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https://www.readbyqxmd.com/read/28211526/stable-optical-trapping-and-sensitive-characterization-of-nanostructures-using-standing-wave-raman-tweezers
#1
Mu-Ying Wu, Dong-Xiong Ling, Lin Ling, William Li, Yong-Qing Li
Optical manipulation and label-free characterization of nanoscale structures open up new possibilities for assembly and control of nanodevices and biomolecules. Optical tweezers integrated with Raman spectroscopy allows analyzing a single trapped particle, but is generally less effective for individual nanoparticles. The main challenge is the weak gradient force on nanoparticles that is insufficient to overcome the destabilizing effect of scattering force and Brownian motion. Here, we present standing-wave Raman tweezers for stable trapping and sensitive characterization of single isolated nanostructures with a low laser power by combining a standing-wave optical trap with confocal Raman spectroscopy...
February 17, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28195722/effects-of-relative-humidity-and-particle-phase-water-on-the-heterogeneous-oh-oxidation-of-2-methylglutaric-acid-aqueous-droplets
#2
Man Mei Chim, Chun Yin Chow, James F Davies, ManNin Chan
Organic aerosols can exist as aqueous droplets, with variable water content depending on their composition and environmental conditions (e.g. relative humidity (RH)). Recent laboratory studies have revealed that oxidation kinetics in highly concentrated droplets can be much slower from those in dilute solutions. However, it remains unclear whether particle phase water affects the formation of reaction products physically and/or chemically. In this work, we investigate the role of particle phase water on the heterogeneous chemistry of aqueous organic droplets consisting of 2-methylglutaric acid (2-MGA), measuring the reaction kinetics and the reaction products upon heterogeneous OH oxidation over a range of RH...
February 14, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28193001/coalescence-sampling-and-analysis-of-aerosols-using-aerosol-optical-tweezers
#3
Allen E Haddrell, Rachael E H Miles, Bryan R Bzdek, Jonathan P Reid, Rebecca J Hopkins, Jim S Walker
We present a first exploratory study to assess the use of aerosol optical tweezers as an instrument for sampling and detecting accumulation- and coarse-mode aerosol. A subpicoliter aqueous aerosol droplet is captured in the optical trap and used as a sampling volume, accreting mass from a free-flowing aerosol generated by a medical nebulizer or atomizer. Real-time measurements of the initial stability in size, refractive index, and composition of the sampling droplet inferred from Raman spectroscopy confirm that these quantities can be measured with high accuracy and low noise...
February 9, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28192297/controlling-and-tracking-of-colloidal-nanostructures-through-two-photon-fluorescence
#4
Dipankar Mondal, Debabrata Goswami
Multiphoton absorbing dye-coated trapped spherical bead at the focal plane of femtosecond optical tweezers shows nonlinear optical (NLO) phenomena. One such NLO process of two-photon fluorescence (TPF) has been used for the background-free imaging of a femtosecond laser-trapping event. Due to the high peak powers of femtosecond laser pulses with low average powers, it is possible to not only trap single nanospheres, but encourage optically directed self-assembly. The TPF signatures of trapped particles show evidence of such a directed self-assembly process which, in turn, can provide information about the structural dynamics during the process of cluster formation...
October 7, 2016: Methods and Applications in Fluorescence
https://www.readbyqxmd.com/read/28186489/folding-behavior-of-a-t-shaped-ribosome-binding-translation-enhancer-implicated-in-a-wide-spread-conformational-switch
#5
My-Tra Le, Wojciech K Kasprzak, Taejin Kim, Feng Gao, Megan Yl Young, Xuefeng Yuan, Bruce A Shapiro, Joonil Seog, Anne E Simon
Turnip crinkle virus contains a T-shaped, ribosome-binding, translation enhancer (TSS) in its 3'UTR that serves as a hub for interactions throughout the region. The viral RNA-dependent RNA polymerase (RdRp) causes the TSS/surrounding region to undergo a conformational shift postulated to inhibit translation. Using optical tweezers (OT) and steered molecular dynamic simulations (SMD), we found that the unusual stability of pseudoknotted element H4a/Ψ3 required five upstream adenylates, and H4a/Ψ3 was necessary for cooperative association of two other hairpins (H5/H4b) in Mg(2+)...
