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Chemically Modified Electrodes Based on Conducting Polymers and Carbon Nanotubes: Application to Voltammetric Determination of Some Biological and Pharmaceutical Compounds

Asadian, Elham | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39791 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Shahrokhian, Saeed
  7. Abstract:
  8. There are high attractions in the development of conducting polymer (CP) coatings to improve the electrochemical properties and biocompatibility of electrodes in the area of biosensors. In the first part of this thesis, a new type of modified electrodes, constructing multi-walled carbon nanotubes (MWCNTs) and polypyrrole is prepared in a layer-by-layer process. In this procedure, the glassy carbon electrode is casted first by a drop suspension of MWCNTs, leading to formation a thin film on its surface. In the second step, electrochemical polymerization of pyrrole in the presence of tiron (used as doping anion) is performed on the surface of the MWCNTs pre-coated electrode. The modification procedure leads to fabrication of a modified electrode that can be used as a sensitive and selective sensor for voltammetric determination of L-dopa. The electrochemical behavior of L-dopa is investigated on the surface of the modified electrode by the means of cyclic voltammetry (CV) in various potential sweep rates and pHs of the buffer solution. The effect of drop size of MWCNT suspension and the number of cycles in the electro polymerization process has been optimized on the electrode response toward L-dopa. Also the utility of modified electrode in clinical and pharmaceutical procedures is investigated by electrochemical determination of L-dopa in the presence of ascorbic acid. The properties of the modified electrode were investigated by atomic force microscopy (AFM) which is indicative of formation of a homogenous micro porous polymeric film on its surface. The results of CV and DPV investigations were shown a considerable enhancement in the peak current of L-dopa from 30μA to 210μA (up to 7 times) associated with decreasing about 180¬mV in anodic peak potential. Furthermore, high reproducibility and low detection limit (1×10-7 M) of the electrode responses as well as wide linear range can be stated as other significant features of the prepared modified electrode. In the second part of the project, a modified carbon paste electrode is prepared by incorporating thionine supported on multi-walled carbon nanotubes (MWCNTs). The electrochemical response characteristics of the modified electrode toward ascorbic acid, acetaminophen and isoniazid were investigated by cyclic and differential pulse voltammetry (CV and DPV). The results show an efficient electro catalytic role for the electro-oxidation of AA and acetaminophen leading to a remarkable potential peak separation (~300mV) for two compounds. On the other hand, the presence of isoniazid, which is considered as important drug interference, does not affect the voltammetric responses of the mixture solution. The mechanism of the electro catalytic process on the surface of the modified electrode was analyzed by monitoring the CVs at various potential sweep rates and pHs of the buffer solution. A linear dynamic range of 1×10-4 to 1×10-6 M is resulted for AA and isoniazid in buffer solution with pH=4. Also the voltammetric response characteristics for acetaminophen are obtained in the range of 1×10-4 to 1×10-7 M. The prepared modified electrode show several advantages such as simple preparation method, high sensitivity, long-term stability, ease of preparation and regeneration of the electrode surface by simple polishing and excellent reproducibility. Also its effective electro catalytic property revealing a good selectivity for voltammetric response toward AA and acetaminophen, make the prepared modified electrode suitable for simultaneous and sensitive voltammetric detection of these compounds in pharmaceutical and clinical preparations.

  9. Keywords:
  10. Carbon Nanotubes ; Polypyrrole ; Cyclic Voltammetry ; Differential Pulse Voltammetry ; Conductive Polymer ; Carbon Nanotubes ; Electropolymerization

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