A tunable bifunctional hollow Co3O4/MO3 (M = Mo, W) mixed-metal oxide nanozyme for sensing H2O2 and screening acetylcholinesterase activity and its inhibitor

Abstract

A self-templated strategy was adopted to design hollow Co₃O₄/MO₃ (M = Mo, W) mixed-metal oxides via the Mo or W doping of ZIF-67, and subsequent pyrolysis under an atmosphere of air at a low temperature of 450 °C. The hollow Co₃O₄/MO₃ (M = Mo, W) mixed-metal oxides displayed tunable oxidase-like and peroxidase-like activities able to efficiently catalyze the oxidation of TMB to generate a deep blue color in the absence or presence of H₂O₂. Relative to that of the un-doped Co₃O₄, the oxidase mimic activity of the Mo-doped Co₃O₄ increased to 1.3 to 2.1-fold, while its peroxidase mimic activity increased to 7.1 to 19.9-fold, depending on different Mo doping amounts. The oxidase mimic activity of the W-doped Co₃O₄ increased to 2.1 to 2.3-fold, while its peroxidase mimic activity increased to 4.8 to 5.9-fold, depending on the different W doping amounts. The Mo- and W-doped Co₃O₄ nanohybrid exhibited both higher O₂ and H₂O₂ activating capability, and their H₂O₂ activating capacity was superior to the O₂ activating capability. Furthermore, the Mo- and W-doped Co₃O₄ nanohybrids exhibited similar O₂ activating abilities, while the Mo-doped one displayed a higher H₂O₂ activating capability than the W-doped one. The discrepant peroxidase-like nature of Mo- and W-doped Co₃O₄ nanohybrids is likely attributed to their different catalytic mechanisms. The peroxidase-like activity of Mo-doped Co₃O₄ is highly related to the ˙OH free radical, while that of W-doped Co₃O₄ is likely ascribed to the electron transfer between TMB and H₂O₂. The K_m values of Co₃O₄/MoO₃ for TMB and H₂O₂ were 0.0352 mM and 0.134 mM, which were 3.2- and 1.9-fold lower than that of pure Co₃O₄, respectively. A Co₃O₄/MoO₃-based colorimetric platform was developed for the determination of H₂O₂ in the 0.1–200 μM range, with a limit of detection of 0.08 μM (3σ). Based on the thiocholine (TCh) inhibition of the excellent peroxidase-like activity of Co₃O₄/MoO₃ and the TCh generation via acetylcholinesterase (AChE) catalyzed hydrolysis of acetylthiocholine chloride (ATCh), the colorimetric platform was extended to screen AChE activity and its inhibitor.