Detecting membrane lipid microdomains by two-photon fluorescence microscopy.

Microscopy images of the generalized polarization (GP) of the lipid probe 2-dimethylamino-6-lauroylnapthalene (LAURDAN) in phospholipid vesicles and in natural membranes were obtained by using two-photon excitation. The images show different distribution of the GP value depending on membrane composition. The use of linearly polarized excitation allowed the attribution of the GP heterogeneity to coexisting membrane domains of different dynamic properties. Based on the photoselection operated by the excitation polarization, a model is proposed to explain the results and to estimate the domains' dimension