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optical tweezers

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https://www.readbyqxmd.com/read/28819244/light-scattering-by-optically-trapped-vesicles-affords-unprecedented-temporal-resolution-of-lipid-raft-dynamics
#1
Liam Collard, David Perez-Guaita, Bayan H A Faraj, Bayden R Wood, Russell Wallis, Peter W Andrew, Andrew J Hudson
A spectroscopic technique is presented that is able to identify rapid changes in the bending modulus and fluidity of vesicle lipid bilayers on the micrometer scale, and distinguish between the presence and absence of heterogeneities in lipid-packing order. Individual unilamellar vesicles have been isolated using laser tweezers and, by measuring the intensity modulation of elastic back-scattered light, changes in the biophysical properties of lipid bilayers were revealed. Our approach offers unprecedented temporal resolution and, uniquely, physical transformations of lipid bilayers can be monitored on a length scale of micrometers...
August 17, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28805878/interfacial-entropy-driven-thermophoretic-tweezers
#2
Linhan Lin, Xiaolei Peng, Zhangming Mao, Xiaoling Wei, Chong Xie, Yuebing Zheng
Directed migration of particles and molecules in a temperature gradient field, which is known as thermophoresis or the Soret effect, is of fundamental importance for mass transfer in colloid science and life sciences. However, thermophoretic tweezers that enable versatile particle manipulation have remained elusive due to the complex underlying physical forces in thermophoresis and the lack of general thermophilic particles above room temperature. Herein, we exploit entropic response and permittivity gradient at the particle-solvent interface to optically generated thermal gradient to achieve the thermophoretic trapping and dynamic manipulation of charged particles over an optothermal-responsive substrate...
August 14, 2017: Lab on a Chip
https://www.readbyqxmd.com/read/28805212/heterogeneous-interface-adsorption-of-colloidal-particles
#3
Dong Woo Kang, Jin Hyun Lim, Bum Jun Park
The heterogeneous adsorption behaviors of charged colloidal particles to oil-water interfaces were quantitatively and statistically investigated. Using optical laser tweezers, the particles in a sessile water drop formed in an oil phase were laterally translated toward the slope of the oil-water interface and their attachment to the interface was attempted. The adsorption probability was found to logarithmically decrease as the ionic strength decreased and to depend on the holding time during which an optically trapped particle was held at the position closest to the interface...
August 14, 2017: Soft Matter
https://www.readbyqxmd.com/read/28798482/retinoblastoma-protein-rb-links-hypoxia-to-altered-mechanical-properties-in-cancer-cells-as-measured-by-an-optical-tweezer
#4
S Khakshour, M P Labrecque, H Esmaeilsabzali, F J S Lee, M E Cox, E J Park, T V Beischlag
Hypoxia modulates actin organization via multiple pathways. Analyzing the effect of hypoxia on the biophysical properties of cancer cells is beneficial for studying modulatory signalling pathways by quantifying cytoskeleton rearrangements. We have characterized the biophysical properties of human LNCaP prostate cancer cells that occur in response to loss of the retinoblastoma protein (Rb) under hypoxic stress using an oscillating optical tweezer. Hypoxia and Rb-loss increased cell stiffness in a fashion that was dependent on activation of the extracellular signal-regulated kinase (ERK) and the protein kinase B (AKT)- mammalian target of rapamycin (MTOR) pathways...
August 10, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28790301/an-early-mechanical-coupling-of-planktonic-bacteria-in-dilute-suspensions
#5
Simon Sretenovic, Biljana Stojković, Iztok Dogsa, Rok Kostanjšek, Igor Poberaj, David Stopar
It is generally accepted that planktonic bacteria in dilute suspensions are not mechanically coupled and do not show correlated motion. The mechanical coupling of cells is a trait that develops upon transition into a biofilm, a microbial community of self-aggregated bacterial cells. Here we employ optical tweezers to show that bacteria in dilute suspensions are mechanically coupled and show long-range correlated motion. The strength of the coupling increases with the growth of liquid bacterial culture. The matrix responsible for the mechanical coupling is composed of cell debris and extracellular polymer material...
