Chemical kinetics and rates of lateral transport (diffusion or flow) can be measured by
observing spontaneous fluctuations in reactant concentrations which occur even when the
system rests in equilibrium. This can be accomplished by using fluorescence to monitor the
numbers of molecules of specified types in a defined open region of the reaction system.
The feasibility of this approach has been demonstrated, and the method, called fluorescence
correlation spectroscopy (FCS) has found practical application. Because it is based on …