Interaction of phospholipid vesicles with smooth metal-oxide surfaces

The interaction of phospholipid vesicles with planar metal oxide supports has been previously reported as a means of preparing supported lipid bilayers, which are useful models of biological membranes. Nevertheless, extant evidence that bilayers are actually formed is rather circumstantial, and the necessary and sufficient conditions for their formation have never been delineated. Here, we tackle this problem by using smooth planar optical waveguides as the support. Analysis of the lightmode spectra of the waveguides, measured in situ during the deposition process, yields the mass of lipid deposited at the solid/liquid interface. By comparing the optogeometric parameters of the structures assembled from the vesicles with those of a lipid bilayer of known structure assembled using the Langmuir-Blodgett technique, we show that in many cases the vesicles remain intact and form a supported layer of vesicles rather than a bilayer, and often mixed structures (intact vesicles embedded in a bilayer partially covering the surface) occur. Careful analysis of the lipid deposition kinetics corroborates this result. We have also found that divalent cations dramatically promote attachment of mixed phosphatidylcholine/phosphatidylglycerol vesicles to form supported vesicle layers, and bilayer formation from pure phosphatidylcholine vesicles.