Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 95-101).

Thesis (M.S.)--Rochester Institute of Technology, 1987. / Typescript. Includes bibliographical references (leaves 107-108).

Thesis (M. Phil.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 142-148).

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xi, 150 p. : ill. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Florida, 1984. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 236-269).

Nanomaterials, in particular carbon nanotubes have been shown to exhibit favourable properties for the enhancement of electrochemical detection of target analytes in complex matrices. There is however scope for improvement in terms of the optimization thereof in electrochemical sensors surface modification. The aim of this thesis was to examine methods that would result in increased current response, lowered passivation and application of such modified surfaces with application to pharmaceutically and industrially relevant analytes. Current methods for enhancing the performance of carbon nanotubes include acid functionalization which not only increases the hydrophilicity of the nanotubes, and consequently their ability to provide stable (aqueous) suspensions, but also introduces electrochemically active sites. This particular approach is however not normalized in the literature. Over-exposure to acid treatment results in loss of structural integrity of the carbon nanotubes, and as such a fine balance exists between achieving these dual outcomes. Guided by high resolution scanning electron microscopy, atomic force microscopy, voltammetric and impedance studies, this thesis examined the role of the length of time of the acid functionalization process as well as the impact of activation of carbon nanotubes and fullerenes on electrochemical sensor performance. Based on desired charge transfer resistances, rate transfer coefficients and sensitivity towards redox probes the optimal length of acid functionalization for multiwalled carbon nanotubes was 9 hours and 4 hours for single-walled carbon nanotubes. Further improvements in the desired outcomes were achieved through electrochemical activation of the modified electrode surface by cycling in the presence of catechol, in a novel approach. By employing electrochemical impedance spectroscopy it was observed that catechol activation resulted in lowered charge transfer resistance, before and after activation, with functionalized multi-walled carbon nanotubes (9 hours) exhibiting the greatest decrease of 90 % and functionalized single-walled carbon nanotubes (4 hours), a 50 % decrease. Corresponding increases in the heterologous rate transfer coefficient showed a 770 % increase for functionalized multi-walled carbon nanotubes (9 hours), following catechol activation. Comparative observations for fullerenes following partial reduction in potassium hydroxide yielded a 30 % decrease in charge transfer resistance, with an increased heterologous rate transfer coefficient at a fullerene modified surface The performance of the nanomaterial modified electrodes was applied to the detection of wortmannin with applications in bioprocess control and in the pharmaceutical sector as well as to the detection and monitoring of the industrial dye Reactive red. Of particular relevance to these analytes was the assessment of the nanomaterial modified electrodes for enhanced stability, reproducibility, sensitivity and decreased passivation effects. In this study the first known account of wortmannin detection through electrochemical methods is reported. Voltammetric characterization of wortmannin revealed an irreversible cathodic process with a total number of 4 electrons and a diffusion coefficient of 1.19 x 10-7 cm².s⁻¹. At a functionalized multiwalled carbon nanotubes modified glassy carbon electrode a limit of detection of 0.128 nmol.cm⁻³ was obtained, and with limited surface passivation the detection scheme afforded pertinent analyses in biological media representing a substantial improvement over chromatographic detection methods. This study also provided the first account of the voltammetric detection of reactive red, competing favourably with traditional spectroscopic methods for monitoring biodegradation of this compound in real time.

Oxytetracycline (OTC) is a broad spectrum antibiotic used extensively in the agricultural and human-health sector, and is effective against various gram positive and –negative bacteria as well as large viruses and certain pathogenic Rickettsiae. This study addresses the lack of voltammetric knowledge regarding the electroanalytical characterisation of OTC and its analysis in complex matrices. Cyclic voltammetry (CV) revealed several irreversible anodic peaks for OTC at a bare glassy carbon electrode (GCE). These current responses were improved through the selection of a diluent for OTC stock preparation, electrolyte solution and electrolyte pH, stir time and applied preconditioning potential. Under enhanced adsorptive conditions and using square wave voltammetry (SWV), a detection limit of 24.3 nM was achieved. The electrode surface could be renewed in vitro for 10 successive scans. OTC oxidation was characterised as a one electron:one proton ECiE mechanisms. Next, investigating the viability of voltammetry in various complex microbiological growth media revealed that selected growth media contained interfering redox active components, which, while simultaneously coating the electrode surface, effectively reduced GCE performance and lowered the active electrode surface area, as ascertained through CV and electrochemical impedance spectroscopy (EIS) studies. This interference lowered OTC current response in the presence of growth media which was partially recovered by appropriate growth media selection and sample dilution. In testing the use of acid functionalised multi-walled carbon nanotubes (MWCNTs) to improve anodic OTC response, charge-based attraction was observed between the MWCNT dispersal agent Nafion® and OTC, while increased surface area associated with prolonged acid functionalisation time aided in improving OTC current response.

