Magister Scientiae - MSc / The main thesis hub was on development of two electrochemical biosensors for the determination of 17β-estradiol-estradiol: an estrogenic endocrine disrupting compound. Endocronology have significantly shown that the endocrine disruptors contribute tremendously to health problems encountered by living species today, problems such as breast cancer, reproductive abnormalities, a decline in male population most significant to aquatic vertebrates, reduced fertility and other infinite abnormalities recurring in the reproductive system of mostly male species. The first biosensor developed for the detection of 17β-estradiol-estradiol endocrine disrupting compound; consisted of an electro-active polymeric 3-mercaptoprorionic acid capped zinc selenide quantum dots cross linked to horseradish peroxidase (HRP) enzyme as a bio-recognition element. The second biosensor developed was comprised of cysteamine self assembled to gold electrode, with 3-mercaptopropionic acid capped zinc selenide quantum dots cross linked to cytochrome P450-3A4 (CYP3A4) enzyme in the presence of 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide hydrochloride and succinimide. / South Africa

Magister Scientiae - MSc / Polyaromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that have been shown to be teratogenic, mutagenic and carcinogenic and pose serious threats to the health of aquatic and human life. Several methods have been developed for their determination such as immunoassay, gas chromatography and high performance liquid chromatography (HPLC) in combination with fluorescence or absorbance detection. However, these methods are known to manifest underlying disadvantages such as complicated pretreatment, high costs and time consuming processes. In this work, a simple, less time consuming electrochemical method in the form of an electrochemical sensor has been developed for the detection of PAHs. The sensor was fabricated by the deposition of silver-gold (1:3) alloy nanoparticles (Ag-AuNPs) on ultrathin overoxidized polypyrrole (PPyox) film which formed a PPyox/Ag-AuNPs composite on glassy carbon electrode (PPyox/Ag-AuNPs/GCE). The silver-gold alloy nanoparticles deposited to form the composite were chemically prepared by simultaneous reduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) using sodium citrate and characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the alloy nanoparticles. Transmission electron microscopy showed that the synthesized nanoparticles were in the range of 20-50 nm. The properties of the composite formed upon deposition of the nanoparticles on the PPyox film were investigated by electrochemical methods. The PPyox/Ag-AuNPs/GCE sensor showed strong catalytic activity towards the oxidation of anthracene, phenanthrene and pyrene, and was able to simultaneously detect anthracene and phenanthrene in a binary mixture of the two. The catalytic peak currents obtained from square wave voltammetry increased linearly with anthracene, phenanthrene and pyrene concentrations in the range of 3.0 x 10-6 to 3.56 x 10-4 M,3.3 x 10-5 to 2.83 x 10-4 M, 3.3 x 10-5 to 1.66 x 10-4 M and with detection limits of 0.169 μM, 1.59 μM and 2.70 μM, respectively. The PPyox/Ag-AuNPs/GCE sensor is simple, has antifouling properties and is less time consuming with a response time of 4 s. / South Africa

>Magister Scientiae - MSc / Glucose oxidase (GOx) and horseradish peroxidase (HRP) are important enzymes for the development of amperometric enzyme linked immunosensors. The selectivity of each enzyme towards its analyte deepens its importance in determining the sensitivity of the resultant immunosensor. In designing immunosensors that have customized transducer surfaces, the incorporation with FAD and iron based enzymes ensures that electron kinetics remains optimal for electrochemical measurement. Various different immobilization strategies are used to produce response signals directly proportional to the concentration of analyte with minimal interferences. The combination of self-assembled monolayers and supramolecular chemistry affords stability and simplicity in immunosensor design. In this work, two electrochemical strategies for the detection of human chorionic gonadotropin(hCG) is presented. This involves the modification of a gold surface with a thiolated β-cyclodextrin epichlorohydrin polymer (βCDPSH) to form a supramolecular inclusion complex with ferrocene (Fc)-functionalised carboxymethyl cellulose polymer (CMC). Cyclic voltammetry indicated that ferrocene is in close proximity to the electrode surface due to the supramolecular complex formed with βCDPSH. Furthermore, strategy (a) for the detection of hCG used α-antihCG labelled (HRP) as reporter conjugate. Strategy (b) maintained the CMC bifunctionalised with Fc and recognition antibody for hCG hormone. However, the system was functionalised with a HRP enzyme and detection is done by using GOx reporter conjugates for in situ production of hydrogen peroxide. The reduction of H2O2 was used for the amperometric detection of hCG by applying a potential of 200 mV. The sensitivity and limit of detection of both strategies were calculated from calibration plots. For strategy (a) the LOD was found to be 3.7283 ng/mL corresponding to 33.56 mIU/mL and a sensitivity of 0.0914 nA ng-1 mL-1. The corresponding values for strategy (b) are 700 pg/mL (6.3 mIU/mL) and 0.94 nA ng-1 mL-1.

