Synthesis Of Composite Nanomaterials And Its Application In Biosensors

Based on the identification of biological molecules and their downstream signal conversion, biosensor has carried out a sequence of analytical methods for the detection of target molecules. Compared with other similar analysis methods, biosensor has many advantages, like the property to improve the speed of analysis and application flexibility. During recent years, researchers continue to make break throughs in the field of nanomaterials, the recognition and detection of biomolecules continuous development of new technologies for building high sensitivity, high selectivity, fast and efficient novel biosensor provides perfect design ideas, as biological sensors to achieve different target site rapid testing analysis provides a more powerful platform. Among them, functional nanomaterials not only possess the advantages of large surface area, good conductivity, and super mechanical property, but also possess high catalytic activity, robust adsorption capacity, and good biocompatibility. Based on the searching of abundant papers, using the chemiluminescent, electrochemical, and the construction of biosensors, the preparation and application of several novel functional nanomaterials has been synthesized.The main pionts of this thesis are summarized as follow:(1) Core-shell Fe3O4 polydopamine(Fe3O4@PDA NPs) nanoparticles were synthesed by a simple and green way, which was used as a recyclable nanocatalyst with tunable shell thickness. Through a one-pot process magnetite Fe3O4 NPs was formed, with a diameter of ~240 nm. PDA could be used as both the reducing agent and the coupling agent, then coated with a polydopamine shell layer with a tunable thickness of 15~45 nm, the deposition of Au NPs onto Fe3O4@PDA NPs was achieved. For the reduction of p-nitrophenol, the Au/Fe3O4@PDA could exhibit high catalytic performance. Moreover, the reuse and recovery of the catalyst was demonstrated several times resulting negligible detectible loss in activity. The synergistic combination of PDA and magnetic NPs establishes unique core-shell NPs for potential applications as a versatile platform.(2) For the detection of a low-abundance protein(Carbohydrate antigen 125, CA125, used in this case) with a sensitive and enhancement traits, a novel colormetric immunoassay strategy was first designed and utilized with its catalytic active substance in the recognition elements which could exhibit high catalytic performance for the reduction of p-nitrophenol resulting in a greater color change and UV signal variations. Thereafter, a specific sandwich-form immunoassay format was claimed for the detection of CA125 by using amplificable polydopamine absorbed gold nanoparticles(PDA-Au) as a reduced catalytic substance for p-nitrophenol and functionalized nano magnet-beads as separable immunosensing probes by recording the change in absorbance of p-nitrophenol. To verify its signal amplification and sensitivity, a conventional colormetric immunoassay was also investigated by using an antibody attaching a signal gold nanoparticle as catalytic substances. Under the optimal conditions, this developed colormetric immunoassay exhibits a wide dynamic range of 0- 100 U/mL toward CA125 with a detection limit of 0.1 U/m L at the 3 S blank level and a correlation coefficient of 0.9924. Additionally, this methodology was validated for the analysis of clinical serum specimens, and resulting in good accordance by using standard addition method.(3) The SPAAB-based ultrasensitive enzymatic immunosensor for protein biomarkers detection was successfully developed. The high capacity and high activity for covalent immobilization of HRP in SPAABs endowed SPAAB-HRP with remarkable signal amplification capability. Using HIgG as a model analyte, the immunosensor could be simply prepared based on a sandwich-type protocol with the primary antibody immobilized onto the surface of GO. After the fabrication of the immunosensor, the electrode was dipped onto the buffer solution containing o-phenylenediamine(OPD) and H2O2, in the presence of HRP, the catalytic oxidation provided DPV response change. The dynamic range of the developed amplified immunoassay for HIgG could achieve 100 pg/m L to 100 μg/m L with a detection limit of 50 pg/m L(S/N = 5). This methodology was also applied for the analysis of clinical serum samples with satisfactory results, which confirmed its promising practical application.(4) The ultrasensitive monitoring of glucose with a fast and accurate method is significant in potential therapeutics and optimizes protein biosynthesis. Incorporation of enzyme into matrix is considered as promising candidates for constructing highly sensitive glucose-responsive systems. In this study, three-dimensional poly(acrylic acid) brushes-nanospherical silica(PAA-nano silica) with high amplification capability and stability were used to covalently immobilize bienzymes for cascade enzymatic catalysis. The major advantages of PAA-nano silica-bienzyme co-incorporation is that the enzymes are proximity distribution, and such close confinement both minimized the diffusion of intermediates among the enzymes in the consecutive reaction and improve the utilization efficiency of enzymes, thereby enhancing the overall reaction efficiency and specificity. Thus, this present bienzymatic biosensor shows robust signal amplification and ultrasensitivity of glucose-responsive properties through motoring UV/vis signatures.(5) A novel photoelectrochemical system ZnO-Au@CdS was developed by depositing Au NPs and CdS NPs on the surface of tremella-like ZnO nanospheres. The photoelectrochemical property of the system was significantly enhanced owing to the efficient separation of the photoexcited charges, resulting from the anisotropic junction of ZnO-Au@CdS. CdS NPs could be bioetched irreversibly by an enzymatic reaction catalyzed by horseradish peroxidase(HRP) and H2O2, leading a decrease of the intensity of the photoelectrochemical property. A novel platform was developed for H2O2 detection based on the decrease of the photoelectrochemical intensity. This sensing platform had a good sensitivity for H2O2 detection of 0.14 μM at S/N = 3, and the linear range was from 0 to 100μM. Glucose oxidase(GOx) was successfully immobilized on ZnO-Au@CdS nanospheres to construct a sensing platform for glucose detection. The sufficient and stable GOx and the special catalytical enzymatic reaction ensured the excellent ability of the glucose biosensor. The inteference free glucose biosensor had a detection limit of 0.50 μM with a linear range of 0 to 400μM.