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Lithographically patterned grids of photoresist, aluminum oxide, or gold on oxidized silicon substrates were used to partition supported lipid bilayers into micrometer-scale arrays of isolated fluid membrane corrals. Fluorescently labeled lipids were observed to diffuse freely within each membrane corral but were confined by the micropatterned barriers. The concentrations of fluorescent probe molecules in individual corrals were altered by selective photobleaching to create arrays of fluid membrane patches with differing compositions. Application of an electric field parallel to the surface induced steady-state concentration gradients of charged membrane components in the corrals. In addition to producing patches of membrane with continuously varying composition, these gradients provide an intrinsically parallel means of acquiring information about molecular properties such as the diffusion coefficient in individual corrals.
The patterning of surfaces into defined regions of contrasting properties has recently received considerable attention. Successes in this field include the development of micrometer-scale patterns in surface wettability (1) and microcontact printing, which has produced patterned self-assembled monolayers with submicrometer features (2, 3). At the same time, light-directed synthesis has been used to generate spatially addressable combinatorial libraries of DNA and protein sequences on solid substrates (4). Here, we describe patterning of surfaces with properties resembling those of living cells: fluid bilayer membranes on solid supports. This work has been stimulated by the desire to create integrated devices capable of manipulating molecules in a bilayer membrane and to pattern spatially addressable libraries of chemically distinct, fluid membrane patches.
Supported membranes are self--ssembling, two-dimensional (2D) fluid systems (Fig. 1). The bilayer membrane consists of two opposed leaflets of phospholipid molecules and is the basic structure central to all living cell membranes. Bilayers on solid supports were originally developed for studies of interactions between living cells, where they have proven highly useful (5, 6). Supported membranes can be formed by spontaneous fusion of lipid bilayer vesicles with an appropriate hydrophilic surface such as oxidized Si (7, 8). Interactions between membranes and surfaces involve electrostatic and hydration forces as well as attractive contributions from long-range van der Waals forces. An energetic minimum tightly traps the membrane near the surface. Supported bilayers are typically separated from the solid substrate by a thin (-10 A) film of water (9-11) and retain many of the properties of free...