>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.

>Magister Scientiae - MSc / Prostate cancer, commonly referred to as adenocarcinoma of the prostate, is the leading cause of cancer death in men in 46 countries, and it was estimated that by the end of 2018 there would approximately be 1.3 million new cases of prostate cancer worldwide. Currently, the Food and Drug Administration (FDA) approved biomarker for prostate cancer disease diagnostics Prostate Specific Antigen (PSA) is not specific to the disease itself but extends to other cases such as Benign Prostate Hyperplasia (BPH) a condition in which the prostate grows uncontrollably. This biomarker is then detected in blood samples via conventional methods which require a qualified individual to operate and are often time consuming. Examples of these methods are spectrophotometry and High Performance Liquid Chromatography (HPLC). Hence, a more efficient biomarker and method of detection is needed for prostate cancer disease diagnostics, as early detection of the disease means early treatment, which could ultimately save lives. Currently, an emerging biomarker for prostate cancer known as Alpha-Methyl CoA Racemase (AMACR) has shown to be more specific to the disease with advantages such as being a non-invasive biomarker. AMACR has been reported to be present in urine, and thus may be detected via a non-invasive method. This study proposed an economical, non-invasive electrochemical biosensor for the rapid detection of AMACR based on mercaptosuccinic acid capped tungsten telluride (MSA-WTe3) quantum dots (QDs). Nanomaterial has shown promise in terms of increasing the sensitivity and specificity of sensors. MSA-WTe3 QDs was successfully synthesized using easy, inexpensive method and was studied by various techniques such as High Resolution Transmission Electron Microscopy (HR-TEM) where the size was confirmed to be within the nanometer scale and was reported to be 2.65 nm with a good crystallinity. X-ray diffraction (XRD) confirmed the structural properties and chemical composition of the QDs and it is reported that the QDs are rich in both tellurium and tungsten and comprise of a hexagonal structure. Scanning Electron Microscopy (SEM) confirmed the successful immobilization of aptamer sequence specific to AMACR onto the electrode surface by showing a distinct conformational change when aptamers were introduced to the QDs under study. This study reports the successful detection of AMACR using an MSA-WTe3 QDs based aptasensor immobilized onto a screen printed glassy carbon electrode, with a detection limit of 0.35651 ng/mL and a limit of quantification calculated to be 1.08033 ng/mL.

Des méthodes électrochimiques à potentiel et à courant imposé appliquées à l'étude des réactions avec dépôt métallique sur un métal de même nature ou sur un substrat étranger sont examinées. Des précisions inédites concernant la voltamétrie à escalier de potentiel et la voltamétrie à signaux carrés de potentiel pour les réactions rapides et lentes avec et sans nucléation tridimensionnelle sont apportées. Les conclusions théoriques sont validées par l'étude du couple Ag(I)/Ag sur les électrodes d'or et d'argent dans HNO3 1 M, KNO3 1 M et dans le liquide ionique [EMIM][NTf2] anhydre ou humide. Le dépôt d'argent s'effectue sans aucune surtension de nucléation tridimensionnelle seulement dans HNO3 et dans [EMIM][NTf2] anhydre. La réaction électrochimique est rapide dans les solutions aqueuses et dans [EMIM][NTf2] humide tandis qu'elle est lente dans [EMIM][NTf2] anhydre. Les paramètres cinétiques sont déterminés par simulation numérique. / Electrochemical methods with potential or current imposing for the study of reactions with metal deposition on the same metal and on foreign substrate are reviewed. New information is provided on staircase voltammetry and square wave voltammetry for fast and slow electrode reactions with and without three-dimensional nucleation. Theory is validated through the study of Ag(I)/Ag couple on gold and silver electrodes in 1 M HNO3, 1 M KNO3 and in dry or wet [EMIM][NTf2] ionic liquid. Silver deposition takes place without any three-dimensional nucleation overvoltage only in HNO3 and in dry [EMIM][NTf2]. The electrochemical reaction is fast in aqueous solutions and in wet [EMIM][NTf2] while it is slow in dry [EMIM][NTf2]. Kinetic parameters are determined by numerical simulation.

