Abstract
We optically trap molecules in free solution, which allows to accumulate 5-base DNA to a hundredfold excess within seconds [1]. The concentration of the trapped DNA scales exponentially with length, reaching trapping potential depths of 14kT for 50 bases. This novel way to trap molecules could be used to enhance diffusion-limited surface reactions, redirect cellular signaling, observe individual biomolecules over a prolonged time or separate small molecules in solution by their diffusion constant.The mechanism is based on the microscale analog of a conveyor belt: a bidirectional flow, driven optically by the recently shown thermo-viscous fluid pump [2,3], is combined with a perpendicular thermophoretic molecule drift. Arranged in a toroidal geometry, no microfluidics, electrodes or surface modifications are required. As a result, the trap can be dynamically relocated.[1] Weinert and Braun, Nano Letters, accepted[2] Weinert, Kraus, Franosch and Braun, PRL 100, 164501 (2008)[3] Weinert and Braun, JAP 104, 104701 (2008)View Large Image | View Hi-Res Image | Download PowerPoint Slide
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