Supported planar bilayer formation by vesicle fusion: the interaction of phospholipid vesicles with surfaces and the effect of gramicidin on bilayer properties using atomic force microscopy.

We have used magnetic alternating current mode atomic force microscopy (MAC-AFM) to investigate the formation of supported phospholipid bilayers (SPB) by the method of vesicle fusion. The systems studied were dioleoylphosphatidylcholine (DOPC) on mica and mica modified with 3-aminopropyl-triethoxy-silane (APTES), and DOPC vesicles with gramicidin incorporated on mica and APTES-modified mica. The AFM images reveal three stages of bilayer formation: localized disklike features that are single bilayer footprints of the vesicles, partial continuous coverage, and finally complete bilayer formation. The mechanism of supported phospholipid bilayers formation is the fusion of proximal vesicles, rather than surface disk migration. This mechanism does not appear to be affected by incorporation of gramicidin or by surface modification. Once formed, the bilayer develops circular defects one bilayer deep. These defects grow in size and number until a dynamic equilibrium is reached.