<p>Zein is a major storage protein of corn, with unique amphiphilic film forming properties. It is insoluble in water, but soluble in 70% ethanol and acetic acid, and has been declared ‘generally recognized as safe’ (GRAS) by the FDA. Due to new advances in food nanotechnology, zein is being investigated for various applications such as biodegradable packaging, oral delivery of proteins and peptides, scaffold for tissue engineering, as well as biodegradable sensor platforms. The time consuming and highly complicated methods for toxin and allergen analysis in the food industry necessitates the need for a rapid, selective, compact and easy-to-use method of detection for analytes. In the scope of this dissertation, we investigated the feasibility of functional zein nanocomposite films and formation of a zein nanocomposite sensor assembly for rapid and highly selective electrochemical measurements of food toxins and allergens. Fabrication of a zein based electrochemical amperometric sensor assembly was studied, first through the comparison of various zein film characteristics changes with the application of Laponite®, graphene oxide and carbon nanotube nanoparticles, followed by a proof-of-concept study by detecting the gluten allergen protein gliadin. </p> <p>To mechanistically study the functional zein nanocomposite films, Laponite®, a silica nanoparticle, was added in the presence of 70% ethanol solvent and oleic acid plasticizer. The films were studied using various characterization techniques like transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), water contact angle measurements etc. Through Si-N bond formation between Laponite® and zein, fabricated zein nanocomposite films showed increase in surface hydrophobicity, water vapor barrier properties, tensile strength and Young’s modulus. Graphene oxide (GO), a carbon nanoparticle, was also incorporated into zein through the solvent casting process. Uniform dispersion of GO nanoparticles within zein matrix were confirmed up to 1% GO loading, and covalent and hydrogen bonding mechanisms were proposed. Similar to zein-Laponite® (Z-LAP) nanocomposites, zein-GO (Z-GO) showed increase in hydrophobic tendencies, rougher surface and a 300% improvement in Young’s modulus and 180% improvement in tensile strength at only 3% GO loading. Both nanoparticles increased tensile strength, thermal stability and water vapor barrier property of the films, indicating a potential for food packaging as an alternative application for the nanocomposite films.</p> Finally, the research focused on the fabrication of an electrochemical amperometric sensor, capable of detecting the protein gliadin, which is responsible for the allergic reaction with people having celiac disease. Novel biodegradable coatings made from zein nanocomposites: zein-graphene oxide, zein-Laponite® and zein-multiwalled carbon nanotubes (Z-CNT) using drop casting technique were tested for fabricating the electrochemical sensors using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) techniques. As Z-CNT produced the strongest signals compared to other nanomaterials, the active tip of the electrochemical sensor was functionalized through a sequence of layer by layer deposition of Z-CNT nanocomposite, antibody and target analyte. Here, Z-CNT acts as a natural linker molecule with large number of functional groups, that causes immobilization of capture antibody and target, to ensure high sensor performance. Both CV curves and SWV curves indicated successful sequential immobilization of gliadin antibody onto the Z-CNT coated electrode. The Z-CNT biosensor was successfully able to give CV signals for gliadin toxins for as low as 0.5 ppm and was highly specific for gliadin in the presence of other interfering molecules, and remained stable over a 30-day period. The low-cost, thin, conductive zein films offered a promising alternative for protein immobilization platforms used in sensors and can be extended to other matrices in biosensors as well as other functional film applications

Research on the cure and early detection of diseases such as diabetes, Alzheimer's, and Parkinson's is becoming of great interest due to the increasing number of people affected by them every year. An accurate and quick detection of various damaging species is highly critical in treatments of such diseases not only for exploring possible cures but also for early detection. If these diseases are detected during the initial stages than the possibility of curing them is much higher. Motivated by this, many researchers today have developed numerous types of sensing devices that can detect various physiological and biological compounds. However, most of these sensors are enzyme based. They have several setbacks such as the lack of sensitivity, restricted selectivity, short shelf life, and biological fouling. To overcome these obstacles, we examine the use of nanoceria modified Pt and Au electrodes for the detection of glucose and reactive oxygen species such as hydrogen peroxide. Amperometric detection of glucose and hydrogen peroxide is critical for biological applications for diabetes and possible Alzheimer's and Parkinson's patients. This dissertation focuses on the exploration of non-enzymatic detection of glucose and reactive oxygen species which has the prospective to be used for biological applications, in addition to an investigation of an odor control technology that uses these reactive oxygen species for the treatment of wastewater plants. The combination of bi-metallic composites with nanoceria showed increased oxidation ability towards glucose and hydrogen peroxide. The following dissertation expands on the relationship between bi-metallic nanoceria composite materials and its electro-oxidation of glucose and hydrogen peroxide towards biological sensing along with an investigation of an odor control technology that utilizes generates hydroxyl radical fine particle mist for the degradation of hydrogen sulfide odor in wastewater treatment plants.

