ABSTRACT
Fluorescence correlation spectroscopy (FCS) and, more broadly, optical microscopy methods that harness information from diffusing particles are important tools for the study of structural and dynamic processes in cells and tissues. This chapter describes three such methods. The rst is FCS, which measures dynamic processes via uorescence uctuations in steady-state systems, and the second is uorescence photobleaching recovery, which measures the relaxation of macroscopic concentration gradients produced by localized photobleaching. These closely related methods supply information about rates of diffusion, convection, chemical reaction, and other dynamic processes. They have been extensively used to measure dynamic molecular behavior both in puried systems and in cells. The third is single particle tracking, which allows the observation of different mechanisms of molecular transport in cells and in very small subcellular domains. These measurements indicate heterogeneity due to localized structures that inuence particle transport. Single particle tracking can also be used to determine the viscoelastic properties of highly localized regions of cells and polymeric systems.
