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Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Apr;79(4 Pt 1):042401. Epub 2009 Apr 28.

Co- and cross-flow extensions in an elliptical optical trap.

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School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, USA.


The extension of a particle (translational deviation) in an isotropic harmonic potential well is linearly proportional and parallel to the applied force. In an anisotropic trapping potential, the extension is instead related to the applied force by a compliance tensor. Using the focal spot of a high numerical aperture zone plate to create an elliptical potential and microfluidics to apply a calibrated force, we measure the two-dimensional extension of a trapped spherical particle. As a function of the orientation of the elliptical potential, the extension sweeps out a circular trajectory, exhibiting extensions both parallel (coflow) and perpendicular (cross flow) to the direction of the flow. The results fit well to a compliance tensor model.

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