[ES] En la presente tesis doctoral se exponen los resultados obtenidos en el desarrollo inicial de un sistema multisensor, tipo lengua electrónica voltamétrica, para el control de la durabilidad de las estructuras de hormigón armado (EHA). Aunque los sistemas multisensores son ampliamente utilizados en diferentes ámbitos, como el del medio ambiente o de la industria alimentaria, su uso en las EHA es novedoso. Igualmente, resulta novedosa la utilización de sensores voltamétricos que, como se demuestra en esta tesis, son de gran eficacia en el análisis de parámetros relacionados con el deterioro del hormigón armado, mejorándose los modelos de durabilidad obtenidos a través de sensores potenciométricos. Todo ello, sin ser aumentada de manera inabordable la complejidad electrónica y computacional del sistema. El prototipo de lengua electrónica diseñado es un sistema de sensores híbridos que consta de cuatro electrodos de trabajo (Au, Ag, Ni e INOX). Se dice que es híbrido porque se usan técnicas tanto voltamétricas (voltametría cíclica) como impedimétricas (espectroscopia de impedancia). Se han utilizado metales nobles (Au y Ag), metales no nobles (Ni) y aleaciones de alta durabilidad (acero inoxidable) con el fin de obtener un comportamiento electroquímico más variado. En la fase previa al desarrollo del sistema se seleccionaron los metales a utilizar en los sensores que formarían parte del sistema multisensor. Para ello se realizó un número ingente de ensayos con distintos metales (Ir, Rh, Pt, Au, Ag, W, Ni y INOX), tanto en disolución (simulando las condiciones de disolución de poro del hormigón), como en hormigón, con el fin de ser seleccionados aquellos metales de cuya respuesta se pudiera extraer una mayor información. Una vez finalizada la fase previa se estudió la respuesta aislada de cada uno de los metales seleccionados (Au, Ag, Ni e INOX), dividiéndose el estudio en 3 fases: ¿ Fase 1. Estudio en disolución: se analizaron los procesos que tienen lugar sobre la superficie del electrodo en disoluciones que simulaban distintas circunstancias que se pueden dar en el hormigón (variación de la disponibilidad de O2, variación del pH y presencia del anión cloro). Los resultados obtenidos se compararon con los encontrados en literatura. ¿ Fase 2. Estudios hechos con el sensor embebido en hormigones convencionales sin adiciones. Se embebieron sensores voltamétricos en hormigones convencionales de distinta relación agua/cemento. Seguidamente, se analizaron las probetas bajo distintas circunstancias que tuvieran influencia en el desencadenamiento y cinética de los procesos de corrosión como son: o Variaciones en la disponibilidad de O2 y H2O. o Carbonatación del hormigón. o Presencia de Cl-. ¿ Fase 3. Se desarrollaron modelos que permitieran identificar variaciones en parámetros relacionados con el deterioro del hormigón armado o estimar y predecir el parámetro de interés. Terminado el estudio de la respuesta aislada de los cuatro sensores, se procedió a evaluar la respuesta cruzada de los sensores siguiendo los protocolos propios de las lenguas electrónicas. Tras analizar y comparar las respuestas aisladas y cruzadas de los sensores, se propuso una rutina de trabajo que en un futuro ayude a optimizar los recursos, tanto operacionales como de fabricación, utilizados en el sistema. Para finalizar, se hizo un estudio inicial para tratar de mejorar la autonomía del sistema, evaluando el efecto producido al simplificar la configuración de celda, reduciendo el número de electrodos de tres a dos. / [CA] En la present tesi doctoral s'exposen els resultats obtinguts en el desenvolupament inicial d'un sistema multisensor, tipus llengua electrònica voltamètrica, pel control de la durabilitat de les estructures de formigó armat (EFA). Encara que l'ús d'aquest tipus de sistema està molt expandit en l'àmbit del medi ambient i de la indústria alimentària, el seu ús en les EFAs és molt nou. Igualment, resulta nova la utilització de sensors voltamètrics, que com és demostra en aquesta tesi, són de gran eficàcia en la determinació de les condicions del formigó armat, millorant-se considerablement els models de durabilitat obtinguts mitjançant sensors potenciomètrics. Tot això, sense augmentar la complexitat electrònica i computacional del sistema d'una forma inabordable. El prototip dissenyat de llengua electrònica és un sistema de sensors híbrids compost per quatre elèctrodes de treball (Au, Ag, Ni i acer inoxidable). Es diu que és híbrid perquè en el sistema de sensors s'utilitzen tècniques voltamètriques i impedimètriques. S'han utilitzat metalls nobles (Au i Ag), metalls no nobles (Ni) i aliatges d'alta durabilitat (acer inoxidable). Amb la finalitat d'obtindre un comportament electroquímic més variat. En la fase prèvia al desenvolupament del sistema, es van seleccionar els metalls a utilitzar en els sensors que formarien part del sistema multisensor. Per a això es va realitzar una quantitat ingent d'assajos amb diferents metalls (Ir, Rh, Pt, Au, Ag, W, Ni i acer inoxidable), tant en dissolució com en formigó, amb l'objectiu de seleccionar aquells metalls dels quals es poguera aconseguir més informació amb la seua resposta. Una vegada finalitzada aquesta fase prèvia, es va estudiar la resposta aïllada de cadascun dels metalls seleccionats (Au, Ag, Ni i acer inoxidable). L'estudi es va dividir en tres fases: ¿ Fase 1. Estudis en dissolució: es van analitzar els processos duts a terme sobre la superfície de l'elèctrode en dissolucions que simulaven diferents circumstàncies que es poden donar en el formigó (variació de la disponibilitat d' O2, variació de pH i presència de l'anió clor). Els resultats obtinguts es van comparar amb els trobats en la literatura. ¿ Fase 2. Estudis fets amb els sensors embeguts en formigó: es van embeure els sensors voltamètrics en formigons convencionals de diferent relació aigua/ciment i sense adicions. A continuació, es van analitzar les provetes sota diferents circumstàncies que tingueren influència en el desencadenament i cinètica dels processos com són: o Variacions en la disponibilitat d' O2 i H2O. o Carbonatació del formigó. o Presencia de Cl-. ¿ Fase 3. Desenvolupament de models que possibiliten identificar variacions en paràmetres relacionats amb el deteriorament del formigó armat o estimar i predir el paràmetre d'interès. Finalitzat l'estudi de la resposta aïllada dels quatre sensors, es va avaluar la resposta creuada mitjançant protocols propis de les llengües electròniques (PCA i PLS). Després d'analitzar i comparar les respostes aïllades i creuades dels sensors, es va proposar una rutina de treball que un futur ajude a optimitzar els recursos, tant operacionals com de fabricació, utilitzats al sistema. Per acabar, es va fer un estudi inicial per a tractar de millorar l'autonomia del sistema, avaluant l'efecte produït al simplificar la configuració de cel·la, reduint el nombre d'elèctrodes de tres a dos. / [EN] In this thesis the results obtained in the development of a multisensor system, known as electronic voltametric tongue, for the reinforcement concrete structures' (RCS) durability control are exposed. Although the use of this multisensor system is widespread in different fields such as: the food industry and environmental control, its use in RCS monitoring is very novel. It is equally novel the use of voltametric sensors, this kind of sensors are very efficient in determining concrete conditions, improving the durability models obtained through potentiometric sensors, all without overly increasing the system's electronic and computational complexity The electronic tongue prototype designed is a hybrid sensor system made up of four working electrodes (Au, Ag, Ni and stainless steel). It has been referred to as hybrid because in the system voltametric and impedimetric electrochemical techniques are used. Noble metals (Au and Ag), non-noble metals (Ni) and high-durability alloys (stainless steel) have also been used with the purpose of achieving a more varied electrochemical behaviour. In the previous development phase of the system, the metals involved in the development of the electronic tongue were selected. In order to do this, a variety of tests with different metals were performed (Ir, Rh, Pt, Au, Ag, W, Ni and SS), in both dissolution (different concrete pore solution conditions were simulated) and hardened concrete. This allowed us to choose the metals which responses contained the most information. The next steps focused on the study of the selected sensors isolated response: ¿ Phase 1: simulation of concrete pore solution in dissolution systems. The results were compared with those already existing in the bibliography. ¿ Phase 2: studies with the sensors embedded in different standard concretes without additions. The samples were tested in different conditions involved in the rebars corrosion kinetics (variations in O2 and humidity availability, concrete carbonation and chlorides presence). ¿ Phase 3: Development of estimation models for the parameters of interest. After finishing the study of the isolated sensors' response, a cross-evaluation of their response was performed using typical protocols used in the electronic tongues (i.e. PCA and PLS). After analysing and comparing the isolated and