<p>This study firstly reports the development, characterisation, and application of thick-film acetylcholinesterase (AChE) biosensors based on a gold electrode modified with a mercaptobenzothiazole (MBT) self-assembled monolayer and either poly(omethoxyaniline) (POMA) or poly(2,5-dimethoxyaniline) (PDMA) in the presence of polystyrene(4-sulphonic acid) (PSSA). The Au/MBT/POMA-PSSA/AChE and Au/MBT/PDMA-PSSA/AChE biosensors were then applied to successfully detect standard organophosphorous and carbamate pesticides in a 0.1 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Secondly, it reports the construction of the Au/MBT/PANI/AChE/PVAc thick-film biosensor for the determination of certain organophosphate and carbamate pesticide solutions in selected aqueous organic solvent solutions.</p>

Magister Scientiae - MSc / The main hypothesis in this study is the development of a nanocomposite mediated amperometric biosensor for detection of hydrogen peroxide. The aim is to combine the electrochemical properties of both polyaniline and ferrocenium hexafluorophosphate into highly conductive nano composites capable of exhibiting electrochemistry in non acidic media; shuttling electrons between HRP and GCE for biosensor applications. / South Africa

Philosophiae Doctor - PhD / This study firstly reports the development, characterisation, and application of thick-film acetylcholinesterase (AChE) biosensors based on a gold electrode modified with a mercaptobenzothiazole (MBT) self-assembled monolayer and either poly(omethoxyaniline) (POMA) or poly(2,5-dimethoxyaniline) (PDMA) in the presence of polystyrene(4-sulphonic acid) (PSSA). The Au/MBT/POMA-PSSA/AChE and Au/MBT/PDMA-PSSA/AChE biosensors were then applied to successfully detect standard organophosphorous and carbamate pesticides in a 0.1 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Secondly, it reports the construction of the Au/MBT/PANI/AChE/PVAc thick-film biosensor for the determination of certain organophosphate and carbamate pesticide solutions in selected aqueous organic solvent solutions. / South Africa

Orientador: Lauro Tatsuo Kubota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-25T06:42:10Z (GMT). No. of bitstreams: 1 Bassetto_VictorCosta_M.pdf: 5997549 bytes, checksum: c28ca3fa1e15c81712b8aab83f1a7f0e (MD5) Previous issue date: 2014 / Resumo: Esta dissertação apresenta os desenvolvimentos realizados para a aplicação de ligas de cobre como detector de aminoácidos em cromatografia de íons. O trabalho apresenta o desenvolvimento desde estudos eletroquímicos fundamentais, onde a propriedade de metais como ouro, atual padrão para a técnica, e cobre são investigados frente aos aminoácidos. Neste passo a técnica de voltametria cíclica foi escolhida, pois permitiu explorar os vários fenômenos que ocorrem nos processos de óxido redução das moléculas sobre os eletrodos. Uma particularidade do trabalho é o eletrólito, que deve ser também a fase móvel da cromatografia, no caso hidróxido de sódio 0,15 mol L-1. Após o entendimento dos mecanismos básicos de óxido redução dos diferentes aminoácidos sobre os eletrodos de ouro e cobre em meio alcalino, este foi transferido para a aplicação em células de fluxo. Nessa fase observou-se que o cobre puro não apresentava suficiente resistência a corrosão que viabilizasse sua aplicação no sistema de cromatografia de íons. Sendo assim, optou-se pela aplicação do bronze como material sensor. O bronze escolhido possui 86% de cobre em sua composição e após comprovação através de estudos viu-se que o comportamento de óxido redução dos aminoácidos é similar ao cobre puro, porém com vantagens na resistência à corrosão. Também foram desenvolvidos, em conjunto com a University of Southampton, substratos de cobre que apresentam o efeito SERS. Este trabalho foi realizado para permitir a investigação das espécies intermediarias que se formam entre o aminoácido e o cobre (II) formado na superfície do eletrodo. Para a aplicação em fluxo foi necessário o desenvolvimento de pulsos de potencial para viabilizar a detecção dos aminoácidos e aumentar o tempo de vida útil do eletrodo. Após o desenvolvimento os pulsos foram otimizados e o sistema foi utilizado para detecção de valina em amostras de suplemento alimentar / Abstract: This dissertation presents the developments made for the application of copper alloys as detector for amino acids in ion chromatography. The work presents the development from fundamental electrochemistry studies, where properties of metals such as gold, current standard for the technique, and copper where tested against amino acids were performed through cyclic voltammetry technique. This method was chosen for the investigation because it allowed exploring the various phenomena that occur in the oxide reduction processes of the molecules on the electrodes. As a feature of the working electrolyte must also be the mobile phase of the chromatography, where 0.15 mol L-1 sodium hydroxide was used. After understanding the basic mechanisms of reduction and oxidation of the different amino acids over gold and copper electrodes in an alkaline medium, the knowledge obtained was transferred to the flow cells. At this time it was observed that the pure copper did not present sufficient resistance to corrosion, limiting its application in ion chromatography system. Thus, we chose the application of brass as sensor material. The chosen brass had 86% copper in its composition and demonstration through the studies, which its redox behavior of the amino acids is similar to those observed on pure copper, but with advantages in corrosion resistance. In addition, copper substrates showing the SERS effect was also developed in conjunction with the University of Southampton. This study was conducted to allow the investigation of intermediary species that are formed between the amino acid and copper (II) on the electrode surface. For application in flow was necessary to develop potential pulses to enable the detection of amino acids and increase the lifetime of the electrode. After the development of the pulses, it was optimized and the system was used for detection of valine in samples of food supplement / Mestrado / Quimica Analitica / Mestre em Química

