Fluorescence correlation spectroscopy: molecular recognition at the single molecule level.

Fluorescence correlation spectroscopy (FCS) is a fluorescence microscopy technique that allows the study of molecular interactions in extremely low volumes, at nanomolar concentrations, even when binding is not accompanied by a fluorescence change. It can be applied directly in living cells. FCS clearly considerably extends the possibilities of the classical techniques used in molecular recognition studies and can be considered to belong to a growing group of techniques that allow detection at the single molecule level. In this review, several applications of FCS, both in vitro and in vivo, will be discussed.