Single-Atom Nanozymes For The Detection Of Organophosphorus Pesticides

Nanozymes,a series of nanomaterials with enzyme-like activities,have gained plentiful eyes in biosensing,environment management,and disease treatment due to the integration of the enzyme-like catalytic abilities and the superiorities of nanomaterials.However,some challenges,like the low activity and poor selectivity of traditional nanozymes,lead to the limitation of the practical applications.Therefore,rational design of nanozymes at the atomic scale and the in-depth understanding of structure-activity relationship are of great significance for boosting nanozyme activity.In this paper,by integrating the concept of“single-atom catalysis",a series of novel single-atom nanozymes(SAzymes)were delicately designed.Then,the atomically dispersed active sites were well characterized and the remarkable nanozyme activities were investigated in detail.Furthermore,the SAzymes-based biosensors were constructed for the detection of organophosphorus pesticides,which widen the application of SAzymes in biosensors.The details were described as follows.1.Oxidase-like Fe-N-C single-atom nanozymes for the detection of organophosphorus pesticidesWhen the size of the catalyst decreases to the atomic level,single-atom catalysts(SACs)exhibit some new advantages,such as high activity,maximized atom utilization,the adjustable structure of active sites and so on.Inspired by this concept,we synthesized an oxidase-like Fe-N-C single-atom nanozymes(SAzymes).Taking advantage of three-dimensional hierarchically porous nanostructures,the atomically dispersed single sites in Fe-N-C SAzymes can be fully exposed and are favorable for the interaction with reactants.As expected,Fe-N-C SAzymes show higher oxidase-like activity in comparison with traditional nanozymes.Furthermore,the inhibition effect of mercapto molecules toward Fe-N-C SAzymes was studied and a SAzyme-based biosensor was constructed for the evaluation of acetylcholinesterase activity based on this phenomenon.The resultant biosensor can effectively detect acetylcholinesterase in the range of 0.1-25 mU mL-1 with the detection limit of 0.014 mU mL-1.Furthermore,the biosensor was further used for tracing organophosphorus pesticides,and the developed biosensor exhibited a wide linear range(0.1-10?g mL-1)with a low detection limit(0.97 ng mL-1).2.Cascade reaction system integrating Cu-N-C SAzymes with abundant active sites for the detection of organophosphorus pesticidesThough great progress has been made in the field of single-atom catalysts,their activities are still limited by the loading of active metal sites.In this work,a salt-template strategy was proposed to synthesize ultrathin two-dimensional Cu-N-C SAzymes with abundant active sites(?5.1 wt%).By increasing the content of active sites,the developed Cu-N-C SAzymes exhibit a high peroxidase-like activity are a super specificity in comparison with Fe-based SAzymes.Taking advantage of the good enzyme-like activity and specificity,Cu-N-C SAzymes were integrated with acetylcholinesterase and choline oxidase to build a cascade reaction system.The developed cascade system can effectively detect acetylcholine,which is an important biomarker.The linear range is 10-8000 ?M with the limit of detection is 1.24 ?M.With a remarkable performance in the acetylcholine detection,the developed biosensor was further used to sense organophosphorus pesticides,which showed a better performance with a wider linear range(1-300 ng mL-1)and lower detection limit(0.60 ng mL-1)than former work.