<title>Ultrasensitive fluorescence detection and photophysics in microdroplets</title>

Abstract

Fluorescence detection of single molecules in room temperature liquids is usually plagued by many difficulties such as finite saturated absorption rate, finite laser-analyte interaction time, and analyte diffusion. Our approach to single molecule detection in liquids has been to use microdroplets as the sample medium which has many advantages over conventional 'bulk' techniques such as extended laser-analyte interaction time, a probe volume defined by the droplet, and modified radiative properties of molecules due to interactions with droplet resonances. We have demonstrated detection of single rhodamine molecules with signal-to-noise ratios on the order or 30 using levitated microdroplets as the sample medium. The focus of current work is on single molecule detection in falling droplet streams with analysis rates on the order of 5-10 kHz.