Lignin-based iron single-atom nanozyme for detection of organophosphorus in soil

Organophosphorus pesticides (OPs) are widely used in agriculture and their residues can pose a threat to human health. Therefore the monitoring of their residue content is necessary. In this study, a colorimetric sensing strategy was designed to detect OPs by combining nanozymes with natural enzymes. Among them, iron single-atom nanozymes (Fe-N/C) were prepared by a one-pot synthesis method by pyrolyzing alkaline lignin. Various characterization tools were used to elucidate the microstructure and reaction mechanism of the nanozymes. N in the material is mainly bound to Fe in the form of pyrrole nitrogen, catalytic H2O2 will produce OH. Fe-N/C has good peroxidase-like activity and produces signals in UV detection upon the addition of 3,3′,5,5′-tetramethylbenzidine (TMB). Combining the catalytic properties of Fe-N/C and introducing acetylcholinesterase (AChE) for the detection of OPs in soil (take chlorpyrifos for example). The product of AChE catalyzed acetylcholine (ATCh) can inhibit the color signal. In contrast, the presence of chlorpyrifos destroys the activity of AChE and restores the reaction absorbance. The amount of chlorpyrifos can be calculated by observing the changes in color. The linear range of chlorpyrifos detection based on this strategy was 0.05–10.0 μg mL−1, the detection limit was 2.11 ng mL−1. This strategy provides a sensitive method for the quantitative determination of OPs, which is important for the monitoring of OPs in the environment.