Fluorescence Correlation Spectroscopy is a powerful method that allows kinetics and diffusion measurements of fluorescent molecules at a single point inside a sample.
The molecules move in and out of a confocal volume irradiated by a laser. The movement of the molecules gives rise to fluorescence intensity fluctuations that can be analyzed through an autocorrelation function. This one reveals different information of the molecules observed (concentration, diffusion coefficient, viscosity and mass). FCS combined with FLIM (FLIM-FCS) allows extending your studies, including also information about mobility and protein interactions in the cell environment.