Diese Arbeit beinhaltet unsere Studien an selbstorganisierenden Monoschichten (engl. SAM = self- assembled monolayer) einiger aromatischer Thiole auf Gold- und Kupferoberflächen. Die Bildung von Monoschichten von Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin auf Au und Cu wurde untersucht und charakterisiert. Das abschirmende Verhalten und die strukturelle Anordnung dieser Monoschichten wurden mit Hilfe elektrochemischer und spektroskopischer Methoden geprüft und bestimmt. Zyklische Voltammetrie und oberflächenverstärkte Raman Spektroskopie wurden intensiv zur Aufklärung von Elektronentransferreaktionen an diesen mit SAMs modifizierten Oberflächen genutzt. Elektrochemische Studien von Monoschichten aus Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin in 0,1 M wässriger KClO4-Lösung lassen schlussfolgern, dass diese Moleküle schwefelseitig an die Substratoberfläche gebunden sind. In 0,1 M wässriger KClO4-Lösung aufgenommene zyklische Voltammogramme an Gold- und Kupferoberflächen, welche mit oben genannten, aromatischen Thiolen beschichtet wurden, legen nahe, dass Adsorptionsschichten von Thiophenol und 1,4-Dithiobenzol eine stärkere Tendenz zum Abschirmen besitzen als andere. Durch das Einbringen von Kupferproben, welche mit genannten aromatischen Thiolen behandelt wurden, in 0,1 M Silbernitrat-Lösung können sehr leicht Silber-Nanodendritstrukturen erhalten werden. Abscheidezeit und Konzentration der Silbernitrat-Lösung haben einen großen Einfluss auf das Wachstum der Silber-Nanodendritstrukturen auf den modifizierten Kupferproben. Diese Silber-Nanodendritstrukturen besitzen eine hohe katalytische Aktivität hinsichtlich der Oxidation von Hydroquinon. Untersuchungen zur Korrosion an polykristallinem Kupfer, welches mit obigen aromatischen Thiolen modifiziert wurde, in 0,1 M Silbernitrate-Lösung ließen vermuten, dass dieses Kupfersubstrat mehr anodisches Verhalten zeigte als reines Kupfer bei ähnlichen Bedingungen. Zyklische Voltammetrie an wie oben behandeltem Kupfer in 0,1M wässriger KClO4-Lösung zeigte, dass die Geschwindigkeit der Kupferauflösung bei diesen Messungen erhöht war gegenüber anderen, in welchen reines Kupfer bei identischen Bedingungen eingesetzt wurde. / It deals with our studies on self-assembled monolayers of aromatic thiols on gold and copper surfaces. Monolayer formation of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mer¬cap¬to¬pyridine and 2-mercaptopyridine on Au and Cu surfaces was studied and characterized. The blocking behaviour and structural arrange¬ments of these monolayers were evaluated and characterized using electrochemical and spec¬troscopic techniques. Cyclic voltammetry and surface enhanced Raman spectroscopy were extensively used for the study of electron transfer reactions on these SAM modified surfaces. Electrochemical and spectroelectrochemical studies of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mercaptopyridine and 2-mercaptopyridine monolayers in aqueous solution of 0.1 M KClO4 suggest that these molecules adsorbed to substrate. Cyclic voltammetry of gold and copper covered with these aromatic thiolates recorded in aqueous solution of 0.1 M KClO4 suggests that adlayers of thio¬phenol and 1,4-dithiobenzene exhibit more blocking behavior than the other ones. Silver nanodendritic structures are easily produced by placing copper samples modified with these aromatic thiolates into 0.1 M silver nitrate solution. Deposition time and concentration of silver nitrate solution have great influence on growing up silver nanodendritic structures on the surface of modified copper samples. These silver nanodendritic structures exhibit electrocatalytic activity towards the oxidation of hydroquinone. Corrosion investigation of polycrystalline copper modified with these aromatic thiolates in 0.1 M silver nitrate solution suggest that copper substrate might be more anodic compared to bare copper under identical condition. Cyclic voltammetry of copper modified with these aromatic thiolates suggests that the rate of dissolution copper in aqueous solution of 0.1 M KClO4 is higher than bare copper in the same condition.

