We present results of detailed calculations of photocount statistics for single molecules in microdroplets. A Monte Carlo approach is used to simulate effects of molecular occupancy, photobleaching, and fluorophor spatial diffusion within the droplet. The excitation rate and fraction of fluorescence collected are both position-dependent, and are computed using classical and semiclassical formalisms. Differences in the single-molecule photocount distributions (and consequently molecular detection efficiencies) are predicted for cases where the RMS diffusion length is either small or large compared to the droplet diameter on the measurement time scale. These calculations provide semiquantitative estimates of molecular detection efficiencies and illustrate some of the unique optical features of a microdroplet approach to single molecule detection.
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