La consommation de fruits est encouragée pour leur apport de composés bioactifs naturels. Ce travail a pour objectif de caractériser dix fruits indignes de la région amazonienne. La caractérisation a été effectuée initialement par des analyses bromatologiques, suivies de la détermination des minéraux Ca, Cu, Fe, Li, Mg, Mn, Na et Zn par spectrométrie d'émission optique ˆ plasma couplé par induction (ICP OES). Ensuite, la capacité antioxydante des fruits a été évalué à l'aide de différentes méthodes colorimétriques (DPPH, ABTS et NBT), ainsi que l'activité antiproliférative contre la lignée cellulaire du cancer du colon humain (caco-2). La composition phénolique a été déterminée par chromatographie en phase liquide à ultra haute performance (UHPLC) couplée à la spectrométrie de masse à haute résolution. Considérant les inconvénients des méthodes conventionnelles de détermination de la capacité antioxydante, un biocapteur enzymatique ampérométrique a été mis au point en utilisant comme transducteur un systéme de trois électrodes sérigraphiées sur PVC, contenant du bleu de Prusse (PB) comme médiateur électrochimique. Une capacité antioxydante lipophile élevée a été observée dans les pulpes de biriba et de bacuri, alors les fruits abiu, inaja et monguba présentaient une capacité antioxydante hydrophile importante. L'activité antiproliférative des fruits de biriba, inaja, monguba et pajura a entrainé une inhibition significative de la croissance cellulaire de caco-2. L'analyse chromatographique des extraits de biriba, inaja et monguba, a permis de quantifier respectivement 11, 25 et 21 composés phénoliques dotés d'activités biologiques importantes. / Fruit consumption is encouraged for their contribution of natural bioactive compounds. This work aims to characterize ten indigenous fruits of the Amazonian region. Characterization was performed initially by bromatological analyzes, followed by the determination of Ca, Cu, Fe, Li, Mg, Mn, Na and Zn minerals by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). Then, the antioxidant capacity of the fruits was evaluated using different colorimetric methods (DPPH, ABTS and NBT), as well as the ant proliferative activity against the human colon cancer cell line (caco-2). The phenolic composition was determined by ultra high performance liquid chromatography (UHPLC) coupled with high-resolution mass spectrometry. Considering the disadvantages of conventional methods of determining antioxidant capacity, an amperometric enzyme biosensor has been developed using as a transducer a system of three screen-printed electrodes on PVC, containing Prussian blue (PB) as electrochemical mediator. A high lipophilic antioxidant capacity was observed in biriba and bacuri pulps, so abiu, inaja and monguba fruit had significant hydrophilic antioxidant capacity. The antiproliferative activity of the fruits of biriba, inaja, monguba and pajura resulted in significant inhibition of caco-2 cell growth. Chromatographic analysis of birib‡, inaj‡ and monguba extracts quantified respectively 11, 25 and 21 phenolic compounds with important biological activities.

