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https://www.readbyqxmd.com/read/28526627/dynamic-fatigue-measurement-of-human-erythrocytes-using-dielectrophoresis
#1
Yuhao Qiang, Jia Liu, E Du
Erythrocytes must undergo severe deformation to pass through narrow capillaries and submicronic splenic slits for several hundred thousand times in their normal lifespan. Studies of erythrocyte biomechanics have been mainly focused on cell deformability and rheology measured from a single application of stress and mostly under a static or quasi-static state using classical biomechanical techniques, such as optical tweezers and micropipette aspiration. Dynamic behavior of erythrocytes in response to cyclic stresses that contributes to the membrane failure in blood circulation is not fully understood...
May 16, 2017: Acta Biomaterialia
https://www.readbyqxmd.com/read/28522581/conformational-dynamics-of-the-frameshift-stimulatory-structure-in-hiv-1
#2
Dustin B Ritchie, Tonia R Cappellano, Collin Tittle, Negar Rezajooei, Logan Rouleau, William Ka Sikkema, Michael T Woodside
Programmed ribosomal frameshifting (PRF) in HIV-1 is thought to be stimulated by a hairpin in the mRNA, although a pseudoknot-like triplex has also been proposed. Because the conformational dynamics of the stimulatory structure under tension applied by the ribosomal helicase during translation may play an important role in PRF, we used optical tweezers to apply tension to the HIV stimulatory structure and monitor its unfolding and refolding dynamics. The folding and unfolding kinetics and energy landscape of the hairpin were measured by ramping the force on the hairpin up and down, providing a detailed biophysical characterisation...
May 18, 2017: RNA
https://www.readbyqxmd.com/read/28521900/diagnosis-of-malarial-infection-using-change-in-properties-of-optically-trapped-red-blood-cells
#3
Apurba Paul, Ponnan Padmapriya, Vasant Natarajan
BACKGROUND: In previous work studying the properties of red blood cells (RBCs) held in an optical tweezers trap, we observed an increase in the spectrum of Brownian fluctuations for RBCs from a Plasmodium falciparum culture-due to increased rigidity of the cells-compared to normal RBCs. We wanted to extend the study to patient samples, since the earlier work was done with cultures grown in the lab. METHODS: Individual RBCs were held in an optical-tweezers trap. Its position fluctuations were measured and the power spectrum determined...
April 2017: Biomedical Journal
https://www.readbyqxmd.com/read/28512659/extensive-characterization-of-magnetic-microrods-observed-using-optical-microscopy
#4
Fabien Gerbal, Yuan Wang, Olivier Sandre, Fabien Montel, Jean-Claude Bacri
The usage of micro or nanorods is steadily increasing in various applications from fundamental research to industry. Therefore their geometrical, mechanical and eventually magnetic properties need to be well determined. Here, using an optical microscope equipped with magnetic tweezers, we report an experimental procedure to obtain all those information on a single magnetic rod. In particular, we measure magnetic susceptibility χ by analyzing the deformation of a rod subjected to a uniform magnetic field. To do so, we refine a theoretical model which takes into account the variation of χ with the internal field...
May 17, 2017: Soft Matter
https://www.readbyqxmd.com/read/28507157/translation-and-folding-of-single-proteins-in-real-time
#5
Florian Wruck, Alexandros Katranidis, Knud H Nierhaus, Georg Büldt, Martin Hegner
Protein biosynthesis is inherently coupled to cotranslational protein folding. Folding of the nascent chain already occurs during synthesis and is mediated by spatial constraints imposed by the ribosomal exit tunnel as well as self-interactions. The polypeptide's vectorial emergence from the ribosomal tunnel establishes the possible folding pathways leading to its native tertiary structure. How cotranslational protein folding and the rate of synthesis are linked to a protein's amino acid sequence is still not well defined...
May 15, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28505722/direct-observation-of-coupling-between-orientation-and-flow-fluctuations-in-a-nematic-liquid-crystal-at-equilibrium
#6
Hiroshi Orihara, Nobutaka Sakurai, Yuji Sasaki, Tomoyuki Nagaya
To demonstrate coupling between orientation and flow fluctuations in a nematic liquid crystal at equilibrium, we simultaneously observe the intensity change due to director fluctuations under a polarizing microscope and the Brownian motion of a fluorescent particle trapped weakly by optical tweezers. The calculated cross-correlation function of the particle position and the spatial gradient of the intensity is nonzero, clearly indicating the existence of coupling.
April 2017: Physical Review. E
https://www.readbyqxmd.com/read/28495612/effect-of-infrared-light-on-live-blood-cells-role-of-%C3%AE-carotene
#7
Surekha Barkur, Aseefhali Bankapur, Santhosh Chidangil, Deepak Mathur
We have utilized Raman tweezers to measure and assign micro-Raman spectra of optically trapped, live red blood cells (RBCs), white blood cells (WBCs) and platelets. Various types of WBCs- both granulocytes, lymphocytes, and their different types have been studied. The Raman bands are assigned to different biomolecules of blood cells. The Raman spectra thus obtained has been enabled detection of β-carotene in these blood cells, the spectral features of which act as a signature that facilitates experimental probing of the effect of 785nm laser light on different blood cells as a function of incident laser power in the mW range...
