Generating an Intracellular Diffusion Map by Two-Photon Fluorescence Correlation Spectroscopy

A new technique for determining cellular viscosity has been developed based on two-photon excitation and fluorescence correlation spectroscopy. We have applied this method to map intracellular diffusion coefficient of small molecules at selected cytoplasmic locations of mouse fibroblast cells. The cytoplasmic diffusion rate is one tenth of that in an aqueous environment.