The voltammetric behavior of selected nitrophenols (2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol) was investigated by differential pulse voltammetry (DPV) and by adsorptive stripping voltammetry (AdSV) at an unmodified electrode (CPE) and a clay-modified carbon paste electrodes modified by montmorillonite (MMT-CPE) and sepiolite (SEP-CPE) using electrochemical reduction and oxidation in Britton-Robinson buffer. For reduction, optimum conditions have been found at pH 2 for 2-NP and 4-NP, at pH 3 for 2,4-DNP and at pH 4 for 2,4,6-TNP. For oxidation, optimum conditions have been found at pH 2 for 2-NP and 4-NP and at pH 5 for 2,4-DNP. Voltammetric determination using electrochemical oxidation is not a suitable method for 2,4,6-TNP. The lowest detection limits were obtained for 2-NP using cathodic AdSV on SEP-CPE with 2,9·10-7 mol.dm-3 , for 4-NP using cathodic DPV on MMT-CPE with 2·10-6 mol.dm-3 , for 2,4-DNP using cathodic AdSV on SEP-CPE with 2,7·10-7 mol.dm-3 and for 2,4,6-TNP using cathodic DPV on unmodified electrode with 4,8·10-7 mol.dm-3 . Determination of mixture 2-NP and 4-NP and the possibility of the selective determination using open circuit sorption with DPV detection was further studied.

In this master s thesis, electrochemical determination of homovanillic acid (HVA) andˈ vanillylmandelic acid (VMA) was performed on carbon paste electrode. The purpose of this thesis was finding out optimal conditions for determination of these analytes by ndifferential pulse voltammetry (DPV) and high pressure liquid chromatography with a carbon paste electrode as an electrochemical detector (HPLC-ED). The electrochemical behavior of the compounds depends mainly on pH of the solution; the best results are obtained in acidic medium. The limits of detection for DPV method were for HVA 0,38 μmol·dm-3 and for VMA 0,25 μmol·dm-3 . The limits of detection for HPLC-ED were for HVA 0,7 μmol·dm-3 and for VMA 0,2 μmol·dm-3 . Developed method was successfully used for the determination of homovanillic and vanillylmandelic acid in urine samples. With HPLC - ED the limits of detection 0,8 μmol·dm-3 (HVA) and 0,5 μmol·dm-3 (VMA) were achieved. Key words: Homovanillic acid, vanillylmandelic acid, carbon paste electrode, DPV, HPLC

