Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2015. / Immunosensors are analytical devices comprising antibody (Ab) molecules intimately integrated with electronic physicochemical transducers. Abs are responsible for specific recognition of an analyte so called antigen (Ag) while transducers are responsible for the conversion of chemical changes brought about by Ab-Ag interactions into measurable and processable signal. Amongst the many analytical tools, immunosensors have shown outstanding performance in applications in fields such as clinical diagnostics, agricultural purposes and environmental monitoring. They have come in place of the many conventional analytical methods which showed a number of disadvantages; high cost and longer time of operation, and requirement of highly knowledgeable personnel. On the other hand, immunosensors have shown potential to overcome these constraints. Their advantages include possibilities of portability, miniaturization, and simplified procedures. Of the possible fields of immunosensor applications, this study focussed on the environmental aspect. The safety of the environment is good for the well-being even though there are still some environmental threats that exist. Polychlorinated biphenyls (PCBs) have reportedly been found to be some of the potential substances to pose such threats due to their toxic and persistent behaviour. In this study, we have developed an electrochemical immunosensor as an analytical tool for the analysis and monitoring of PCBs. The development was based on the use of silver nanoparticles-doped polyaniline (PANI/Ag NPs) for modification of an electrode as a process for fabrication of the transducer. The PANI/Ag NPs composite was deposited on the glassy carbon (GC) and platinum (Pt) electrodes by oxidative electropolymerization of aniline in the presence of Ag NPs in 1 M HCl using cyclic voltammetry (CV) by ramping the potential from -0.1 to 1.4 V at 50 mV/s. The composite was then characterized and evaluated as a potential material for electrochemical transduction. Evaluation was on electroactivity, which is the main property of interest for materials used in the fabrication of electrochemical devices. The PANI composites were characterized using spectroscopic (FTIR), microscopic (TEM) and electrochemical CV techniques. Results confirmed the formation of PANI in its emeraldine form and the presence of Ag NPs. Characteristic functional groups and peaks of PANI were observed in FTIR and CV respectively. TEM micrograms showed one dimensional nanofibric tubes and crystalline-like structure of the composite. The incorporation of Ag NPs was indicated by the transition from the amorphous (PANI) to crystalline (PANI/Ag NPs) structure accompanied by increase in size as well as smoothness of the tubes. EDS-TEM counts increase of the chlorine (Cl) peaks is due to the closeness of these peaks to those of Ag, thus confirming incorporation of Ag NPs.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and, (B.S.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1976. / Microfiche copy available in Archives and Engineering. / Bibliography: leaves 65-66. / B.S.

Thesis (M. Phil.)--University of Hong Kong, 1987.

Thesis (M. Phil.)--University of Hong Kong, 1984.

Thesis (M. Sc.)--York University, 1999. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 210-217). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ56188.

This dissertation explores the use of nanocarbons both as conductive supports for redox enzyme electrochemistry and as electrocatalytic components for the nonmediated detection of biogenic analytes. More specifically, the influence of nitrogen doping of these nanocarbons (referred to herein as nitrogen-doped carbon nanotubes, or N-CNTs) on their bioelectrocatalytic performance is studied through direct enzyme adsorption and exploitation of the N-CNTs' inherent reactivity toward H₂O₂ to create H₂O₂-based sensing strategies. Both nondoped CNTs and N-CNTs may be effectively incorporated into biogenic sensing assemblies, as demonstrated herein using a variety of electrochemical techniques. Chapter 1 gives a general overview of the scope of this research and describes previous studies conducted within our laboratories that demonstrate our CNTs' promise as biogenic electrode materials. Chapter 2 describes the chemical vapor deposition (CVD) method used to prepare both CNTs and N-CNTs and establishes their suitability for use in the detection schemes outlined in later chapters through long-term stability studies. Additionally, the redox activity of Fe nanoparticles entrapped in the CNTs as a result of this CVD growth process is examined using a host of electrochemical experiments. Importantly, the data presented in this chapter show that these Fe particles do not explain the observed electrocatalytic response of the CNTs. Chapter 3 explores the direct adsorption of horseradish peroxidase (HRP) at both nondoped and N-CNTs. Spectroscopic and electrochemical assays are used to compare the extent of HRP enzymatic activity upon immobilization at both types of CNTs. Both types of HRP/CNT composites are then utilized in a quantitative H₂O₂ sensing strategy. Chapter 4 discusses the intrinsic reactivity of N-CNTs toward H₂O₂. Koutecky-Levich plots are used to demonstrate differences in H₂O₂ consumption mechanisms between NCNTs and traditional peroxidases. By replacing HRP with N-CNTs in an amperometric glucose detection scheme, the versatility of N-CNTs as a peroxidase substitute for biogenic analyte detection is demonstrated. Chapter 5 outlines future directions for this research, including possible strategies for improving electron transfer between HRP and both types of CNTs. This chapter also presents a newly developed, mediated oxidase-substrate electrochemical detection method that can easily be modified to incorporate CNTs.