February 10, 2017: ELife
https://www.readbyqxmd.com/read/28178815/unfolding-dna-condensates-produced-by-dna-like-charged-depletants-a-force-spectroscopy-study
#6
C H M Lima, M S Rocha, E B Ramos
In this work, we have measured, by means of optical tweezers, forces acting on depletion-induced DNA condensates due to the presence of the DNA-like charged protein bovine serum albumin (BSA). The stretching and unfolding measurements performed on the semi-flexible DNA chain reveal (1) the softening of the uncondensed DNA contour length and (2) a mechanical behavior strikingly different from those previously observed: the force-extension curves of BSA-induced DNA condensates lack the "saw-tooth" pattern and applied external forces as high as ≈80 pN are unable to fully unfold the condensed DNA contour length...
February 7, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28176394/single-molecule-force-spectroscopy-reveals-the-effect-of-bip-chaperone-on-protein-folding
#7
María Paz Ramírez, Maira Rivera, Diego Quiroga-Roger, Andrés Bustamante, Marcela Vega, Mauricio Baez, Elias M Puchner, Christian A M Wilson
BiP (Immunoglobulin Binding Protein) is a member of the Hsp70 chaperones that participates in protein folding in the endoplasmic reticulum. The function of BiP relies on cycles of ATP hydrolysis driving the binding and release of its substrate proteins. It still remains unknown how BiP affects the protein folding pathway and there has been no direct demonstration showing which folding state of the substrate protein is bound by BiP, as previous work has used only peptides. Here, we employ optical tweezers for single molecule force spectroscopy experiments to investigate how BiP affects the folding mechanism of a complete protein and how this effect depends on nucleotides...
February 8, 2017: Protein Science: a Publication of the Protein Society
https://www.readbyqxmd.com/read/28164445/holographic-optical-tweezers-based-in-vivo-manipulations-in-zebrafish-embryos
#8
Florian Hörner, Robert Meissner, Sruthi Polali, Jana Pfeiffer, Timo Betz, Cornelia Denz, Erez Raz
Understanding embryonic development requires the characterization of the forces and the mechanical features that shape cells and tissues within the organism. In addition, experimental application of forces on cells and altering cell and organelle shape allows determining the role such forces play in morphogenesis. Here, we present a holographic optical tweezers-based new microscopic platform for in vivo applications in the context of a developing vertebrate embryo that unlike currently used setups allows simultaneous trapping of multiple objects and rapid comparisons of viscoelastic properties in different locations...
February 6, 2017: Journal of Biophotonics
https://www.readbyqxmd.com/read/28156096/manipulation-and-motion-of-organelles-and-single-molecules-in-living-cells
#9
Kamilla Norregaard, Ralf Metzler, Christine M Ritter, Kirstine Berg-Sørensen, Lene B Oddershede
The biomolecule is among the most important building blocks of biological systems, and a full understanding of its function forms the scaffold for describing the mechanisms of higher order structures as organelles and cells. Force is a fundamental regulatory mechanism of biomolecular interactions driving many cellular processes. The forces on a molecular scale are exactly in the range that can be manipulated and probed with single molecule force spectroscopy. The natural environment of a biomolecule is inside a living cell, hence, this is the most relevant environment for probing their function...