Dizertační práce je zaměřena na studium elektrických a dielektrických vlastností iontových kapalin. Iontové kapaliny mohou nacházet uplatnění v široké škále aplikací, především pak v elektrotechnice. Teoretická část se věnuje popisu základních vlastností iontových kapalin a možností jejich uplatnění v kondenzátorech a elektrochemických senzorech plynů. Experimentální část se věnuje použitým metodám charakterizace vlastností iontových kapalin, jsou zde popsány teoretické poznatky o dielektrické spektroskopii včetně metod stanovení fyzikálních vlastností a vyhodnocení experimentálních dat. Experimentální část je rozdělena na dvě základní části. První se věnuje studiu iontových kapalin pro použití jako elektrolytu v kondenzátorech, druhá část se věnuje studiu vlastností připravených experimentálních senzorů na NO2, zejména vlivem vlastností iontových kapalin na sledované parametry senzoru.

Nesta tese de doutorado foram desenvolvidos e caracterizados nanomateriais eletroativos, explorando estratégias de estabilização e os efeitos sinérgicos em nanomateriais multifuncionais baseados em alfa-hidróxido de níquel, com potencial aplicação nas mais essências e urgentes áreas de atuação científica e tecnológicas, como por exemplo na conversão e armazenamento de energia, e sensores amperométricos. Nesse sentido, foram desenvolvidos nanopartículas (NPs) de alfa-hidróxidos de níquel (&#945;-Ni(OH)2) estabilizados pela formação de nanocompósitos com óxido de grafeno (GO), denominados de &#945;-Ni(OH)2@GO. Analogamente, foram preparados NPs de sais de hidróxido duplo de níquel e cobalto (&#945;- NiCo(OH)2), estabilizados pela incorporação cátions Co2+ na estrutura do &#945;-Ni(OH)2, e o correspondente nanocompósito com óxido de grafeno reduzido (rGO) denominado de &#945;- NiCo(OH)2@rGO. De modo geral, os nanocompósitos exibiram alta capacidade de carga em elevadas densidades de corrente, alta capacidade de retenção de carga e elevada estabilidade como consequência da interação sinergística de seus componentes, com potencial aplicação em dispositivos de armazenamento de energia de alto desempenho, como por exemplo em supercapacitores híbridos. Por outro lado, um dos principais desafios no campo da conversão de energia, concentra-se no desenvolvimento de eletrocatalisadores eficientes e robustos para impulsionar a cinética intrinsecamente lenta da reação de evolução de oxigênio (OER), que envolve etapas de transferência de elétrons acopladas a de prótons. Para isso, foram preparados nanocompósitos ternários baseados em NPs de &#945;Ni(OH)2 de diferentes tamanhos, octacarboxiftalocianina de ferro (FeOCPc) e rGO (&#945;-NiFeOCPc@rGO). As NPs de &#945;- Ni@rGO-K maiores e mais cristalinas e seus respectivos nanocompósitos mostraram propriedades eletrocatalíticas superiores para a OER quando comparados com os respectivos derivados de &#945;-Ni(OH)2-Na, indicando a relevância do tamanho do nanocristal de &#945;-Ni(OH)2 na estrutura do nanocompósito e consequente efeitos sinérgicos nas propriedades eletroquímicas e eletrocatalíticas dos nanocompósitos ternários. Além disso, foram desenvolvidos eletrodos modificados com NPs de hidróxido duplo lamelar de NiCe (&#945;-NiCe) como sensores de alta sensibilidade, e de fundamental importância para detecção e quantificação de prednisona, uma droga proibida pelo Comitê Olímpico Internacional (COI). Em resumo, a incorporação de 20% em mols de íons Ce(III/IV) em nanopartículas de &#945;- Ni(OH)2 aumentou a estabilidade deste material na fase alfa, conferindo melhores propriedades eletrocatalíticas responsáveis pela rápida oxidação da prednisona e de seus subprodutos de degradação, permitindo a preparação de sensores amperométricos com elevada sensibilidade e baixo limite de detecção (LOD) em comparação aos eletrodos modificados já reportando na literatura. Em suma, as estratégias no design de nanomateriais foram exploradas com sucesso para gerar novos nanomateriais e nanocompósitos com propriedades eletrocatalíticas e de armazenamento de carga aprimoradas, com potencial de aplicação em sensores e supercapacitores híbridos. / In this doctoral thesis, nanomaterials design strategies were explored in order to improve the stability of alpha-nickel hydroxide nanoparticles while developing synergistic effects, generating multifunctional electrochemically active nanomaterials and nanocomposites with potential application in amperometric sensors and energy conversion and storage devices. In this context, the &#945;-Ni(OH)2 NPs were stabilized by generating double hydroxide salts, by interaction with octacarboxyphthalocyanine molecules and graphene oxide (GO) generating hybrid and nanocomposite materials, for example &#945;-Ni(OH)2@GO. Nickel hydroxide NPs was stabilized by incorporation of Co2+ cation to produce &#945;-NixCoy(OH)2 double hydroxide salts and the corresponding nanocomposite with reduced graphene oxide (rGO) designated - NiCo(OH)2@rGO. In this way, nanocomposites with potential application in high performance energy storage devices such as hybrid supercapacitors were produced, since exhibited large charge capacities at high current densities and great stability as a consequence of the synergistic interaction of their componentes. One of the main challenges in the field of energy conversion, the development of efficient and robust electrocatalysts to boost the intrinsically slow multielectronic multiprotonic transfer kinetics of the oxygen evolution reaction (OER) was also addressed using ternary nanocomposites based on &#945;-Ni(OH)2 NPs, iron octacarboxyphthalocyanine (FeOCPc) and rGO (&#945;-NiFeOCPc@rGO). The more crystalline - Ni@rGO-K NPs and their respective nanocomposites showed superior electrocatalytic properties when compared to the respective &#945;-Ni(OH)2-Na derivatives, indicating the relevance of the &#945;-Ni(OH)2 nanocrystal size and synergistic effects on their electrochemical and electrocatalytic properties. In addition, amperometric sensors based on NiCe layered doublehydroxide NPs (&#945;-NiCe) were developed for determination of prednisone, a drug forbidden by the International Olympic Committee (IOC). The incorporation of 20 m% of Ce3+/4+ ions in &#945;- Ni(OH)2 nanoparticles increased its stability in the alpha phase, conferring improved electrocatalytic properties responsible for the rapid oxidation of prednisone and its degradation byproducts, responsible for the higher sensitivity and lower detection limits (LOD) than similar devices reported in the literature. In short, nanomaterials design strategies were successfully explored to generated new nanomaterials and nanocomposites with enhanced electrocatalytic and charge storage properties with potential application in sensors and hybrid supercapacitors.

