Nanostructured Electrode with Titania Nanotube Arrays: Fabrication, Electrochemical Properties, and Applications for Biosensing

Titania nanotube (TNT) arrays were fabricated by anodic oxidation of titanium foil in various electrolytes and were calcined in dry nitrogen at various temperatures. The morphology, crystallinity, and chemical composition of TNT arrays were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) was employed to investigate the electrical conductivity and capacitance of TNT arrays prior to and after calcination. The results showed that the electrical conductivities of TNT arrays calcined in nitrogen for 3 hours were improved significantly as compared to the as-grown TNT arrays or annealed in air or argon. Well defined oxidation and reduction peaks were observed during the cyclic voltammetric scans at 0.1 V/s in 10 mM K₃[Fe(CN)₆] solution. For the application in biosensing, TNT electrodes co–adsorbed with horseradish peroxidase (HRP) and thionine chloride (Th) were studied for their sensitivity to hydrogen peroxide by means of cyclic voltammetric. The experiments showed that TNT arrays possessed appreciably different sensitivities to H₂O₂ due to their different conductivity. The best result was found in the TNT arrays annealed in nitrogen. Further analyses revealed that the sensitivity of TNT arrays annealed in nitrogen was increased 4–6 times compared with as-grown TNT arrays, the dynamic range on H₂O₂ is in the range of 2 × 10⁻⁵ M to 3.6 × 10⁻³ M at pH = 6.7 and at a potential of −600 mV (vs. Ag/AgCl).