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Chemically Modified Electrode Based on Carbon Nanostructures and Metal Nanoparticles: Preparation, Characterization and Application in Determination of the Pharmaceutical and Biological Compounds and Oxygen Reduction at Soft Interfaces Catalyzed by in Situ Generated Reduced Graphene Oxide

Rastgar Kafshgarkolaei, Shokoufeh | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45081 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Shahrokhian, Saeed
  7. Abstract:
  8. In the first part, the preparation of metallic, bi-metallic (alloy or mixtures) and metallic oxide nanoparticles on the substrate of carbon nanostructures (carbon nanotube and graphene based nanosheets) has been performed using chemical and electrochemical procedures. Then, the prepared nanostructures were characterized by electron microscopy, spectroscopy and electrochemical techniques. Finally, the nanofilms have been evaluated for sensing applications as a modifier on the electrode surface for accurate determination of trace amounts of some important pharmaceutical and biological compounds. In the first work, multi-walled carbon nanotubes decorated with Fe3O4 nanoparticles (Fe3O4NPs/MWCNT) were prepared and used to construct a novel biosensor for the simultaneous detection of adenine and guanine. The direct electro-oxidation of adenine and guanine on the modified electrode were investigated by linear sweep voltammetry.The results indicate a remarkable increase in the oxidation peak currents together with negative shift in the oxidation peak potentials for both adenine and guanine, in comparison to the bare glassy carbon electrode (GCE). The surface morphology and nature of the composite film deposited on GCE were characterized by transmission electron microscopy, atomic force microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The Fe3O4NPs/MWCNT based electrochemical biosensor exhibits linear ranges of 0.01–10 μM and 0.05–8 μM with detection limits of 1 nM and 5 nM for adenine and guanine, respectively. The proposed method was successfully applied for a highly sensitive simultaneous determination of trace amounts of adenine and guanine in DNA of fish sperm samples with satisfactory results. The experimental detection limit was found to be equal to 3 ng mL−1 DNA. The value of (G+C) /(A+T) in DNA was calculated to be 0.81. The fabricated electrode showed excellent reproducibility, repeatability and stability. In the second work, the electrochemical reduction of tinidazole (TNZ) is studied on gold-nanoparticle/carbon-nanotubes (AuNP/CNT) modified glassy carbon electrodes using the linear sweep voltammetry. An electrochemical procedure was used for the deposition of gold nanoparticles onto the carbon nanotube film pre-cast on a glassy carbon electrode surface. The resulting nanoparticles were characterized by scanning electron microscopy and cyclic voltammetry. The effect of the electrodeposition conditions, e.g., salt concentra-tion and deposition time on the response of the electrode was studied. Also, the effect of experimental parameters, e.g., potential and time of accumulation, pH of the buffered solutions and the potential sweep rate on the response is examined. Under the optimal conditions, the modified electrode showed a wide linear response toward the concentration of TNZ in the range of 0.1–50 µM with a detection limit of 10 nM. The prepared electrode was successfully applied for the determination of TNZ in pharmaceutical and clinical samples.
    In the third work, a modified glassy carbon electrode, prepared by potentiostatic electrodeposition of platinum–ruthenium nanoparticles (Pt–RuNPs) onto a multi-walled carbon nanotube (MWCNT) layer, offers dramatic improvements in the stability and sensitivity of voltammetric responses toward methyldopa (m-dopa) compared to glassy carbon electrodes individually coated with MWCNT or Pt–RuNPs. The surface morphology and nature of the hybrid film (Pt–RuNPs/MWCNT) deposited on glassy carbon electrodes was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. A remarkable enhancement in the microscopic area of the electrode together with the catalytic role of the composite modifier resulted in a considerable increase in the peak current (110 times) and a negative shift (−200 mV) in the oxidation peak potential of m-dopa. The mechanism of the electrocatalytic process on the surface of the modified electrode was analyzed via cyclic voltammograms at various potential sweep rates and pHs of the buffer solutions. Differential pulse voltammetry was applied and shown to provide a very sensitive analytical method for the determination of sub-micromolar amounts of m-dopa, for which a linear dynamic range of 0.05–40 µM and a detection limit of 10 nM was obtained. The modified electrode was successfully used for accurate determination of trace amounts of m-dopa in pharmaceutical and clinical preparations.
