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Based On The Phytic Acid / Gold Nanoparticles, Nano-metal Oxide Sensor Interface To Build Its Electrochemical Research

Posted on:2011-07-10Degree:MasterType:Thesis
Country:ChinaCandidate:Y WangFull Text:PDF
GTID:2208360302492085Subject:Analytical Chemistry
Abstract/Summary:PDF Full Text Request
With the soaring development in nanotechnology, its application has expanded into the field of sensors. Nanomaterials have particular qualities such as large specific surface area, high stability and excellent biocompatibility. And also manifest their specific catalytic effect in the electron transfer process of certain enzyme. Phytic acid is an environment-friendly naturally occurring acid which has 6 noncoplanar phosphate bonds structurally. Its intrinsic property makes phytic acid show a strong tendency to complex and chelate with metal or metal oxide nanoparticles. These new functional materials act as good electron transfer mediator were widely used in the field of electrochemistry, which attracted great interest of researchers to explore their configuration, property and application.Biosensors are expected to be of promising prospect of application in health and safety test, environmental monitoring, clinical medicine and many other fields. How to immobilize a specific biomolecule onto transducer and retain its natural bioactivity is the most crucial step in the fabrication of biosensor. This thesis is aimed at solving the problem by means of nanotechnology, self-assembly and other techniques, employing the functional nanomaterials to construct series electrochemical sensing interface. Four specific hydrogen peroxide biosensors have been developed as follows:(1) A simple and effective strategy for fabrication of hydrogen peroxide (H2O2) biosensor has been introduced by successfully immobilized hemoglobin (Hb) on gold nanoparticles (AuNPs) / phytic acid (PA) composite chain on glassy carbon electrode through self-assembly. The entrapped Hb in nano-chain was characterized by UV-vis absorption spectroscopy and investigated by cyclic voltammetry. These results suggested that the absorbed Hb retain its bioactivity and realize direct electron transfer due to the improved biocompatibility and conductivity of AuNPs. The biosensor displayed good bioelectrocatalytic ability toward the reduction of H2O2, and the linear calibration was obtained in the range from 2.2×10-5 to 3.6×10-4 mmol L-1 with a detection limit of 7.4×10-6 mmol L-1 (at the ratio of signal to noise, S/N = 3). The apparent Michaelis-Meten constant ( K Mapp) was estimated to be 1.47 mmol L-1.(2) A Hemoglobin-ZnO solution was prepared based on the difference in isoelectric point. Layer-by-layer (LBL) assembly films of Hb-ZnO and phytic acid were fabricated by alternately immersing the glassy carbon electrode (GCE) into the solution of PA and as-prepared Hb-ZnO. Field emission scanning electron microscopy (FESEM) was applied to observe the morphology of multilayer films. The electrode modification process was characterized with electrochemical impedance spectroscopy (EIS). Cyclic voltammetry showed that Hb encapsulated in the {Hb-ZnO/PA}n framework realized direct electron transfer with the underlying GCE and kept good catalytic activity. The {Hb-ZnO/PA}6/GCE responded rapidly (less than 3 s) to H2O2 in the linear range form 2.0×10-6 to 1.2×10-4 mol L-1 with a detection limit (S/N = 3) of 1.4×10-6 mol L-1. The K Mapp value was evaluated to be 5.1 mmol L-1.(3) Phytic acid and gold nanoparticles AuNPs were assembled onto the surface of gold electrode layer-by-layer to form a three-dimensional ordered mesoporous gold interface. And then a high sensitive horseradish peroxidase (HRP) biosensor was prepared based on the proposed mesoporous interface. Atomic force microscopy (AFM) and cyclic voltammetry were applied to characterizing the process of forming nanofilm. Hydrogen peroxide was detected with the aid of hydroquinone mediator to transfer electrons between the electrode and HRP. The immobilized HRP displayed the feature of a peroxidase and gave an excellent electrocatalytic response to the reduction of H2O2. The biosensor showed a linear response to H2O2 over a concentration range from 6.5×10-6 to 1.4×10-5 mol L-1 with a detection limit of 3.3×10-6 mol L-1 (S/N = 3). The K Mapp value was estimated to be 0.078 mmol L-1. The biosensor exhibited high sensitivity, good accuracy, satisfactory stability and repeatability.(4) A nanohybrid membrane based on the immobilization of horseradish peroxidase, gold nanoparticles and titanium dioxide nanoparticles (TiO2) on glassy carbon electrode was explored. Field emission scanning electron microscopy, electrochemical impedance spectroscopy and UV-vis spectrum were used to investigate the characteristic. The results indicated that the framework of TiO2 could effectively prevent AuNPs from aggregation, the AuNPs promoted the electron transfer, and the HRP retained its bioactivity in the matrix. The cyclic votammetric results showed that the entrapped HRP achieve direct electron transfer and the electrochemical behaviors were improved in virtue of the synergic effect of TiO2 and AuNPs. Excellent biocatalytic activity of HRP in the modified system was confirmed by the reduction of hydrogen peroxide. The amperometric response to H2O2 ranged form 6.0×10-5 to 1.4×10-4 mol L-1 was obtained, with a detection limit of 6.5×10-6 mol L-1 (S/N = 3). The calculated K Mapp is 1.2 mmol L-1. Moreover, the biosensor possesses long-time stability and reproducibility.
Keywords/Search Tags:Nanomaterials, Phytic acid, Self-assembly, Direct electron transfer, Biosensor
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