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

A novel nanostructure noble metal-TiO 2 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 TiO 2 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 TiO 2 NTs by one-step electrodeposition to form AuNCs-TiO 2 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 TiO 2 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-TiO 2 NTs composite electrode, either immobilized on the electrode or dissolved in solutions. The immobilized Cyt c exhibited favorable electrocatalytic activity toward the reduction of H 2 O 2 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-TiO 2 NTs composite electrode a promising platform for fabricating third-generation biosensors.