published_or_final_version / Chemistry / Master / Master of Philosophy

This study has two aspects. One concerns the development of a sensitive differential pulse polarographic (DPP) method and its use to conduct a preliminary study of natural waters to detect the presence of nitrosoamines, and the second, where the study was carried out in greater detail, is the investigation of the kinetics of reduction of N-nitrosodimethylamine (NDMA) in aqueous solution. An optimization study was first conducted to identify the conditions that give the greatest sensitivity. Conditions investigated were different supporting electrolytes and solvent mixtures. Supporting electrolytes used were 0.10 M solutions of acids, bases and salts, and the solvent mixtures studied were ethanol/water mixtures. The effect of various supporting electrolytes and various ethanol/water mixtures on peak current was studied in order to select the conditions that give the greatest sensitivity for the determination of nitrosoamine concentrations. The lowest nitrosoamine concentration that can be detected in a solution (limit of detection) was determined. The optimum supporting electrolytes for N-nitrosoamines and the C-nitrosoamine were respectively found to be 0.10 M H2S04 and 0.10 M NaOH. Aqueous solutions were also found to give greater sensitivity than ethanol/water mixtures. The presence of nitrosoamines in some natural water samples was then checked using differential pulse polarography (DPP).Concentrations of nitrosoamines in these water samples were determined using the optimum conditions. The analyte analytes studied were 4-nitroso-N,N-dimethylaniline (4NDMA); Nnitrosodibutylamine (NDBA),N-nitrosodi-n-propylamine (NDPA) and N-nitrosodiphenylamine (NDPhA). All four nitrosoamines were detected in some of the selected natural water samples . The kinetics of the electrochemical reduction of NDMA was studied using controlled potential coulometry, linear scan voltammetry (LSV) and cyclic voltammetry (CV). Controlled potential coulometry was first used to determine the number of electrons transferred (n) in the reduction reaction. Two moles of electrons were found to be required for the reduction of one mole of NDMA solution, at a stationary mercury drop electrode (SMDE). The major product obtained, identified by UVNIS spectroscopy, was dimethylamine (DMA). / Ph.D. (Chemistry) North-West University, Mafikeng Campus, 2005

The objective of this research was to design and evaluate an instrumental method for electroanalysis in highly resistive media. A coulostatic detector for high performance liquid chromatography was designed and constructed. Equations were developed to describe the detector's performance under regenerative and nonregenerative experimental conditions. With mobile phases of high resistance, the detector was found to respond to both electroactive and ionic electroinactive species with the magnitude of the observed signal depending on the recent history of the electrode. Thus, the elimination of iR drop by the coulostatic method does not provide a straightforward method for electroanalysis in highly resistive media. At low electrolyte concentrations, double-layer effects become prominent. A method was devised to quantitate the static double-layer effect at solid electrodes.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.