Magister Scientiae - MSc / The toxicity of microcystin is associated with the inhibition of serine/threonine protein phosphatases 1 and 2A, which can lead to hepatocyte necrosis and haemorrhage. Analysis of microcystin is most commonly carried out using reversed-phase high performance liquid chromatographic methods (HPLC) combined with ultra-violet (UV) detection .The ability of these techniques to identify unknown microcystin in environmental samples is also restricted by the lack of standard reference materials for the toxins. Highly specific recognition molecules such as antibodies and molecularly imprinted polymers (MIPs) have been employed in the pre-concentration of trace levels of microcystin from water and show great potential for the clean-up of complex samples for subsequent analysis. New biosensor technologies are also becoming available, with sufficient sensitivity and specificity to enable rapid ‗on-site‘ screening without the need for sample processing. In this work we constructed a Protein phosphatase biosensor for detection of microcystin-LR in aqueous medium, onto polyamic acid/graphene oxide (PAA: GO) composite electrochemically synthesised in our laboratory. The composites were synthesised at three different ratios i.e. 50:50, 80:20 and 20:80 to evaluate the effect of each component in the search to produce highly conductive mediator platforms. The electrochemistries of the three different composites were evaluated using CV and SWV to study interfacial kinetics of the materials as thin films at the glassy carbon electrode. The phosphatase biosensor parameters were evaluated using CV, SWV, EIS and Uv-vis spectroscopy. The affinity binding of the microcystin-LR to protein phosphatase 2A was investigated using electrochemical impedance spectroscopy which is a highly sensitive method for measuring interfacial kinetics of biosensor systems.

Le domaine de la bioénérgétique traîte de la circulation et de la transformation de l’énergie dans et entre des organismes et leur environnement. Dans ce manuscrit de thèse, la respiration cellulaire et plus particulièrement la première enzyme de la chaîne respiratoire, la NADH:ubiquinone oxidoreductase (Complexe I) ont été étudiées, dans l’objectif de clarifier sa fonction et son implication dans certaines maladies. Dans une première partie, la création d’une sonde impliquant l’enzyme immobilisée de façon biomimétique est décrite. La caractérisation de ce système est effectuée via spectroscopie infrarouge par exaltation de surface (SEIRAS) couplée à de l’électrochimie. Sa réponse à l’ajout de substrats et d’inhibiteurs est ensuite présentée. Dans une seconde partie, l’interaction du Complexe I avec des lipides et des inhibiteurs (Zn2+ et NADH-OH) ainsi que le rôle d’une Tyrosine située au site de fixation du NADH ont été étudiés par spectroscopies IR et UV-Vis différentielles induites par électrochimie. L’exploration des résultats obtenus sous un angle structural a finalement permis de proposer un modèle pour le mécanisme de couplage entre la réduction d’ubiquinone et le pompage de protons par le Complexe I. / The field of bioenergetics deals with the flow and transformation of energy within and between living organisms and their environment. The work presented in this thesis report focuses on cellular respiration and more specifically on the first enzyme of the respiratory chain, NADH:ubiquinone oxidoreductase (Complex I). This was done to clarify details about its function and its implication in disease. First, the creation of a sensor involving the biomimetically immobilized enzyme is presented and probed through a combination of surface enhanced infrared absorption spectroscopy (SEIRAS) and electrochemistry. This sensor is then tested against different substrates and inhibitors. In a second part, the interaction of Complex I with lipids, inhibitors (Zn2+ and NADH-OH) and the role of a Tyrosine residue situated in the NADH binding pocket are investigated through electrochemically induced UV-Vis and FTIR difference spectroscopies. The results gathered through these experiments are then explored under a structural perspective and a coupling mechanism between quinone reduction and proton translocation by Complex I is proposed.

