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 membra nes as the basis for development of biosensors, but limitations in thr physical stability of such membranes have prevented practical applica tions. The reliability and reproducibility of surface-stabilized bilay er lipid membranes (sBLMs), that have been reported to spontaneously f orm on metallic electrodes, may offer an attractive approach to develo pment of a practical method of device fabrication. An important questi on which has been raised about sBLMs is whether the membranes are actu ally of a thickness of st bilayer lipid membrane. The physical structu re of sBLMs have been studied indirectly by electrochemical methods, a nd the results show some differences from those obtained from freely s uspended planar BLMs. Tn this present work, we report direct ellipsome tric studies of the thickness of lipid films that spontaneously thin o n silver metal. Silver metal was vacuum deposited on polyvinylidenedif luoride (PVDF) polymer. Such surfaces are analogous to metal wire whic h is encapsulated by Teflon, as is typically used in experiments for s BLM formation. Ellipsometry of surfaces was done using a closed soluti on cell that allowed for hydration of lipid films. Silver surfaces tha t 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 minu tes. There was no dependence of membrane thickness or thinning rates o n 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 chro mium layer that was first applied to the PVDF was important in establi shing increased speed of thinning and the physical stability of the sy stem. (C) 1997 Elsevier Science B.V.