Fabrication of Electroactive Layer-by-Layer Films of Myoglobin with Gold Nanoparticles of Different Sizes

Abstract

Alternate adsorption of oppositely charged myoglobin (Mb) and gold nanoparticles with different sizes were used to assemble {Au/Mb}_n layer-by-layer films on solid surfaces by electrostatic interaction between them. The direct electrochemistry of Mb was realized in {Au/Mb}_n films at pyrolytic graphite (PG) electrodes, showing a pair of well-defined, nearly reversible cyclic voltammetry (CV) peaks for the Mb heme Fe^III/Fe^II redox couple. Quartz crystal microbalance (QCM), electrochemical impedance spectroscopy (EIS), and CV were used to monitor or confirm the growth of the films. Compared with other Mb layer-by-layer films with nonconductive nanoparticles or polyions, {Au/Mb}_n films showed much improved properties, such as smaller electron-transfer resistance (R_ct) measured by EIS with Fe(CN)^3-/4- redox probe, higher maximum surface concentration of electroactive Mb (Γ*_max), and better electrocatalytic activity toward reduction of O₂ and H₂O₂, mainly because of the good conductivity of Au nanoparticles. Because of the high biocompatibility of Au nanoparticles, adsorbed Mb in the films retained its near native structure and biocatalytic activity. The size effect of Au nanoparticles on the electrochemical and electrocatalytic activity of Mb in {Au/Mb}_n films was investigated, demonstrating that the {Au/Mb}_n films assembled with smaller-sized Au nanoparticles have smaller R_ct, higher Γ*_max, and better biocatalytic reactivity than those with larger size.