Enhancement of Au Nanoparticles Formed by in Situ Electrodeposition on Direct Electrochemistry of Myoglobin Loaded into Layer-by-Layer Films of Chitosan and Silica Nanoparticles

In the present work, a new kind of myoglobin (Mb)/Au nanoparticles composite film was fabricated on pyrolytic graphite (PG) electrodes. Oppositely charged chitosan (CS) and silica (SiO2) nanoparticles were alternately adsorbed on the PG surface by the electrostatic interaction between them, forming {CS/SiO2)(5) layer-by-layer films. Mb and HAuCl4 in solution were then simultaneously loaded into {CS/SiO2)(5) films. The loaded Au(III) in the films were electrochemically reduced into Au nanoparticles, forming nanocomposite films, designated as {CS/SiO2}(5)-Mb-Au. Various techniques such as cyclic voltammetry (CV), square wave voltammetry (SWV), quartz crystal microbalance (QCM), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis were used to characterize the films. Compared with {CS/SiO2}(5)-Mb films without Au nanoparticles inside, the {CS/SiO2}(5)-Mb-Au films exhibited much better behavior in electrochemistry and electrocatalysis of Mb, mainly because the Au nanoparticles formed inside the films were located in proximity to Mb and acted as electron bridges between Mb molecules, making more Mb molecules in the films become electroactive. In addition, the permeability or porosity of the films also played an important role in realizing the direct electrochemistry of Mb. This system provides a novel platform to develop electrochemical biosensors based on the direct electron transfer of redox enzyme,; without using mediators.