Single-Molecule Detection by Laser-Induced Fluorescence Technique with a Position-Sensitive Photon-Counting Apparatus

A new method of detecting single-molecule fluorescence has been implemented using a conventional optical microscope and a position-sensitive photon-counting apparatus. The samples were solvent-free fluorescent dyes adsorbed on a solid substrate in air at room temperature by spraying microdroplets of a dye solution followed by solvent evaporation. At the concentration used, each droplet contained a very small number of dye molecules. Quantized fluorescence intensity was determined and the number of occurrences of the quantized intensity agreed well with that calculated from Poisson's formula, thus confirming success of the position-sensitive single-molecule fluorescence detection.