Ellipsometric determination of the structure of surface-stabilized bilayer lipid membranes on silver metal

There has been substantial interest in the use of bilayer lipid membranes as the basis for development of biosensors, but limitations in the physical stability of such membranes have prevented practical applications. The reliability and reproducibility of surface-stabilized bilayer lipid membranes (sBLMs), that have been reported to spontaneously form on metallic electrodes, may offer an attractive approach to development of a practical method of device fabrication. An important question which has been raised about sBLMs is whether the membranes are actually of a thickness of a bilayer lipid membrane. The physical structure of sBLMs have been studied indirectly by electrochemical methods, and the results show some differences from those obtained from freely suspended planar BLMs. In this present work, we report direct ellipsometric studies of the thickness of lipid films that spontaneously thin on silver metal. Silver metal was vacuum deposited on polyvinylidenedifluoride (PVDF) polymer. Such surfaces are analogous to metal wire which is encapsulated by Teflon, as is typically used in experiments for sBLM formation. Ellipsometry of surfaces was done using a closed solution cell that allowed for hydration of lipid films. Silver surfaces that were coated with dry phospholipid, and with phospholipid in hexane : ethanol solvent, both showed that spontaneous thinning of lipid films to monolayer, bilayer and trilayer thicknesses occurred in a few minutes. There was no dependence of membrane thickness or thinning rates on the diameter of the silver metal support over the range of 3.5 to 7.5 mm used in these studies. Immobilization of silver metal onto a chromium layer that was first applied to the PVDF was important in establishing increased speed of thinning and the physical stability of the system.