Growth and Favorable Bioelectrocatalysis of Multishaped Nanocrystal Au in Vertically Aligned TiO2 Nanotubes for Hemoprotein

Abstract

A novel nanostructure noble metal-TiO2 nanotube composite electrode was constructed for effective immobilization of cytochrome c (Cyt c) and successful realization of its direct electrochemistry and electrocatalysis. Highly ordered and vertically aligned TiO2 nanotubes (NTs) successfully in situ grew on titanium substrate by anodic oxidation of Ti, possessing large surface areas and a high aspect ratio of nanotubular structure. They can be used as excellent templates. Au nanocrystal (Au NCs) were subsequently introduced into the TiO2 NTs by one-step electrodeposition to form AuNCs-TiO2 NTs hybrids, aiming at enhancing the electrochemical performance and biocompatibility of the electrode. The formation mechanism of the Au NCs was elucidated from field-emission scanning electron microscopy (SEM) and X-ray diffraction (XRD) character. Au NCs could grow to different shaped nanostructures such as polyhedral nanorods with high-index facets, honey-cave-like nanocages, etc., due to the tubular confinement of the TiO2 NTs. Experimental results also indicated that this novel nanocomposite electrode provided a good environment for protein immobilization and biosensor preparation. The multishapes of Au NCs resulted in better promotion for direct electrochemistry and fast electron transfer of Cyt c on the Au NCs-TiO2 NTs composite electrode, either immobilized on the electrode or dissolved in solutions. The immobilized Cyt c exhibited favorable electrocatalytic activity toward the reduction of H2O2 with good stability and sensitivity. The linear range was 2 × 10−6 to 3.49 × 10−4 mol·L−1, with a detection limit of 1.21 × 10−6 mol·L−1. Moreover, it could be adapted to different pH circumstances, ranging from 3 to 8, with good response and resolution. This makes the AuNCs-TiO2 NTs composite electrode a promising platform for fabricating third-generation biosensors.