| Natural enzymes have the advantages of high efficiency and specificity,and play an important role in the biological reaction of life system.However,due to its inherent defects such as variability,complicated preparation,high cost and difficult recovery,the practical application of natural enzyme is limited.In order to solve these problems,researchers have been committed to the development of natural enzyme substitutes-"artificial enzyme".As a new type of artificial enzyme research field,the nanomaterials with similar enzyme characteristics have attracted great attention of researchers.Nanozymes have the characteristics of low cost,high stability,adjustability and recyclability.Therefore,they have been widely concerned in the fields of in vivo and in vitro detection,disease diagnosis and treatment,and environmental degradation.How to improve the catalytic activity and the selectivity of enzyme-like substrate is the focus and bottleneck in the research of nanozymes.Therefore,the design of nanomaterials with high stability,substrate selectivity and catalytic activity is a key scientific problem to be solved in the development of nanozymes.Therefore,it is important to improve the catalytic performance of nanozymes by adjusting the interfacial properties.On the basis of previous work,we have constructed cobalt and manganese oxide nanozyme sensors controlled by surface engineering for peroxidase and oxidase-like catalysis,and successfully applied in the detection of environmental and biological target small molecules.The main research content is divided into the following five parts.In Chapter I,the research progress of cobalt and manganese based nanozymes,oxidase like and peroxidase like enzymes were reviewed.The interface control strategies of catalytic performance of nanozymes and the research status of nanozyme colorimetric sensor were introduced.Finally,the research objectives and contents of this thesis were divided into five chapters as follows:In Chapter ?,?-cyclodextrin(?-CD)surface modified Co3O4 nanocomposites were synthesized by one-pot method.The morphology and structural composition of ?-CD nanocomposites were characterized by high resolution electron microscopy(HRTEM),X-ray powder diffraction(XRD).Besides,X-ray photoelectron spectroscopy(XPS),thermogravimetry(TGA)and Fourier transform infrared spectroscopy(FT-IR)were proved the modified of ?-CD on the surface of Co3O4.Co3O44@?-CD NPs displayed higher affinity to 3,3',5,5'-tetramethy lbenzidine(TMB)through Michaelis-Menten mechanism after modification with ?-CD.The catalytic efficiency of Co3O4@?-CD NPs for TMB oxidation was 9.5-fold higher than that of the pure Co3O4 NPs because of the effective host-guest interactions between Co3O4@?-CD NPs and TMB.Further,the hydrophobic cavity of ?-CD while hosting TMB could reduce the transfer distance of electrons between TMB and Co3O4 catalyst,which could lead to faster oxidation of TMB.The synergistic effects between Co3O4 and ?-CD enhanced the peroxidase-mimicking property.The efficient and visual colorimetric determination of Ascorbic Acid(AA)assay was achieved.The limit of detection was 1.09 ?M(S/N=3)and the linear range was 10?60 ?M based on the Co3O4@?-CD NPs peroxidase-mimicking-mediated 3.0-fold signal magnification strategy.Moreover,the outstanding selectivity toward the detection of AA was achieved,which could exhibit prospects in biomedical analysis.In Chapter ?,?-MnO2@?-CD nanocomposites were successfully synthesized by hydrothermal method.In the absence of hydrogen peroxide(H2O2),the colourless TMB substrate can turn into blue oxidized TMB products.Compared with the original ?-MnO2nanocomposites,?-MnO2@?-CD nanocomposites have better OXD-like activity.Through further optimization of the reaction conditions,it was found that the catalytic reaction kinetics of the composite conformed to Michaelis-Menten equation.By further calculation,the Michaelis constant(Km)of ?-MnO2@?-CD nanozyme is 17.0 times lower than that of ?-MnO2,and its catalytic efficiency(kcat/Km)is 57.8 times higher than that of ?-MnO2.It was proved by ESR that hydroxyl radical(·OH)is the main active radical component in OXD-like system.In addition,based on its OXD-like catalytic reaction mechanism,the detection of 4-chlorophenol(4-CP),a common organic pollutant in the environment was established.The results showedthat the modification of ?-CD promoted the adsorption between the tested substances and nanozyme,and improved the effective utilization of radicals.Therefore,the efficient detection of 4-CP could be realized.In Chapter ?,Mn3O4 nanomaterials exhibit intrinsic molecular oxygen activation properties in biomimetic and environmental catalysis.Modulating the oxygen vacancies(OVs)and identifying the oxygen activation mechanism of Mn3O4 nanomaterials are vital for designing high-performance nanozymes.Herein,the synthesized OV-Mn3O4 Nanoflowers(NFs)possesses different OVs concentrations by regulating oxygen partial pressure.The oxidase-mimicking OV-Mn3O4 NFs showed high catalytic reaction efficiency were 26.86-fold higher than Mn3O4 with poor-OVs.The changes of substrates absorption,reactive oxygen species(ROS),and Mn2+/Mn3+/Mn4+ contents are attempted to illustrate clearly with the participation of OVs.Modulation OVs of Mn3O4 nanozymes can enhance the oxygen storage capacity and increase Mn species with lower valence states,which can generate abundant and multifarious ROS for the oxidation of TMB substrates.Besides,L-cysteine(L-Cys)is a pivotal amino acid for antiaging and reducing melanin.Colorimetric detection for L-Cys was established based on the enhanced oxidase-like properties of OV-Mn3O4.Compared with Mn3O4 NFs,OV-Mn3O4 NFs are exhibited more sensitive limit of detection.Overall,the in-depth mechanism understanding of OVs can provide new perspective to rational design nanozymes and detection sensor with satisfactory property.In Chapter ?,Interfacial electron transfer process regulated by surface Lewis acid-base is remarkable meaningful for oxidation catalysis.Understanding the mechanism of catalysts and substances(TMB and H2O2)induced by Lewis acid-base sites is important to develop the efficiency in peroxidase-like reaction process.Herein,ultrathin Co3O4 nanosheets with abundant Lewis acid-base sites were prepared,which exhibited high-efficiency peroxidase-lik e properties compared with original Co3O4 nanosheets.The ultrathin Co3O4 nanosheets surface structures of Lewis acid-base sites were owing to coordination unsaturation status of the Co ions and O ions and the defect sites.Ultrathin Co3O4 nanosheets had 18.26-fold higher catalytic efficiency than that of original Co3O4 when oxidizing TMB.The surface acid and base sites induced the interfacial electron transfer process of Co3O4 nanosheets,which could be favor of absorption substrates and breaking chemical bonds.Furthermore,the limit of detection of hydroquinol was 0.58 ?M for ultrathin Co3O4 nanosheets,965-fold lower than original Co3O4(560.0 ?M).Besides,the linear range of ultrathin Co3O4 nanosheets was widely with the concentration of 5.000 to 1000 ?M.Colorimetric detection of hydroquinol by agarose-based hydrogel membrane was provided based on excellent peroxidase-like properties.This study represented insights into designing high-performance nanozymes for peroxidase-like catalysis via a strategy of solid surface acid-base sites engineering. |
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