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 / HIV and AIDS are among the world's pandemics that pose serious concern to almost every individual in the world. With the current level of availability of anti-retroviral (ARV) drugs and the ease of accessibility of treatment in many countries such as South Africa, the disease can be controlled by suppressing the viral load of an infected individual. These anti HIV drugs such as delavirdine are metabolised by enzymes which are found in the liver microsomes, particularly those of the cytochrome P450 family. Due to the fact that the metabolic rate of a patient determines the effect of the drug, the drug could either have a beneficial or an adverse effect once it is administered. It is therefore imperative that the metabolic profile of a patient is determined at point-of-care is necessary for proper dosing of the ARV drugs. In this project a nanobiosensor system was devised and used for the determination of the metabolism of delavirdine, a non-nucleoside reverse transcriptase inhibitor (NNRTI) ARV drug. The nanobiosensor was prepared by the entrapment of the isoenzyme CYP3A4 into a pre-formed electro active carrier matrice consisting of a dendrimeric copper generation-2 poly (propylene imine)-co-polypyrrole star copolymer (Cu(G2PPI)-co-PPy). The metallo-dendrimer was used as a host for the enzyme and provided thenecessary bio-compatible environment that allowed the direct transfer of electrons between the enzyme's active centres and platinum electrode surface. Copper was the choice of metal used in the study due to its properties. Copper is a malleable, ductile and a good conductor of both heat and electricity. It is a better conductor than most metals. Silver which also belongs to group 1b in the periodic table is a better electrical conductor than copper but copper has better corrosion resistance and is a more abundant and hence it is a cheaper material to use. Cu(G2PPI)-co-PPy was prepared by the incorporation of the copper metal into the G2PPI and the electropolymerization of pyrrole onto the Cu(G2PPI). The incorporation of Cu into G2PPI was determined by FTIR which did not show the presence of the Cu but showed an increase in the intensities of the peaks after the incorporation. The surface morphology of Cu (G2PPI) was confirmed by the use of HRSEM which showed a difference in the surface morphology of the dendrimer moiety with the addition of the copper metal. The HRSEM images after Cu incorporation resulted in the change from rough surface to smooth surface with open cavities which were essential for the entrapment of the biological systems (CYP3A4). Energy dispersive spectrometry (EDS) and HRTEM were used to confirm the presence of spherically shaped copper nanoparticles in the Cu (G2PPI) and were found to have a size distribution of 12-17 nm with an average particle size of 15nm. The star copolymer (Cu(G2PPI)-co-PPy) was characterised using cyclic voltammetrywhere it was confirmed that the material was electroactive and conducting due to electron movement along the polymer chain. A diffusion co-efficient (D₀) value of 8.64 x 10⁻⁵ cm²/s was determined for the material indicating a slow electron transfer kinetics within the diffusion layer. The constructed nanobiosensor was developed using copper poly (propylene imine) – polypyrrole star copolymer, bovine serum albumin and glutaraldehyde coupled to the enzyme CYP3A4. The resultant nanobiosensor parameters include a dynamic linear range (DLR) of 0.01-0.06 nM, a limit of detection (LOD) of 0.025 nM and a sensitivity value of0.379 μA/nM.

L'énergie électrique (de préférence d’origine renouvelable) peut être stockée dans des liaisons chimiques grâce à un électrolyseur approprié. Les réactions typiques comprennent la production d'hydrogène, la production d'hydrocarbures et la synthèse d'ammoniac. Ces électrocarburants permettent de faciliter l'intégration de sources d'énergie renouvelables dans le mix de production électrique. Ils sont compatibles avec l'infrastructure industrielle actuelle et la chaîne d'approvisionnement et peuvent être stockés facilement. En outre, ce procédé est à la fois un moyen de stocker l'électricité dans des liaisons chimiques (vecteurs énergétiques) et une technique de synthèse de composés chimiques à partir de matières premières comme le CO2 plutôt que de ressources fossiles.La thèse s’intéresse au développement de nouveaux catalyseurs moléculaires pour la conversion sélective du CO2 en CO en utilisant uniquement des matériaux abondants sur Terre, comme les porphyrines de Fer. Tout d'abord, les tentatives pour obtenir de nouveaux catalyseurs avec divers substituants sont détaillées. Une fois qu'un catalyseur hydrosoluble actif est identifié, une évaluation des performances est réalisée en utilisant des techniques électrochimiques telles que la voltammétrie cyclique / Electrical energy (preferably issued from renewable sources) can be stored in chemical bonds thanks to an appropriate electrolyzer. Typical reactions include hydrogen generation, the production of hydrocarbons and oxygenates, and ammonia synthesis. Such electrofuels supplement the integration of renewable energy sources in the electrical production mix; they are compatible with the current industrial infrastructure and supply chain, while they can be stored easily. Besides, they may be used either as a means to store the electricity in the chemical bonds of high-energy-content molecules or as various feedstocks to manufacture high value compounds.The thesis focused on the development of new molecular catalysts for the selective CO2-to-CO conversion in water using only earth-abundant materials, namely iron-based porphyrin derivatives. First, successful and unsuccessful attempts to derive new catalysts with various substituents are reviewed. Once an active water-soluble catalyst is identified, a performance assessment is completed using electrochemical techniques such as cyclic voltammetry investigations.Then, the immobilization of said catalysts onto the electrode surface is discussed. Once a robust integration in the catalytic film is secured, the coupling with a heterogeneous water-oxidation catalyst can be considered. The subsequent assembly of a whole electrolysis cell is reported, where a cobalt-based film was picked for the anode. Finally, economic perspectives provide a clear, rational basis for future optimization of the device

No description available.

