Planar bilayer lipid membranes supported on mesoporous aerogels, xerogels, and Vycor® glass: an epifluorescence microscopy study

We report the deposition and characterization of fluid synthetic biomembranes on various mesoporous materials. Planar phospholipid bilayers consisting of 97 mol% l-α-phosphatidylcholine (egg PC) and 3 mol% fluorescently labeled lipid N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn -glycero-3-phosphoethanolamine (NBD-PE) were formed by fusion of ∼30 nm diameter unilamellar vesicles on four different silica-based substrates: aerogels, xerogels, Vycor® glass, and microscope cover glass. Epifluorescence microscopy was used to examine the micrometer-scale homogeneity of the resulting planar membranes. Fluorescence recovery after photobleaching analysis was used to determine the lateral mobility retained in the membranes. Diffusion coefficients of 0.6 ± 0.2, 2 ± 1, 1.7 ± 1.1, and 2.5 ± 0.4 μm2 s−1 were obtained for membranes supported on aerogels, xerogels, Vycor®, and glass, respectively. In the same order, the average immobile lipid fractions, defined by the normalized magnitudes of recovery, were ∼75%, 81%, 94%, and 100%. Both lateral mobility and immobile fraction exhibited ranges of standard variations, especially pronounced for xerogels and Vycor®, suggesting that the long-range translational dynamics of lipids in the supported membranes are sensitive to local defects and geometry of the underlying surface. Micrometer-scale clefts on the aerogel and xerogel surfaces limited the lipid lateral exchange, as shown by the reduced diffusivity and recovery.