Two birds with one stone: Mn metal-organic gel-derived multifunctional nanozyme for dual-mode colorimetric assay of acetylcholinesterase and organophosphorus pesticides

It is a pressing necessity to establish a valid approach for precise and sensitive monitoring of the acetylcholinesterase (AChE) activity and its inhibitor, organophosphorus pesticides (OPs), for public health and food safety. Herein, a dual-mode colorimetric sensor was designed for sensitive and accurate sensing of AChE and OPs based on Mn metal-organic gels (Mn-MOGs)-derived multifunctional nanozyme. The nanozyme was synthesized by pyrolyzing the Mn-MOGs, which show superior oxidase (OXD)-like and laccase (LAC)-like activities. It can catalyze the 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation into blue TMB (oxTMB) and 2,4-dichlorophenol to generate the red quinone imine (QI). The OXD-like and LAC-like activities can be inhibited by the thiocholine generated from AChE hydrolysis of acetylthiocholine (ATCh), causing a significant reduction in the absorption of oxTMB and QI. OPs can restrain the AChE activity, which prevents the hydrolysis of ATCh, causing the recovery of absorption of oxTMB and QI. Thus, a dual-mode colorimetric sensor was designed for sensing of AChE and OPs. Moreover, this sensor was also utilized to detect OPs in real samples with satisfactory results. This study not only provides a valid way for sensitive and accurate monitoring of AChE and OPs but also affords new insights for designing multifunctional nanozymes used to develop multimodal sensors.