crossed sensor's response, an optimized multisensory routine work was proposed which could, in the future, help optimize the resources used in the system. Finally, a study was carried out to improve the system's autonomy, in which the repercussion of the cell configuration simplification by means of the removal of the reference electrode was evaluated. / La autora quiere expresar su agradecimiento al Ministerio de Educación, Cultura y Deporte por la beca predoctoral FPU 16/00723 / Martínez Ibernón, A. (2023). Lenguas electrónicas para la evaluación de la durabilidad de estructuras de hormigón armado y el seguimiento de la corrosión [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/192263

Capteur électrochimique basé sur des matériaux carbonés fonctionnalisés, pour la détection de deux micropolluants faisant partie des substances prioritaires de la Directive Cadre européenne sur l’Eau (DCE2000/60/CE) : le plomb et l’anthracène. Les capteurs électrochimiques permettent d’atteindre des limites de détection et une sélectivité adéquates pour l’analyse de micropolluants dont les concentrations sont de l’ordredu μg/L, et sont simples d’utilisation pour des analyses in situ à moindre coût comparés aux appareils d’analyses conventionnels. Leur robustesse est un paramètre important afin de permettre des mesures en continu ou semi-continu dans les eaux. Cette thèse propose tout d’abord le développement du capteur pour la détection du plomb. La formulation d’une encre conductrice de carbone est étudiée pour la sérigraphie de ’électrode réceptrice, permettant ainsi de contrôler la composition de l’encre et d’étudier l’influence de la phase carbonée sur les propriétés électrocatalytiques des électrodes. La fonctionnalisation des électrodes par greffage électrochimique d’un sel de diazonium est également étudiée afin de maîtriser la sensibilité et la reproductibilité des électrodes greffées, en contrôlant l’épaisseur et la qualité des couches. Avec cet objectif, la fonctionnalisation dans un liquide ionique protique qui permet le contrôle de la monocouche en modulant la viscosité de ce milieu a été étudiée. Les électrodes greffées montrent des performances analytiques améliorées notamment en termes de répétabilité et de reproductibilité. Enfin ce travail de thèse porte également sur le développement du capteur pour la détection électrochimique de l’anthracène, molécule sans fonctions chimiques. Les électrodes sont, dans ce cas, fonctionnalisées par un polymère à empreinte moléculaire, matériau connu pour sa très grande sélectivité. Les performances de ce capteur, dont la sélectivité est basée uniquement sur le facteur de forme de la molécule, pour la détection de l’anthracène sont alors mises en évidence. / Electrochemical sensor based on functionalized carbon materials, for the detection of two micropollutants, lead and anthracene, which are among of the priority substances of the European Framework Directive on Water(DCE 2000/60 / EC). Electrochemical sensors allow to achieve detection limits and selectivities for the analysis of micropollutants whose concentrations are of the order of μg/L. They are easy to use for in situ analyzes at lower costs compared to those of the conventional analysis equipment. Their robustness is an important parameter in order to allow continuous or semi-continuous measurements in water. First of all, this thesis proposes the development of a sensor for lead detection. The conductive carbon ink formulation is studied for the screen-printing of the receiving electrode, thus allowing to control the ink composition and to study the influence of the carbon phase on the electrocatalytic properties of electrodes. Functionalization of electrodes by electrochemical grafting of a diazonium salt is also studied in order to control the sensitivity and reproducibility of grafted electrodes, by controlling the thickness and the quality of the layers. With this aim it has been studied the functionalization in a protic ionic liquid in order to allow the control of the monolayer bymodulating the viscosity of this medium. The grafted electrodes show improved analytical performance especially in terms of repeatability and reproducibility. Finally, this work reports the development of a sensor for the electrochemical detection of anthracene, a molecule without chemical functions. In this case, a molecularly imprinted polymer, a material known for its very high selectivity, functionalizes the electrodes.Having a selectivity is only based on the form factor of the molecule, the performance of the sensor developed for the detection of anthracene is also highlighted.

