Light-Driven Formation and Rupture of Droplet Bilayers

Abstract

We demonstrate optical manipulation of nanoliter aqueous droplets containing surfactant or lipid molecules and immersed in an organic liquid using near infrared light. The resulting emulsion droplets are manipulated using both the thermocapillary effect and convective fluid motion. Droplet pair-interactions induced in the emulsion upon optical initiation and control provide direct observations of the coalescence steps in intricate detail. Droplet-droplet adhesion (bilayer formation) is observed under several conditions. Selective bilayer rupture is also realized using the same infrared laser. The technique provides a novel approach to study thin film drainage and interface stability in emulsion dynamics. The formation of stable lipid bilayers at the adhesion interface between interacting water droplets can provide an optical platform to build droplet-based lipid bilayer assays. The technique also has relevance for understanding and improving microfluidics applications by devising Petri dish based droplet assays requiring no substrate fabrication.