Research On Mimetic Enzyme Properties And Analytical Applications Of Co₃O₄Nanomaterials

Inorganic nanomaterials are generally considered as biologically inert substances. In recent years, it is surprising that some nanomaterials exhibit the catalytic properties of enzymes, such as magnetic iron oxide nanoparticles, cerium oxide nanomaterials, precious metals nanomaterials and so on. The novel properties of nanomaterials promote the establishment of a new field─nanomaterial-based artificial enzymes. We studied Co3O4nanomaterials and constructed the new nanomaterial-based artificial enzymes. The catalytic properties, kinetics and mechanisms of their mimetic peroxidase and mimetic catalase were studied in detail. And Co3O4nanomaterials were applied in the detection of some substances.Based on the systematic research, Co3O4nanoparticles were found to show the peroxidase mimetic activity. The effect of various factors on the catalytic activity of Co3O4nanoparticles was studied, the results showed that the catalytic activity was dependent on pH, temperature and H2O2concentration. The catalytic kinetics of Co3O4nanoparticles were investaged with the Michaelis-Menten equation. Michaelis constants showed that Co3O4nanoparticles had a higher affinity for TMB than that of natural peroxidase. The catalytic constants indicated that the catalytic activity of Co3O4nanoparticles was lower than natural peroxidase. The reaction mechanism was investigated with fluorescence probe and electrochemical methods. The catalytic activity of Co3O4nanoparticles was due to the electron transfer in the catalytic process. Co3O4nanoparticles were applied in the detection of H2O2and glucose with its mimetic peroxidase activity. The linear range for H2O2was from0.05to25mmol/L and the detection limit was10μmol/L. The linear range for glucose was from0.01to10mmol/L and the detection limit was5μmol/L. The demonstrated biosensing system was highly selective for glucose detection.The impact of structure of Co3O4nanomaterials on their peroxidase mimic activity was studied, including morphology and surface modification with functional groups. The Co3O4nanomaterials of different morphology including nanoplates, nanorods and nanocubes were synthesized, and HRTEM results showed that their mainly exposed planes were {112},{110} and {100} planes, respectively. The catalytic activities of Co3O4nanomaterials with different morphology followed the order of nanoplates>> nanorods> nanocubes. The results indicated that the difference in catalytic activity might be related to their explosed planes. The surface atomic configurations in different crystal planes were stuided by relative software, indicating that planes were the important factor on the catalytic activity. Finally, the surfaces of Co3O4nanosheets were modified by different functional groups, including-NH2,-SH,-COOH and-OH, which were verified using infrared spectroscopy, thermal analysis instruments and Zeta potential analysis. Other than the complex modified by hydroxy, the catalytic activities of the complexs were higher than Co3O4nanosheets. The order of their catalytic activities was Co3O4(-NH2)> Co3O4(-SH)> Co3O4(-COOH)> Co3O4> Co3O4(-OH), which might be related with the different electric charges on the surface of the complexs. Studies on the relationship between the structure and the catalytic ability of peroxidase mimic provided an effective method for constructing the peroxidase mimic with high catalytic activity. Surface modification can also increased their biological affinity and promoted their potential applications.The catalytic properties of Co3O4nanoparticles as catalase mimic was firstly studied. The external factors, catalytic kinetics and stability were studied. The results showed that: the catalytic activity increased as pH and temperature; the activation energy of Co3O4nanoparticles and catalase were obtained by Arrhenius formula to be43.3KJ/mol and42.8KJ/mol, indicating close catalytic decomposition barriers; the close Kcat and Kcat/Km values of Co3O4nanoparticles and catlase showed Co3O4nanoparticles had high catalase mimic activity; the stability of Co3O4nanoparticles was higher than that of catalase. Based on the mimetic catalase activity of Co3O4nanoparticles, they were used as the amperometric sensor for the detection of H2O2. The linear range of the H2O2sensor was from10μmol/L to4mmol/L, with the detection limit of3μmol/L. Compared with some other catalases, it had wide range and low detedction.The catalytic properties of Co3O4nanomaterials as catalase mimic with different morphology are studied. The catalytic kinetics of Co3O4nanomaterials as catalase mimic were studied, the activation energies followed the order of nanoplates <nanorods <nanocubes, and the order of their catalytic activity was: nanoplates> nanorods> nanocubes. The catalytic mechanism of Co3O4nanomaterials as catalase mimic was proposed: firstly, the Co(III) of Co3O4nanomaterials obtained electrons easily from H2O2and turned into Co(II), oxidizing H2O2into oxygen and water; secondly, Co(II) in Co3O4nanomaterials transferred electrons to H2O2and changed back to Co(III), reducing H2O2to OH. The difference of catalase mimic activities was due to the different electron transfer ability of Co3O4nanomaterials. Calcium ion was found to dramatically increase the catalase mimic activity of Co3O4nanomaterials. Based on the stimulation of calcium ion, an amperometric biosensor with Co3O4nanoplates was developed to detect Ca2+. The linear range of for detecing Ca2+was0.1and1mmol/L with a detection limit of4μmol/L. It showed high selectivity against other metal ions and good reproducibility. The proposed method was successfully applied for the determination of calcium in milk samples, showing high accuracy.