Study On Enzyme - Free Electrochemical Sensor Based On Graphene Construction And Its Application

The discovery of graphene by K. S. Novoselov and A. K, Geim in2004at the University of Manchester in England, using micromechanical exfoliation of graphite flatc to prepare the unique graphene, has greatly led to the research sensation in the scientific community, not only because it has broken the two-dimensional crystal that was thermodynamically unstable and could not exist, but more importantly, it greatly enriched the families of the carbon material. Graphene has been showing the great scientific significance and application value in both theory and experiment research owing to its special nanostructure and properties, and the research related to this advanced materials has been becoming a new direction. Within the past few years, graphene has shown the infinite charm in the field of theoretical research and practical application, and has become the most active research frontiers in the areas of material science, nano electronic device and condensed matter physics.Graphene, a single-atom-thick sheet of hexagonally arrayed sp2-bonded carbon atoms, is a two-dimensional (2D) macromolecule exhibiting extremely high specific surface area. Its inert surface structure makes it with highly chemical stability. However, the attractive van der Waals forces between the graphene sheets limits its solubility in common organic solvents. This leads to the difficulty in the in-depth research. In order to address this challenge and obtain the stable dispersion of graphene suspension, the graphene is modified with metal or inorganic nanoparticles via forming the covalcnt bonds or non-covalent bonds, which not only avoids the agglomeration of graphene, but also improves the inter-miscibility with the targeted substrate.Phytic acid, also called Inositol hexakisphosphoric (IP6), is a kind of naturally produced specie and is the principal storage form of phosphorus in many plant tissues, especially in brans and seeds, and holds the unique properties, such as biocompatibility, nontoxicity, and benignity to the environment. IP6with six phosphates can form π-πconjugate system with graphene, which resulting in a stable graphene suspension. It is expected that the botanical IP6micelle can replace the synthetic polymer as the dispersant. Because of its unique tubular structure, carbon nanotubes (CNTs) is also used to mix with two-dimensional graphene, which not only helps avoid the agglomeration, but also helps bridge the graphene sheets and enhance the continuity of carbon structures. Traditionally, graphene is mainly produced via chemical reduction method, which causes the concern of chemical contamination of the resulting product for practical application. The green approach or in-situ reduction method like directly electrochemical reduction of graphite oxide (GO) into graphene has been becoming interesting recently and received a large amount of attention. By introducing various active materials into the process of electrochemical reduction, it is expected that a new form of graphene composites with multi-functional properties can be formed and can used for different applications, especially the electrochemical sensing and detection. The present thesis has been focused on preparing the graphene or graphene composites based electrodes with different active materials and different methods as the electrochemical sensors for the detection of acetaminophen (AP) and dopamine (DA).1. Graphene nanosheets (G) were dispersed in deionized water with the aid of IP6, which exhibits great stability of well-dispersive state at least3months. Such G-IP6aqueous solution was self-assembled onto an electrode surface for different applications. In this study, a glassy carbon electrode modified by graphene (G) and phytic acid (IP^) was investigated by voltammctric methods in the buffer solution. The G-IP6/GC electrode demonstrated the substantial enhancements in electrochemical sensitivity and selectivity towards the detection of acetaminophen (AP). The G-IP6films was found to promote the electron transfer reaction of AP at pH under7.0. The linear calibration plots were obtained in the AP concentration range between0.1μM and3.5mM and the detection limit of the AP oxidation current was determined to be0.052μM at a signal-to-noise ratio of3. The results indicated that the modified electrode can be used to determine AP without interference from DA、AA and UA, while ensuring good sensitivity, selectivity, and reproducibility. 2.The graphene nanosheet was synthesized by chemical method, which usedhydrazine hydrate as the reduction. The graphene nanosheet was characterized usingIJV-visibJe absorption spectroscopy (UV-Vis), X-ray diffraction (XRD)，atomic forcemicroscopy (AFM), and field emission scanning electron microscopy (FC-SEM). Themixed multi-wall carbon nanotubcs and graphene nanosheet were used to modify theglassy carbon electrodc (G-MWCNTs/GCE), which was then applied for theelectrocatalytic reaction of dopamine (DA) in the presence of amount of ascorbic acid(AA). This modiifed electrode exhibited an enhanced current response for DA.Electrochemical parameters, such as the surface area of the electrode (A), electron transferrate constant (ks)，and the diffusion coefifcient (D), were calculated and comparable withthe prior reports. A linear ranging for oxidation of DA is about0.01-10jiM in thepresence of1mM AA, with a low detection limit0.003[iM (S/N=<3), This outstandingperformance was due to the synergistic effects of graphene nanosheet and the multi-wallcarbon nanotubes. In addition, this modified electrode was successfully used to detectionDA in the real samples of dopamine hydrochloride injection,3.An electrochemical sensor of acetaminophen (AP) based on electrochemicallyreduced graphene (ERG) loaded nickel oxides (NiiOj-NiO) nanoparticles coated ontoglassy carbon electrode (ERG/N i?03-N iO/GC E) was prepared by a one-stepelectrodeposition process. The as-prepared electrode was characterized by scanningelectron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Theelectrocatalytic properties of ERG/Ni203-NiO modified glassy carbon electrode towardthe oxidation of acetaminophen were analyzed via cyclic voltammetry (CV) anddifferential pulse voltammetry (DPV). The electrodes of NijOrNiO/GCE. ERG/GCE，and Ni203-Ni0deposited ERCi/GCE were fabricated for ihe comparison and the catalyticmechanism understanding. The studies showed that the onc-slep preparedERG/Ni203-NiO/GCE displayed the highest electro-catalytic activity, attributing to thesynergetic effect derived from the unique composite structure and physical propetries ofnickel oxides nanoparticles and graphene. The low detection limit of0.02f.iM (S/N=3) with the wide linear detection range from0.04to100(xM (R=0.998) was obtained.The resulting sensor was successfully used to detect acetaminophen in commercialpharmaceutical tablets and urine samples.4. Copper oxide (CuO) prepared by electrospinning and subsequent thermaltreatment processes were demonstrated for glucose non-enzymatic determination. Thestructures and morphologies of CuO were characterized by ifeld emission scanningelectron microscopy (FE-SEM) and X-ray diffraction spectrum (XRD). Differentdispersants were utilized for the suspension preparation the films electrode fabricationwas investigated in detail. The assay performances to glucose were evaluated by cyclicvoltammetry (CV) and chronoamperometry (I—t). The results revealed the long-termstability and excellent resistance towards electrode fouling in the glucose determination at0.50V. The improved performances of CuO films electrode for elcctro-oxidation glucosewere ascribed to the high surface-to-volume ratio, complex pore structure of theas-prcpared CuO,...