Made available in DSpace on 2017-07-24T19:38:07Z (GMT). No. of bitstreams: 1 Cleverson S Santos.pdf: 2872449 bytes, checksum: 6d5838a843155793c2eb115ea3d233c4 (MD5) Previous issue date: 2012-03-13 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The research focused on the development of electrochemical sensors based on LBL films have grown exponentially in recent years. In this context, this paper reports the development of an electrochemical sensor using the Layer-by-layer (LbL) technique, which enables the construction of ultrathin films from electrostatic interactions between oppositely charged polyelectrolytes. For this purpose, the tetrasulfonated nickel phthalocyanine (NiTsPc) was used as polyanion molecule and the 3-n-propilpyridinium silsesquioxane chloride (SiPy+Cl-) as the polycation. This silsesquioxane polyelectrolyte is an excellent ion exchange and has high ability to form stable films on the surface of solid substrates. The LbL films were built using two different architectures: one with an outer layer of phthalocyanine designated as (SiPy+Cl-/NiTsPc)n and another with the phthalocyanine as the inner layer, (NiTsPc/SiPy+Cl-)n with different bilayers, (where n = number of bilayers). The deposition of the bilayers was monitored using the UV-VIS spectroscopy in the region from 500 to 800 nm, where the phthalocyanines exhibit two absorption bands, one related to the dimeric species at 630 nm and another at 669 nm related to monomeric form. It was observed that the parameters:immersion time, pH and concentration directly influenced the construction of these films and therefore they were optimized. The optimized parameters were: immersion time of 280 s, pH = 8 and concentrations of polyeletrolytes solutions of 2 mg mL-1, which provided stable and homogeneous films, with higher concentrations of monomeric species. Monitoring the bilayers deposition in the UV-VIS region, a linear relationship was obtained between the absorbance and the number of bilayers deposited. FTIR and Raman spectra showed that the interactions between the polyelectrolytes occurs by the SO3 groups in the structure of tetrasulfonated phthalocyanines with the pyridinium groups present in the structure of the SiPy+Cl-. Using the AFM technique, it was observed that the average roughness of the films decreased with the increase of bilayers. On the other hand, the thickness of the films increased with the number of bilayers, and the average thickness of each bilayer was 22 nm for the architecture (SiPy+Cl-/NiTsPc)n, and 19.2 nm for the opposite configuration. The electrodes were applied for simultaneous determination of dopamine (DA) in the presence of the interfering species, such as ascorbic acid (AA) and uric (UA). It was observed that the architecture as well as the thickness of the films has influenced significantly the electrochemical response in the presence of analytes. The film with the highest current density and less positive potential values for these analytes was (SiPy+Cl-/NiTsPc)2. For this electrode, f om the cyclic voltammetry technique, anodic peaks were observed at 0.30 V,0.68 V and 0.74 V in the presence of DA, AA and UA, respectively. Studies in different scan rates in presence of dopamine showed that the kinetics of electron transfer is controlled by diffusion of species to the electrode surface. Using the square wave voltammetry, DA was detected in presence of AA with a peak separation potential of 350 mV. However, for a fixed concentration of DA, it was observed an increase of the intensity of peak current with increasing of AA concentration, which is an indication that the AA electrocatalyzes the oxidation reaction of DA to dopaminequinone, causing an increase in the current, which prevents the accurate determination of these analytes simultaneously. On the other hand, in the presence of UA in a fixed concentration of 4.7 x 10-4 mol L-1, it was possible to quantify DA in the range of 1.0 x 10-5 to 9.9 x 10-5 mol L-1 with a detection limit of 2.37 x 10-6 mol L-1 and quantification limit of 7.9 x 10-6 mol L-1 with peak separation Ep= 500 mV. By varying both the concentration of DA and UA, in the range of 1.0 x 10-4 to 9.0 x 10-4 mol L-1 for DA and 1.0 x 10-5 to 9.9 x 10-5 mol L-1 for UA, it was obtained a correlation coefficient of R = 0.997 and R = 0.988 for AU and DA respectively. The results showed that the