Philosophiae Doctor - PhD / The human epidermal growth factor receptor (HER)-family of receptor tyrosine kinases; human epidermal growth factor receptor 1, human epidermal growth factor receptor 2, human epidermal growth factor receptor 3 and human epidermal growth factor receptor 4 (EGFR/HER1, ErbB2/HER2, ErbB3/HER3, and ErbB4/HER4) plays a major role in the pathogenesis of many solid tumours, in approximately 25 - 30% of breast cancers. Breast cancer is the second most common type of cancer and affects around 3000 women annually in South Africa alone. While the benefits of treatment and cancer progress to enhance therapeutic effectiveness for the patient are well documented, it is also important to employ or fabricate methods in which cancer can be screened at an early stage. A number of gene and protein based biomarkers have shown potential in the early screening of cancer. One specific biomarker that is over-expressed in 20 - 30% of human breast cancers is the human epidermal growth factor receptor 2 (Her2/neu). Several methods have been developed for detection of Her2/neu oncogene including immunohistochemistry (IHC), enzyme-linked immunosorbent assay (ELISA), fluorescent in situ hybridisation (FISH) and polymerase chain reaction(PCR). However, these methods are subjected to interference problem. For these reasons an ultrasensitive, cheap and easy to use genosensor has been developed for early detection of the Her2/neu oncogene using electrochemical and spectroscopic methods. Due to their high surface-to-volume ratio, electro-catalytic activity as well as good biocompatibility and novel electron transport properties quantum dots are highly attractive materials for ultra-sensitive detection of biological macromolecules via bio-electronic or bio-optic devices. In this study a quantum dots (QDs)-based genosensor was developed in which Ga2Te3-based quantum dots were synthesised using a novel aqueous solution approach by mixing 3-mercaptopropionic acid (3MPA)-capped gallium metal precursor with reduced tellurium metal. The morphological, compositional and structural characterisation of the QDs was investigated prior to their utilization in DNA sensor construction.

The aim of this thesis was to investigate the physical and electrochemical properties of sub monolayer and monolayer of copper deposition on the polycrystalline iridium, ruthenium and its conductive oxide. The electrochemical methods cyclic voltammetry (CV) and chronocoulometry were used to study the under potential deposition. The electrochemical methods to oxidize the ruthenium metal are presented, and the electrochemical properties of the oxide ruthenium are studied. The full range of CV is presented in this thesis, and the distances between the stripping bulk peak and stripping UPD peak in various concentration of CuSO4 on iridium, ruthenium and its conductive oxide are shown, which yields thermodynamic data on relative difference of bonding strength between Cu-Ru/Ir atoms and Cu-Cu atoms. The monolayer of UPD on ruthenium is about 0.5mL, and on oxidized ruthenium is around 0.9mL to 1.0mL. The conductive oxide ruthenium presents the similar properties of ruthenium metal. The pH effect of stripping bulk peak and stripping UPD peak of copper deposition on ruthenium and oxide ruthenium was investigated. The stripping UPD peak and stripping bulk peak disappeared after the pH ≥ 3 on oxidized ruthenium electrode, and a new peak appeared, which means the condition of pH is very important. The results show that the Cl- , SO42- , Br- will affect the position of stripping bulk peak and stripping UPD peak: the stripping bulk peak will shift and decrease if the concentration of halide ions is increasing, and the monolayer of UPD will increase at the same time.

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Philosophiae Doctor - PhD / A highly dispersive gold nanoparticle-dotted 4-nitrophenylazo functionalised graphene nanocomposite (AuNp/G/PhNO2) was successfully synthesised and applied in enhancing sensing platform signals. Three label-free electrochemical immunosensors for the detection of deoxynivalenol mycotoxin (DON) based on the systematic modification of glassy carbon electrodes (GCE) with AuNp/G/PhNO2 was effectively achieved. General electrochemical impedance method was employed for the sensitive and selective detection of DON in standard solutions and reference material samples. A significant increase in charge transfer resistance (Rct) of the sensing interface was observed due to the formation of insulating immune-complexes by the binding of deoxynivalenol antibody (DONab) and deoxynivalenol antigen (DONag). Further attachments of DONab and DONag resulted in increases in the obtained Rct values, and the increases were linearly proportional to the concentration of DONag. The three immunosensors denoted as GCE/PDMA/AuNp/G/PhNH2/DONab, GCE/Nafion/[Ru(bpy)3]2+/AuNp/G/PhNH2/DONab and GCE/Nafion/[Ru(bpy)3]2+/G/PhNH2/DONab have detection range of 6 – 30 ng/mL for DONag in standard samples. Their sensitivity and detection limits were 43.45 ΩL/ng and 1.1 pg/L; 32.14ΩL/ng and 0.3 pg/L; 9.412 ΩL/ng and 1.1 pg/L respectively. This result was better than those reported in the literature and compares reasonably with Enzyme Linked Immunosorbent Assay (ELISA) results. The present sensing methodology represents an attractive alternative to the existing methods for the detection of deoxynivalenol mycotoxin and other big biomolecules of interest due to its simplicity, stability, sensitivity, reproducibility, selectivity, and inexpensive instrumentation. And they could be used to develop high-performance, ultra-sensitive electrochemiluminescence, voltammetric or amperometric sensors as well.

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