LIPID VESICLE ADSORPTION VERSUS FORMATION OF PLANAR BILAYERS ON SOLID-SURFACES

The adsorption and spreading behavior of lipid vesicles composed of ei ther palmitoyloleoylphosphatidylcholine (POPC) or Escherichia coli lip id upon contact with a glass surface was examined by fluorescence meas urements. Fluorescently labeled lipids were used to determine 1) the a mount of lipid adsorbed at the surface, 2) the extent of fusion of the vesicles upon contact with the surface, 3) the ability of the adsorbe d lipids to undergo lateral diffusion, and 4) the accessibility of the adsorbed lipids by external water soluble molecules. The results of t hese measurements indicate that POPC vesicles spread on the surface an d form a supported planar bilayer, whereas E. coli lipid vesicles adso rb to the surface and form a supported vesicle layer. Supported planar bilayers were found to be permeable for small molecules, whereas supp orted vesicles were impermeable and thus represented immobilized, topo logically separate compartments.