N-doped TiO₂ based visible light activated label-free photoelectrochemical biosensor for detection of Hg²⁺ through quenching of photogenerated electrons

A novel photoelectrochemical (PEC) biosensor was fabricated based on N-doped TiO₂ for the detection of Hg²⁺ through the quenching of photogenerated electrons. The N-doped TiO₂ was synthesized by a sol-gel method with urea and tetrabutyl titanate as the N and Ti sources. Compared with the undoped TiO₂, the N-doped TiO₂ showed an enhanced photocurrent response under visible light (λ > 420 nm). The sensing surface was functionalized with 5′-amino-modified T-rich oligonucleotides. The photoelectrochemical biosensor bound Hg²⁺ on the surface by a highly specific T-Hg²⁺-T recognition. Hg²⁺ on the surface of the N-doped TiO₂ film withdrew the photogenerated electrons and decreased the recorded current signal. The dynamic linear range for Hg²⁺ has been determined to be as low as 2-6 μM.