Formation of silica precipitates on membrane surfaces in two and three dimensions

Ether lipids with alkyl chains of uniform length and varying amine headgroups were synthesized and assembled into bilayer structures in aqueous solution, which served as templates for the formation of silica in two and three dimensions produced under ambient conditions. Dynamic light scattering revealed that unilamellar vesicles of the aminolipids are formed by the extrusion method. The alkylation of the polar amine headgroup was systematically increased from a primary, secondary, and tertiary amine to a quaternary ammonium salt, and the amount of silica was quantified by the beta-silicomolybdate method as a function of the headgroup. A lysinol-connected ether lipid harboring two primary amine groups was also investigated. This variation enabled us to compare the influence of the headgroup on the properties of the precipitated silica in detail. By spreading of unilamellar aminolipid vesicles onto planar silicon substrates, two-dimensional planar bilayers can be produced. By means of ellipsometry in conjunction with atomic force microscopy, we were able to demonstrate that very thin silica layers with a thickness of a few nanometers are formed within minutes on the surface of the aminolipid bilayers. All layers are composed of silica nanospheres, and the thickness turned out to be independent of the amine headgroup.