Portable paper-based multicolor sensor for sensitive on-site detection of organophosphorus pesticides using a high-efficiency Au+-induced gold nanobipyramids aspect ratio regulation strategy

[Display omitted] •Au+-induced reaction efficiently regulates the aspect ratio of gold nanobipyramids.•The reaction within the paper-based device is uniform, efficient, and reproducible.•Gold nanobipyramids deposited on membranes are long-term stable.•The paper-based multicolor sensor is portable, sensitive, reliable, and practical.•The sensor enables sensitive visual detection of dichlorvos via eight color changes. On-site visual detection of organophosphorus pesticides (OPs) is crucial for safeguarding environmental and food safety. This study presents a robust, sensitive, and portable paper-based multicolor sensor (PMS) for the on-site detection of OPs. The PMS involves a novel Au+-induced gold nanobipyramids (AuNBPs) morphology transformation reaction within a paper-based analytical device (PAD) coupled with a bienzymatic hydrolysis system. The Au+-induced reaction sensitively regulates the aspect ratio of AuNBPs through Au+ disproportionation, which decreases the length of AuNBPs and simultaneously increases the width, accompanied by distinct multicolor changes. Upon performing in the PAD incorporating easily-prepared AuNBPs-deposited nylon membranes, a metal heater, and an oscillator, the Au+-induced reaction exhibits excellent reaction sensitivity, efficiency, reproducibility, AuNBPs stability, and color uniformity. In the bienzymatic hydrolysis system, acetylcholinesterase (AChE) and choline oxidase hydrolyze acetylcholine to product H2O2, which consumes tris(2-carboxyethyl)phosphine hydrochloride (TCEP), maintaining free Au+ for the disproportionation in the Au+-induced system, while the presence of OPs inhibits AChE activity, preserving TCEP to chelate Au+ and hindering the disproportionation. Under optimized conditions, the PMS exhibited eight dichlorvos concentration-corresponding color changes with a visual detection limit of 30 μg/L and a spectrometry detection limit of 8.1 μg/L. It achieved recoveries of 85.4–101.9 % in river water, drinking water, rice, and Chinese cabbage samples with relative standard deviations (n = 5)