Electrochemical SERS study of a biomimetic membrane supported at a nanocavity patterned Ag electrode

Lipid bilayers in which two leaflets were made of dimyristoyl-phosphatidylcholine (DMPC) and hybrid bilayers with one leaflet composed of hydrogenated lipid and another leaflet of deuterium substituted molecules (d63-DMPC) were deposited on highly ordered nanocavity patterned Ag electrodes using LB-LS and vesicle fusion techniques. In situ electrochemical surface enhanced Raman scattering (EC-SERS) was then used to study potential driven changes in these model biological membranes. The nanocavity structures provided a SERS active substrate with uniformly distributed surface enhancement. To ensure that the bilayer was separated from the metal surface by a hydrophilic space layer, the electrodes were chemically modified with a self-assembled monolayer (SAM) of β-thioglucose (TG) molecules. The monolayer of TG ensured that the solid substrate surface was hydrophilic. The electrochemical properties of the bilayer were monitored by recording differential capacitance curves. EC-SERS indicated that at the silver surface modified by the monolayer of TG the lower leaflet (in contact with the support) is more ordered than the top leaflet that is contact with solution. However, both leaflets remained in the liquid crystalline (LC) state for the entire range of investigated potentials. The results of this study show that the DMPC bilayer at the nanocavity patterned Ag surface may be used as a good biomimetic membrane model in future SERS studies of membrane proteins. The information concerning the effect of the electrode potential on membrane stability may be useful for the development of biosensors.