Quantitation of fluorophores in solution by pulsed laser excitation and time-filtered detection

A fluorimeter employing single photon counting and mode-locked laser excitation was constructed to test the concept of time-filtered detection. Expressions for a figure of merit and a signal-to-noise ratio are developed and utilized with experimental data to gain an understanding of operational principles. Other data are examined to ascertain calibration curve characteristics. The usable linear dynamic range is about 3 orders of magnitude, the sensitivity is 2 x 10/sup 13/ counts M/sup -1/ s/sup -1/, and the lower limit of detection (S/N = 2) is 1.8 x 10/sup -13/ M for a 100-s counting period. Finally, future instrumental advances are discussed that should allow better than an order of magnitude improvement in the lower limit of detection.