Dopamine and serotonin are two neurotransmitters known to both play a very important role in the human brain. For example, the death of dopamine producing neurons in a region of the brain known as the substantia nigra are known to cause the motor symptoms of Parkinson's disease. Also, many antidepressants are believed to work by increasing the extracellular level of serotonin in the brain. For the first time, it is now possible to measure the release of these two chemicals at sub-second time resolution in a human brain using a technique known as fast-scan cyclic voltammetry, for example from patients undergoing deep brain stimulation (DBS) electrode implantation surgery. In this work, we aimed to assess the feasibility of obtaining veridical dual measurements of serotonin and dopamine from substrates with mixtures of both chemicals. In the wet lab, data was collected on known concentrations of dopamine and serotonin and then used to make models capable of estimating the concentration of both chemicals from the voltammograms recorded in the patients. A method of linear regression known as the elastic net was used to make models from the wet lab data. The wetlab data was used to compare the performance of univariate and multivariate type models over various concentration ranges from 0-8000nM of dopamine and serotonin. Cross validation revealed that the multivariate model outperformed the univariate model both in terms of the linear correlation between predictions and actual values, and pH induced noise. The pH induced noise for the univariate model was 3.4 times greater for dopamine and 4.1 times greater for serotonin than the multivariate model. Raman spectroscopy was also investigated as a possible alternative to fast-scan cyclic voltammetry. Raman spectroscopy could have several benefits over fast-scan cyclic voltammetry, including the ability to chronically implant the measurement probe into a patient's brain and make observations over a long period of time. Raman spectroscopy data was collected on known concentrations of dopamine to investigate its potential in making in vivo measurements, however this data collection failed. Therefore, simulations were made which revealed the potential of the elastic net algorithm to determine the Raman spectra of several neurotransmitters simultaneously, even when they are in mixtures and the spectra are obstructed by the noisy background. The multivariate type model outperformed the univariate type model on Raman spectroscopy data and was able to predict dopamine with an error of 805nM RMS and serotonin with an error of 475nM RMS after being trained on concentrations smaller than 5uM of both dopamine and serotonin. In addition, the original Raman spectra of both neurotransmitters was extracted from the noise and reproduced very accurately by this method. / Master of Science

Three non-peripherally substituted liquid crystalline bisphthalocyanine (Pc) compounds have been studied to examine the role of central metal ions lutetium (Lu), and gadolinium (Gd) and substituent chain lengths, i.e. octyl (C8H17) and hexyl (C6H13), in determining the physical properties. For the octyl substituted Pc molecules, the head-to-tail or Jaggregates within the as-deposited spun films produced a redshift of the optical absorption Q bands in relation to their 0.01 mgml-1 solutions. Annealing at 80˚C produced a well-ordered discotic liquid crystalline (LC) mesophase causing additional redshifts irrespective of the metal ion in case of C8LuPc2 and C8GdPc2. Formation of face-to-face or H-aggregated monomers led to blueshifts of the Q bands with respect to solution spectra for C6GdPc2, both as-deposited and annealed films. Stretching and bending vibrations of pyrrole, isoindole, and metal-nitrogen bonds in Pc rings showed Raman bands at higher energy for smaller metal ion. However, no change was observed for the difference in chain lengths. As-deposited C8LuPc2 and C6GdPc2 produced comparable Ohmic conductivity, of the value 67.55 Scm-1 and 42.31 Scm-1, respectively. C8GdPc2 exhibited two orders of magnitude less conductivity than the other two due to the size effect of the central ion and side chain length. On annealing, an increase of Ohmic conductivity was noticed in the isostructural octyl substituted phthalocyanines on contrary to a reduced conductivity in hexyl substituted one. An optical band shift of the C8LuPc2 and C8GdPc2 thin films occurred on oxidation by bromine vapour. Oxidations of Pc-coated ITO were also achieved by applying potential at 0.88 V and 0.96 V electrochemically for the C8LuPc2 and C8GdPc2 compounds, respectively. To explore the applications of these compounds in biosensing, in situ interaction studies between bromine oxidised compounds and biological cofactors nicotinamide adenine dinucleotide (NADH) and L-ascorbic acid (vitamin C) were carried out using optical absorption spectroscopy. Thin films of a non-peripherally octyl substituted LC lead phthalocyanine was exposed to 99.9 % pure hydrogen sulfide gas to produce hybrid nanocomposites consisting of lead sulphide quantum dots embedded in the analogous metal free phthalocyanine matrix. Trapping of charge carriers caused hysteresis in the current-voltage characteristics of the film on interdigitated gold electrodes. The charge hopping distance was found to be 9.05 nm, more than the percolation limit and responsible for forming two well-defined conducting states with potential application as a memristor.

