Ultrasensitive and rapid detection of organophosphates using a dual-signal naked-eye hydrogel sensor based on acetylcholinesterase inhibition.

Accurate determination of pesticide residues is crucial for food safety. A self-calibration method was developed for dual-signal "naked-eye" detection of organophosphorus pesticides (OPs) using bifunctional gold nanozymes (AuNEs). OPs inhibit the cascade reaction of acetylcholinesterase/choline oxidase (AChE/CHO) to reduce hydrogen peroxide (HO) production, which affects the AuNE-catalyzed color reaction and quenches the fluorescence of AuNEs with the assistance of Fe. The multi-enzyme cascade system can be integrated into hydrogel sheets for smartphone-assisted digital, quantitative, and onsite detection of OPs in real food samples by analyzing the linear changes in colorimetric and fluorometric signals, which closely match liquid chromatography-mass spectrometry (LC-MS) results. This method displays a lowest 'naked-eye' detection concentration of 7 ppb, a wide linear range (0-2000 ng/mL), and particularly the advantage of anti-interference via self-calibration when one of the signals is abnormal.