High electric resistance polymer/lipid composite films on indium-tin-oxide electrodes

We report the design of polymer/lipid composite films on polarizable indium-tin-oxide (ITO) electrodes and the characterization of their electrical properties by impedance spectroscopy. The polymer films separating the solid surfaces and the lipid membranes were composed of `hairy-rod' macromolecules and provided a fluid and homogeneous ultrathin `cushion' for the deposition of lipid membranes. Two types of polymer cushions were designed: First, electrically insulating multilayers of cellulose derivatives with substituted alkyl chains forming a fluid hydrophobic `brush' at the surface. Second, conducting cellulose multilayers exposing hydrophilic surfaces for the deposition of self-healing lipid bilayers. The electrical properties, the defect densities, and the homogeneities of the stratified films were studied by impedance spectroscopy in the frequency range between 90 mHz and 50 kHz. Impedance spectra were analyzed in terms of equivalent circuits with resistances, capacitances, and so-called `constant phase elements'. Resistances of up to 440 kΩ cm² were achieved for the polymer-supported lipid bilayers, which corresponds to about 10% of the value for black lipid membranes containing hexane. The gramicidin channels reconstituted into the supported lipid bilayers exhibited the expected cation selectivity.