| FCS is a spectroscopic technique for the study of molecular interactions in solution. FCS monitors the random motion of fluorescently labelled molecules inside a defined volume element irradiated by a focused laser beam. These fluctuations provide information on the rate of diffusion or diffusion time of a particle and this, in turn, is directly dependent on the particle's mass. As a consequence, any increase in the mass of a biomolecule, e.g. as a result of an interaction with a second molecule, is readily detected as an increase in the particle's diffusion time. Not least due to its simple underlying principle, FCS is an ideal approach for the study of thermodynamic and kinetic features of molecular interactions in solution.
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