Hydrosomes: Optically trapped femtoliter containers for single molecule studies and microfluidics

We demonstrate a novel technique for creating, manipulating, and combining femtoliter volume chemical containers. Possible uses include creating controlled chemical reactions involving small quantities of reagent, and studying the dynamics of single molecules within the containers by fluorescence imaging techniques. The containers, which we call hydrosomes, 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 hydrosomes can be optically trapped by single focus laser beams, i.e. optical tweezers. Here we trap and manipulate individual hydrosomes. We demonstrate a controlled chemical reaction by the fusion of a hydrosome containing DNA segments approximately 1000 base pairs in length with a hydrosome containing YOYO-1, a DNA intercalating dye. We furthermore detect the fluorescence from single dye molecules in a hydrosome, and observe single pair fluorescence resonance energy transfer (spFRET) from Cy3-Cy5 molecules attached to a single-stranded 16mer DNA molecule.