Cette thèse porte sur l’étude de nanocristaux semi-conducteurs ternaires, et leur application dansdes cellules solaires hybrides organiques/inorganiques. Les nanocristaux semi-conducteurs absorbentla lumière à des longueurs d’ondes déterminées par leur taille et leur composition, et conduisent lescharges électriques. Ils sont stables en solution, ce qui permet un dépôt de couches minces à bascout. Aujourd’hui les meilleurs rendements en cellules solaires hybrides sont obtenus à partir de nanocristauxbinaires contenant soit du plomb, soit du cadmium. Les nanocristaux ternaires conserventles propriétés particulières des nanocristaux binaires tout en permettant de s’affranchir des élémentstoxiques. Cependant, leur synthèse reste à optimiser pour contrôler de leur structure cristalline et leurcomposition.Nous avons réalisé, par voie chimique, la synthèse de nanocristaux de CuInS2 de taille et de compositioncontrôlées. En suivant in situ la synthèse de ces nanocristaux par diffraction des rayons X sous rayonnementsynchrotron nous avons trouvé que les précurseurs s’organisent avant nucléation sous forme deplans espacés par deux longueurs du ligand utilisé (ici dodécanethiol, DDT). Cela impacte nucléationet croissance des nanocristaux. Les ligands stabilisent les nanocristaux en solution colloïdale, maisleur caractère isolant peut inhiber le transfert et le transport de charges. Le remplacement du ligandd’origine (DDT) par un ligand plus court, l’éthylhexanethiol (EHT), modifie les niveaux d’énergie etpermet d’augmenter la conductivité des films de nanocristaux. Nous avons intégré des nanocristauxde CuInS2 entourés d’EHT dans des cellules hybrides constituées d’un polymère conjugué (P3HT) etd’un fullerène (PCBM). L’efficacité des cellules solaires contenant des nanocristaux entourés d’EHTest significativement améliorée par rapport à celle des cellules de P3HT :PCBM réalisées dans lesmêmes conditions. Le transfert et la mobilité des charges sont étudiés par RPE sous éclairement etphoto-CELIV respectivement. De ces études il ressort que l’amélioration des cellules provient d’unemeilleure génération et dissociation des charges. / This work is devoted to the study of ternary semiconductor nanocrystals, and their application inhybrid organic/inorganic solar cells. Semiconductor nanocrystals absorb light at controlled wavelength(depending on their size and composition) and are able to transport charges. They form a colloidalsolution in organic solvent compatible with low-cost deposition in thin films. Nowadays, the bestefficiency for such hybrid solar cells is obtained with binary nanocrystals containing lead or cadmium.Ternary nanocrystals preserve the opticla and electronic properties of binary nanocrystals withoutrelying on toxic elements, but it is still a challenge to control their composition and structure.In this thesis, CuInS2 nanocrystals of controlled size and composition were syntesized. A study ofnucleation and growth was carried out by following the synthesis in situ with X-ray radiation at thesynchrotron. This has shown that precursors’ organize themselves into plans of atoms separated by twotimes the length of the ligand (here dodecanethiol, DDT). Ligands stabilize the nanocrystals in colloidalsolution, but their insulating character inhibits efficient charge transfer and transport. Ligand exchangewith ethylhexanethiol (EHT) improves the conductivity of thin films and changethe energetic level ofthe nanocrystals.We studied an approach of hybrid solar cell design, consisting in a bulk heterojunctionof two semiconductor organic components (P3HT and PCBM) and CuInS2 nanocrystals. The efficencyof the cells where nanocrystals are added are better than the one with only P3HT:PCBM. The chargetransfer and mobility was studied by the mean of light induced ESR and CELIV respectively. It hasshown that the improvement of the solar cell efficiency is mainly related to an improvement of thecharge generation and dissociation in the ternary blend.

Amino derivatives of polycyclic aromatic hydrocarbons are well-known chemical carcinogens which should be carefully monitored in our environment. They are amenable to anodic oxida- tion on suitable solid or paste electrodes. This fact was exploited for voltammetric determina- tion of 4-aminobiphenyl on unmodified carbon paste electrode and carbon paste electrodes modified by montmorillonite and sepiolite. The optimum pH of BR buffer for measurement on unmodified carbon paste electrode is pH 2, pH 10 for CPE-SEP and pH 11 for CPE-MMT. It was possible to increase sensitivity of the determination using adsorptive stripping voltam- metry on modified electrodes. The optimum time for accumulation of 4-aminobiphenyl is 5 minutes. The limits of quantification of the order of 10−6 mol dm−3 were obtained for each electrode. After accumulation, the limits of quantification decreased to the 10−7 mol dm−3 . The newly developed method was tested for the determination of 4-aminobiphenyl in model sam- ples of drinking and river water, reaching limits of quantification of the order of 10−7 mol dm−3 .

