Design and characterization of novel tether layer for coupling of a bilayer lipid membrane to the surface of gold.

An innovative type of monolayer system was synthesized as a support for a bilayer lipid membrane on a gold electrode surface. The coupling of the phospholipid bilayer to the support layer is accomplished using zirconium-phosphate-carboxylate (ZPC) chemistry that provides coordinative linkage between the self-assembled, functionalized alkanethiol support monolayer and phosphatidylserine (PS). Binding the PS to the interface in this manner prevents the lipids from coming into direct contact with the metal electrode and leaves sufficient space for an aqueous supporting electrolyte to reside between the lipid and tether layers. The presence of an aqueous environment was confirmed by neutron reflectivity measurements of this interfacial system. We expect that the bilayer lipid membrane coupled to the solid support by a ZPC linkage will be almost as flexible as a natural membrane because of the labile nature of the interactions between PS and the alkanethiol layer. We anticipate that this interfacial system will provide nearly physiological conditions for membrane proteins, allowing them to retain their activity following reconstitution into the bilayer structure. In this work, the organization of the tethering monolayer was assessed using cyclic voltammetry, and corrections for dielectric permittivity values for the alkanethiol layer were calculated based on the neutron reflectometry results. Neutron reflectometry was also used to assess the organization of the tether layer and the degree of its hydration. Finally, this layer was used for the formation of a PS lipid bilayer structure by vesicle fusion and spreading, where the liposome deposition was monitored by atomic force microscopy (AFM).