Fluorescence correlation spectroscopy (FCS)
FCS is a method to detect molecular parameters like e.g. diffusion time, diffusion coefficent. Threrefore FCS can be used to analyse interaction of molecules (Elson & Magde, 1974; Magde et al., 1974; overview: Schwille & Haustein, 2001). In Fluorescence Correlation Spectroscopy the fluctuation of the fluorescence intensity is recorded in a very small volume, i.e. in femtoliter range via a confocal optic system.