20 August 2009 Depletion-enhanced optical trapping in nanoparticle suspensions
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With the right proportions, a binary suspension of different sized particles may be subject to entropic effects that can generate a depletion-induced attraction between large particles. A manifestation of the induced attraction is the enhanced osmotic compressibility of the larger species in the presence of the smaller species. We conducted an experimental study on how such an enhancement is affected for 190 nm polystyrene spheres in the presence of polyethelyne-oxide in aqueous solutions. Using the gradient force from a tightly focused laser, we can locally concentrate the polystyrene nanoparticles in suspension, and from the changes of local particle density under the known gradient force, we deduce a quantitative measure of the isothermal compressibility of the particles. We report the analysis of these compressibilities and their enhancement by the added polymers for a broad range of particle and polymer concentrations.
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Joseph Junio, Joseph Junio, H. Daniel Ou-Yang, H. Daniel Ou-Yang, "Depletion-enhanced optical trapping in nanoparticle suspensions", Proc. SPIE 7400, Optical Trapping and Optical Micromanipulation VI, 74001C (20 August 2009); doi: 10.1117/12.826386; https://doi.org/10.1117/12.826386

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