Enhanced Photoelectrochemical Aptasensing for Sensitive Detection of Diazinon Pesticide Used N-Hydroxyphthalimide as an Effective Hole Mediator

Signal amplification strategies are of great interest in photoelectrochemical (PEC) sensing research. Herein, we explored a novel approach whereby hole transfer was accelerated from the photosensitive material Blue-TiO2 (B-TiO2) to the hole mediator N-hydroxyphthalimide (NHPI). Simultaneously, the introduction of the organic molecule NHPI can promote the efficiency of visible light absorption and expand the absorption range of B-TiO2. Under visible light irradiation, the photocurrent value of NHPI/B-TiO2 is 2.7-fold larger than that of B-TiO2, which can be ascribed to the acceleration of hole transfer by NHPI. More specifically, NHPI acts as a hole mediator, which effectively transfers photo-generated holes from the valence band (VB) of B-TiO2 to NHPI. NHPI can be oxidized to phthalimide-N-oxyl radical (PINO*), thereby causing inhibition of photo-generated carrier recombination and enhancement of the photocurrent. Furthermore, a PEC aptasensor for the sensitive detection of diazinon (DIA) was constructed by combining specific aptamers on an NHPI/B-TiO2 nanocomposite surface. The oxidation product of NHPI, PINO*, oxidizes the DIA captured by the aptamer. Under optimized experimental conditions, the linear range for DIA detection was 0.1–1000 nM, and the detection limit of the NHPI/B-TiO2 nanocomposite aptamer sensing was 0.03 nM (S/N = 3). Therefore, this proposed method involving the hole mediator can be used as a new strategy to improve the performance of PEC.