Voltammetric methods for the determination amphenicol antibiotic chloramphenicol (CAP) and quinolone antibiotic Ofloxacin (OFL) were developed. TTechniques differential pulse voltammetry (DPV) and DC voltammetry (DCV) for determination of both substances at boron doped diamond film electrode (BDDFE) were used. The effect of pH of Britton-Robinson buffer was tested and the stability of the signal with repeated measurements was monitored. Optimal pH 6 was used for determining of CAP by both, DPV and DCV techniques. Media of pH 4 for determining of OFL by DPV and DCV was optimal. Under these conditions linear dependences in the calibration concentration region 1.10 -6 - 1.10-4 mol.l -1 were obtained. The limit of determination for the method for CAP by DPV at 3.10 mol.l , by -6 -1 DCV at 3.10 mol.l and for -6 -1 OFL by DPV at 1.10 mol.l -6 -1 and by DCV at 4.10 mol.l -7 -1 was found. The developed methods were used for the determination of CAP in the drug samples Spersadex comp. and OFL determination in drug samples Zanocin 200. Method for solid phase extraction of OFL from samples of urine with voltammetric detection was developed with limit of determination at 7.10 mol.l . -6 -1

L-glutamate (Glu) is the major excitatory neurotransmitter in the mammalian central nervous system. Monitoring extracellular Glu is critical to understanding Glu regulation to discriminate physiological and pathological roles. To overcome the limitations of previous in vivo extracellular Glu studies, we developed Glu selective microelectrode arrays with better spatial and temporal resolutions than commonly used techniques like microdialysis. We used these microelectrode arrays to characterize basal and potassium-evoked Glu neurotransmission in the normal rat brain. We then investigated disease-related Glu alterations in a rat model of Parkinson's disease and normal Glu regulation in young and aged rhesus monkeys. In the normal anesthetized rat striatum and frontal cortex, basal Glu was regulated by active release and uptake mechanisms, fully TTX-dependent, and measured at ~2 micromolar levels. Potassium-evoked Glu kinetics were fast, concentration-dependent, and rapidly reproducible at 15-20 seconds intervals. In the unilateral 6-hydroxydopamine-lesioned rat, there were significant bilateral increases in potassium-evoked Glu release in the striatum and frontal cortex compared to hemisphere-matched non-lesioned rats. Ipsilateral striatal effects may have been related to DA loss, while contralateral striatal effects and the bilateral frontal corticaleffects may have resulted from parkinsonian neurotransmitter changes or bilateral neuranatomical connectivity, especially in the cortex. There were also alterations in Glu kinetics in the nucleus accumbens in both non-lesioned and lesioned rats. With appropriate technological and methodological modifications, we successfully recorded normal Glu signaling in anesthetized nonhuman primates in the operating room. Fast potassium-evoked Glu signals were recorded in the motor cortex of all monkeys, and Glu ejections showed robust Glu uptake in the motor and frontal cortices of all monkeys. These findings are comparable to initial rat studies. Slow evoked Glu kinetics and high basal Glu levels with oscillatory behavior were recorded in the frontal cortex. The primary age-related differences between monkeys were the nearly ten-fold increases in the volumes of Glu ejected needed in the aged monkey to achieve amplitude-matched signals in the motor and frontal cortices and a decreased uptake rate in the motor cortex. Preliminary work with excised human tissue and future plans for patient-oriented research and clinical applications are discussed.

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