Supported phospholipid bilayers

Abstract

Phospholipid bilayers have been formed on glass, quartz, and silicon surfaces by a sequential transfer of two monolayers at a pressure of approximately 40 dyn/cm from the air-water interface to the solid substrates. Lateral diffusion measurements of L-alpha-dipalmitoylphosphatidylcholine (DPPC) bilayers supported on oxidized silicon wafers reveal two sharp phase transitions at temperatures similar to those found in multilayer systems with several different techniques. The diffusion measurements obtained using fluorescence recovery after pattern photobleaching provide evidence for the existence of an intermediate (probably P beta' or ripple) phase in single bilayers. While in the intermediate and high temperature (liquid-crystalline L alpha) phase, the diffusion coefficients do not vary very much with temperature, a strong temperature dependence is observed in the low temperature (gel L beta') phase. This is attributed to defect-mediated diffusion. Lipids in silicon supported bilayers made from L-alpha-dioleoylphosphatidylcholine (DOPC) or L-alpha-dimyristoylphosphatidylcholine (DMPC) diffuse rapidly above their respective chain-melting transition temperatures. Arrhenius plots show straight lines with activation energies of 40.9 and 43.7 kJ/mol, respectively. Supported DPPC bilayers on oxidized silicon form long tubular liposomes when heated through their oxidized silicon form long tubular liposomes when heated through their chain-melting-phase transition, as viewed with epifluorescence microscopy. It is suggested that this is a consequence of the expansion of the lipid on the fixed solid support. Conversely, DOPC bilayers form large void areas on this substrate upon cooling. Large circular membrane defects (holes) are observed under rapid coating conditions. The formation of these defects is modulated by including small amounts of lyso-L-palmitoyl phosphatidylcholine in the DMPC-supported bilayers. A simple model describes the dependence of hole size and hole number on the concentration of lysolecithin.

Polymer-Supported Lipid Bilayers on Benzophenone-Modified Substrates

“…8 Lipid bilayers that are directly supported on glass or quartz are separated from the solid surface by a thin (10-20 Å) lubricating layer of water. 9 This water layer seems to be sufficient to support the lateral mobility of lipids in both layers. However, if one deposits a lipid bilayer containing transmembrane proteins directly onto the solid substrate, the substrate can interact with the proteins due to insufficient separation between the lipids and solids.…”

Micropattern Formation in Supported Lipid Membranes

“…6 Supported membranes can be assembled by spontaneous adsorption and fusion of unilamellar phospholipid vesicles with an appropriate substrate. 15,26 Alternative methods such as Langmuir-Blodgett dipping 16 or membrane spreading 27 can also produce high-quality supported membranes. Interactions between membranes and surfaces involve electrostatic and hydration forces as well as attractive contributions from long-range van der Waals forces.…”

Nanoscale Patterning in Mixed Fluorocarbon−Hydrocarbon Phospholipid Bilayers

“…2a Supported bilayers are conveniently fabricated and, because the lipid molecules are free to laterally diffuse within each leaflet, their structure reflects the self-assembly of their component molecules. 16 We detail here the phase behavior and nanoscale self-assembly of bilayers composed of compound 1 combined with its all-hydrocarbon congener, dipalmitoylphosphatidylcholine (DPPC). Despite their similar structures and close phase transition temperatures, these lipids exhibit an unusual phase separation behavior unprecedented in hydrocarbon lipids.…”