Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate

The authors demonstrate an optical manipulation mechanism of gas bubbles for microfluidic applications. Air bubbles in a silicone oil medium are manipulated via thermocapillary forces generated by the absorption of a laser in an amorphous silicon thin film. In contrast to previous demonstrations of optically controlled thermally driven bubble movement, transparent liquids can be used, as the thermal gradient is formed from laser absorption in the amorphous silicon substrate, and not in the liquid. A variety of bubbles with volumes ranging from 19 pl to 23 nl was transported at measured velocities of up to 1.5 mm/s.