Vapor-surface sol-gel deposition of titania alternated with protein adsorption for assembly of electroactive, enzyme-active films

Combining vapor-surface sol-gel deposition of titania with alternate adsorption of oppositely charged iron heme proteins provided ultrathin (TiO2/protein)(n) films with reversible voltammetry extended to 15 TiO2/protein bilayers, more than twice that of more conventional polyion-protein or nanoparticle-protein films made by alternate layer-by-layer adsorption. Catalytic activity toward O-2, H2O2, and NO2- was also improved significantly compared to the conventionally fabricated films. The method involves vaporization of titanium butoxide into thin films of water., forming porous TiO2 sol-gel layers. Myoglobin (Mb), hemoglobin (Hb), and horseradish peroxidase (HRP) were assembled by adsorption alternated with the vapor-deposited TiO2 layers. Improved electrochemical and catalytic performance may be related to better film permeability leading to better mass transport within the films, as suggested by studies with soluble voltammetric probes, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical and electrocatalytic activity of the films can be controlled by tailoring the amount of water with which the metal alkoxide precursor vapor reacts and the number of bilayers deposited in the assembly.