Peroxidase-mimetic carbon dot based nanozyme hydrogel colorimetric sensor for visual trichlorfon detection

Organophosphorus pesticide residues pose considerable threats to the environment and public health and have become a global concern. This paper reports the development of a visual sensing platform for the detection of trichlorfon based on a carbon-based nanozyme (abbreviated as Fe-CDs) with peroxidase-mimetic catalytic activity in conjunction with acetylcholinesterase (AChE). The peroxide-mimetic enzyme activity of Fe-CDs can be inhibited by sulfhydryl (-SH) compounds, and AChE can decompose thiocholine (ATCh) to produce -SH-containing thiocholine (TCh), leading to the inability of Fe-CDs to oxidise 3,3',5,5'-tetramethylbenzidine (TMB) to turn the solution blue, while trichlorfon can inhibit the activity of AChE, thereby recovering the blue colour. This platform achieves sensitive detection of trichlorfon with a linear range of 200-50,000 pM and a detection limit of 157.57 pM and has been successfully applied to the detection of trichlorfon in Chinese cabbage. In addition, encapsulating Fe-CDs, ATCh and TMB in sodium alginate hydrogels and using a smartphone and colour analysis software, a colorimetric hydrogel portable kit is developed, realising the simple and rapid detection of the trichlorfon residue in real samples. This study provides a direct, simple and rapid strategy for the detection of trichlorfon in agricultural products and offers a potential on-site detection tool for food safety monitoring.