electrode (SiPy+Cl-/NiTsPc)2 is selective and sensitive for DA determination in presence of interfering species AA and UA. / As pesquisas voltadas para o desenvolvimento de sensores eletroquímicos a base de filmes LbL têm crescido exponencialmente nos últimos anos. Neste âmbito, este trabalho relata o desenvolvimento de um sensor eletroquímico, utilizando a técnica Layer-by-Layer (LbL), a qual possibilita a construção de filmes ultrafinos a partir de interações eletrostáticas entre polieletrólitos de cargas opostas. Para tanto foi utilizado como poliânion a molécula ftalocianina tetrassulfonada de níquel (NiTsPc), e como policátion o cloreto de 3-npropilpiridínio silsesquioxano (SiPy+Cl-). Tal composto constitui um excelente trocador iônico, além de apresentar alta capacidade de formação de filmes estáveis sobre a superfície de substratos sólidos. Foram construídos filmes em duas arquiteturas: uma com a ftalocianina na camada mais externa designada como (SiPy+Cl-/NiTsPc)n e outra com esta na camada mais interna, (NiTsPc/SiPy+Cl-)n com diferentes bicamadas, (onde n= número de bicamadas). A deposição das bicamadas foi monitorada utilizando-se a técnica de espectroscopia de absorção na região do UV-VIS, mais precisamente na região de 500 a 800 nm, onde as ftalocianinas apresentam duas bandas de absorção, uma referente a forma agregada em 630 nm e outra referente a forma monomérica em 669 nm. Foi observado que as variáveis: tempo de imersão, pH e concentração dos polieletrólito influenciam diretamente na construção dos filmes e portanto estas foram otimizadas. Os parâmetros otimizados foram: tempo de imersão de 280 s, pH = 8 e concentrações de 2 mg mL-1 obtendo-se filmes estáveis e homogêneos, com maiores concentrações de espécies monoméricas em relação a espécies agregadas. O monitoramento da deposição das bicamadas na região do UV-VIS mostrou uma relação linear entre absorbância e o número de bicamadas depositadas. Os espectros de FTIR e Raman, evidenciaram as interações entre os grupos SO3 presentes na estrutura das ftalocianinas tetrassulfonadas com os grupos piridínios presentes na estrutura do SiPy+Cl-. Utilizando a técnica de microscopia de força atômica foi possível verificar que a rugosidade média dos filmes diminuiu em função do aumento do número de bicamadas. Por outro lado, a espessura dos filmes aumentou com o número de bicamadas, sendo que a espessura média de cada bicamada foi de 22 nm para a configuração (SiPy+Cl-/NiTsPc)n, e de 19,2 nm para a configuração oposta. Os eletrodos foram aplicados na determinação simultânea de dopamina (DA) em meio aos interferentes ácido ascórbico (AA) e úrico (AU). Observou-se que a arquitetura assim como a espessura dos filmes influenciaram de maneira significativa na resposta eletroquímica na presença dos analitos. O filme que apresentou maior intensidade de corrente e valores de potencial de pico menos positivos foi (SiPy+Cl-/NiTsPc)2. Para este eletrodo, a partir da técnica de voltametria cíclica, foram observados picos anódicos em 0,30 V, 0,68 V e 0,74 V, na presença de DA, AA e AU, respectivamente. Estudos da variação da velocidade de varredura para dopamina mostraram que a cinética de transferência eletrônica é controlada pela difusão de espécies a superfície do eletrodo. Utilizando a técnica de voltametria de onda quadrada, detectou-se DA na presença de AA, com separação de potenciais de pico de 350 mV. No entanto, para uma concentração fixa de DA, foi observado um aumento da intensidade de corrente de pico com o aumento da concentração de AA, o que é um indicativo de que o AA eletrocatalisa a reação de oxidação de dopaminaquinona a DA novamente, o que impossibilita a determinação precisa destes analitos simultaneamente. Por outro lado, na presença de AU com concentração fixa de 4,7 x 10-4 mol L-1, foi possível quantificar DA na faixa de 1,0 x 10-5 a 9,9 x 10-5 mol L-1 com limite de detecção de 2,4 x 10-6 mol L-1 e quantificação de 7,9 x 10-6 mol L-1 com separação de potencial de pico de 500 mV. Variando-se simultaneamente a concentração das duas espécies, DA e AU, na faixa de 1,0 x 10-4 a 9,0 x 10-4 mol L-1 para DA e 1,0 x 10-5 a 9,9 x 10-5 mol L-1 para AU, obteve-se coeficiente de correlação iguais a R = 0,997 e R = 0,988, para AU e DA respectivamente. Os resultados mostram que o eletrodo é seletivo e sensível a determinação de DA em meio aos interferentes AA e AU.

