We describe instrumentation for real-time detection of single-molecule fluorescence in guided streams of 1-μm (nominal) water droplets. In this technique, target molecules were confined to droplets whose volumes were comparable with illumination volumes in diffraction-limited fluorescence microscopy and guided to the waist of a cw probe laser with an electrostatic potential. Concentration detection limits for Rhodamine 6G in water were determined to be ~1 fM, roughly 3 orders of magnitude lower than corresponding limits determined recently with diffraction-limited microscopy techniques for a chemical separation of similar dyes. In addition to its utility as a vehicle for probing single molecules, instrumentation for producing and focusing stable streams of 1–2-μm-diameter droplets may have other important analytical applications as well.
© 1999 Optical Society of America
Chung-yi Kung, Michael D. Barnes, Noah Lermer, William B. Whitten, and J. Michael Ramsey, "Single-Molecule Analysis of Ultradilute Solutions with Guided Streams of 1-–m Water Droplets," Appl. Opt. 38, 1481-1487 (1999)