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      Microparticle manipulation using laser-induced thermophoresis and thermal convection flow

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      Scientific Reports
      Nature Publishing Group UK
      Lab-on-a-chip, Optical manipulation and tweezers

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          Abstract

          We demonstrate manipulation of microbeads with diameters from 1.5 to 10 µm and Jurkat cells within a thin fluidic device using the combined effect of thermophoresis and thermal convection. The heat flow is induced by localized absorption of laser light by a cluster of single walled carbon nanotubes, with no requirement for a treated substrate. Characterization of the system shows the speed of particle motion increases with optical power absorption and is also affected by particle size and corresponding particle suspension height within the fluid. Further analysis shows that the thermophoretic mobility ( D T ) is thermophobic in sign and increases linearly with particle diameter, reaching a value of 8 µm 2 s −1 K −1 for a 10 µm polystyrene bead.

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          Most cited references47

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          Observation of a single-beam gradient force optical trap for dielectric particles

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            Why molecules move along a temperature gradient.

            Molecules drift along temperature gradients, an effect called thermophoresis, the Soret effect, or thermodiffusion. In liquids, its theoretical foundation is the subject of a long-standing debate. By using an all-optical microfluidic fluorescence method, we present experimental results for DNA and polystyrene beads over a large range of particle sizes, salt concentrations, and temperatures. The data support a unifying theory based on solvation entropy. Stated in simple terms, the Soret coefficient is given by the negative solvation entropy, divided by kT. The theory predicts the thermodiffusion of polystyrene beads and DNA without any free parameters. We assume a local thermodynamic equilibrium of the solvent molecules around the molecule. This assumption is fulfilled for moderate temperature gradients below a fluctuation criterion. For both DNA and polystyrene beads, thermophoretic motion changes sign at lower temperatures. This thermophilicity toward lower temperatures is attributed to an increasing positive entropy of hydration, whereas the generally dominating thermophobicity is explained by the negative entropy of ionic shielding. The understanding of thermodiffusion sets the stage for detailed probing of solvation properties of colloids and biomolecules. For example, we successfully determine the effective charge of DNA and beads over a size range that is not accessible with electrophoresis.
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              Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy.

              Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. Here we describe these techniques and illustrate them with examples highlighting current capabilities and limitations.
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                Author and article information

                Contributors
                John.Marsh@glasgow.ac.uk
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                5 November 2020
                5 November 2020
                2020
                : 10
                : 19169
                Affiliations
                GRID grid.8756.c, ISNI 0000 0001 2193 314X, James Watt School of Engineering, , University of Glasgow, ; Glasgow, G12 8QQ UK
                Article
                76209
                10.1038/s41598-020-76209-9
                7644619
                33154506
                4b55186f-926f-4098-b151-b019b1af5ff8
                © The Author(s) 2020

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 2 March 2020
                : 19 October 2020
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                © The Author(s) 2020

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                lab-on-a-chip,optical manipulation and tweezers
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                lab-on-a-chip, optical manipulation and tweezers

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