Single-Molecule Detection in Microdroplets

Abstract

Detection of single molecules in condensed phase with high signal-to-noise ratios is important for applications which involve detection of fluorescent tags such as DNA sequencing1, fluorescence immunoassay2, or hydrology.3 In addition, observation of photophysical phenomena unique to the interaction of a radiation field with an isolatedmolecule, such as photon antibunching,4 depends upon having such high sensitivity. As demonstrated by the experiments of Moerner5 and Orrit,6 very high sensitivity at the single molecule level can be achieved by probing "guest" molecules in solid hosts at cryogenic temperatures. However, practical applications requiring single molecule detection usually require measurements on liquid phase solutions at room temperature. These demands pose new problems such as solvent dependent quantum yield, finite photochemical lifetime (the number of absorption-emission cycles which occur before irreversible bleaching of fluorescence), and solvent Raman scattering and fluorescence.