FORMATION OF SUPPORTED PLANAR BILAYERS BY FUSION OF VESICLES TO SUPPORTED PHOSPHOLIPID MONOLAYERS

A technique for the production of supported phospholipid bilayers by adsorption and fusion of small unilamellar vesicles to supported phospholipid monolayers on quartz is described. The physical properties of these supported bilayers are compared with those of supported bilayers which are prepared by Langmuir-Blodgett deposition or by direct vesicle fusion to plain quartz slides. The time courses of vesicle adsorption, fusion and desorption are followed by total internal reflection fluorescence microscopy and the lateral diffusion of the lipids in the adsorbed layers by fluorescence recovery after photobleaching. Complete supported bilayers can be formed with phosphatidylcholine vesicles at concentrations as low as 35-mu-M. However, the adsorption, fusion and desorption kinetics strongly depend on the used lipid, NaCl and Ca2+ concentrations. Asymmetric negatively charged supported bilayers can be produced by incubating a phosphatidylcholine monolayer with vesicles composed of 80% phosphatidylcholine and 20% phosphatidylglycerol. Adsorbed vesicles can be removed by washing with buffer. The measured fluorescence intensities after washing are consistent with single supported bilayers. The lateral diffusion experiments confirm that continuous extended bilayers are formed by the monolayer-fusion technique. The measured lateral diffusion coefficient of NBD-labeled phosphatidylethanolamine is (3.6 +/- 0.5) . 10(-8) cm2/s in supported phosphatidylcholine bilayers, independent of the method by which the bilayers were prepared.