Fluorescence correlation spectroscopy example: shift of autocorrelation curve

Fluorescence correlation spectroscopy (FCS) has become a powerful and sensitive tool in biochemistry and biophysics. It directly obtains physical parameters such as the average number of fluorescent molecules and their diffusion time in a tiny detection area. It also provides other useful information such as the brightness of molecules. Ultimately, it can give precise information about molecular interactions in the aqueous condition. In FCS experiments, the fluctuation of fluorescence emission intensity from the tiny detection area is monitored as a function of time. The monitored fluorescence fluctuation signals are transformed to an autocorrelation curve according to the autocorrelation calculator unit and the curves are then fitted to an appropriate physical model. This protocol outlines an FCS example involving a shift of the autocorrelation curve.