The first aim of this work was to develop copper modified carbon felt electrode for detection of amino acids, which are not electrochemically active on ordinary carbon electrodes. Phenylalanine solution at a concentration 1.0 mmol dm-3 was chosen as the testing solution. Electrode modified with electrochemical deposition of copper from mixture of copper(II) sulphate and sodium sulphate provided very low responses which were decreasing during first measurements, apparently because of insufficient amount of copper. Therefore, further experiments were performed using copper microparticles as a modifier. Copper microparticles activated in nitric acid at a concentration 80 mmol dm-3 were applied at carbon felt by several techniques and in different parts of the felt, i.e. by stirring the felt in microparticles suspension, by dripping of the suspension to the part of the felt in contact with capillary (proximal), between two parts of the carbon felt (sandwich) and at a part of the carbon felt in contact with electrolyte in a measuring cell (distal). Electrodes modified in the distal and in the sandwich arrangement were chosen as the best ones. In the last part, calibration dependences for phenylalanine in concentration range from 0.025 mmol dm-3 to 1.0 mmol dm-3 were measured on the last two electrodes....

The aim of this Thesis is development of electroanalytical methods for determination of cholesterol and 7-dehydrocholesterol on boron doped diamond electrodes based on electrochemical oxidation of products of acid-induced dehydration reaction. Two approches have been applied, relying on their detection in 0,1 mol.l-1 perchloric acid in acetonitril containing variable water content 0,43 % - 40 %. Cyclic voltammetry revealed substantial difference in oxidation peak pontecials for 7-dehydrocholesterol (+850 mV) and cholesterol (+1500 mV) in 0,1 mol.l-1 perchloric acid in acetonitrile containing 5 % of water. The limit of detection using differential pulse voltammetry were 6,19 µmol.l-1 a 19,2 µmol.l-1 for a mixture of 7-dehydrocholesterol and cholesterol, respectively. For flow injection analysis with amperometric detection (FIA-AD) the water content in run buffer, detection potencial and the distance between the capillary outlet and electrode surface in wall-jet arrangement of amerometric flow-through detection cell were optimized. Achieved detection limits are in range of 0,61 - 3,43 µmol.l-1 depending on the detection potencial and water concent in the run buffer. The developed FIA-AD method was used for determination of a model mixture solution of 7- dehydrocholesterol and cholesterol. Key words...

