DETECTION AND LIFETIME MEASUREMENT OF SINGLE MOLECULES IN FLOWING SAMPLE STREAMS BY LASER-INDUCED FLUORESCENCE

The detection and measurement of fluorescence lifetimes of single Rhod amine-110 molecules in a flowing, aqueous sample stream is described. Time-correlated single-photon counting, used in combination with mode- locked picosecond pulsed excitation, allows the detection of single fl uorescent molecules in the presence of significant solvent Raman and R ayleigh backgrounds. The fluorescence lifetime of a detected molecule is estimated from the record of arrival times (relative to the excitat ion pulse) of photons detected during the molecule's passage through t he approximately 1 pL excitation volume.