Saberi, Reyhanesadat | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42888 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Shahrokhian, Saeed
  7. Abstract:
  8. In the first part, preparation of different kinds of polypyrrole/carbon composites and their application for drug analysis are described. In the first work, A very sensitive electrochemical sensor constructed from a glassy carbon electrode modified with a layer-by-layer MWCNT/doped overoxidized polypyrrole (oppy/MWCNT /GCE) was used for the determination of acetaminophen (AC) in the presence of codeine and ascorbic acid (AA). In comparison to the bare glassy carbon electrode, a considerable shift in the peak potential together with an increase in the peak current was observed for AC on the surface of oppy/MWCNT/GCE, which can be related to the enlarged microscopic surface area of the electrode. Under the optimized conditions, the calibration curve was obtained over two concentration ranges of 2×10−7–6×10−6 M and 4×10−5–1×10−4 M of AC with a linear correlation coefficient (R2) of 0.9959 and 0.9947, respectively. The estimated detection limit (3σ) for AC was obtained to be 5×10−8 M. The developed method was successfully applied to analyze the pharmaceutical preparations of AC with a recovery of 95%. In the second work, A composite film of surfactant doped over-oxidized polypyrrole and multi-walled carbon nanotube was prepared on the surface of glassy carbon electrode by the electro-polymerization method. Surface characterization of the modified electrode was performed by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectrometry. It was proved that over-oxidation of the modifier film results in a porous thin layer that improves the interlayer diffusion mechanism of the electroactive species. On the other hand, the negative charge density on the surface of the electrode excludes the negative analytes (e.g. ascorbate and Fe(CN)63−/4−) and attracts the positive ones (e.g. dopamine and epinephrine). A remarkable enhancement in the microscopic area of the electrode resulted in a considerable increase of the anodic peak current of epinephrine (EN) (∼35 times). Differential pulse voltammetry has been applied as a very sensitive analytical method for the determination of sub-micromolar amounts of EN. Two linear ranges have been obtained for the EN within the concentration ranges of 0.1–8.0 and 10–100 μM. The voltammetric detection limit of the modified electrode for EN (based on 3σ) was 40 nM. On the other hand, this sensor has an excellent selectivity and sensitivity for the EN determination in the presence of clinical interferences (e.g. uric acid, ascorbic acid, and the human serum contents). In the third work, a composite surface coating is prepared on the surface of a glassy carbon electrode (GCE) by electropolymerization in a mixture of pyrrole and carbon nanoparticles The microscopic structure and morphology of the composite film is characterized by scanning electron microscopy. The modified electrode offers a considerable improvement in voltammetric sensitivity toward methyldopa (m-dopa), compared to the bare and polypyrrole-coated GCEs. A significantly enhanced anodic peak current together with a remarkable increase in the sharpness of the cyclic voltammetric (CV) signals are observed for the detection of m-dopa. The effect of experimental parameters, such as scan rate and pH, are investigated by monitoring CV responses toward m-dopa. It is found that a maximum current response can be obtained at pH 3.0 under a diffusion controlled process. A wide linear dynamic range (0.2–50 μM) with a detection limit of 60 nM is achieved for m-dopa. The excellent response characteristics, e.g., high sensitivity, very good repeatability and reproducibility, and low detection limit, have made the prepared sensor suitable for the analysis of mdopa in pharmaceutical and clinical preparations. In the second part, preparation of polyaniline/gold nanoparticles bilayer is described for in biosensor applications. In this work, the improved electrochemical performance of graphite screen printed electrode with low cost electropolymerized conducting polymer, polyaniline, is described. Since polyaniline is only applicable in acidic solutions, which is not suitable for biological assays, gold nanoparticles (AuNPs) are electrodeposited at the surface of polyaniline to improve its conductivity in neutral pH. In addition, gold nanoparticles are helpful for immobilization of thiolated bioreceptors. The modified electrode is characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The application of this modified electrode is tested as an oligonucleotide target biosensor. Various parameters, including incubation times in reagents, number of cycles for electropolymerization of aniline and electrodeposition of gold and concentration of reagents, were optimized. Optimization and characterization of the GSPC/PANI/AuNPs/ssDNA was characterized using differential pulse voltammetry (DPV) that exhibited a good dynamic range, correlation coefficient (0.5-100nM and 0.986, respectively) and a detection limit of 0.37 nM. In the third part, the electrochemical behavior of lamotrigine (LMT) at the pyrolytic graphite electrode (PGE) is investigated in detail by means of cyclic voltammetry. During the electrochemical reduction of LMT, an irreversible cathodic peak appeared. Cyclic voltammetric studies indicated that the reduction process has an irreversible and adsorption-like behavior. The observed reduction peak is attributed to a two-electron process referring to the reduction of azo group. The electrode showed an excellent electrochemical activity toward the electro-reduction of LMT, leading to a significant improvement in sensitivity as compared to the glassy carbon electrode. The results of electrochemical impedance spectroscopy and cyclic voltammetry showed that edge-plane pyrolytic graphite electrode has excellent electrochemical response properties toward LMTs with respect to GCE modified with carbon nanotubes. High sensitivity, low detection limit and very good repeatability together with excellent recovery make the electrode a powerful devise for accurate determination of LMT in pharmaceutical and biological samples
  9. Keywords:
  10. Polypyrrole ; Carbon Nanotubes ; Composite ; Polyaniline ; Gold Nanoparticle ; DNA-Based Electrochemical Biosensor ; Carbon Nanoparticles ; Epinephrine ; Pyrolytic Graphite Electrode ; Screen Printed Electrode ; Lamotrigine ; Methyldopa

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