such as magnetic or optical tweezers, suffer from low parallelizability. To address this issue, we introduce a chip-based platform that enables flexible three-dimensional control over individual magnetic microparticles. Our system relies on microwire crossbar arrays for simultaneous generation of magnetic and dielectric forces, which actuate the particles along highly localized traps...
November 16, 2016: Lab on a Chip
Philipp C Nickels, Bettina Wünsch, Phil Holzmeister, Wooli Bae, Luisa M Kneer, Dina Grohmann, Philip Tinnefeld, Tim Liedl
Forces in biological systems are typically investigated at the single-molecule level with atomic force microscopy or optical and magnetic tweezers, but these techniques suffer from limited data throughput and their requirement for a physical connection to the macroscopic world. We introduce a self-assembled nanoscopic force clamp built from DNA that operates autonomously and allows massive parallelization. Single-stranded DNA sections of an origami structure acted as entropic springs and exerted controlled tension in the low piconewton range on a molecular system, whose conformational transitions were monitored by single-molecule Förster resonance energy transfer...
October 21, 2016: Science
Adam G Hendricks, Yale E Goldman
Optical tweezers have been instrumental in uncovering the mechanisms motor proteins use to generate and react to force. While optical traps have primarily been applied to purified, in vitro systems, emerging methods enable measurements in living cells where the actively fluctuating, viscoelastic environment and varying refractive index complicate calibration of the instrument. Here, we describe techniques to calibrate optical traps in living cells using the forced response to sinusoidal oscillations and spontaneous fluctuations, and to measure the forces exerted by endogenous ensembles of kinesin and dynein motor proteins as they transport cargoes in the cell...
2017: Methods in Molecular Biology
Christine M Ritter, Josep Mas, Lene Oddershede, Kirstine Berg-Sørensen
As described in the previous chapters, optical tweezers have become a tool of precision for in vitro single-molecule investigations, where the single molecule of interest most often is studied in purified form in an experimental assay with a well-controlled fluidic environment. A well-controlled fluidic environment implies that the physical properties of the liquid, most notably the viscosity, are known and the fluidic environment can, for calibrational purposes, be treated as a simple liquid.In vivo, however, optical tweezers have primarily been used as a tool of manipulation and not so often for precise quantitative force measurements, due to the unknown value of the spring constant of the optical trap formed within the cell's viscoelastic cytoplasm...
2017: Methods in Molecular Biology
Michael J Greenberg, Henry Shuman, E Michael Ostap
The myosin superfamily of molecular motors utilizes energy from ATP hydrolysis to generate force and motility along actin filaments in a diverse array of cellular processes. These motors are structurally, kinetically, and mechanically tuned to their specific molecular roles in the cell. Optical trapping techniques have played a central role in elucidating the mechanisms by which myosins generate force and in exposing the remarkable diversity of myosin functions. Here, we present thorough methods for measuring and analyzing interactions between actin and non-processive myosins using optical trapping techniques...
2017: Methods in Molecular Biology
Sinan Can, Ahmet Yildiz
Optical tweezers permit measuring motor-filament rupture forces with piconewton sensitivity. For deeper structural and mechanistic understanding of motors, different structural constraints can be induced by pulling motor proteins at various positions and manipulating the direction of the exerted force. Here, we present an optical-trapping approach to investigate the effect of the magnitude and direction of tension applied to the linker element of cytoskeletal motors on motor-filament interactions. Using this approach, force-dependent microtubule release rates of monomeric kinesins can be directly measured by pulling on kinesin's "neck linker" with a constant force...
2017: Methods in Molecular Biology
Marian Baclayon, Svenja-Marei Kalisch, Ed Hendel, Liedewij Laan, Julien Husson, E Laura Munteanu, Marileen Dogterom
Microtubules are dynamic cytoskeletal polymers that polymerize and depolymerize while interacting with different proteins and structures within the cell. The highly regulated dynamic properties as well as the pushing and pulling forces generated by dynamic microtubule ends play important roles in processes such as in cell division. For instance, microtubule end-binding proteins are known to affect dramatically the dynamic properties of microtubules, and cortical dyneins are known to mediate pulling forces on microtubule ends...
2017: Methods in Molecular Biology
Junyi Jiao, Aleksander A Rebane, Lu Ma, Yongli Zhang
How proteins fold from linear chains of amino acids to delicate three-dimensional structures remains a fundamental biological problem. Single-molecule manipulation based on high-resolution optical tweezers (OT) provides a powerful approach to study protein folding with unprecedented spatiotemporal resolution. In this method, a single protein or protein complex is tethered between two beads confined in optical traps and pulled. Protein unfolding induced by the mechanical force is counteracted by the spontaneous folding of the protein, reaching a dynamic equilibrium at a characteristic force and rate...
2017: Methods in Molecular Biology
Shixin Liu, Sara Tafoya, Carlos Bustamante
The past decade has seen an explosion in the use of single-molecule approaches to study complex biological processes. One such approach-optical trapping-is particularly well suited for investigating molecular motors, a diverse group of macromolecular complexes that convert chemical energy into mechanical work, thus playing key roles in virtually every aspect of cellular life. Here we describe how to use high-resolution optical tweezers to investigate the mechanism of the bacteriophage φ29 DNA packaging motor, a ring-shaped ATPase responsible for genome packing during viral assembly...
2017: Methods in Molecular Biology
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