Optimum detergent dosage during a washing process depends on water quality, degree of pollution and quantity of laundry. Particularly, water quality is an important factor. Other parameters like carbonate- or non-carbonate hardness and calcium / magnesium (Ca / Mg) ratio in addition to total hardness of water have an impact on the amount of detergent. This work discusses the possibilities realizing a detergent sensor that measures important parameters for the washing process and assess the ideal necessary amount of detergent during the washing process. The approach is to combine impedance spectroscopy with cyclic voltammetry in order to determine both water quality and concentration of detergent in the suds which build up the basis for an optimum detergent dosage. The results of cyclic voltammetry show that it is possible to identify the Ca / Mg ratio and the carbonate hardness separately, which is necessary for the optimization of the washing process. Impedance measurements identify total hardness and detergent concentrations.

[pt] O objetivo deste trabalho foi o desenvolvimento de métodos eletro-analíticos utilizando eletrodos modificados com nanomateriais a base de carbono para determinação de analitos de interesse biológico (creatinina) e farmacológico (primaquina, INHHQ, tiomersal). A determinação de primaquina (antimalárico) e de INHHQ (potencial medicamento para o tratamento de doenças neurodegenerativas) foi proposta usando eletrodo de carbono vítreo (GC) modificado com nanotubos de carbono de paredes múltiplas (MWCNTs) o qual promoveu uma melhora significativa na corrente faradaica e na resolução de pico obtida usando voltametria de onda quadrada (SWV) em tampão Britton-Robinson (BR) 0.02 mol L-1; pH 7.00 e KCl (0.25 mol L-1). Embora vários métodos para quantificar primaquina estejam reportados, muitos deles dependem de procedimentos considerados complexos e trabalhosos, portanto, a modificação proposta de GC usando MWCNTs é comparativamente fácil, levando a uma modificação robusta que produz resultados repetitivos, fornecendo também amplificação do sinal eletroquímico devido à área ativa aumentada e a taxa de transferência eletrônica aprimorada. Os GC/MWCNTs também forneceram, ao trabalhar em um pH adequado, maior resolução na detecção das diferentes etapas eletroquímicas envolvidas no processo redox da primaquina. O eletrodo permitiu o limite de detecção (LOD) de 28 nmol L-1 para a primaquina e, quando associado a um procedimento simples baseado na extração líquido-líquido (LLE) e cromatografia em camada fina (TLC), foi alcançada a seletividade e a capacidade de determinar os níveis mais baixos esperados em amostras de urina. No caso do INHHQ, um método para quantificação por SWV foi relatado pela primeira vez. Além do uso do eletrodo GC/MWCNTs um prévio procedimento de TLC, permitiu a seletividade necessária para determinar o INHHQ no tecido cerebral de ratos Wistar. O LOD foi de 0.85 μmol L-1 e a faixa dinâmica linear cobriu duas ordens de magnitude (10-6 a 10-5 mol L-1). Os pontos quânticos de grafeno (GQDs) foram escolhidos para modificar quimicamente os eletrodos utilizados para determinar tiomersal e creatinina. GQDs são fragmentos nanométricos de grafeno (presentes em dispersões como monocamada, poucas camadas ou multicamadas) onde o transporte de elétrons é confinado em suas dimensões. GQDs são estruturas baseadas em carbono que são biocompatíveis e apresentam baixa toxicidade. A pesquisa apresenta uma nova abordagem para a determinação de tiomersal (conservante em vacinas e cosméticos) em vacinas contra influenza usando GQDs como modificador do eletrodo de GC e explorando o efeito sinérgico entre GQDs, radiação visível e a diferença de potencial aplicado. Este sistema promove a oxidação do tiomersal, produzindo um aumento significativo na resposta (par redox Hg/Hg2positivo) em termos de intensidade de corrente usando SWV e tampão BR (0.02 mol L-1; pH 4.00 com KCl a 0.25 mol L-1). O LOD foi de 0.85 μmol L-1 e a faixa dinâmica linear cobriu três ordens de grandeza (10-6 a 10-4 mol L-1). Para a creatinina (um biomarcador para a disfunção renal), um composto de GQDs-cobre foi usado para modificar um eletrodo de ouro. A