Made available in DSpace on 2017-07-24T19:38:14Z (GMT). No. of bitstreams: 1 RAFAELA D OLIVEIRA.pdf: 2756499 bytes, checksum: e1e60d222b6dbe62066658f22ea4de0b (MD5) Previous issue date: 2014-08-22 / In this work, starch-stabilized silver nanoparticles (AgNPs-Am) were synthesized by reduction of AgNO3 using the NaBH4. The temperature and concentration of reagents of the synthesis were optimized. The formation of AgNPs-Am was monitored by UV-Vis spectroscopy and dynamic light scattering (DLS). The optimum conditions found for the AgNPs-Am synthesis were starch 0.6 % (w/v), 3.6 x 10-3 mol L-1 NaBH4, 0.9 x 10-3 mol L-1 AgNO3 and synthesis in bath ice. The average size of the AgNPs-Am was between 21 and 77 nm. Transmission electron microscopy (TEM) confirmed the AgNPs-Am formation inside and outside of the starch chains, however the smaller sizes were referred to the NPs stabilized by starch. Measurements of Potential zeta indicated stability of the particles, confirmed by DLS monitoring that demonstrated low agglomeration of NPs in a period of 115 days. For the characterization of AgNPs-Am it was also used infrared spectroscopic (FTIR) and X-ray diffraction (XRD). The AgNPs-Am were applied as polyanion for the construction of films by Layer-by-Layer technique (LbL), alternating with polycation 3-n-propylpyridinium-silsesquioxane (SiPy+Cl-). In order to obtain the films, pH and immersion time of the polyelectrolytes were optimized, as well as the concentration of SiPy+Cl-, monitoring the deposition by UV-Vis. The optimum parameters were immersion time 240 seconds, 2 mg/mL SiPy+Cl- pH 6.5 and AgNPs-Am pH 9.0. Atomic force microscopy (AFM) images showed that film thickness increases linearly and the roughness decrease with the bilayers number. FTIR spectra and Raman confirmed the interaction between the polyelectrolytes in the assembly of LbL films. The LbL films with architecture (SiPy+Cl-/AgNPs-Am)n (n = bilayers number) were applied as modified electrodes for iodine detection, using differential pulse voltammetry (DPV). It was verified that interaction of the components in the LbL films improved the current intensity. The film (SiPy+Cl-/AgNPs-Am)n (n=5) showed better current response in phosphate buffered saline (PBS) 0.1 mol L-1 pH 7.0. The instrumental parameters Epulse, and tpulse were optimized by 23 factorial design. It was verified a significant effect for third order interaction for the intensity of iodine redox peak currents, so the instrumentals parameters were evaluated together. The results of optimization were tpulse = 0.05 s, = 40 mV/s e Epulse = 50 mV. Accordingly, the modified electrode obtained a linear response for iodine concentrations ranging from 4.34 x 10-5 to 3.47 x 10-4 mol L-1 (R=0,9936) and from 4.40 x 10-4 to 4.24 x 10-3 mol L-1 (R=0,9938). It was obtained limit of detection (LOD) 5.56 x 10-6 and 1.51 x 10-5 mol L-1 and for limit of quantification (LOQ) 1.85 x 10-5 and 5.04 x 10-5 mol L-1, respectively. The AgNPs-Am synthesized in this work also acted as colorimetric sensor for iodine, with three regions of linearity. Two analytical curves were obtained for iodine concentration range from 2.40 x 10-7 to 9.50 x 10-7 mol L-1 and from 2.40 x 10-6 mol L-1 to 1.60 x 10-5 mol L-1. It was obtained a LOD of 1.71 x 10-8 and 1.06 x 10-6 mol L-1 and LOQ of 5.69 x 10-8 to 3.55 x 10-6 mol L-1, respectively for each range. Color variations obtained in these concentrations correspond to interaction between iodine and silver, which were monitored by UV-Vis band showed in 410 nm. At concentrations above 5.50 x 10-5 mol L-1 there is the appearance of blue color, absorbance in 600 nm, corresponding to the interaction between starch and iodine. It was also obtained a linear relationship for iodine concentration from 5.50 x 10-5 mol L-1 to 9.50 x 10-5 mol L-1. For this concentration range, LOD and LOQ were respectively 1.37 x 10-6 and 4.58 x 10-6 mol L-1. The results presented confirm the potential use of AgNPs-Am for iodine detection, both for the modification of electrodes for electrochemical determination as a colorimetric sensor. / Neste trabalho foram sintetizadas nanopartículas de prata estabilizadas em amido (AgNPs-Am). A síntese foi realizada por redução do sal AgNO3 utilizando o NaBH4. A temperatura de síntese e concentração dos reagentes foram otimizadas, a formação das AgNPs-Am foi monitorada por espectroscopia na região do UV-Vis e medidas de espalhamento dinâmico da luz (DLS). As condições ótimas encontradas para síntese de AgNPs-Am foram amido 0,6 % (m/v), 