TiO2 nanotube arrays fabricated by anodization in different electrolytes for biosensing

Titania nanotube arrays were fabricated by anodic oxidation of titanium foil in different electrolytes. The morphology, crystallinity and composition of the as-prepared nanotube arrays were studied by XRD, SEM and EDX. Electrochemical impedance spectroscopy (EIS) was employed to investigate their electrical conductivity and capacitance. Titania nanotube arrays co-adsorbed with horseradish peroxidase (HRP) and thionine chloride (Th) were studied for their sensitivity to hydrogen peroxide by means of cyclic voltammetric and galvanostatic measurements. The experiments showed that TiO₂ nanotube arrays possessed appreciably different sensitivities to H₂O₂ due to their different conductivity. Further experiments revealed that TiO₂ nanotubes have noticeably different ability of adsorbing HRP and Th, and the best sensitivity was achieved when the density of HRP is the highest. The TiO₂ nanotube arrays fabricated in potassium fluoride solution demonstrated the best sensitivity on hydrogen peroxide in the range of 10⁻⁵–3 × 10⁻³ M at pH 6.7 and at a potential of −600 mV (vs. Ag/AgCl).