Fluorescence Correlation Spectroscopy

Fluorescence Correlation Spectroscopy (FCS) can be used to quantify diffusion of fluorescent molecules.  The basic idea behind FCS is that if a very small volume is monitored, generally the fixed focal spot of a confocal microscope, when fluorescent molecules diffuse through a brief increase in fluorescence will be detected.  The duration and number these events are recorded and over time enough accumulate to permit the calculation of diffusion coefficients.  Furthermore alterations in FCS measurements can be correlated to changes in the multimerization status of fluorescent-tagged molecules, and multi-color Fluorescence Cross-Correlation Spectroscopy (FCCS) experiments can be performed which can allow quantification of protein-protein interactions.