Sorting single molecules: application to diagnostics and evolutionary biotechnology.

A method is described that provides for detection and identification of single molecules in solution. The method is based on fluorescence correlation spectroscopy, which records spatio-temporal correlations among fluctuating light signals, coupled with devices for trapping single molecules in an electric field. This technique is applied to studies of molecular evolution, where it allows fast screening of large mutant spectra in which targets are labeled by specific fluorescent ligands. The method expands the horizon in molecular diagnostics by making it possible to monitor concentrations down to (less than) 10(-15) M without any need for amplification.