Facility for optical trapping of multiple DNA molecules in combination with microfluidicsWe designed and built an optical-tweezers instrument that allows manipulation of two DNA molecules in three dimensions simultaneously and independently by trapping micrometer-sized polystyrene beads attached to the ends of the DNA molecules. Four optical traps are generated by first splitting a laser beam in two orthogonally polarized beams. One of these beams generates a continuous trap; the other beam is time-shared over three trap positions using acousto-optic deflectors. Forces acting on the bead in the continuous trap can be detected with subpicoNewton resolution using back-focal-plane interferometry. To attach DNA between the four beads held in the optical traps, we have previously designed and constructed a flow chamber with multiple laminar flows of solution running parallel to each other. By moving the chamber relative to the optical traps, the four trapped beads can be moved into different solutions.
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