Supersensitive Photoelectrochemical Aptasensor Based on Br,N-Codoped TiO₂ Sensitized by Quantum Dots

Here, we fabricated a novel photoelectrochemical (PEC) aptasensor based on Br,N-codoped TiO₂/CdS quantum dots (QDs) sensitization structure with excellent energy level arrangement for supersensitive detection of carcinoembryonic antigen (CEA). The prepared Br,N-codoped TiO₂ could reduce the energy bandwidth of TiO₂ from 3.2 to 2.88 eV, which could dramatically reduce the basic signal and obviously broaden the absorption of light (400-700 nm). In addition, the energy bandwidth of Br,N-codoped TiO₂ (2.88 eV) matched well with that of CdS QDs (2.4 eV), making CdS QDs an ideal signal enhancer for amplifying the photocurrent signal of Br,N-codoped TiO₂. More importantly, the constructed Br,N-codoped TiO₂/CdS QDs sensitization structure with narrow energy level gradient enabled the effective promotion of electron-transfer capability and dramatic improvement of photoelectric conversion efficiency. Simultaneously, a small amount of the CEA was transformed into substantial single-chain DNA (T-DNA) via exonuclease III (Exo-III)-assisted cycle strategy. Under optimum conditions, the designed PEC aptasensor demonstrated a wide detection range from 1 fg/mL to 1 ng/mL and a low detection limit as 0.46 fg/mL for CEA assay. This strategy prepared a new photoactive material to markedly improve photoelectric conversion efficiency and initiated a new way to realize the highly sensitive PEC biomolecules detection.