Molecular diffusion measurement in lipid bilayers over wide concentration ranges: a comparative study.

Molecular diffusion in biological membranes is a determining factor in cell signaling and cell function. In the past few decades, three main fluorescence spectroscopy techniques have emerged that are capable of measuring molecular diffusion in artificial and biological membranes at very different concentration ranges and spatial resolutions. The widely used methods of fluorescence recovery after photobleaching (FRAP) and single-particle tracking (SPT) can determine absolute diffusion coefficients at high (>100 microm(-2)) and very low surface concentrations (single-molecule level), respectively.