Near-Field Scanning Optical Microscopy to Identify Membrane Microdomains

Near-field scanning optical microscopy (NSOM) allows optical imaging with a spatial resolution that is significantly better than the diffraction limited resolution achievable with conventional optical microscopy. NSOM has the potential to study the nanoscale organization of membrane surfaces and ultimately to resolve questions concerning lipid rafts in both model-supported membranes and cellular membranes. Supported phospholipid monolayers and bilayers of phase separated binary and ternary lipid mixtures that model the composition of lipid rafts in natural membranes have been studied by NSOM. The results illustrate the ability of NSOM measurements with 50–100 nm probe apertures to obtain detailed nanoscale information for small, closely spaced domains, and the utility of two-color experiments to probe localization of raft markers in supported membranes.