determinação da creatinina foi realizada utilizando SWV (tampão BR 0.02 mol L-1; pH 4.00 com KCl a 0.25 mol L-1). O método contou com a diminuição do pico de oxidação Cu/Cu2positivo na presença de creatinina, permitindo LOD de 50 nmol L-1 e faixa dinâmica linear, cobrindo três ordens de magnitude (10-6 a 10-4 mol L-1). A resposta SWV da creatinina foi atribuída à formação do complexo creatinina-Cu2+, sendo razoavelmente seletiva em relação a este analito. Todos os procedimentos desenvolvidos por voltametria foram adequadamente comparados com métodos de referência, sendo estatisticamente compatíveis. / [en] The goal of this work was the development of electro-analytical methods using electrodes modified with carbon-based nanomaterials for determination of analytes of biological (creatinine) and pharmacological interest (primaquine, INHHQ, thiomersal). The determination of primaquine (antimalarial) and INHHQ (potential drug for treatment of neurodegenerative diseases) was proposed using glassy carbon (GC) electrode modified with multi-walled carbon nanotubes (MWCNTs) that promoted significant improvement in faradaic current and better peak resolution obtained using square-wave voltammetry (SWV) in Britton-Robinson (BR) buffer 0.02 mol L-1; pH 7.00 and KCl (0.25 mol L-1). Although several methods to quantify primaquine are reported, many of these depend on procedure considered complex and laborious, therefore, the proposed GC modification using MWCNTs is comparatively easy, leading to a robust modification that produce repetitive results also providing amplification of the electrochemical signal due to the increased active area and improved electron-transfer rate. The GC/MWCNTs also provided, when working on a proper pH, higher resolution in detecting the different electrochemical steps involved in the redox process of primaquine. The electrode enabled limit of detection (LOD) of 28 nmol L-1 for primaquine and, when associated with a simple developed procedure, relying of liquid-liquid extraction (LLE) and thin-layer chromatography (TLC), it was achieved the selectivity and the capability to determine the lower levels expected in urine samples. In the case of INHHQ, a method for quantification by SWV was reported for the first time. In addition to the use of GC/MWCNTs electrode, a previous TLC procedure, enabled the selectivity required to determine INHHQ in brain tissue from Wistar rats. The LOD was 0.85 mol L-1 and the linear dynamic range covered two orders of magnitude (10-6 to 10-5 mol L-1). Graphene quantum dots (GQDs) was chosen to chemically modify electrodes used to determine thiomersal and creatinine. GQDs are nanometric fragments of graphene (present in dispersions as monolayer, few layer or multilayer) where electron transport is confined in their dimensions. GQDs are carbon-based structure that are bio-compatible and present low toxicity. The research presents a new approach for the determination of thimerosal (preservative in vaccines and cosmetics) in influenza vaccines using GQDs as a modifier of the GC electrode and exploring the synergistic effect between GQDs, visible radiation and the applied potential difference. This system promotes thiomersal oxidation, producing a significant increase in response (Hg/Hg2 positive redox pair) in terms of current intensity using SWV and BR buffer (0.02 mol L-1; pH 4.00 with KCl at 0.25 mol L-1). The LOD was 0.85 μmol L-1 with linear dynamic range covering three orders of magnitude (10-6 to 10-4 mol L-1). For creatinine, a biomarker for the renal dysfunction, a GQDs-copper composite was used to modify a gold electrode. Determination of creatinine was made using SWV (BR buffer 0.02 mol L-1; pH 4.00 with KCl at 0.25 mol L-1). The method relied on the decreasing of the Cu2+/Cu oxidation peak in the presence of creatinine, enabling LOD of 50 nmol L-1 and linear dynamic range covering three orders of magnitude (10-6 to 10-4 mol L-1). The SWV response of creatinine was attributed to the formation of creatinine-Cu2 positive complex being reasonably selective towards this analyte. All procedures developed by voltammetry were adequately compared with reference methods, being statistically compatible.

