Laser switching and sorting for high speed digital microfluidics

We used thermocapillary stresses locally induced by laser on flowing drops to build high throughput drop switchers and sorters for digital microfluidics. Since the laser is disconnected to the chip, the method does not require dedicated micropatterning. We show switching efficiencies of 100% for drop velocities up to 1.3 cm/s, demonstrate the involved mechanism, and apply laser switching for sorting droplets of different natures for lab-on-a-chip applications. (C) 2008 American Institute of Physics.