Construction Of Optical Sensing System Biosensor Based On Nanozymes For Biomolecule Visual Detection

Natural enzymes, due to high substrate specificities and high efficiency under mild conditions, have significant practical applications in medicine, chemical industry, food processing and agriculture. They, however, also suffer from some intrinsic drawbacks such as sensitivity of catalytic activity to environmental conditions and relatively low stability(denaturation and digestion). In addition, high costs in preparation and purification also limit their large scale applications. Thus, the creation of efficient, simple, and sustainable materials as peroxidase mimetics represents a central challenge of this field. Thus, the creation of efficient, simple, and sustainable materials as peroxidase mimetics represents a central challenge of this field. Recently, the increasing availability of nanomaterials has created widespread interest in their use as high-efficiency catalysts due to their large surface-to-volume ratio. Indeed, a series of nanostructured materials, such as Fe3O4 nanoparticles, noble mental, double metal composite materials, carbon-based nano-material and other nanomaterials have been demonstrated to possess peroxidase-like catalytic activities and be used in biomedical and environmental detection. Based on this, in this paper, we carried out the work from the following three aspects: exploit and synthesis new nanozymes mimics, build nano composite materials to enhance enzyme catalytic activity and construct optical sensing system visual detection application. This work is devided into three sections:(1) Manganese selenides nanoparticals(MnSe NPs) with graphene-like structures have been prepared through a facile hydrothermal process in an alkaline glycerol/water solution system and used as peroxidase mimetics for ultrasensitive detection of hydrogen peroxide and glucose. The obtained products were characterized by XRD, SEMand TEM, which showed that the obtained products were orthorhombic dittmarite MnSe structures with lateral size ranging from 100 to 200 nm. The MnSe NPs show much higher catalytic activity compared to the HRP. In addition, MnSe NPs exhibit excellent stability in the form of aqueous colloidal suspensions makes the application of the MnSe NPs easier in aqueous systems. On the basis of these unique properties of the as-prepared MnSe NPs, we have developed a label-free colorimetric detection system for H2O2 and glucose.(2) Manganese selenide(MnSe) nanoparticles as nanocatalysts may present enhanced peroxidase-like catalysis if loaded on conductive graphite carbon nitride(g-C3N4) supports. In this work, MnSe nanoparticles were successfully loaded on the surface of polymeric g-C3N4 as a cocatalyst through a thermal condensation method by calcinating the mixture of pure MnSe, dicyandiamide and cyanuric acid. The morphology and composition of thus-prepared MnSe loaded doped graphite phase carbon nitride nanosheets(MnSe-g-C3N4) were characterized by TEM, high resolution TEM, XRD, FT-IR and XPS. Structural analyses revealed that the MnSe-g-C3N4 nanoparticles are composed of ultrathin nanosheets with 20 nm lateral diameter. Compared with original MnSe and g-C3N4, the prepared MnSe-g-C3N4 nanosheets could achieve higher aqueous stability and, especially, much stronger peroxidase-like catalysis, presumably resulting from the synergetic effects of conductive carbon nitride and lamellate MnSe nanocatalysts effectively loaded. Significantly, MnSe-g-C3N4 nanosheets were proved to be novel peroxidase mimetics which could quickly catalyze oxidation of the peroxidase substrate TMB in the presence of H2O2, producing a blue colored solution. Kinetic analysis indicates that the catalytic behavior satisfy typical Michaelis-Menten kinetics and follows a ping-pong mechanism. Colorimetric detections of H2O2 and glucose using the MnSe-g-C3N4 nanosheets were conducted with high detection sensitivities, demonstrating the feasibility of practical sensing applications.(3) Selenium has been successfully doped into graphite phase carbon nitride(g-C3N4) by a simple thermal condensation method through calcinating the mixture of dicyandiamide, cyanuric acid and selenium dioxide. The morphology and composition of thus-prepared selenium doped graphite phase carbon nitride(Se-g-C3N4) nanosheets were characterized by TEM, high resolution TEM, XRD, FT-IR and XPS. Characterization results revealed that the resultant products have typical ultrathin lamellar structure with the uniform lateral diameter of 20 nm. The amount of Se dopant is ca. 2.1 atomic% based on the XPS result. For the first time, ultrathin Se-g-C3N4 nanosheets have been demonstrated to possess an intrinsic peroxidase activity by following the Michaelis-Menten kinetics and even have higher affinity to peroxidase substrates TMB and H2O2 in comparison to that of HRP. Se-g-C3N4 nanosheets is conducive to mediating electron transfer and thus to enhancing the catalytic oxidation of the substrate TMB in the presence of H2O2 to produce a blue color change in aqueous solution. More importantly, a sensitive and selective method for xanthine detection was developed using xanthine oxidase and the as-prepared Se-g-C3N4 nanosheets. On the basis of the high catalytic activity of Se-g-C3N4 nanosheets, a rapid, sensitive and convenient approach was developed for colorimetric detection of xanthine with detection limit 1.6?10-8 mol L-1.