Synergistic ultrasensitive detection of paraoxon via a photoelectrochemical-fluorescent dual-mode aptasensor with S-scheme Zn0.1Cd0.9S/Cu2MoS4 heterostructure and Zr-MOF nanozyme

Abstract

Detecting pesticides is of crucial importance for food safety and environmental monitoring. Photoelectrochemical sensors are a promising route towards monitoring pesticides. In this article, a novel photoelectrochemical and fluorescence (PEC/FL) dual-mode aptasensor was constructed for ultrasensitive detection of paraoxon, a commonly existing organophosphorus pesticide. The core structure of the sensor is a Zn_0.1Cd_0.9S/Cu₂MoS₄ S-scheme heterojunction which was constructed as a photoactive material. The S-scheme transfer pathway enhanced the separation efficiency of photogenerated charge carriers, thereby generating a stable photocurrent. The PEC signal amplification and FL response generation were achieved by utilizing zirconium-based metal organic framework (Zr-MOF) nanozyme with aggregation induced emission (AIE) characteristics. Zr-MOF simultaneously attenuated the PEC response through steric hindrance and competing for substrate material light absorption, while exhibiting AIE fluorescence. Upon paraoxon recognition, the aptamer detachment reduced steric hindrance, leading to PEC signal recovery. Concurrently, Zr-MOF catalyzed paraoxon hydrolysis, generating a FL quencher p-nitrophenol (p-NP). The dual-response system achieved ultrasensitive detection of paraoxon with exceptional analytical performance. Under optimal conditions, the fabricated dual-mode aptasensor demonstrated sensitive detection across linear ranges of 0.1 ng/mL - 400 ng/mL (PEC mode) and 5 ng/mL - 50 μg/mL (FL mode), achieving remarkably low detection limits of 3.32 pg/mL and 1.67 ng/mL, respectively. This work provides a novel strategy for designing multi-signal PEC/FL sensors in monitoring organophosphorus pesticides.