Domain formation in thin lipid films probed with near-field scanning optical microscopy

High-resolution near-field scanning optical microscopy (NSOM) fluorescence and topographic images of L-alpha-dipalmitoylphosphatidylcholine (DPPC) monolayers doped with a fluorescent dye are presented. DPPC monolayers are deposited onto mica substrates from the air-water interface at several surface pressures using the Langmuir-Blodgett technique. Sub-diffraction limit phase domain structures are observed in both fluorescence and topographic NSOM images of the lipid films. The morphology of the resulting monolayers depends strongly on the surface pressure and composition of the subphase used in the film transfer. Mechanisms for lipid domain formation and growth are discussed.