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.