Studies On Small Biomolecules Electrochemical Sensor Based On Graphene And Its Nanocomposites

Dopamine（DA）, ascorbic acid（AA）, uric acid（UA） and nitrite（Na NO2） play a very important role in human metabolism, and are also closely related to human health. Low level of DA may cause neurological disorder, such as schizophrenia and Parkinson’s disease; The accumulation of UA in human body can induce many disease, such as gout, hyperuricaemia and Lesch-Nyhan disease; AA as antioxidant, can be used for the prevention and treatment of common cold, mental illness, infertility, cancer and AIDS; Nitrite, a precursor to carcinogenic nitrosamines, is important in environmental, food and physiological systems. Therefore, the development of a sensitive and rapid method for simultaneous detection of these small bimoleculars will be important in investigating their physiological functions and early diagnostic applications.In the past few decades, electrochemical techniques have been received considerable for the detection of this biomolecules due to the high sensitivity, rapid response, simple operation and low expense. However, it is difficult to determine DA,UA and Na NO2 selectively or simultaneously at bare electrodes because of overlapped oxidation waves caused by the adsorption of their oxidation products.Graphene（GE） has an elusive two-dimensional structure and possesses high mechanical capacity, perfect electrical properties and optical property. Since singlelayer graphene was striped first time in 2004, graphene and its nanocomposites have been attracted interests of many chemistry scientists. In our experiments, graphene and its nanocomposite materials are used to detect UA, AA, DA and Na NO2. The main contents of this thesis are as follows:（1） A facile and cost effective approach has been developed towards electrochemical fabrication of graphene-modified carbon fiber electrode（Er GO/CFE） to simultaneous determination of ascorbic acid, dopamine and uric acid. The SEM images show that CFE is uniformly and wholly wrapped by Er GO layers. Compared with bare carbon fiber electrode（CFE）, the Er GO/CFE possesses higher peak current intensity and lower oxidation potential. This is due to its unique structural features and excellent electrochemical properties. This experiment provides a feasible way for the development of new type and environmental protection material to determine biological molecules.（2） A promising electrochemical sensor for nitrite, Pt nanoparticles decorated on the surface of reduced graphene oxide（RGO） sheets were facilely synthesized by a onepot hydrothermal method. The morphology and composition of as-prepared Pt–RGO composites have been characterized by transmission electron microscopy（TEM）, energy dispersive X-ray spectroscopy（EDX）, X-ray photoelectron spectroscopy（XPS）, Raman spectroscopy and X-ray diffraction（XRD）. The cyclic voltammetry shows that Pt–RGO nanocomposite has a higher electron transfer rate and remarkable increase electrochemical activity toward the oxidation of nitrite. The amperometry reveals that the Pt–RGO modified electrode exists a good linear relationship between peak current and concentration of nitrite with a low detection limit of 0.1μM and high sensitivity of 496.4 μA m M-1.（3） An electrochemical sensor using a novel three dimensional（3D） ternary Pt nanodendrites/reduce graphene oxide/MnO₂ nanoflowers（Pt/RGO/MnO₂） modified glassy carbon electrode for the selective and sensitive determination of dopamine（DA） in the presence of ascorbic acid（AA） and uric acid（UA）. The sensor was prepared by a two-steps method. First, an oil bath was used to synthesis of dendritic Pt nanostructures modified RGO nanosheets. Second, MnO₂ nanoflowers were harvested by a hydrothermal method. The 3D ternary Pt/RGO/MnO₂ nanocomposite was obtained via mixing the as-prepared Pt/RGO and the MnO₂ nanoflowers by ultrasonication. The DPV curves showed that the oxidation peak current of DA is linearly proportional to its concentration in the range from 1.5–290.03 μM, with a detection limit of 0.1 μM（at S/N = 3） containing 5 m M AA, 0.1 m M UA.