A presente dissertação de mestrado tem o propósito de relatar o desenvolvimento de um sensor planar eletroquímico com três eletrodos para o monitoramento de nitrito e seus interferentes (ácido úrico, ácido ascórbico e paracetamol). Para tal, no procedimento experimental é descrito o desenvolvimento do aparato extracorpóreo (mini-bomba compressora, válvulas solenóides e cela de análise). Esse é acoplado a um sistema de Análise por Injeção em Fluxo Automatizada (do inglês, Flow-injection Analysis) FIA-automatizada. Este trabalho também descreve a fabricação dos sensores em substrato de alumina, o processo de limpeza padrão dos eletrodos, o processo de obtenção dos eletrodos de referência em HCl (0,1 mol L-1) e ativação eletroquímica da superfície do eletrodo de trabalho com H2SO4 (0,1 mol L-1). Em seguida, é mostrada a estabilização dos eletrodos de referência Ag/AgCl em solução salina contendo cloretos, o estudo da secagem dos eletrodos em temperatura ambiente com exposição à luz e a caracterização dos mesmos por três métodos distintos, a saber: i) teste de reversibilidade (corrente redox vs. potencial); ii) variação do potencial com o tempo (coeficiente de degradação termodinâmica) e iii) variação do potencial com a concentração de cloretos. Também, apresenta-se a caracterização da área efetiva exposta do eletrodo de medição (trabalho) e os resultados da deposição de 1-2 Diaminobenzeno (DAB) como polímero seletivo. Além disso, são apresentados os resultados e discussões dos pseudo-eletrodos (recoberto ou não com Náfion® 117). Um ponto relacionado, a histerese associada à irreversibilidade dos eletrodos de referência resultou da ordem de 40 mVAg/AgCl Náfion® 117. Os potencias termodinâmicos observados foram da ordem de 100 ± 6 mVAg/AgCl Náfion® 117 para pseudo-eletrodo de referência sem e com Náfion® 117. Depois, foi realizado um estudo criterioso dos potenciais de resposta ao nitrito e aos interferentes por meio da técnica de DPV (do inglês, Differencial Pulse Voltammetry). Para evitar degradação acelerada (corrosão) do polímero sobre o eletrodo de trabalho, optou-se por realizar as medições com potencial igual a 0,50 VAg/AgCl Náfion® 117. Nessa condição, apresenta-se a monitoração de nitrito por FIA-automatizada na faixa de concentração de 50 a 250 mol L-1. Os resultados para a medição de nitrito mostraram que o sensor planar eletroquímico amperométrico desenvolvido é promissor, pois esse apresentou ótimo desempenho de reprodutividade (99,66%), sensibilidade (90 microA mol-1 L mm-2), seletividade (0,32%), repetitividade (91,28%) e estabilidade (15 ± 0,3 pA). / In this Master of Science, it has been developed an electrochemical planar sensor defined with three electrodes for nitrite measuring and its interferents (uric acid, ascorbic acid and paracetamol). In the experimental procedure, it is shown the development of an extracorporis set up (mini-pump, solenoid valves and analysis cell) which is coupled to a system of Flow-injection Analysis (FIA). This work also describes the sensor fabrication using alumina substrates, the standard cleaning of the electrodes, the process to obtain Ag/AgCl reference electrodes in HCl (0.1 mol L-1) and electrochemical activation of the working-electrode surface with H2SO4 (0.1 mol L-1). Following, it is shown the study of drying for electrodes at room temperature with exposition to room light and their characterization using three different methods: i) reversibility test (redox current vs. potential); ii) variation of the potential with the time (thermodynamics degradation coefficient) and iii) variation of the potential with the chloride concentration. Also, it is presented the characterization of the effective exposed area of the working electrode and the results of the deposited 1-2 Diaminobenzene (DAB) is presented as a selective polymer. In addition, the results and discussions of the pseudo-reference (recovered or not with Nafion® 117) are presented. Related to irreversibility is the hysteresis associated to the reference electrodes which resulted in the order of 40 mVAg/AgCl Nafion® 117. The observed thermodynamic potentials were of (100 ± 6) mVAg/AgCl Nafion® 117 for pseudo-electrodes recovered with Nafion® 117. Later on, a careful study of the response to nitrite and to its interferents was performed by means of the DPV technique (Differential Pulse Voltammetry). In order to avoid accelerated degradation (corrosion) of the polymer, measurements were performed at a potential of 0,5 VAg/AgCl Nafion® 117. In this condition, nitrite was monitored using the automatized-FIA (Flow Injection Analysis) for concentration in the range of 50 to 250 mol L-1. The results have shown that the planar amperometric sensor for nitrite measuring is usefull since it was observed excellent performance related to reproducibility (99.66%), sensitivity (90 microA mol-1 L mm-2), selectivity (0.32%), repetibility (91.28%) and stability (15.0 ± 0.3 pA).