Differential pulse voltammetry (DPV) was used for developing a method for the determination of phenothiazine derivatives, namely chlorpromazine (CHP) and levomepromazine (LMP), using a glassy carbon electrode (GCE) and a graphite electrode, both with a 2 mm disc diameter. Comparison of quantification limits (LQ) for both substances on both electrodes was performed. After optimizing and processing the results, the optimal conditions for measuring calibrations were as follows: Britton- Robinson (BR) buffer at pH 4.0. Calibration dependences were measured inthe concentration range from 1·10-7 to 1·10-4 mol·dm-3 . There was no need for electrochemical electrode regeneration or matrix pretreatment. The results showed higher measurement sensitivity for CHP, and the graphite electrode also showed higher sensitivity. Although there were measured lower concentrations with the graphite electrode in comparison to the GCE, because of the low repeatability of the measurements in the lower concentration range 1-10·10-7 mol·dm-3 , the LQ is comparable to the results reached on the GCE. Besides to the BR buffer, measurements in other matrices (drinking water and river water) were also made. The following LQ values were achieved: 1.0·10-6 mol·dm-3 (in BR buffer), 1.1·10-6 -1.4·10-6 mol·dm-3 (in drinking water) and...

>Magister Scientiae - MSc / Tuberculosis (TB) is a disease that results from infection by Mycobacterium tuberculosis, which is regarded the most common infecting organism. TB has killed countless numbers of people particularly in underdeveloped countries. TB bacteria can remain inactive or in dormant state for years without causing symptoms or spreading to other subjects, but as soon as the immune system of the host becomes weakened, the bacteria become active and infect mainly the lungs along with other parts of body. TB cases are further aggravated by other illnesses that affect the immune system, such as human immune virus (HIV), which is very prevalent in resource-poor countries. Interferon-gamma (IFN-γ) is a TB biomarker that has found to have all the qualities that are needed to help and cure Tuberculosis disease. Early diagnosis and treatment are essential measures for effectively controlling the disease. Traditional microbial culture-based tests are the most common methodologies currently used. Usually, these methods involve cell culture, cell counts, and cell enrichment, but this process is time-consuming and laborious, especially for the slow-growing bacteria like M. tuberculosis. Sputum smear is one of the methods currently used to detect acid fast bacilli (AFB) in clinical specimens or fluorescent staining. It is a cost-effective tool for diagnosing patients with TB and to monitor the progress of treatment especially in developing countries. The traditional method of inoculating solid medium such as Lowerstein-Jensen (L-J) or 7H10/7H11 media is also used currently it is slow and takes 6-8 weeks of incubation to diagnose the infection and further more time to determine the susceptibility patterns. The microscopic observation drug susceptibility (MODS) assay they are also used currently they rely on light microscopy to visualize the characteristic cording morphology of M. tuberculosis in liquid culture. MODS has shorter time to culture positivity (average 8 days) compared with LJ medium (average ~26 days), they are very expensive. The Gen-Probe assay specific for M. tuberculosis complex is a rapid detection that is also used, nucleic acid amplification (NAA) test results can be obtained as fast as in two hours (provided if a positive culture is present); it also has a high sensitivity of 99% and specificity of 99.2%. It holds the disadvantage of needing of positive culture that can take several days. Enzyme-linked immunosorbent assay (ELISA), is a test that uses antibodies and colour change to identify a substance. ELISA is an assay that uses a solid-phase enzyme immunoassay (EIA) to detect the presence of a substance, usually an antigen, in a liquid sample or wet sample. It can be used to detection of Mycobacterium antibodies in tuberculosis. The Amplified Mycobacterium Tuberculosis Direct Test (AMTDT) is used for the detection of M. tuberculosis it enables the amplification and detection of M. tuberculosis rRNA directly from respiratory specimens. The diagnostic methods employing genetechnology based on the amplification of DNA or RNA are expected to improve the speed, sensitivity, and specificity of Mycobacterium tuberculosis detection. TB rapid cultivation detection technique, such as MB/BacT system, BactecMGIT 960 system and flow cytometry. The BACTEC MGIT960 system (Becton Dickinson, Sparks, MD) performs incubation and reading of the tubes continuously inside the machine using a predefined algorithm to interpret the fluorescent signal and giving the results as positive or negative. When performing DST, the BACTEC MGIT960 interprets the results as susceptible or resistant to the antibiotic under study. Results are available within 8 days. A recent meta-analysis of the published studies found high accuracy and high predictive values associated with the use of BACTEC MGIT960. These methods are more sensitive and rapid than the traditional microbial culture-based methods. However, they cannot provide the detection results in real-time and most of these methods are centralized in large stationary laboratories because complex instrumentation and highly qualified technical staff are required. Recently, Food and Drug Administration (FDA) approved two new assays that were introduced. These two assays detect in vitro a specific immune response to M. tuberculosis. These tests are the QuantiFERON-TB Gold In-Tube (Cellestis/Qiagen, Carnegie, Australia) and the T-SPOT.TB assay (Oxford Immunotec, Abingdon, United Kingdom). Both assays use whole blood from the patient and measure the production of interferon gamma after the whole blood is exposed to specific antigens from M. tuberculosis. These tests are based on the knowledge that IFN-γ is a product of an active cell-mediated immune response induced by M. tuberculosis. However, TB detection remains a major obstacle due to several drawbacks of these methods. To date, the number of diagnosis approaches for TB has increased as the disease continues to be a major public health problem worldwide and most conventional detection technologies present difficulties in recognizing the presence of M. tuberculosis, since they are time consuming, do not provide clinically reliable results and significantly lack of sensitivity. This thesis focusedon developing two binary and one ternary-electrochemically quantum dots, all synthesised at room temperature in aqueous media for detecting (IFN-γ). Copper telluride (CuTe) and Zinc telluride (ZnTe) was prepared to check how does the two quantum dot behave individual and also to check on how they behave when they are combined and formed ternary quantum dots (CuZnTe). The electrochemical studies of the binary CuTe quantum dots, ZnTe quantum dots and the ternary CuZnTe core-shell quantum dots reveal that ternary quantum dots were stable and showed a significant enhancement in the conductivity of CuZnTe core-shell solution compared to that of CuTe and ZnTe, all studied in solution. The three different quantum dots were capped with three different capping reagents which are tetraethyl orthosilicate (TEOS), thioglycolic acid (TGA), (3-mercaptopropyl) trimethoxysilane (MPS). In the study, a label-free electrochemical immunosensor for the detection of interferon gamma (IFN-γ) was prepared for the first time using ternary quantum dots. The biosensor consists of water-soluble silica coated Copper Zinc telluride (CuZnTe core-shell) quantum dots conjugated to a gold electrode. The antibody-antigen were then conjugated on the CuZnTe core-shell QD modified gold electrode. Results from synthesis of two different binary quantum dots are also presented in the study and compared to the results of the CuZnTe core-shell QDs. The CuTe quantum dots had a small average size which was confirmed through HRTEM, SAXS and XRD analysis

