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| 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50480 (07)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Aashuri, Hossein; Simchi, Abdolreza
  7. Abstract:
  8. We demonstrated efficient direct electron transfer from the enzyme glucose oxidase to vertically aligned gold nanorods with a diameter of ~160 nm and a length of ~2 μm that are covalently linkage to a 3-dimensional network of reduced graphene oxide nanosheets. The assembly can be prepared by a 2-step electrochemical procedure. This hybrid structure holds the enzyme in a favorable position while retaining its functionality that ultimately provides enhanced performance for enzymatic sensing of glucose without utilizing mediators. The nanorod assembly was applied to the voltammetric detection of glucose. Figures of merit include an electrochemical sensitivity of 12 µA⋅mM-1⋅cm-2 (obtained from cathodic peak current at a voltage of -0.45 V vs. Ag/AgCl), a 3 μM detection limit (signal/noise = 3), and a wide linear range (0.01-7 mM). Moreover, the hybrid nanostructure shows the heterogeneous electron transfer rate constant (ks) of 2.9 s−1. The high electrochemical activity is attributed to the synergistic effect of a large active surface and an enhanced electron transfer efficiency due to covalent amide linkage. In the second part, we presented a novel hybrid electrode based on reduced graphene oxide/nickel/zinc oxide heterostructures. The sensor was fabricated by template-free hydrothermal growth of ZnO nanorod arrays on conductive glass substrates (FTO) followed by conformal electrodeposition of nickel nanoparticles with an average size of 18 nm. Then, in-situ reduction and electrophoretic deposition of graphene oxide (GO) nanosheets on the structured ZnO/Ni electrode was performed. The prepared three-dimensional nanostructure exhibited fast electrocatalytic response (<3s) towards glucose oxidation due to the large surface area and high electro-activity. The prepared biosensor possessed a wide linear range over 0.5 μM to 1.11 mM, a low detection limit of 0.15 μM at signal/noise ratio of 3, and a sensitivity of 2030 µAcm-2mM-1. Therefore, the performance of the sensor regarding the detection limit and sensitivity is better than many other 3D electrodes utilized for non-enzymatic glucose detection. No interference from different electroactive substances such as uric acid and ascorbic acid was also noticed. The potential application of the 3D hybrid biosensors for detection of glucose in real human serum samples was shown. These novel structured electrodes hold great promise for the development of biosensors and other electrochemical devices
  9. Keywords:
  10. Biosensor ; Gold ; Electrochemistry ; Zinc Oxide ; Graphene ; Glucosoxidase Enzyme ; Nanorod

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