August 9, 2017: Nature Communications
https://www.readbyqxmd.com/read/28782558/exploring-the-denatured-state-ensemble-by-single-molecule-chemo-mechanical-unfolding-the-effect-of-force-temperature-and-urea
#6
Emily Guinn, Susan Marqusee
While it is widely appreciated that the denatured state of a protein is a heterogeneous conformational ensemble, there is still debate over how this ensemble changes with environmental conditions. Here, we use single-molecule chemo-mechanical unfolding, which combines force and urea using the optical tweezers, together with traditional protein unfolding studies to explore how perturbants commonly used to unfold proteins (urea, force and temperature) affect the denatured state ensemble. We compare the urea m-values, which report on the change in solvent accessible surface area for unfolding, to probe the denatured state as a function of force, temperature and urea...
August 3, 2017: Journal of Molecular Biology
https://www.readbyqxmd.com/read/28762410/accurate-nanoscale-flexibility-measurement-of-dna-and-dna-protein-complexes-by-atomic-force-microscopy-in-liquid
#7
Divakaran Murugesapillai, Serge Bouaziz, L James Maher, Nathan E Israeloff, Craig E Cameron, Mark C Williams
The elasticity of double-stranded DNA (dsDNA), as described by its persistence length, is critical for many biological processes, including genomic regulation. A persistence length value can be obtained using atomic force microscopy (AFM) imaging. However, most AFM studies have been done by depositing the sample on a surface using adhesive ligands and fitting the contour to a two-dimensional (2D) wormlike chain (WLC) model. This often results in a persistence length measurement that is different from the value determined using bulk and single molecule methods...
August 1, 2017: Nanoscale
https://www.readbyqxmd.com/read/28762198/directly-watching-biomolecules-in-action-by-high-speed-atomic-force-microscopy
#8
REVIEW
Toshio Ando
Proteins are dynamic in nature and work at the single molecule level. Therefore, directly watching protein molecules in dynamic action at high spatiotemporal resolution must be the most straightforward approach to understanding how they function. To make this observation possible, high-speed atomic force microscopy (HS-AFM) has been developed. Its current performance allows us to film biological molecules at 10-16 frames/s, without disturbing their function. In fact, dynamic structures and processes of various proteins have been successfully visualized, including bacteriorhodopsin responding to light, myosin V walking on actin filaments, and even intrinsically disordered proteins undergoing order/disorder transitions...
July 31, 2017: Biophysical Reviews
https://www.readbyqxmd.com/read/28745508/assessment-of-local-heterogeneity-in-mechanical-properties-of-nanostructured-hydrogel-networks
#9
Zhaokai Meng, Teena Thakur, Chandani Chitrakar, Manish K Jaiswal, Akhilesh K Gaharwar, Vladislav V Yakovlev
Our current understanding of the mechanical properties of nanostructured biomaterials is rather limited to invasive/destructive and low-throughput techniques such as atomic force microscopy, optical tweezers, and shear rheology. In this report, we demonstrate the capabilities of recently developed dual Brillouin/Raman spectroscopy to interrogate the mechanical and chemical properties of nanostructured hydrogel networks. The results obtained from Brillouin spectroscopy show an excellent correlation with the conventional uniaxial and shear mechanical testing...
July 26, 2017: ACS Nano
https://www.readbyqxmd.com/read/28738141/quantification-of-chemical-and-mechanical-effects-on-the-formation-of-the-g-quadruplex-and-i-motif-in-duplex-dna
#10
Sangeetha Selvam, Shankar Mandal, Hanbin Mao
The formation of biologically significant tetraplex DNA species, such as G-quadruplexes and i-motifs, is affected by chemical (ions and pH) and mechanical [superhelicity (σ) and molecular crowding] factors. Because of the extremely challenging experimental conditions, the relative importance of these factors on tetraplex folding is unknown. In this work, we quantitatively evaluated the chemical and mechanical effects on the population dynamics of DNA tetraplexes in the insulin-linked polymorphic region using magneto-optical tweezers...
