Dopamine sensitized nanoporous TiO2 film on electrodes: Photoelectrochemical sensing of NADH under visible irradiation

Dopamine-coordinated photoactive TiO2 nanoporous films with a wide excitation range of light in the visible region (up to 580 nm) were prepared and used for sensitive detection of NADH. Colloidal TiO2 was firstly covered on an indium–tin oxide (ITO) electrode surface and sintered at 450 °C to form a nanoporous TiO2 film, then the electrode was dipped in a dopamine solution to form a dopamine–TiO2 charge transfer complex via coordinating dopamine with undercoordinated titanium atoms on the electrode surface. This charge transfer complex provided an anodic photocurrent under visible light and the photocurrent could be largely enhanced by NADH. The photocurrent enhancement might be due to the electron transfer between NADH and the holes localized on dopamine. A new photoelectrochemical methodology for sensitive detection of NADH at a relatively low potential was developed. The detection limit of NADH was 1.4 × 10−7 M, and the detection range could extend up to 1.2 × 10−4 M. The dopamine–TiO2 modified electrode exhibits its major advantages such as effective electronic transducer, fast response and easy fabrication for photoelectrochemical determination of NADH. This strategy largely reduces the destructive effect of UV light and the photogenerated holes of illuminated TiO2 to biomolecules and opens a new avenue for the applications of TiO2 in photoelectrochemical biosensing.