Droplet Navigation by Photothermal Pumping in an Optofluidic System.

Droplets with guided motion have potential applications as microreactors and delivery vehicles. Directing long-range migration powered solely by light is particularly advantageous since light can be applied remotely, patterned with a photomask, and readily translated to irradiate specified locations. Herein, we describe a universal platform that allows fast directional navigation and collective merging of droplets controlled by either ultraviolet or visible light. The guided motion of water and oil droplets follows density-driven convective flows arising from photothermal conversion at a light-absorbing amphiphobic substrate. Because of the relatively high photothermal efficiency, a low-intensity light beam can be employed. Further, we demonstrate that the moving droplets can function as carriers and on-demand reaction chambers.