Liposome Adhesion on Mica Surface Studied by Atomic Force Microscopy

The dynamic topography change of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) liposomes from a vesicle form to a flat bilayer through their direct adhesion on a mica surface has been recorded by atomic force microscopy (AFM) in situ. Controlled experiments demonstrated that immediately the liposome adhered on the mica surface and the spherical shape of the vesicle ruptured spontaneously and deformed to a flat supported bilayer on the mica. In the PC liposome, however, the second bilayer was hardly formed and only a saturated first bilayer was extended over all the mica surface. The formation rate of the PC bilayer depended on the salt and vesicle concentrations in the medium and increased with increasing content of these materials. On the other hand, in the PE liposome system, a vertical growth of lipid molecules was recognized and a clear difference between PC and PE systems has been found. This different behavior has been interpreted by the existence of a hydration layer around the PC surface.