Fluorescence Correlation Spectroscopy (FCS) is a powerful technique used to study the dynamics of fluorescent molecules in solution. By analyzing fluctuations in fluorescence intensity over time, FCS can provide information about molecular concentration, diffusion rates, and interactions. This method is particularly useful in biological research for observing processes at the cellular level. In FCS, a focused laser beam excites fluorescent molecules, and the emitted light is detected by a sensitive photodetector. The resulting data allows researchers to calculate parameters such as diffusion coefficients and binding affinities, making FCS a valuable tool in fields like biophysics, biochemistry, and cell biology.