No description available.

Cette thèse porte sur l'étude de nanocristaux semi-conducteurs ternaires, et leur application dansdes cellules solaires hybrides organiques/inorganiques. Les nanocristaux semi-conducteurs absorbentla lumière à des longueurs d'ondes déterminées par leur taille et leur composition, et conduisent lescharges électriques. Ils sont stables en solution, ce qui permet un dépôt de couches minces à bascout. Aujourd'hui les meilleurs rendements en cellules solaires hybrides sont obtenus à partir de nanocristauxbinaires contenant soit du plomb, soit du cadmium. Les nanocristaux ternaires conserventles propriétés particulières des nanocristaux binaires tout en permettant de s'affranchir des élémentstoxiques. Cependant, leur synthèse reste à optimiser pour contrôler de leur structure cristalline et leurcomposition.Nous avons réalisé, par voie chimique, la synthèse de nanocristaux de CuInS2 de taille et de compositioncontrôlées. En suivant in situ la synthèse de ces nanocristaux par diffraction des rayons X sous rayonnementsynchrotron nous avons trouvé que les précurseurs s'organisent avant nucléation sous forme deplans espacés par deux longueurs du ligand utilisé (ici dodécanethiol, DDT). Cela impacte nucléationet croissance des nanocristaux. Les ligands stabilisent les nanocristaux en solution colloïdale, maisleur caractère isolant peut inhiber le transfert et le transport de charges. Le remplacement du ligandd'origine (DDT) par un ligand plus court, l'éthylhexanethiol (EHT), modifie les niveaux d'énergie etpermet d'augmenter la conductivité des films de nanocristaux. Nous avons intégré des nanocristauxde CuInS2 entourés d'EHT dans des cellules hybrides constituées d'un polymère conjugué (P3HT) etd'un fullerène (PCBM). L'efficacité des cellules solaires contenant des nanocristaux entourés d'EHTest significativement améliorée par rapport à celle des cellules de P3HT :PCBM réalisées dans lesmêmes conditions. Le transfert et la mobilité des charges sont étudiés par RPE sous éclairement etphoto-CELIV respectivement. De ces études il ressort que l'amélioration des cellules provient d'unemeilleure génération et dissociation des charges.

