Optically trapped aqueous droplets for single molecule studies

Abstract

We demonstrate a technique for creating, manipulating, and combining femtoliter volume chemical containers. The containers are surfactant-stabilized aqueous droplets in a low index-of-refraction fluorocarbon medium. The index-of-refraction mismatch between the container and fluorocarbon is such that individual droplets can be optically trapped by single focus laser beams, i.e., optical tweezers. Here, we trap and manipulate individual droplets, detect the fluorescence from single dye and red fluorescent protein molecules encapsulated in droplets, and observe fluorescence resonance energy transfer from a single dye pair on a deoxyribonucleic acid molecule encapsulated in a droplet.