High Sensitivity Fluorophotometer Using Photon-Counting

An apparatus based upon photon counting has been constructed that permits detection of very weak fluorescence. The sensitivity of the apparatus was checked by measuring the fluorescence from aqueous solutions of riboflavin. The photon counts increased linearly with the concentration of the solution from 4 x 10(-11)g/ml to 1 x 10 (-6) g/ml. The emission spectra of monolayers of both chlorophyll a and b were also measured with a high signal-to-noise ratio.