Developlment Of Metal Nanomaterials As Peroxidase Mimetics And Their Analytical Applications

Peroxidase, a natural enzyme with a heme as prosthetic group, involved in the physiological metabolism. In biological processes, peroxidase can catalyze oxidation of some substances by oxide or peroxide, especially efficient activation of H2O2. Peroxidation involved in the pathogenesis of a variety of important diseases, causing biological cells, tissues, and even organ damage. H2O2is an important intermediate substance in the bioreactor processe; therefore it has a great significance to accurate determination of H2O2in analytical chemistry and clinical medicine. As the representative of peroxidase, horseradish peroxidase (HRP) is extracted from natural plants. In addition to expensive and easy to inactivation. HRP has a larger molecule which goes against antigen-antibody binding in the enzyme-linked immunoassay. Therefore, it is a great significance to search analog replace of HRP enzyme to improve the catalytic activity of mimetic peroxidase. The magnetic iron oxide nanoparticles with peroxidase-like catalytic activity have been first discovered by Yan in2007. In the presence of hydrogen peroxide, the iron oxide nanoparticles react with the peroxidase substrate3,3’,5,5’-tetramethyl benzidine (TMB) and diazoamino benzene (DAB) to produce identical peroxidase reaction product, thereby generating catalytic activity similar to HRP.Due to the large specific surface area and surface activation center of nanoparticles, the catalytic activity and efficiency are greatly enhanced, making continuously new achievements in the field of catalysis research. Thus, a variety of nanoparticles are used as enzyme mimics, such as magnetic nanoparticles, metal nanoparticles, carbon-based material, oxide nanoparticles and other nanoparticles. This study concentrated on the development of new metal nanomaterials as mimetic peroxidase, construction of the composite nanomaterials for further enhancing the catalytic activity and metal nanomaterials as mimetic peroxidase applied in chemiluminescence analysis and colorimetric sensing research.1. A chemiluminescence method for the determination of ascorbic acid was developed based on the inhibited effect of ascorbic acid on the chemiluminescence generated from the oxidization of luminol in the presence of H2O2catalyzed by chitosan functionalized silver nanoparticles in this paper. Under the optimum conditions, the linear range of the method for ascorbic acid determination was8.0×10-8～1.0÷10-5mol L-1and the detection limit was5.0×10-8mol L-1. The relative standard deviation was4.2%at an ascorbic acid concentration of1.0×10-6mol L-1(n=11). The proposed method has been applied to the determination of ascorbic acid in tablets with satisfactory results.2. Monodisperse, water-soluble Fe1-xCox NPs (x=0.0.5. and1) were prepared by a very simple in situ reduction method and characterized by XRD、TEM/EDX、XPS. The experimental results show that the non-noble metal FeCo NPs、Fe NPs and CoNPs can catalyze oxidation of the peroxidase substrate3,3’,5,5’-tetramethyl benzidine (TMB) by H2O2to produce a blue color in aqueous solution and bimetallic alloy FeCo NPs were found to possess enhanced peroxidase-like activity compared to monometallic Fe NPs and Co NPs. ESR spectra suggest that FeCo NPs have the higher catalytic ability of the decomposition of hydrogen peroxide compared with Fe NPs and CoNPs. The high catalytic activity of bimetallic FeCo NPs is mainly due to the synergy effect of Fe and Co. Finally, we constructed a highly sensitive colorimetric determination of of hydrogen peroxide and glucose analysis using the efficient catalytic activity FeCo NPs. Under optimal conditions, as low as1.0×10-8mol L-1H2O2could be detected with a linear range from1.0×10-7to1.0×10-5mol L-1via this method. More importantly, a sensitive and selective method for glucose detection was developed using glucose oxidase (GOx) and the as-prepared Feo.5Co0.5NPs. The detection limit of this assay for glucose was1×10-8mol L-1with a linear range from5.0×10-7to1.0×10-5mol L-1. In comparison with noble metals, FeCo bimetallic alloy nanoparticles have advantages of low cost, easy preparation, and tunable catalytic activity, which make them a promising enzyme mimetic candidate and may find potential applications in biocatalysis, bioassays, and nano-biomedicine.3. In this study, FeCo-rGO hybrids were prepared by coupling of FeCo NPs and reduced graphene oxide through a simple one step reducing method and characterized by TEM、XRD and Raman spectrum. We constructed peroxidase system by using FeCo-rGO nanocomposites as catalyst. The experimental results show that FeCo-rGO nanocomposites possess enhanced peroxidase-like activity. Reaction conditions on the catalytic activity of FeCo-rGO nanocomposite such as pH, temperature, concentration of catalyst and hydrogen peroxide were investigated and compared with the bare FeCo NPs. It was found that the peroxidase activity of FeCo-rGO nanocomposites was higher than that of the individual components FeCo NPs. Significantly, the new nanocomposite possesses both excellent properties of rGO and FeCo NPs and the synergetic effects between rGO and FeCo NPs make the FeCo-rGO hybrids exhibit enhanced performances in the oxidation of TMB. On this basis, a selective and fast colorimetric assay was proposed for detection of H2O2and glucose. Under the optimal conditions, as low as5.0×10-8mol L-1H2O2could be detected with a linear range from1.0×10-7to1.0×10-5mol L"’. More importantly, a sensitive and selective method for glucose detection was developed using glucose oxidase (GOx) and the as-prepared FeCo-rGO hybrids. The detection limit of this assay for glucose was8×10-7mol L-1with a linear range from1.0×106to1.0×10mol L-1. In comparison with the individual components FeCo NPs. FeCo-rGO nanocomposites have advantages of higher peroxidase-like activity and good solubility in water, making them an effient mimetic candidate.