Supported lipid bilayers membranes on SiO2 and TiO2:: Substrate effects on membrane formation and shape transformation

Lipid bilayer membranes deposited on solid surfaces are called "supported planar bilayers" (SPBs), and expected to be an effective cell-membrane-mimicking model system in vitro. We have investigated the influence of the substrate surface properties on the SPB formation process and on the photo-induced shape transformation of bilayers, by means of atomic force microscopy and fluorescence microscopy. The SPB of dipalmitoleoylphosphatidylcholine was formed on SiO2/Si(100) surfaces and rutile-TiO2(100) Surface by the vesicle fusion method. On the SiO2 surface, one or a few adsorbed vesicles can transform to a SPB resulting in a small bilayer patches. The SPB formation rate was accelerated on thermally treated SiO2 surfaces, which had less hydrophilicity, but the initial SPB formation process did not change. On the TiO2(100), the surface was completely covered with the adsorbed vesicles prior to the SPB formation, and the planar bilayer was obtained only if the lipid concentration in the suspension was sufficiently high. Photo-induced activation of molecular motion through the fluorescence dye excitation achieved the area-selective SPB formation from the adsorbed vesicular layers with small SPB domains on the TiO2(100). This photo-activation transformed the SPB shapes three-dimensionally on the SiO2 and TiO2 surfaces in different way.