Comparative bioelectrochemical study of two types of myoglobin layer-by-layer films with alumina: Vapor-surface sol–gel deposited Al2O3 films versus Al2O3 nanoparticle films

Two types of layer-by-layer films of myoglobin (Mb) and Al2O3 were assembled on different surfaces and compared in Mb electrochemistry and bioelectrocatalysis. One type, designated as {SG-Al2O3/Mb}n, was assembled by alternate deposition of Al2O3 by vapor-surface sol–gel method from liquid aluminum butoxide and Mb by adsorption from its solution. Another type, designated as {NP-Al2O3/Mb}n, was constructed by alternate adsorption of Al2O3 nanoparticles and Mb from their dispersion or solution in the conventional layer-by-layer way. Quartz crystal microbalance (QCM), UV–vis spectroscopy, and cyclic voltammetry (CV) were used to monitor the growth of the two types of {Al2O3/Mb}n films. UV–vis and IR spectroscopy demonstrated that Mb in both types of {Al2O3/Mb}n films retained its near native structure. While both Mb films assembled on pyrolytic graphite (PG) electrodes exhibited a pair of well-defined, nearly reversible CV reduction–oxidation peaks for Mb heme Fe(III)/Fe(II) redox couple and good electrocatalytic reactivity toward reduction of oxygen and hydrogen peroxide, the {SG-Al2O3/Mb}n films demonstrated distinct advantages over the {NP-Al2O3/Mb}n films in larger maximum surface concentration of electroactive Mb and better biocatalytic performances. This may be mainly attributed to the higher porosity of {SG-Al2O3/Mb}n films than that of {NP-Al2O3/Mb}n films, which may be beneficial to counterion transport in the charge-hopping mechanism and the diffusion of catalytic substrates through the films.