This work put forward a chemiluminescence method for rapid screening of nanoparticles-based mimetic enzymes, which is based on H 2 O 2 -luminol chemiluminesent reaction as a model system and six ferrite nanoparticles, namely, CoFe 2 O 4 、CuFe 2 O 4 、 γ -Fe 2 O 3 、MnFe 2 O 4 、precursor of NiFe 2 O 4 and precursor of magnesium ferrite as mimetic enzymes, and the results were compared with that of horseradish peroxidase (HRP). The results indicate: (1) Like HPR, the six ferrite magnetic nanoparticles are able to catalyze the oxidation of luminol by H 2 O 2 to produce enhanced chemiluminescence, and the catalytic activity of the studied six ferrite magnetic nanoparticles depends on the pH, temperature and substrate (H 2 O 2 ) concentration. Also, they could catalytically oxidize 3,3',5,5'-tetramethyl benzidine (TMB) by H 2 O 2 to produce a typical colour reaction. These results show that the ferrite magnetic nanoparticles possess intrinsic peroxidase properties. (2) The apparent Michaelis constants ( K m ) using H 2 O 2 as substrates were higher than that of HRP, in the order of CoFe 2 O 4 γ -Fe 2 O 3 2 O 4 2 O 4 2 O 4 < precursor of magnesium ferrite. (3) The ferrite magnetic nanoparticles show better pH and temperature tolerance than HRP. The proposed method promises the advantages of simplicity and rapidity, thus can be used for screening of the nanoparticles-based mimetic enzymes in large scale.
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 Km 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.
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