April 27, 2017: Journal of Photochemistry and Photobiology. B, Biology
https://www.readbyqxmd.com/read/28490794/thermally-induced-micro-motion-by-inflection-in-optical-potential
#8
Martin Šiler, Petr Jákl, Oto Brzobohatý, Artem Ryabov, Radim Filip, Pavel Zemánek
Recent technological progress in a precise control of optically trapped objects allows much broader ventures to unexplored territory of thermal motion in non-linear potentials. In this work, we exploit an experimental set-up of holographic optical tweezers to experimentally investigate Brownian motion of a micro-particle near the inflection point of the cubic optical potential. We present two complementary views on the non-linear Brownian motion. On an ensemble of stochastic trajectories, we simultaneously determine (i) the detailed short-time position statistics and (ii) the long-distance first-passage time statistics...
May 10, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28486639/dna-synthesis-determines-the-binding-mode-of-the-human-mitochondrial-single-stranded-dna-binding-protein
#9
José A Morin, Fernando Cerrón, Javier Jarillo, Elena Beltran-Heredia, Grzegorz L Ciesielski, J Ricardo Arias-Gonzalez, Laurie S Kaguni, Francisco J Cao, Borja Ibarra
Single-stranded DNA-binding proteins (SSBs) play a key role in genome maintenance, binding and organizing single-stranded DNA (ssDNA) intermediates. Multimeric SSBs, such as the human mitochondrial SSB (HmtSSB), present multiple sites to interact with ssDNA, which has been shown in vitro to enable them to bind a variable number of single-stranded nucleotides depending on the salt and protein concentration. It has long been suggested that different binding modes might be used selectively for different functions...
May 9, 2017: Nucleic Acids Research
https://www.readbyqxmd.com/read/28483696/spatial-distributions-of-pericellular-stiffness-in-natural-extracellular-matrices-are-dependent-on-cell-mediated-proteolysis-and-contractility
#10
M Keating, A Kurup, M Alvarez-Elizondo, A J Levine, E Botvinick
Bulk tissue stiffness has been correlated with regulation of cellular processes and conversely cells have been shown to remodel their pericellular tissue according to a complex feedback mechanism critical to development, homeostasis, and disease. However, bulk rheological methods mask the dynamics within a heterogeneous fibrous extracellular matrix (ECM) in the region proximal to a cell (pericellular region). Here, we use optical tweezers active microrheology (AMR) to probe the distribution of the complex material response function (α = α' + α'', in units of µm/nN) within a type I collagen ECM, a biomaterial commonly used in tissue engineering...
May 5, 2017: Acta Biomaterialia
https://www.readbyqxmd.com/read/28474852/the-ribosome-destabilizes-native-and-non-native-structures-in-a-nascent-multi-domain-protein
#11
Kaixian Liu, Joseph E Rehfus, Elliot Mattson, Christian Kaiser
Correct folding is a prerequisite for the biological activity of most proteins. Folding has largely been studied using in vitro refolding assays with isolated small, robustly folding proteins. A substantial fraction of all cellular proteomes is composed of multi-domain proteins that are often not amenable to this approach, and their folding remains poorly understood. These large proteins likely begin to fold during their synthesis by the ribosome, a large molecular machine that translates the genetic code. The ribosome affects how folding proceeds, but the underlying mechanisms remain largely obscure...
May 5, 2017: Protein Science: a Publication of the Protein Society
https://www.readbyqxmd.com/read/28470421/how-should-the-optical-tweezers-experiment-be-used-to-characterize-the-red-blood-cell-membrane-mechanics
#12
Julien Sigüenza, Simon Mendez, Franck Nicoud
Stretching red blood cells using optical tweezers is a way to characterize the mechanical properties of their membrane by measuring the size of the cell in the direction of the stretching (axial diameter) and perpendicularly (transverse diameter). Recently, such data have been used in numerous publications to validate solvers dedicated to the computation of red blood cell dynamics under flow. In the present study, different mechanical models are used to simulate the stretching of red blood cells by optical tweezers...
May 3, 2017: Biomechanics and Modeling in Mechanobiology
https://www.readbyqxmd.com/read/28439980/nanophotonic-trapping-precise-manipulation-and-measurement-of-biomolecular-arrays
#13
REVIEW
James E Baker, Ryan P Badman, Michelle D Wang
Optical trapping is a powerful and widely used laboratory technique in the biological and materials sciences that enables rapid manipulation and measurement at the nanometer scale. However, expanding the analytical throughput of this technique beyond the serial capabilities of established single-trap microscope-based optical tweezers remains a current goal in the field. In recent years, advances in nanotechnology have been leveraged to create innovative optical trapping methods that increase the number of available optical traps and permit parallel manipulation and measurement of arrays of optically trapped targets...
