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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 45382 (48)
- University: Sharif University of Technology
- Department: Nanoscience and Nanotechnology
- Advisor(s): Ghorbani, Mohammad; Dolati, Abolghasem; Vosoughi, Manouchehr
- Abstract:
- Detection and determination of ultra-trace electroactive materials using electrochemical methods have been widely employed by researchers since they offer a fast, easy and reliable approach. In this way, developing of new nanoelectrodes with special and unique properties plays a profound role on the achievement of better results.
Gold nanoelectrode ensembles are one of the most important nanoelectrodes which due to the high surface area, chemical, electrochemical and physical stability, and integration of a large number of individual nanoelectrodes, introduce excellent opportunities to be employed as promising nanoelectrodes in determinations applications.
In this work, preparation and application of gold nanoarrays have been elucidated in detail which could be divided in three major parts.
In the first part, gold nanowires and gold nanotubes were fabricated inside the membranes through electrochemical method. Two types of templates were used: polycarbonate (PC) template which is a polymeric membrane and anodic aluminum oxide template (AAO) which is ceramic membrane. Templates were gold-sputtered before the electrodeposition experiments to be electron conductive and served as working electrodes. Nickel was first electrodeposited inside the pores to facilitate the gold electrodeposition. A step potential was employed for the electrodeposition of gold and chronoamperometric curves were recorded in each experiment. Gold nanowires and nanotubes were fabricated using different conditions. At high concentrations of the solution (more than 20mM) the gold nanowires were obtained as the dominant structure. For preparing the gold nanotubes, the pore walls were modified by a molecular anchor for preferential adsorption of gold onto the pore wall. Nickel was again fabricated inside the pores before electrodeposition of gold but with a very short length. Concentrations lower than 10mM and slow kinetic (low overpotentials) were necessary for electrodeposition of gold nanotubes. Yet, in high overpotentials (-1.4V vs Calomel) the structure could be again nanotubes using hydrogen evolution. Gold nanotubes with different length up to the membrane thickness were prepared (which was about 6µm).
In the second part, a nanoelectrode was developed using the nanoarrays and employing carbon paste electrode as substrate. A heat treatment process was applied for sealing the template around nanotubes for obtaining better results. The template with embedded nanotubes was heated at 150C for 15min. Three dimensional gold nanotubes were developed by employing the CH2Cl2 and ethanol as etching solvent which introduced a high surface area and a strong response toward the Fe2+/Fe3+ redox couple.
In the third part, application of the nanoelectrode has been described in determination of metronidazole as a clinical application. A new reaction was also observed for electro-oxidation of metronidazole. Square wave voltammetry technique demonstrated excellent response toward metronidazole and was selected for its analytical determination.
The strongest response was observed at pH=7. The nanoelectrodes showed a wide range of detection with linear relations to the metronidazole concentration over two different ranges from 1nM to 150nM and from 150nM to 2µM. A quite strong detection limit (0.1nM) was obtained which has not been previously reported.
Moreover, determination of mercury(II) in water was described as another application of gold nanotubes which showed a linear relation between peak current and concentration in the range of 0-10ppb with a detection limit of 0.1ppb which is the lowest value ever reported for determination of mercury(II).
- Keywords:
- Metronidasole ; Mercury ; Electrodeposition ; Gold Nanotubes ; Sensing
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