Regulating Gold Nanobipyramid\nMorphology via Au<sup>+</sup>‑Disproportionation System on\nPaper Toward a Paper-Based\nMulticolor Sensor for Sensitive Visual Detection of Acetylcholinesterase\nActivity

On-site\nquick detection of acetylcholinesterase (AChE) activity\nis of great significance for diagnosing nervous diseases, screening\ndrugs, and monitoring poisoning. Herein, we developed a system for\nsensitively regulating gold nanobipyramid (AuNBP) morphology on a\npaper-based analytical device (PAD) via an Au<sup>+</sup>-disproportionation\nsystem, and further developed a high-resolution paper-based multicolor\nsensor (PMS) for both on-site visual detection and laboratory precision\nquantification of AChE activity using the system as a signal reporter\nand a dual-enzyme strategy as a receptor. The paper-based Au<sup>+</sup> disproportionation-mediated AuNBP morphology system not only has\nexcellent stability, reproducibility, and robust resistibility against\nreducing substances existing in biological samples but also can effectively\nsuppress the color interference from reagents and greatly improve\nthe sensitivity of regulating AuNBP morphology transformation, making\nit capable of generating long-term stable and more colorful/clearer\ncolor changes corresponding to Au<sup>+</sup> concentrations. The\ndeveloped PMS exhibited eight color changes corresponding to AChE\nactivity within 0.0–1.0 U/L and the color changes could be\nstably maintained for 30 days, which makes both on-site visual detection\nand laboratory sensitive quantification possible. The PMS was successfully\nused to detect AChE activity in serum and erythrocyte samples with\na visual detection limit (LOD) of 50 mU/L, a spectrometry LOD of 26\nmU/L, and a recovery of 81–102%. The results obtained with\nthe PMS were consistent with those obtained with Ellman’s method,\nverifying its reliability. All of the above features make the PMS\na promising assay for the rapid detection of AChE activity in clinical\ndiagnosis. Importantly, the proposed paper-based Au<sup>+</sup> disproportionation-mediated\nAuNBP morphology system can serve as a promising general signal reporter\nfor developing various sensitive multicolor colorimetric sensors for\ntarget detection in various fields.