The photoelectrochemical detection method is a newly developed and promising analytical method for biosensing. In this work, photoactive TiO(2) nanotubes (TNs) immobilized with horseradish peroxidase (HRP) were prepared and used for visible-light-activated photoelectrochemical detection of H(2)O(2). TNs were fabricated by anodic oxidation of titanium substrate and possessed large surface areas, good uniformity and conformability, and high porosity, which were favorable for enzyme immobilization. Electrochemical and UV-vis spectroscopic measurements demonstrated that TNs provided excellent matrixes for the adsorption of HRP and the adsorbed HRP effectively retained its bioactivities. The photocurrent spectra of HRP/TNs showed an obvious photocurrent response under visible-light irradiation (lambda > or = 400 nm), suggesting the possibility of photoelectrochemical detection of H(2)O(2) upon visible-light irradiation. It was found that the generated photocurrent of HRP/TNs at 400 nm was significantly enhanced after the addition of H(2)O(2) in solution and the photocurrent intensity increased with the increase of the H(2)O(2) concentration. The HRP/TNs electrode displayed a linear range of 5.0 x 10(-7)-3.5 x 10(-5) M and a low detection limit of 1.8 x 10(-7) M for H(2)O(2) determination. Thus, the protein-immobilized TNs would be expected to be a novel photoactive material for photoelectrochemical biosensing. This proposed strategy may open a new avenue for the applications of nanotubular TiO(2) in visible-light-activated photoelectrochemical biosensing, which could largely reduce the destructive effect of UV light and the photoholes generated by illuminated TiO(2) to biomolecules.