[pt] A busca pela diminuição da dependência de combustíveis fósseis faz com que a ciência avance, diariamente, na utilização de combustíveis ecológicos, como o H2. Uma das formas de sua obtenção é através da fotocatálise. Esse processo consiste em uma reação catalítica com o uso de energia, na forma de luz. A fotólise da água é amplamente utilizada, principalmente com luz solar como fonte luminosa, que é abundante e reduz os custos de sua produção. O desempenho desta reação depende da posição das bandas de condução (BC) e valência (BV) do fotocatalisador. O TiO2 é utilizado como fotocatalisador em diversas reações, inclusive para a produção de H2. Os fotocatalisadores utilizados na forma de pós nanométricos apresentam dificuldade de separação após a reação. A transformação do pó em um material compacto é uma alternativa para retirá-lo do meio reacional evitando perdas e custos com separação. Desse modo, a compactação do pó é uma alternativa para facilitar sua reciclagem. O principal método de sua produção é pelo processo de sinterização, que envolve temperaturas elevadas (geralmente, 75 por cento do ponto de fusão do material) e longo tempo, podendo durar até dias. Para diminuir os gastos energéticos, o processo de sinterização a frio é uma opção, que consiste na densificação do material com uso de pressão e um solvente (aquoso ou não) e, temperaturas de sinterização de até 500 Graus C. O objetivo do estudo consistiu na produção de pastilhas de TiO2, comercial, e P25, através de uma variação do método de sinterização a frio, onde aplicou-se a pressão no pó, junto com o solvente, antes de seu tratamento térmico. As pastilhas produzidas foram caracterizadas pelas técnicas de TGA/DSC, XRD, MEV, CV, e DRS. / [en] The quest to reduce dependence on fossil fuels makes science advance, daily, in the use of ecological fuels, such as H2. One of the ways to obtain it is through photocatalysis. This process consists on a catalytic reaction using energy, in the form of light. Water photolysis is widely used, mainly with sunlight as a light source, which is abundant and reduces production costs. The performance of this reaction depends on the position of the conduction (CB) and valence (VB) bands of the photocatalyst. TiO2 is used as a photocatalyst in several reactions, including the production of H2. Photocatalysts used in the form of nanometric powders have difficulty in separating after the reaction. The transformation of the powder into a compact material is an alternative to remove it from the reaction medium, avoiding losses and costs with separation. Thus, the compaction of the powder is an alternative to facilitate its recycling. The main method of its production is through the sintering process, which involves high temperatures (generally 75 percent of the material s melting point) and a long time, which can last up to days. To reduce energy costs, the cold sintering process is an option, which consists of densifying the material using pressure and a solvent (aqueous or not) and sintering temperatures of up to 500 C degrees. The aim of the study was the production of commercial TiO2 and P25 pellets, through a variant of the cold sintering method, where pressure was applied to the powder, with the proper solvent, before the heat treatment. The pellets produced were characterized by the techniques of TGA/DSC, XRD, SEM, CV, and DRS.

The analysis of literature data has shown that the methods used in laboratory diagnostics for determining the concentration of glucose and hydrogen peroxide have a number of disadvantages, for the elimination of which it is proposed to use electrochemical methods of determination. The electrochemical properties of complex oxides with a perovskite-like structure were studied using voltammetry and chronoamperometry. It has been established that all the complex oxides studied exhibit electrocatalytic activity with respect to glucose and hydrogen peroxide. It is shown that the scanning speed and the time of ultrasonic treatment of oxides have no significant effect on the process. Compounds that can be used as catalysts for creating sensors for determining glucose and hydrogen peroxide are proposed. / Анализ литературных данных показал, что применяемые в лабораторной диагностике методы для определения концентрации глюкозы и пероксида водорода имеют ряд недостатков, для устранения которых предлагается использовать электрохимические методы определения. Изучены электрохимические свойства сложных оксидов с перовскитоподобной структурой с применением вольтамперометрии и хроноамперометрии. Установлено, что все исследованные сложные оксиды проявляют электрокаталитическую активность по отношению к глюкозе и пероксиду водорода. Показано, что скорость сканирования и время ультразвуковой обработки оксидов не оказывает существенного влияния на процесс. Предложены соединения, которые могут быть использованы в качестве катализаторов для создания сенсоров для определения глюкозы и пероксида водорода.

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