August 15, 2017: Biochemistry
https://www.readbyqxmd.com/read/28712542/investigating-the-effect-of-cell-substrate-on-cancer-cell-stiffness-by-optical-tweezers
#11
Muhammad Sulaiman Yousafzai, Giovanna Coceano, Serena Bonin, Joseph Niemela, Giacinto Scoles, Dan Cojoc
The mechanical properties of cells are influenced by their microenvironment. Here we report cell stiffness alteration by changing the cell substrate stiffness for isolated cells and cells in contact with other cells. Polydimethylsiloxane (PDMS) is used to prepare soft substrates with three different stiffness values (173, 88 and 17kPa respectively). Breast cancer cells lines, namely HBL-100, MCF-7 and MDA-MB-231 with different level of aggressiveness are cultured on these substrates and their local elasticity is investigated by vertical indentation of the cell membrane...
July 5, 2017: Journal of Biomechanics
https://www.readbyqxmd.com/read/28691145/the-effect-of-saliva-on-the-fate-of-nanoparticles
#12
Birgit J Teubl, Biljana Stojkovic, Dominic Docter, Elisabeth Pritz, Gerd Leitinger, Igor Poberaj, Ruth Prassl, Roland H Stauber, Eleonore Fröhlich, Johannes G Khinast, Eva Roblegg
OBJECTIVES: The design of nanocarriers for local drug administration to the lining mucosa requires a sound knowledge of how nanoparticles (NPs) interact with saliva. This contact determines whether NPs agglomerate and become immobile due to size- and interaction-filtering effects or adsorb on the cell surface and are internalized by epithelial cells. The aim of this study was to examine the behavior of NPs in saliva considering physicochemical NP properties. MATERIALS AND METHODS: The salivary pore-size distribution was determined, and the viscosity of the fluid inside of the pores was studied with optical tweezers...
July 9, 2017: Clinical Oral Investigations
https://www.readbyqxmd.com/read/28684757/stochastic-analysis-of-time-series-for-the-spatial-positions-of-particles-trapped-in-optical-tweezers
#13
S M Mousavi, S N Seyed Reihani, G Anvari, M Anvari, H G Alinezhad, M Reza Rahimi Tabar
We propose a nonlinear method for the analysis of the time series for the spatial position of a bead trapped in optical tweezers, which enables us to reconstruct its dynamical equation of motion. The main advantage of the method is that all the functions and parameters of the dynamics are determined directly (non-parametrically) from the measured series. It also allows us to determine, for the first time to our knowledge, the spatial-dependence of the diffusion coefficient of a bead in an optical trap, and to demonstrate that it is not in general constant...
July 6, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28678267/dynamic-plasmonic-nano-traps-for-single-molecule-surface-enhanced-raman-scattering
#14
Yuquan Zhang, Junfeng Shen, Zhenwei Xie, Xiujie Dou, Changjun Min, Ting Lei, Jun Liu, Siwei Zhu, Xiaocong Yuan
Intense electric fields at the nanoscale are essential for single molecule surface-enhanced Raman scattering (SERS) detection. Such fields can be achieved in plasmonic nano-gaps between nanoparticles and metal films through hybridization of surface plasmons. The nano-gaps could be formed and dynamically controlled by using plasmonic tweezers; however, the aggregation of particles in the plasmonic field degrades each particle's enhancement and spoils the nanosized-spatial resolution. Here, dual-plasmonic tweezers are proposed and demonstrated to accurately control the number of nano-gaps and enhancement by tailoring a crater-shaped potential well in the nano-trap system...
August 3, 2017: Nanoscale
https://www.readbyqxmd.com/read/28667966/three-dimensional-characterization-of-tightly-focused-fields-for-various-polarization-incident-beams
#15
Yanan Cai, Yansheng Liang, Ming Lei, Shaohui Yan, Zhaojun Wang, Xianghua Yu, Manman Li, Dan Dan, Jia Qian, Baoli Yao
Tightly focused vectorial optical beams have found extensive applications in variety of technical fields like single-molecule detection, optical tweezers, and super-resolution optical microscopy. Such applications require an accurate measurement and manipulation of focal optical fields. We have developed a compact instrument (with dimensions of 35 × 35 × 30 cm(3)) to rapidly measure the intensity distribution in three dimensions of the focused fields of vectorial beams and any other incident beams. This instrument employs a fluorescent nanoparticle as a probe to scan the focal region to obtain a high spatial resolution of intensity distribution...