February 3, 2017: Chemical Reviews
https://www.readbyqxmd.com/read/28150950/force-dependent-folding-and-unfolding-kinetics-in-dna-hairpins-reveals-transition-state-displacements-along-a-single-pathway
#10
Anna Alemany, Felix Ritort
Biomolecules diffusively explore their energy landscape overcoming energy barriers via thermally activated processes to reach the biologically relevant conformation. Mechanically induced unfolding and folding reactions offer an excellent playground to feature these processes at the single-molecule level by monitoring changes in the molecular extension. Here we investigate two-state DNA hairpins designed to have the transition states at different locations. We use optical tweezers to characterize the force-dependent behavior of the kinetic barrier from nonequilibrium pulling experiments by using the continuous effective barrier approach (CEBA)...
February 9, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28150204/force-measurements-for-cancer-cells
#11
Vivek Rajasekharan, Varun K A Sreenivasan, Brenda Farrell
During cytoskeleton remodeling, cancer cells generate force at the plasma membrane that originates from chemical motors (e.g., actin). This force (pN) and its time course reflect the on and off-rates of the motors. We describe the design and calibration of a force-measuring device (i.e., optical tweezers) that is used to monitor this force and its time course at the edge of a cell, with particular emphasis on the temporal resolution of the instrument.
2017: Methods in Molecular Biology
https://www.readbyqxmd.com/read/28115714/direct-measurement-of-sequence-dependent-transition-path-times-and-conformational-diffusion-in-dna-duplex-formation
#12
Krishna Neupane, Feng Wang, Michael T Woodside
The conformational diffusion coefficient, D, sets the timescale for microscopic structural changes during folding transitions in biomolecules like nucleic acids and proteins. D encodes significant information about the folding dynamics such as the roughness of the energy landscape governing the folding and the level of internal friction in the molecule, but it is challenging to measure. The most sensitive measure of D is the time required to cross the energy barrier that dominates folding kinetics, known as the transition path time...
February 7, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28115614/feedback-traps-for-virtual-potentials
#13
REVIEW
Momčilo Gavrilov, John Bechhoefer
Feedback traps are tools for trapping and manipulating single charged objects, such as molecules in solution. An alternative to optical tweezers and other single-molecule techniques, they use feedback to counteract the Brownian motion of a molecule of interest. The trap first acquires information about a molecule's position and then applies an electric feedback force to move the molecule. Since electric forces are stronger than optical forces at small scales, feedback traps are the best way to trap single molecules without 'touching' them (e...
March 6, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28113367/high-speed-in-situ-observation-system-for-sonoporation-of-cells-with-size-and-position-controlled-microbubbles
#14
Nobuki Kudo
A high-speed in situ microscopic observation system developed for basic studies on mechanisms of sonoporation is introduced in this paper. The main part of the system is an inverted-type fluorescence microscope, and a high-speed camera of 20 MHz in maximum framing rate was used to visualize dynamics of cavitation bubbles that causes a sonoporation effect. Differential interference contrast and fluorescence techniques were used for sensitive visualization of cell changes during sonoporation. The system is also equipped with optical tweezers that can move a microbubble of several microns in size by using a donut-shaped light beam...
September 7, 2016: IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
https://www.readbyqxmd.com/read/28101425/study-of-in-vitro-rbcs-membrane-elasticity-with-aod-scanning-optical-tweezers
#15
Huadong Song, Ying Liu, Bin Zhang, Kangzhen Tian, Panpan Zhu, Hao Lu, Qi Tang
The elasticity of red cell membrane is a critical physiological index for the activity of RBC. Study of the inherent mechanism for RBCs membrane elasticity transformation is attention-getting all along. This paper proposes an optimized measurement method of erythrocytes membrane shear modulus incorporating acousto-optic deflector (AOD) scanning optical tweezers system. By use of this method, both membrane shear moduli and sizes of RBCs with different in vitro times were determined. The experimental results reveal that the RBCs membrane elasticity and size decline with in vitro time extension...