Made available in DSpace on 2014-07-29T16:11:48Z (GMT). No. of bitstreams: 1 Dissertacao Nusia Luisa Barbosa.pdf: 2056559 bytes, checksum: f824e285e4418fd90c2ef8f911077cde (MD5) Previous issue date: 2011-02-28 / Parabens are antimicrobial preservatives widely used in the pharmaceutical, cosmetic and food industries. The alkyl side chain connected to the ester group defines some important physicochemical characteristics of these compounds, including the partitioning coefficient and redox properties. The voltammetry and computational analysis were carried out in order to evaluate the redox behavior of these compounds and other phenolic analogues. Correlations between chemical substituents inductive effects of parabens with potential shifts were observed. Using cyclic voltammetry and glassy carbon working electrode, in aqueous, only one single irreversible anodic peak was observed around 0.8 V for methylparaben (MP), etylparaben (EP), propylparaben (PP), butylparaben (BP), benzylparaben (BzP) and phenolic analogues. The positive inductive effect of alkyl groups was demonstrated by the anodic oxidation potential shift to lower values as the carbon number increases and, therefore the parabens (and other phenolic analogues) oxidation processes to the quinoninic forms showed great dependence of substituent pattern. It was further evaluated the influence of pH and composition of supporting electrolyte in voltammetric profile of parabens. / Os parabenos são conservantes antimicrobianos amplamente utilizados na indústria farmacêutica, cosmética e alimentícia. A cadeia alquílica, ligada ao grupo éster, define algumas características físico-químicas destes compostos, incluindo coeficiente de partição e propriedades redox. A voltametria e a análise computacional foram realizadas a fim de avaliar o comportamento redox desses compostos fenólicos e de outros análogos. Correlações entre as alterações de potenciais e os efeitos indutivos dos substituintes químicos dos parabenos foi observada. Usando voltametria cíclica e eletrodo de trabalho de carbono vítreo, em meio aquoso, apenas um único e irreversível pico anódico foi observado em torno de 0,8 V para metilparabeno (MP), etilparabeno (EP), propilparabeno (PP), butilparabeno (BP), benzilparabeno (BzP) e análogos fenólicos. O efeito indutivo positivo de grupos alquila foi demonstrado pela mudança do potencial de oxidação para valores mais baixos conforme o aumento do número de carbonos e, portanto, o processo de oxidação dos parabenos (e outros análogos fenólicos) às formas quinonínicas mostrou grande dependência do padrão de substituição. Foi também avaliada a influência do pH e da composição do eletrólito suporte no perfil voltamétrico dos parabenos.

Philosophiae Doctor - PhD / Breast cancer is regarded as the most common cancer in South Africa and its rate of occurrence is increasing. About one in every 31 South African women are at the risk of developing breast cancer and early diagnosis and treatment guarantee 90% survival rate. Tamoxifen is the drugs of choice for the treatment of all stages of breast cancer. The drug binds with estrogen receptor (ER) to minimize the transcription of estrogen dependent genes. However, nearly 50% of ER-positive breast cancer patients either become resistant or fail to respond to tamoxifen resulting in a serious clinical challenge in breast cancer management. The Grand Health Challenges of South Africa includes the development of cost effective diagnostic systems suitable for early detection of diseases and drug resistivity for timely invention and better patient management. / 2020-08-31

Cette thèse a pour objectif de proposer une modélisation performante des supercondensateurs à électrodes à base de carbone activé, composants de puissance présents dans un nombre croissant d’applications de stockage d’énergie. La première étape des travaux a consisté à mettre en évidence les phénomènes physico-chimiques, qu’ils soient électrostatiques ou électrochimiques grâce à des essais de caractérisation spécifiques et de vieillissement. L’analyse des résultats associée à la connaissance des matériaux constitutifs a conduit à attribuer le comportement non linéaire du supercondensateur aux phénomènes d’adsorption-désorption (électrosorption) et de diffusion anomale des espèces adsorbées dans le réseau microporeux de l’électrode. La prise en compte de ces phénomènes et de la capacité de double couche a permis de définir un modèle non linéaire fractionnaire dont les paramètres dépendent des grandeurs physico-chimiques de la cellule. La procédure proposée pour l’identification des paramètres du modèle repose sur la réponse en tension du supercondensateur à des profils de charges-décharges. Malgré la simplicité de l’identification, le modèle traduit fidèlement le comportement du supercondensateur soumis à des profils en courant typiques d’applications véhicules électriques et hybrides. / This work aim is an efficient modelling proposal for supercapacitors made of activated carbon electrodes which are power components used in many energy storage applications. In the first part of this study, the purpose is to evidence physico-chemical phenomena, electrostatic or electrochemical as well, thanks to characterization and aging tests. The results analysis combined with materials knowledge leads to suppose that the supercapacitor non linear behavior is due to adsorption-desorption processes and also to anomalous diffusion of adsorbed species into the electrode microporous network. These mechanisms in addition with the double layer capacitor principle allow us to define a non linear fractional model with parameters that depend on physic0-chemical characteristics of the cell. The proposed identification procedure is based on the voltage response to charges-discharge current profiles. In spite of the simplicity of this identification method, the model matches very well the behavior of the supercapacitor under current profiles that are typical of hybrid and electric vehicle applications.

