Self-assembly of thiolipid molecular layers on gold surfaces: optical and electrochemical characterization

Abstract

This paper describes the preparation and characterization of mono- and bilayers of three newly synthesized disulfide-bearing lipids and of mixed bilayers containing conventional phospholipids adsorbed onto gold substrates by the self-assembly technique. The polar group of the lipid is coupled to a spacer of variable length (1–3 ethoxy units) terminating at a disulfide group. The properties of these films were investigated by plasmon surface polariton (PSP) and electrochemical capacitance measurements. The capacitance data for all the pure disulfide lipid films suggest a low defect density, comparable to that found for thioalkane self-assembly films. While this is supported by the optical experiments for the films formed by the lipid with the longest spacer, for the films self-assembled from the other two lipids a relatively low refractive index must be assumed, indicating the influence of the spacer on the packing of the molecules. On the contrary, films of conventional phospholipids self-assembled onto thiolipid monolayers show a high optical density and a comparable pure electrical behaviour.