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(Color online) Optical trapping setup with integrated microfluidic system.
(Color online) (a) PDMS chip and supply tubing encapsulated in transparent epoxy. (b) Used device mounted on a microscope adapter.
Transverse trapping strengths of diameter latex spheres as a function of the laser output power and trapping depth in water.
(Color online) [(a)–(d)] Rapid flow switching in the microchip with trapped beads. For better visualization beads were chosen. (e) Modeling of flow switching (sketch and diagram). The width of a flow and the flow velocity , which is equal for all flows, can be derived as functions of the side channel inlet pressures , , and and the pressure on the exit from the flow equations ( is the channel index, the volume flow rate, the hydrodynamic resistance, and the channel height, ) for the side channels and for the main channel under the constraint ( is the main channel width, ):andThe diagram shows the variation of (solid curves) and (hatched lines) with the pressure using the resistances ( tubing) , , for constant and equal pressures . The curve ( and ) pairs 1, 2, and 3 are for , 23.25, and , respectively. Each pressure contains a hydrostatic pressure contribution of a reservoir. In practice the setting of the calculated and is not instantaneous due to the elasticity in the system. Fluorescence detection allows to discriminate labeled beads (, Molecular Probes A8858). Selected beads can be sorted downstream by individually switching the laser diodes. The trap distance is .
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