Principles and applications of Fluorescence Correlation Spectroscopy (FCS)

Abstract

Fluorescence correlation spectroscopy (FCS) is one of the various modern optical techniques that allow access to single fluorescently labeled biomolecules in aqueous solution. In contrast to other fluorescence measurements, however, the parameter of primary interest is not the emission intensity itself, but rather spontaneous intensity fluctuations caused by the minute deviations of a small ensemble of molecules from thermal equilibrium. In general, all physical parameters that give rise to fluctuations in the fluorescence signal are accessible by FCS. It is, for example, rather straightforward to determine local concentrations, mobility coefficients or characteristic rate constants of inter-or intramolecular reactions of fluorescently labeled biomolecules at nanomolar to micromolar concentrations. © 2011 Springer Science+Business Media B.V.