Study of the potential driven changes in a collagen film self-assembled on a polycrystalline gold electrode surface

Abstract

The influence of the potential applied to the polycrystalline gold electrode on the adsorption state and structure of collagen molecules were studied by means of electrochemistry, in situ ellipsometry and in situ polarization modulation infrared reflection–absorption spectroscopy. At the macroscopic level, potential and the corresponding charge accumulated on the gold electrode determine the adsorption process of the collagen film on the Au electrode surface. The protein film is stable on the electrode surface at potentials close to the potential of zero charge. The protein film sustains a large negative potential drop (ΔϕM|S⩾−0.5V) whereas it is unstable at a small positive potential drop (ΔϕM|S≈0.1V) across the film. Positive net charge accumulated on the Au surface causes electrostatic repulsions of collagen molecules bearing a positive net charge. Loosening of water and destabilization of the protein film reflect repulsions between the Au electrode and the collagen molecules. In contrast, at charge densities between −8<σM<−20μCcm−2 electrostatic attractions between the electrode surface and the protein molecule appear. A stable, well hydrated collagen film is formed on the Au surface. Higher negative charges accumulated on the electrode surface lead to swelling on the protein film by water and lead to the desorption of the protein film from the Au surface. In situ spectroelectrochemical studies show that at the molecular level neither the secondary structure nor the orientation of collagen molecules are affected by electrical potentials. Independently of the applied potential and electric fields acting on the film the collagen molecule maintains its native structure. Collagen molecules adsorbed on the Au surface form a heterogeneous film with well-defined structure and unusual stability at the molecular level.