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Synthesis of Hybrid Graphene Nanostructures and Their Application in Design and Fabrication of Electrochemical Sensors for Pharmaceutical and Biological Applications

Asadian, Elham | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 48109 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Shahrokhian, Saeed; Iraji Zad, Azam; Mohajerzadeh, Shamsoddin
  7. Abstract:
  8. Recent years have witnessed an increasing interest in graphene and graphene-based materials due to their extraordinary electrical properties, large specific surface area, fascinating mechanical properties, good chemical stability and remarkable electrochemical activity. The combination of these properties make graphene an attractive candidate for a wide range of applications including energy conversion and storage devices (batteries and supercapacitors), electronic devices (transistors and memory devices) and solar cells. On the other hand, graphene has a potential application in constructing different kind of sensors such as biosensors and electrochemical sensors due to its planar structure, large active surface area and numerous edge atoms as active sites for electron transfer. As a result, the objective of the present dissertation is to prepare and synthesize different kind of graphene nanostructures based on chemical and physical methods. Then in the next step, the prepared graphene-based materials were used for design and fabrication of electrochemical sensors. In the first part, the capability of narrow graphene nanoribbons (GNRs) in constructing new sensing platforms. Graphene nanoribbons have been synthesized via a simple hydrothermal route through unzipping of carbon nanotubes, which was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy analysis. These narrow carbon sheets were used to form a composite film by in-situ electropolymerization with aniline. The produced graphene nanoribbon/polyaniline (GNR/PANI) composite film showed impressive performance in electrochemical determination of dobutamine (DBT). Under optimal conditions, in comparison to bare glassy carbon electrode a significant increase in peak current was observed on the surfaceof GNR/PANI modified glassy carbon electrode (up to 10 times), which is ascribed to the higher specific surface area induced by GNRs in combination with the electrocatalytic effect of polyaniline layer. It is believed that such a composite film has a great potential in different applications including sensors, supercapacitors and etc. In the second section, by using graphene nanosheets decorated with Ag nanoparticles (AgNPs-G) as an effective approach for the surface modification of pyrolytic graphite electrode (PGE), a sensing platform was fabricated for the sensitive voltammetric determination of Azathioprine (Aza). The prepared AgNPs-G nanosheets were characterized using different microscopic (TEM) and spectroscopic (UV–vis and Raman spectroscopy) techniques. The electrochemical behavior of Aza was investigated by means of cyclic voltammetry on the surface of pyrolytic graphite electrode, PGE (unmodified or modified with Ag NPs decorated graphene sheets). Comparing to the bare PGE, a remarkable enhancement was observed in the response characteristics of Aza on the surface of the modified electrode (AgNPs-G/PGE) as well as a noticeable decrease in its reduction overpotential. These results can be attributed to the incredible enlargement in the microscopic surface area of the electrode due to the presence of graphene nanosheets together with strong adsorption of Aza on its surface. The effect of experimental parameters such as accumulation time, the amount of modifier suspension and pH of the supporting electrolyte were also optimized toward obtaining the maximum sensitivity. Under the optimum conditions, the calibration curve studies demonstrated that the peak current increased linearly with Aza concentrations in the range of 7 × 10-7 to 1 × 10-4 mol L-1 with the detection limit of 68 nM. Further experiments revealed that the modified electrode can be successfully applied for the accurate determination of Aza in pharmaceutical preparations.The third section of the thesis was devoted to three-dimensionally graphene architectures. Herein, a 3D porous graphene-carbon nanotube (G-CNT) network is successfully constructed on the surface of glassy carbon electrode (GCE) by electrochemical co-deposition from a concentrated graphene dispersion. The large accessible surface area provided by the interpenetrated graphene backbone in one hand and the enhanced electrical conductivity of the 3D network by incorporating CNTs on the other hand, dramatically improved the electrochemical performance of the GCE in determination of Methotrexate (MTX) as an important electroactive drug compound. Under the optimum conditions, the electrode modification led to a significant increase in the anodic peak current (~25 times) along with a considerable shift in the anodic peak potential (~111mV). Voltammetric investigations revealed that the proposed method can determine MTX in a wide dynamic linear range with a low detection limit of 75 nM. Moreover, good sensitivity and high accuracy of the prepared modified electrode in voltammetric detections of MTX, which was further confirmed by UV-Vis spectroccopy and HPLC methods, make it very suitable for accurate determinations of MTX in pharmaceutical formulations (commercial tablets) and clinical preparations (blood serum) with excellent recoveries. Finally, a hierarchical core-shell structure composed of ZnO nanotubes/MnO2 nanosheets was fabricated via a two-step electrochemical deposition procedure on the surface of 3D graphene network (3DGN) as a freestanding monolithic electrode. The highly porous interconnected graphene backbone offers very high conductivity and large accessible surface area. On the other hand, the inner parts of ZnO nanotubes (ZnO NTs) can act as reservoirs, which increase the electrode/electrolyte interface, while the porosity of MnO2 nanosheets is a great matrix for immobilizing biomolecules due to its good biocompatibility. The combination of these properties makes the prepared electrode a promising candidate for constructing biosensing platforms. As a proof of concept, the prepared composite electrode was used for the fabrication of a biosensor by immobilizing glucose oxidase (GOD) as a model enzyme and used for the detection of glucose. Amperometry results revealed very short response times. The obtained high sensitivity (3.9 mA μM-1cm-2) and low detection limit (10 nM) for glucose exhibit that the proposed electrode provides a favorable platform for bioelectrochemical applications
  9. Keywords:
  10. Electrochemical Sensor ; Graphene Nanoribbons ; Three Dimentional Graphene Foam ; Three Dimensional Mesh ; Metal Oxide Nanoparticles ; Graphene Nanosheets

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