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optical tweezers

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https://www.readbyqxmd.com/read/28634334/image-guided-transplantation-of-single-cells-in-the-bone-marrow-of-live-animals
#1
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
#2
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
#3
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
#4
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
#5
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
https://www.readbyqxmd.com/read/28594002/vector-assembly-of-colloids-on-monolayer-substrates
#6
Lingxiang Jiang, Shenyu Yang, Boyce Tsang, Mei Tu, Steve Granick
The key to spontaneous and directed assembly is to encode the desired assembly information to building blocks in a programmable and efficient way. In computer graphics, raster graphics encodes images on a single-pixel level, conferring fine details at the expense of large file sizes, whereas vector graphics encrypts shape information into vectors that allow small file sizes and operational transformations. Here, we adapt this raster/vector concept to a 2D colloidal system and realize 'vector assembly' by manipulating particles on a colloidal monolayer substrate with optical tweezers...
June 8, 2017: Nature Communications
https://www.readbyqxmd.com/read/28588196/direct-measurement-of-optical-trapping-force-gradient-on-polystyrene-microspheres-using-a-carbon-nanotube-mechanical-resonator
#7
Masaaki Yasuda, Kuniharu Takei, Takayuki Arie, Seiji Akita
Optical tweezers based on optical radiation pressure are widely used to manipulate nanoscale to microscale particles. This study demonstrates direct measurement of the optical force gradient distribution acting on a polystyrene (PS) microsphere using a carbon nanotube (CNT) mechanical resonator, where a PS microsphere with 3 μm diameter is welded at the CNT tip using laser heating. With the CNT mechanical resonator with PS microsphere, we measured the distribution of optical force gradient with resolution near the thermal noise limit of 0...
June 6, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28585264/metasurfaces-and-colloidal-suspensions-composed-of-3d-chiral-si-nanoresonators
#8
Ruggero Verre, Lei Shao, Nils Odebo Länk, Pawel Karpinski, Andrew B Yankovich, Tomasz J Antosiewicz, Eva Olsson, Mikael Käll
High-refractive-index silicon nanoresonators are promising low-loss alternatives to plasmonic particles in CMOS-compatible nanophotonics applications. However, complex 3D particle morphologies are challenging to realize in practice, thus limiting the range of achievable optical functionalities. Using 3D film structuring and a novel gradient mask transfer technique, the first intrinsically chiral dielectric metasurface is fabricated in the form of a monolayer of twisted silicon nanocrescents that can be easily detached and dissolved into colloidal suspension...
June 6, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28561826/microfluidic-based-high-throughput-optical-trapping-of-nanoparticles
#9
Abhay Kotnala, Yi Zheng, Jianping Fu, Wei Cheng
Optical tweezers have emerged as a powerful tool for multiparametric analysis of individual nanoparticles with single-molecule sensitivity. However, its inherent low-throughput characteristic remains a major obstacle to its applications within and beyond the laboratory. This limitation is further exacerbated when working with low concentration nanoparticle samples. Here, we present a microfluidic-based optical tweezers system that can 'actively' deliver nanoparticles to a designated microfluidic region for optical trapping and analysis...
June 13, 2017: Lab on a Chip
https://www.readbyqxmd.com/read/28548627/combined-single-molecule-experimental-and-computational-approaches-for-understanding-the-unfolding-pathway-of-a-viral-translation-enhancer-that-participates-in-a-conformational-switch
#10
My-Tra Le, Wojciech K Kasprzak, Bruce A Shapiro, Anne E Simon
How plus-strand [+]RNA virus genomes transition from translation templates to replication templates is a matter of much speculation. We have previously proposed that, for Turnip crinkle virus, binding of the encoded RNA-dependent RNA polymerase (RdRp) to the 3'UTR of the [+]RNA template promotes a regional wide-spread conformational switch to an alternative structure that disassembles the cap-independent translation element (CITE) in the 3'UTR. The active 3'CITE folds into a tRNA-like T-shaped structure (TSS) that binds to 80S ribosomes and 60S subunits in the P-site...
May 26, 2017: RNA Biology
https://www.readbyqxmd.com/read/28526627/dynamic-fatigue-measurement-of-human-erythrocytes-using-dielectrophoresis
#11
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 17, 2017: Acta Biomaterialia
https://www.readbyqxmd.com/read/28522581/conformational-dynamics-of-the-frameshift-stimulatory-structure-in-hiv-1
#12
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
#13
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
#14
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 31, 2017: Soft Matter
https://www.readbyqxmd.com/read/28507157/translation-and-folding-of-single-proteins-in-real-time
#15
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 30, 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
#16
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
#17
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...
June 2017: Journal of Photochemistry and Photobiology. B, Biology
https://www.readbyqxmd.com/read/28490794/thermally-induced-micro-motion-by-inflection-in-optical-potential
#18
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
#19
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
#20
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
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