An Atomic Force Microscopy Study on Small Unilamellar Vesicle Structures on Mica

The vesicle structures of egg yolks phosphatidylcholine/didodecyldimethylammonium bromide (1:1, mass ratio) deposited on mica were studied by atomic force microscopy (AFM) both in aqueous phase and air. In aqueous phase both bilayer and domelike vesicles with a mean diameter of 45 nm were observed, whereas in air the structure was more complicated depending on the initial concentration of vesicles. Vesicles with the original size could only be visualized at very low concentration with a mean diameter of 55 nm, which is a little larger than the result obtained in aqueous phase. At higher concentrations, fused large aggregates and multiple bilayer with a thickness ca. 4 nm of each bilayer were dominated. A plausible adsorption mechanism was proposed based on the experimental results.