>Magister Scientiae - MSc / infarction (MI) affects many parts of the western world and in South Africa alone it is estimated that MI is responsible for 1 in 6 deaths (17.3%). Traditional diagnostic methods for MI include an electrocardiograms and blood tests. The problem with these diagnostic methods are that they are time consuming, require large sample volumes, expensive equipment and complicated machinery. To achieve early detection of MI the discovery of specific, sensitive and reliable biomarkers are required. Brain natriuretic peptide (BNP) has been identified as a reliable biomarker for MI due to the fact that it has a defined cutoff of 100 pg/ml and it is not susceptible to patient‘s age which could make early detection of BNP complicated. Early detection methods for BNP has been based on immunoradiometric assays but problems associated with immunoradiometric assays are that there is a restricted availability of antigens and incubation of the labeled antibody could take up to two weeks which affects the patients waiting time on results. Electrochemical biosensors are emerging as early detection method for MI because they can be designed to be sensitive, specific to BNP at a low cost. This research study reported for the first the successful fabrication and implementation of highly sensitive mercaptosuccinic acid capped nickel selenide quantum dots (MSA-NiSe2 QDs) aptasensor for the detection of BNP. The poly-dispersed MSA-NiSe2 QDs were synthesized via an inexpensive, simple and reproducible aqueous microwave assisted irradiation method. The prepared MSA-NiSe2 QDs were characterized by Ultraviolet spectroscopy (UV-Vis), X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), High Resolution Transmission/Scanning Electron Microscopy (HR TEM/SEM) and Small Angle X-ray Scattering (SAXSpace). The electrochemical properties of the MSA-NiSe2 QDs were investigated by Cylic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). HR-TEM revealed the formation of small sized MSA-NiSe2 QDs about 4 nm in diameter which was complemented by SAXSpace. UV-Vis studies showed absorption peaks in the ultraviolet region (100-400 nm) confirming the small size of these QDs as well confirming the direct and indirect bandgap of the QDs. XRD confirmed that the QDs are crystalline and belong to the bulk cubic MSA-NiSe2 QDs phase. FTIR studies confirmed the successful capping of MSA on the QDs due to the disappearance of the thiol peak at 2652 cm-1. Electrochemical studies revealed that the MSA-NiSe2 QDs showed good electrochemical properties on screen printed carbon electrodes (SPCE) which allowed them to be used as a mediating platform between the aptamer and SPCE. The successful detection of BNP was achieved by an incubation process between the aptamer drop coated on the MSA-NiSe2 QDs/SPCE surface overnight. The response of the MSA-NiSe2 QDs based aptasensor towards different concentrations of BNP was studied by differential pulse voltammetry (DPV). DPV showed a good linearly with correlation coefficient of R2 = 0.98. DPV also showed a high sensitivity (0.4513 μA/ pg/mL) towards detecting BNP with a detection limit of 11.93 pg/ml. The value of 11.93 pg/ml falls within the negative predictive value range of 10-100 pg/ml for early-stage diagnosis of BNP.

<p>The main thesis hub was on development of two electrochemical biosensors for the determination of 17&beta / -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 17&beta / -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.</p>