Les travaux présentés dans ce manuscrit décrivent le développement de trois supports innovants basés sur des nanofibres de matériaux hybrides obtenus par électrofilage pour la réalisation de biocapteur électrochimiques. La performance des biocapteurs est fortement améliorée du fait de l'utilisation de matériaux nanostructurés qui leurs confèrent des propriétés uniques. Les fibres obtenues par électrofilage trouvent des applications dans de nombreux domaines, mais leur utilisation pour l'élaboration de biocapteurs, bien que très prometteuse, est encore très peu abordée. Dans ce travail, différentes nanofibres polymériques contenant des nanotubes de carbone ou recouvertes de nanoparticules d'or ou d'un film de copolymère polypyrolle / poly(pyrolle-3-carboxylique acide) ont été utilisées comme support pour le développement de biocapteurs. La glucose oxydase a été utilisée comme enzyme modèle pour valider les performances des biocapteurs réalisés. Cette enzyme a été incorporée directement dans les nanofibres ou fixée de façon covalente à leur surface. Les biocapteurs ainsi obtenus, caractérisés par différentes techniques microscopiques et électrochimiques, ont permis la détection du glucose avec succès, en utilisant la voltammétrie cyclique et la spectroscopie d'impédance électrochimique, tout en montrant des performances (sensibilité, reproductibilité, stabilité) supérieures à celles des biocapteurs conventionnels / The work detailed within this manuscript describes the development of three novel efficient electroactive platforms based on electrospun nanofibrous hybrid materials for further application to electrochemical biosensors elaboration. The performance of biosensors is enhanced by their coupling with nanoscale materials, due to the unique properties that the latter exhibit. Although electroctrospun fibers find applications in various fields, their exploitation for biosensing is still in an early but promising stage. Herein, different polymeric nanofibers incorporating carbon nanotubes, decorated with gold nanoparticles or coated with conducting polypyrrole/poly(pyrrole-3-carboxylic acid) films were used as platforms for the development of biosensors. Glucose oxidase was used as a model enzyme to validate the performance of the developed biosensors. The enzyme was either incorporated into the nanofibers or covalently immobilized onto their surface. These innovative biosensors, characterized by different microscopic and electrochemical techniques, enabled successful detection of glucose by employing cyclic voltammetry and electrochemical impedance spectroscopy, whilst demonstrating enhanced performances over conventional biosensors in terms of sensitivity, reproducibility and stability

<div>The present thesis was completed to satisfy two functions in our laboratory: (1) explore carbon-black (CB) as an additive for electrodeposited intrinsically conductive polymers (ICPs) to improve electrical properties across the electrode-electrolyte interface for use in neuromodulation; and (2) design a histology protocol that will analyze peripheral nerve system (PNS) tissue following implantation of conventional metal and modified conventional metal electrodes with the ICP poly(3,4-ethylenedioxythiophere):poly(styrenesulfonate)/carbon-black (PEDOT:PSS/CB). It would appear that the functions explored may seem unrelated, however, these two topics play a crucial role in designing a viable electrode for use in acute and chronic neuromodulation and the subsequent analysis required to determine the mechanical properties and overall biocompatibility of design.</div><div><br></div><div><div>A series of experiments with different PEDOT:PSS solutions containing varying amounts of suspended CB (n=19; 0 mg/mL to 2 mg/mL) were explored. Solutions were characterized using cyclic voltammetry (CV) using the intended electrode for deposition, composed of stainless steel (SS), as the working electrode (WE) to determine respective redox potentials. SS was chosen because of its inherently bad electrochemical properties, meaning that improved functionality post electrodeposition would be easy to identify. Immediately following CV, stainless-steel electrodes were electrodeposited using one of two techniques: (1) potentiostat, allowing the cell to rest at the redox potential required for bipolaron formation (0.9 V); or (2) galvanostat, where the electrode was submitted to a constant current of 200 mA and allowed to coat. Rapid electrochemical impedance spectroscopy was performed prior to and immediately following coating to determine the pre-electrochemical and post-electrochemical impedance characteristics. Results indicate that there was a positive relationship between the amount of CB additive and the relative impedance drop between the uncoated and coated counterparts. Furthermore, the modified electrochemical interfaces are substantially improved for use in frequency ranges of 10 Hz to 50 kHz, which encompass the ranges of our labs recently discovered low frequency alternating current (LFAC) for use in neuromodulation; thus indicating that PEDOT:PSS/CB modification may be used to improve impedance characteristics during our future LFAC experiments. This protocol, the one that contains the ideal concentration of carbon-black, was then recorded and will be used in our lab.</div></div><div><br></div><div><div>Histology protocols were developed to improve our labs capabilities of post-mortem analysis of PNS tissue. Processing and embedding preparations that explored included paraffin, acrylic, and frozen. Subsequently, staining protocols were developed; however, they varied as a function of the embedding media used; staining protocols developed incorporated progressive and regressive hematoxylin and eosin (H&E) staining as well as toluidine blue (TB). Tissue was sectioned and observed using light microscopy.</div></div>