Physicochemical Mapping of Phase Heterogeneity in Biomembrane Films

Langmuir-Blodgett (L-B) films have long served as models of cell membranes and lung surfactant systems. However, these monomolecular films are difficult to image due to their fragile and dynamic nature. Raman-spectral microscopy and TEM sug- gested the presence of phase heterogeneity in such systems. Using correlated atomic force and fluorescence microscopy with secondary ion mass spectral mapping of L-B films, snap- shots of the heterogeneity were imaged as gel-fluid domains or lipid rafts in phase coex- istence. The molecular tilt of lipid chains, chemical composition, rigidity and dynamics of these phase transitory structures could be monitored from an air-water interface. The physicochemical organization of such struc- tures suggests dynamic lipid-protein organi- zation in membranes.