One-pot hydrothermal route to fabricate nitrogen doped graphene/Ag-TiO2: Efficient charge separation, and high-performance “on-off-on” switch system based photoelectrochemical biosensing

• NGR/Ag-TiO2 nanocomposites were prepared by a facile one-pot hydrothermal route.
• The photocurrent of NGR/Ag-TiO2 exhibited 18.2 times higher than that of pure TiO2.
• A novel kind of “on-off-on” PEC aptasensor was established.
• The proposed sensor showed a wide linear range, a low detection limit, and etc.

Charge separation is crucial for increasing the performances of semiconductor-based materials in many photoactive applications. In this paper, we designed novel nanocomposites consisting of TiO2 nanocrystals, Ag nanoparticles (NPs) and nitrogen doped graphene (NGR) via a facile one-pot hydrothermal route. The as-prepared ternary nanocomposites exhibited enhanced photoelectrochemical (PEC) performances owing to the introduction of Ag NPs and NGR, which increase the excitons’ lifetime and improve the charge transfer. In particular, it is shown by means of the transient-state surface photocurrent responses that the photocurrent intensity of the as-fabricated composites exhibited 18.2 times higher than that of pristine TiO2. Based on the robust photocurrent signal, a new kind of “on-off-on” PEC aptasensor was established with the assistance of Pb2+ aptamer, which integrates the advantages of low background signal and high sensitivity. Under optimal conditions, a wide linear response for Pb2+ detection was obtained from 1 pM to 5 nM as well as a detection limit down to 0.3 pM. With its simplicity, selectivity, and sensitivity, this proposed strategy shows great promise for Pb2+ detection in food and environment analysis.