January 1, 2017: Biomedical Optics Express
https://www.readbyqxmd.com/read/28097727/energetics-kinetics-and-pathway-of-snare-folding-and-assembly-revealed-by-optical-tweezers
#16
REVIEW
Yongli Zhang
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are universal molecular engines that drive membrane fusion. Particularly, synaptic SNAREs mediate fast calcium-triggered fusion of neurotransmitter-containing vesicles with plasma membranes for synaptic transmission, the basis of all thought and action. During membrane fusion, complementary SNAREs located on two apposed membranes (often called t- and v-SNAREs) join together to assemble into a parallel four-helix bundle, releasing the energy to overcome the energy barrier for fusion...
January 18, 2017: Protein Science: a Publication of the Protein Society
https://www.readbyqxmd.com/read/28097712/force-generation-by-titin-folding
#17
Zsolt Mártonfalvi, Pasquale Bianco, Katalin Naftz, György G Ferenczy, Miklós Kellermayer
Titin is a giant protein that provides elasticity to muscle. As the sarcomere is stretched, titin extends hierarchically according to the mechanics of its segments. Whether titin's globular domains unfold during this process and how such unfolded domains might contribute to muscle contractility are strongly debated. To explore the force-dependent folding mechanisms, here we manipulated skeletal-muscle titin molecules with high-resolution optical tweezers. In force-clamp mode, after quenching the force (<10 pN), extension fluctuated without resolvable discrete events...
January 18, 2017: Protein Science: a Publication of the Protein Society
https://www.readbyqxmd.com/read/28096424/%C3%AE-actinin-titin-interaction-a-dynamic-and-mechanically-stable-cluster-of-bonds-in-the-muscle-z-disk
#18
Marco Grison, Ulrich Merkel, Julius Kostan, Kristina Djinović-Carugo, Matthias Rief
Stable anchoring of titin within the muscle Z-disk is essential for preserving muscle integrity during passive stretching. One of the main candidates for anchoring titin in the Z-disk is the actin cross-linker α-actinin. The calmodulin-like domain of α-actinin binds to the Z-repeats of titin. However, the mechanical and kinetic properties of this important interaction are still unknown. Here, we use a dual-beam optical tweezers assay to study the mechanics of this interaction at the single-molecule level...
January 31, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28069763/photokinetic-analysis-of-the-forces-and-torques-exerted-by-optical-tweezers-carrying-angular-momentum
#19
Aaron Yevick, Daniel J Evans, David G Grier
The theory of photokinetic effects expresses the forces and torques exerted by a beam of light in terms of experimentally accessible amplitude and phase profiles. We use this formalism to develop an intuitive explanation for the performance of optical tweezers operating in the Rayleigh regime, including effects arising from the influence of light's angular momentum. First-order dipole contributions reveal how a focused beam can trap small objects, and what features limit the trap's stability. The first-order force separates naturally into a conservative intensity-gradient term that forms a trap and a non-conservative solenoidal term that drives the system out of thermodynamic equilibrium...
February 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28067430/editorial-process-file-includedexogenous-lysophospholipids-with-large-head-groups-perturb-clathrin-mediated-endocytosis
#20
Ieva Ailte, Anne Berit Dyve Lingelem, Audun Sverre Kvalvaag, Simona Kavaliauskiene, Andreas Brech, Gerbrand Koster, Paul Gunnar Dommersnes, Jonas Bergan, Tore Skotland, Kirsten Sandvig
In this study, we have investigated how clathrin-dependent endocytosis is affected by exogenously added lysophospholipids (LPLs). Addition of LPLs with large head groups strongly inhibits transferrin (Tf) endocytosis in various cell lines, while LPLs with small head groups do not. Electron and total internal reflection fluorescence microscopy (EM and TIRF) reveal that treatment with lysophosphatidylinositol (LPI) with the fatty acyl group C18:0 leads to reduced numbers of invaginated clathrin-coated pits (CCPs) at the plasma membrane, fewer endocytic events per membrane area and increased lifetime of CCPs...
January 9, 2017: Traffic
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