April 24, 2017: Wiley Interdisciplinary Reviews. Nanomedicine and Nanobiotechnology
https://www.readbyqxmd.com/read/28423909/ripping-rna-by-force-using-gaussian-network-models
#14
Changbong Hyeon, D Thirumalai
Using force as a probe to map the folding landscapes of RNA molecules has become a reality thanks to major advances in single molecule pulling experiments. Although the unfolding pathways under tension are complicated to predict, studies in the context of proteins have shown that topology is the major determinant of the unfolding landscapes. By building on this finding we study the responses of RNA molecules to force by adapting Gaussian network model (GNM) that represents RNAs using a bead-spring network with isotropic interactions...
April 20, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28414807/interactions-between-the-breast-cancer-associated-muc1-mucins-and-c-type-lectin-characterized-by-optical-tweezers
#15
Soosan Hadjialirezaei, Gianfranco Picco, Richard Beatson, Joy Burchell, Bjørn Torger Stokke, Marit Sletmoen
Carbohydrate-protein interactions govern many crucial processes in biological systems including cell recognition events. We have used the sensitive force probe optical tweezers to quantify the interactions occurring between MGL lectins and MUC1 carrying the cancer-associated glycan antigens mucins Tn and STn. Unbinding forces of 7.6 pN and 7.1 pN were determined for the MUC1(Tn)-MGL and MUC1(STn)-MGL interactions, at a force loading rate of ~40 pN/s. The interaction strength increased with increasing force loading rate, to 27 and 37 pN at a force loading rate of ~ 310 pN/s...
2017: PloS One
https://www.readbyqxmd.com/read/28373648/optimizing-phase-to-enhance-optical-trap-stiffness
#16
Michael A Taylor
Phase optimization offers promising capabilities in optical tweezers, allowing huge increases in the applied forces, trap stiff-ness, or measurement sensitivity. One key obstacle to potential applications is the lack of an efficient algorithm to compute an optimized phase profile, with enhanced trapping experiments relying on slow programs that would take up to a week to converge. Here we introduce an algorithm that reduces the wait from days to minutes. We characterize the achievable in-crease in trap stiffness and its dependence on particle size, refractive index, and optical polarization...
April 3, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28365483/structural-transitions-in-torsionally-constrained-dna-and-their-dependence-on-solution-electrostatics
#17
Jaspreet Singh, Prashant K Purohit
Experimental studies on single molecules of DNA have reported a rich variety of structural transitions, including coexistence of three phases, in a torsionally constrained molecule. A comprehensive knowledge of these structural transitions is useful for unraveling the in vivo and in vitro behavior of DNA. Our objective is to understand the structural transitions in a torsionally constrained DNA molecule when it is pulled using optical or magnetic tweezers. We use foundational concepts from the Zimm-Bragg helix-coil transition theory and merge them with ideas from the theory of fluctuating elastic rods to model the mechanics of DNA...
March 29, 2017: Acta Biomaterialia
https://www.readbyqxmd.com/read/28362777/optical-concatenation-of-a-large-number-of-beads-with-a-single-beam-optical-tweezer
#18
Remy Avila, Joaquín Ascencio-Rodríguez, Daniel Tapia-Merino, Oscar G Rodríguez-Herrera, Arturo González-Suárez
Optical tweezers consist of the spatial confinement of microscopic dielectric particles by the action of forces produced by the change in momentum of the photons of a highly focused laser beam that are deviated by the particle. In experiments that use a single laser beam, it is common to capture not only one but a few particles in the optical trap. However, to our knowledge, the formation of a long chain of beads optically confined with a single laser beam has never been reported. In this work, up to 73 silica spheres immersed in water are seen concatenated along the propagation direction of a 976-nm wavelength Gaussian laser of 300 mW of power...
April 1, 2017: Optics Letters
https://www.readbyqxmd.com/read/28345878/multispectral-optical-tweezers-for-biochemical-fingerprinting-of-cd9-positive-exosome-subpopulations
#19
Randy P Carney, Sidhartha Hazari, Macalistair Colquhoun, Di Tran, Billanna Hwang, Michael S Mulligan, James D Bryers, Eugenia Girda, Gary S Leiserowitz, Zachary J Smith, Kit S Lam
Extracellular vesicles (EVs), including exosomes, are circulating nanoscale particles heavily implicated in cell signaling and can be isolated in vast numbers from human biofluids. Study of their molecular profiling and materials properties is currently underway for purposes of describing a variety of biological functions and diseases. However, the large, and as yet largely unquantified, variety of EV subpopulations differing in composition, size, and likely function necessitates characterization schemes capable of measuring single vesicles...
April 25, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28345092/integrating-optical-tweezers-with-up-converting-luminescence-a-non-amplification-analytical-platform-for-quantitative-detection-of-microrna-21-sequences
#20
Cheng-Yu Li, Di Cao, Chong-Yang Song, Chun-Miao Xu, Xu-Yan Ma, Zhi-Ling Zhang, Dai-Wen Pang, Hong-Wu Tang
We report a single-microsphere based imaging assay method by integrating up-converting luminescence with optical tweezers for detecting microRNA-21 sequences. This method achieves a competitive detection limit of 12 fM with good selectivity and no dedicated signal amplification designs.
March 27, 2017: Chemical Communications: Chem Comm
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