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.

The aim of the thesis was to study the possibility of employment of cyclic voltammetry as a detection technique in liquid chromatography. The phenothiazine derivatives (chlorpromazine hydrochloride, diethazine hydrochloride, and thioridazine hydrochloride) were used as model compounds. Firstly, the comparison of two potential detectors (tubular detector and bulk "wall-jet" detector) was accomplished. Only bulk "wal-jet" detector satisfied. Next, the conditions for the separation and detection of studied phenothiazines on RP-select B LiChrospher® 60 (250×4 mm) column with cyclic voltammetry as the detection techniques were optimized. The best separation is achieved in mobile phase consisted from the solution of 0.1 mol dm-3 sodium perchlorate in acetonitrile-water (80:20) mixture. The effect of flow rate of mobile phase and scan rate of polarization of the electrode on the symmetry of chromatographic peak was also followed, and optimal values of 0.5 ml min-1 for flow rate, and of 0.5 V s-1 for scan rate, were found. Under optimized conditions the calibration dependences of studied phenothiazines were measured in the range from 5×10-5 to 1×10-3 mol dm-3 for chlorpromazine, and in the range from 8×10-5 to 1×10-3 mol dm-3 for diethazine and thioridazine. The developed method was applied to...

The current option for the management of Intermediate-Level Waste (ILW) and High-Level Waste (HLW) in the UK is to store it in stainless steel containers and then placed in a deep underground Geological Disposal Facility (GDF). This may subsequently be backfilled with a cementitious material generating very high pH conditions. The eventual corrosion of the stainless steel canisters containing the waste used for disposal will lead to reducing conditions thereby promoting a low Eh environment. Electrochemical experiments are needed to determine which uranium species is/are present at a particular pH and to model the redox behaviour of aqueous uranium in a potential GDF. The main aim of this project is to use cyclic voltammetry to deduce peak potentials for the various uranium redox couples in aqueous solution across the pH range and in particular the hyperalkaline range, as the surroundings of a GDF will be in high pH conditions. Data in the literature have been obtained only under acidic conditions where they were subsequently extrapolated to obtain data for alkaline conditions in some reports. Is this valid however? Experiments are therefore needed to obtain fundamental data under alkaline conditions to fill in gaps in the literature. In addition to radionuclides, complexing organic ligands present in a cementitious repository could have an important effect on the immobilisation of radionuclides in concrete. This is due to the ability of the ligands to form complexes with cations, thereby enhancing their solubility and mobility in the cement pore water. Four different ligands were investigated in this project that are relevant to nuclear waste disposal which comprised of carbonate, ethylenediaminetetraacetic acid (EDTA), gluconic acid and α-isosaccharinic acid (α-ISA). The peak potentials of each uranium redox reaction in aqueous solution were measured and the potentials were compared in ligand and non-ligand systems. The voltammograms were compared to obtain their similarities and differences in terms of the shape of the cyclic voltammograms, peak potentials, reversibility, current responses and etc. Analysis of the similarities and differences was needed to be able to increase the understanding of the complexation effects of these ligands with uranium under different pH conditions in aqueous solution.

Electrochemical and spectroelectrochemical techniques were employed to investigate the redox characteristics of dyes for dye sensitized solar cells (DSCs) adsorbed at the surface of fluorine-doped tin oxide (FTO) and FTO TiO2 electrodes. In this work are studied Ru-based dyes such as cis-bis(isothiocyanato)-bis(2,2’-bipyridyl- 4,4’dicarboxylato)-ruthenium(II) (N719) and (cis-RuLL'(SCN)2 with L=4,4'- dicarboxylic acid-2,2'-bipyridine and L'=4,4'-dinonyl-2,2'-bipyridine) known as Z907, and indoline organic dyes coded as D102, D131, D149, and D205. The adsorption, diffusion and stability of adsorbed dyes were studied using cyclic voltammetry in acetonitrile and 0.1 M NBu4PF6. The adsorption technique at FTO electrodes was optimized in order to be reproducible so that electrochemical studies as a function of dye coverage were carried out. Langmuirian binding constants were approximately estimated for all dyes adsorbed at FTO electrodes. Rate constants for the chemical degradation of the oxidized dye were also obtained. Is shown that degradation of the dyes mainly occurs at the surface of FTO and only insignificant degradation is evident once the dyes are adsorbed on TiO2. The degradation of dye adsorbed on FTO is shown to affect charge transport from the nonporous TiO2 via electron hopping. Spectroelectrochemical studies of indoline dyes adsorbed on FTO/TiO2 electrodes revealed a red shift of absorption peaks after oxidation and the presence of a strong charge transfer band in the near IR that suggest delocalization of holes in the dye layer. This is consistent with observation that the diffusion coefficient for hole conduction in the adsorbed dye layer is several orders of magnitude higher for the organic dyes compared to the Ru-based dyes. DSCs fabricated using indoline dyes showed good performance. Incident photon-tocurrent conversion efficiency (IPCE) spectra and I-V characteristics are presented.