June 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28634334/image-guided-transplantation-of-single-cells-in-the-bone-marrow-of-live-animals
#16
Raphaël Turcotte, Clemens Alt, Judith M Runnels, Kyoko Ito, Juwell W Wu, Walid Zaher, Luke J Mortensen, Lev Silberstein, Daniel C Côté, Andrew L Kung, Keisuke Ito, Charles P Lin
Transplantation of a single hematopoietic stem cell is an important method for its functional characterization, but the standard transplantation protocol relies on cell homing to the bone marrow after intravenous injection. Here, we present a method to transplant single cells directly into the bone marrow of live mice. We developed an optical platform that integrates a multiphoton microscope with a laser ablation unit for microsurgery and an optical tweezer for cell micromanipulation. These tools allow image-guided single cell transplantation with high spatial control...
June 20, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28618627/experimental-comparison-of-forces-resisting-viral-dna-packaging-and-driving-dna-ejection
#17
Nicholas Keller, Zachary T Berndsen, Paul J Jardine, Douglas E Smith
We compare forces resisting DNA packaging and forces driving DNA ejection in bacteriophage phi29 with theoretical predictions. Ejection of DNA from prohead-motor complexes is triggered by heating complexes after in vitro packaging and force is inferred from the suppression of ejection by applied osmotic pressure. Ejection force from 0% to 80% filling is found to be in quantitative agreement with predictions of a continuum mechanics model that assumes a repulsive DNA-DNA interaction potential based on DNA condensation studies and predicts an inverse-spool conformation...
May 2017: Physical Review. E
https://www.readbyqxmd.com/read/28618573/%C3%AE-cyclodextrin-polymer-binding-to-dna-modulating-the-physicochemical-parameters
#18
J C B Rocha, E F Silva, M F Oliveira, F B Sousa, A V N C Teixeira, M S Rocha
Cyclodextrins and cyclodextrins-modified molecules have interesting and appealing properties due to their capacity to host components that are normally insoluble or poorly soluble in water. In this work, we investigate the interaction of a β-cyclodextrin polymer (poly-β-CD) with λ-DNA. The polymers are obtained by the reaction of β-CD with epichlorohydrin in alkaline conditions. We have used optical tweezers to characterize the changes of the mechanical properties of DNA molecules by increasing the concentration of poly-β-CD in the sample...
May 2017: Physical Review. E
https://www.readbyqxmd.com/read/28605454/stacks-off-tracks-a-role-for-the-golgin-atcasp-in-plant-endoplasmic-reticulum-golgi-apparatus-tethering
#19
Anne Osterrieder, Imogen A Sparkes, Stan W Botchway, Andy Ward, Tijs Ketelaar, Norbert de Ruijter, Chris Hawes
The plant Golgi apparatus modifies and sorts incoming proteins from the endoplasmic reticulum (ER) and synthesizes cell wall matrix material. Plant cells possess numerous motile Golgi bodies, which are connected to the ER by yet to be identified tethering factors. Previous studies indicated a role for cis-Golgi plant golgins, which are long coiled-coil domain proteins anchored to Golgi membranes, in Golgi biogenesis. Here we show a tethering role for the golgin AtCASP at the ER-Golgi interface. Using live-cell imaging, Golgi body dynamics were compared in Arabidopsis thaliana leaf epidermal cells expressing fluorescently tagged AtCASP, a truncated AtCASP-ΔCC lacking the coiled-coil domains, and the Golgi marker STtmd...
June 9, 2017: Journal of Experimental Botany
https://www.readbyqxmd.com/read/28599556/acoustic-force-measurements-on-polymer-coated-microbubbles-in-a-microfluidic-device
#20
Gianluca Memoli, Christopher R Fury, Kate O Baxter, Pierre N Gélat, Philip H Jones
This work presents an acoustofluidic device for manipulating coated microbubbles, designed for the simultaneous use of optical and acoustical tweezers. A comprehensive characterization of the acoustic pressure in the device is presented, obtained by the synergic use of different techniques in the range of acoustic frequencies where visual observations showed aggregation of polymer-coated microbubbles. In absence of bubbles, the combined use of laser vibrometry and finite element modelling supported a non-invasive measurement of the acoustic pressure and an enhanced understanding of the system resonances...
May 2017: Journal of the Acoustical Society of America
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