MOF-based Ag NPs/Co₃O₄ nanozyme for colorimetric detection of thiophanate-methyl based on analyte-enhanced sensing...

Silver nanoparticles supported on metal-organic framework (ZIF-67)-derived Co₃O₄ nanostructures (Ag NPs/Co₃O₄) were synthesized via a facile in situ reduction strategy. The resulting materials exhibited pH-switchable peroxidase/catalase-like catalytic activity. Ag NP doping greatly enhanced the catalytic activity of Ag NPs/Co₃O₄ towards 3,3',5,5'-tetramethylbenzidine (TMB) oxidation and H₂O₂ decomposition which were 59 times (A₆₅₂ of oxTMB) and 3 times (A₂₄₀ of H₂O₂) higher than that of ZIF-67, respectively. Excitingly, thiophanate-methyl (TM) further enhanced the peroxidase-like activity of Ag NPs/Co₃O₄ nanozyme due to the formation of Ag(I) species in TM-Ag NPs/Co₃O₄ and generation of more radicals resulting from strong interaction between Ag NPs and TM. The TM-Ag NPs/Co₃O₄ nanozyme exhibited lower K_m and higher V_max values towards H₂O₂ when compared with Ag NPs/Co₃O₄ nanozyme. A simple, bioelement-free colorimetric TM detection method based on Ag NPs/Co₃O₄ nanozyme via analyte-enhanced sensing strategy was successfully established with high sensitivity and selectivity. Our study demonstrated that hybrid noble metal NPs/MOF-based nanozyme can be a class of promising artificial nanozyme in environmental and food safety applications.