    In the fourth work, mixtures of gold–platinum nanoparticles (Au–PtNPs) are fabricated consecutively on a multi-walled carbon nanotubes (MWNT) coated glassy carbon electrode (GCE) by the electrodeposition method. The surface morphology and nature of the hybrid film (Au–PtNPs/MWCNT) deposited on glassy carbon electrodes is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode is used as a new and sensitive electrochemical sensor for the voltammetric determination of cefotaxime (CFX). The electrochemical behavior of CFX is investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable improvement in the oxidation peak current of CFX compared to glassy carbon electrodes individually coated with MWCNT or Au–PtNPs. Under the optimized conditions, the modified electrode showed a wide linear dynamic range of 0.004–10.0 µM with a detection limit of 1.0 nM for the voltammetric determination of CFX. The modified electrode was successfully applied for the accurate determination of trace amounts of CFX in pharmaceutical and clinical preparations. In the fifth work, electrochemical deposition, as a well-controlled synthesis procedure, has been used for subsequently layer-by-layer preparation of nickel hydroxide nanoparticle-reduced graphene oxide nanosheets (Ni(OH)2-RGO) on a graphene oxide (GO) film pre-cast on a glassy carbon electrode surface. The surface morphology and nature of the nano-hybrid film (Ni(OH)2-RGO) was thoroughly characterized by scanning electron and atomic force microscopy, spectroscopy and electrochemistry techniques. The modified electrode was appeared as an effective electo-catalytic model for analysis of rifampicin (RIF) by using linear sweep voltammetry (LSV). The prepared modified electrode exhibited a distinctly higher activity for electro-oxidation of RIF than either GO, RGO nanosheets or Ni(OH)2 nanoparticles. Enhancement of peak currents is ascribed to the fast heterogeneous electron transfer kinetics arises from the synergistic coupling between the excellent properties of RGO nanosheets (such as high density of edge plane sites, subtle electronic characteristics and attractive π-π interaction) and unique properties of metal nanoparticles. Under the optimized analysis conditions, the modified electrode showed two oxidation processes for rifampicin at potentials about 0.08 V (peak I) and 0.69 V (peak II) in buffer solution of pH 7.0 with a wide linear dynamic range of 0.006 - 10.0 µM and 0.04 - 10 µM with a detection limit of 4.16 nM and 2.34 nM considering peak I and peak II as an analytical signal, respectively. The results proved the efficacy of the fabricated modified electrode for simple, low cost and highly sensitive medicine sensor well suited for the accurate determinations of trace amounts of RIF in the pharmaceutical and clinical preparations. In second part, graphene oxide (GO) in water was reduced heterogeneously by decamethylferrocene (DMFc) or ferrocene (Fc) in 1,2-dichloroethane (DCE), to act as a catalyst for an interfacial oxygen reduction reaction (ORR) and production of hydrogen peroxide (H2O2). The reduced graphene oxide (RGO) produced at the liquid/liquid interface was characterized by electron microscopy, spectroscopy (Raman, infra-red, and electron energy loss) and electrochemical techniques. The oxygenated functional groups remaining at the edge/defects of the RGO surface activate O2 adsorption forming superoxide like adducts that can be protonated at the liquid/liquid interface and reduced by DMFc or Fc. This process is facilitated by the higher electrical conductivity of RGO sheets. The key feature of this catalytic reaction is the in situ partial reduction of GO at the liquid/liquid interface forming an efficient and inexpensive catalyst for the production of hydrogen peroxide
  9. Keywords:
  10. Adenine ; Guanine ; Cefotaxime ; Platinum-Gold Nanoparticles ; Nickel Hydroxide Nanoparticles ; Methyldopa ; Carbon Nanotubes ; Gold Nanoparticle ; Hydrogen Peroxide

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