Designing Hierarchically Porous Single Atoms of Fe-N₅ Catalytic Sites with High Oxidase-like Activity for Sensitive Detection of Organophosphorus Pesticides

Abstract

Recently, single-atom catalysts (SACs) have been used to construct biosensors for the determination of organophosphorus pesticides (OPs). However, most nanozymes including SACs are peroxidase-like enzymes and require highly toxic and unstable hydrogen peroxide (H 2 O 2 ) as a co-reactant to generate reactive oxygen species. Inspired by the heme site of cytochrome c oxidases (Ccos), the construction of Fe-N 5 -coordinated SACs by introducing axial N ligands is expected to bind O 2 to generate active metal−oxygen intermediates. Herein, a SAC with an Fe-N 5 active center confined by hierarchically porous carbon nanoframes (Fe SAs/N 5 -pC-4) was prepared by a polymerization−pyrolysis− evaporation−etching strategy, and its underlying enzyme-like mechanism was uncovered through experiments and density functional theory calculations. The 100% metal atom utilization, increased accessible active sites, accelerated mass transfer, excellent hydrophilicity, and an electron-driven mechanism of axial N endow the SAC with enhanced oxidase-like activity. Notably, its catalytic rate constant (0.398 s −1 ) is 569 times greater than that of the commercial Pt/C catalyst. Similar to the catalytic mechanism of Ccos, O 2 can be converted into reactive oxygen species, avoiding the use of co-reactant H 2 O 2 effectively. In addition, based on the inhibitory effect of thiols on the active site of Fe SAs/N 5 -pC-4, a biosensor was constructed and applied to the colorimetric analysis of OPs. This provides a facile, cost-effective method for efficient OP screening at sites to help control their contamination.

Bioinspired porous three-coordinated single-atom Fe nanozyme with oxidase-like activity for tumor visual identification via glutathione

“…These results imply that pFeSAN may mediate the complete O2-towater reduction without the release of free ROS during oxidation, analogy with the catalytic pathways of natural CcO (Fig. 5b) 23,40 . Afterwards, the electron transfer process analyzed by electrochemical methods was explored to understand the oxidase-like mechanisms of pFeSAN.…”

“…A typical diamondshaped sign signal at g=2.03, consistent with  2 -peroxo heme species, indicated the formation of Fe(IV)=O intermediate in pFeSAN for oxidation (Fig. 5f) 21,23 . Therefore, the oxidase-like activity of pFeSAN proceeds through the O2-to-H2O pathway, analogy with that of natural CcO.…”

“…Furthermore, the trapping agent 5,5-dimethyl-1-pyrroline N-oxide was also employed to probe the possible involved active species by electron paramagnetic resonance (EPR) 23,40 . No apparently detectable signals of any ROS further proved that ROSs were not the main intermediates for the oxidase-like activity of pFeSAN (Supplementary Fig.…”

“…Impressively, pFeSAN delivered outstanding oxidase-like activity, which was 3.3-and 8791-times higher than those of four-coordinated Fe-N single-atom (Fe-N4) and Fe3O4 nanozymes, respectively. Most importantly, the extensive mechanism investigations illustrated that pFeSAN underwent a catalytic pathway of the fourelectron reduction of oxygen into H2O, being identical to that of CcO [21][22][23][24] . Abnormal high concentration of glutathione (GSH) in cells and tissues at millimolar level generally suggests high risk of many diseases [25][26][27] .…”

Broad-Specificity Screening of Pyrethroids Enabled by the Catalytic Function of Human Serum Albumin on Coumarin Hydrolysis

“…Therefore, a convenient, specific, and broad-spectrum pyrethroid screening strategy has become a pressing issue in environmental science and food safety. Presently, enzyme inhibition coupled with different transduction technologies (optical − and electrochemical − ) has emerged for pesticide screening. However, current enzyme inhibition strategies mainly use cholinesterase and carboxylesterase as key enzymes, which are often responsive to various organophosphates and carbamates and cannot specifically screen for pyrethroids in a broad-spectrum way.…”