SINGLE-MOLECULE DETECTION LIMITS IN LEVITATED MICRODROPLETS

Laser-excited fluorescence from electrodynamically levitated microdroplets is used to detect small numbers of rhodamine-6G molecules. The small sample volume, typically a few picoliters reduces the background due to solvent and impurity Raman and fluorescence emission. With 514.5-nm excitation from an argon ion laser, as few as 12 molecules have been detected in glycerol-water droplets. Our present detection limit, due to variations in the impurity concentration in the blanks, corresponds to a signal-to-noise ratio of 3 for a single molecule of rhodamine-6G contained in a 1-pL volume (droplet diameter of congruent-to 12-mu-m).