3,6.10-3 mol.L-1 de NaBH4, 0,9.10-3 mol.L-1 de AgNO3 e síntese em banho de gelo. O tamanho médio das AgNPs-Am foi entre 21 e 77 nm. Imagens de microscopia eletrônica de transmissão (TEM) confirmaram que houve formação das AgNPs no interior e fora das cadeias de amido, sendo os menores tamanhos referentes às NPs estabilizadas pelo amido. Medidas de Potencial zeta indicaram estabilidade das NPs, confirmada por acompanhamento DLS que demonstrou baixa aglomeração em um período de 115 dias. Para caracterização das AgNPs-Am utilizou-se também espectroscopia na região do infravermelho (FTIR) e difração de raios X (XRD). As AgNPs-Am foram utilizadas como poliânion para construção de filmes pela técnica Layer-by-Layer (LbL), alternando com policátion 3-n-propilpiridínio-silsesquioxano (SiPy+Cl-). Para construção dos filmes, pH e tempo de imersão dos polieletrólitos foram otimizados, assim como concentração de SiPy+Cl-, monitorando a deposição por UV-Vis. Os parâmetros ótimos foram tempo de imersão 240 segundos, solução de 2 mg/mL de SiPy+Cl- pH 6,5 e AgNPs-Am pH 9,0. Imagens de microscopia de força atômica (AFM) mostram que a espessura dos filmes aumenta linearmente e a rugosidade decresce com o número de bicamadas. Espectros FTIR e Raman confirmaram a interação entre os polieletrólitos na montagem dos filmes. Os filmes LbL com configuração (SiPy+Cl-/AgNPs-Am)n (n = número de bicamadas) foram aplicados como eletrodos modificados para detecção de iodo, utilizando-se voltametria de pulso diferencial (VPD). Verificou-se que a interação dos componentes no filme LbL melhorou a intensidade de corrente. O filme (SiPy+Cl-/AgNPs-Am)n (n=5) apresentou melhor resposta de corrente em eletrólito suporte tampão fosfato salino (PBS) 0,1 mol.L-1 pH 7,0. Os parâmetros instrumentais Epulso, e tpulso foram otimizados por planejamento fatorial 23. Verificou-se efeito significativo para interação de terceira ordem para intensidade de corrente do pico de redução do iodo, portanto os parâmetros instrumentais foram avaliados em conjunto. Os resultados da otimização foram tpulso = 0,05 s, = 40 mV/s e Epulso = 50 mV. Nestas condições, o eletrodo modificado obteve resposta linear para concentrações de iodo que variam de 4,34.10-5 a 3,47.10-4 mol.L-1 (R=0,9936) e de 4,40.10-4 a 4,24.10-3 mol.L-1 (R=0,9938). Respectivamente, obteve-se limite de detecção 5,56.10-6 e 1,51.10-5 mol.L-1 e para o limite de quantificação 1,85.10-5 e 5,04.10-5 mol.L-1. As AgNPs-Am sintetizadas neste trabalho também atuaram como sensor colorimétrico de iodo, com três regiões de linearidade. Duas curvas analíticas foram construídas para concentrações de iodo de 2,40.10-7 a 9,50.10-7 mol.L-1 e de 2,40.10-6 mol.L-1 a 1,60.10-5 mol.L-1. Obteve-se LD de 1,71.10-8 e 1,06.10-6 mol.L-1 e LQ de 5,69.10-8 e 3,55.10-6 mol.L-1, respectivamente para cada intervalo. As variações de cores obtidas nestas concentrações correspondem a interação entre o iodo e a prata, as quais foram acompanhadas pela banda UV-Vis apresentada em 410 nm. Em concentrações acima de 5,50.10-5 mol.L-1 observa-se o aparecimento de coloração azul, absorbância em 600 nm, correspondente a interação entre amido e iodo. Obteve-se linearidade para concentrações de 5,50.10-5 mol.L-1 a 9,50.10-5 mol.L-1. Para este intervalo de concentração, os LD e LQ são respectivamente 1,37.10-6 e 4,58.10-6 mol.L-1. Os resultados apresentados confirmam a potencialidade do uso das AgNPs-Am para detecção de iodo, tanto na modificação de eletrodos para determinação eletroquímica, quanto o uso como sensor colorimétrico.

Afin de réaliser un appareil innovant pour la mesure de gaz polluants, la société SVS@CAP s’est associée avec le laboratoire de physique corpusculaire en 2009 pour la création du projet EREBUS. Ce projet a pour but la réalisation d’un ensemble de dispositifs sans fil permettant d’effectuer une surveillance de la concentration de gaz polluants. L’autonomie et la compacité d’un tel dispositif étant essentielles, la problématique principale porte sur la réduction de la consommation. A partir d’une première étude menée sur les différentes technologies existantes, les capteurs électrochimiques ont été identifiés comme les moins consommateurs d’énergie. Pour chacun des gaz cibles, un modèle électrique du capteur associé a été déterminé. A partir de ces modèles, une architecture dédiée et épurée a pu être déduite. Pour atteindre et même dépasser les objectifs de consommation, les efforts ont aussi été portés sur un dimensionnement avec la méthode gm/id. La réalisation de cette électronique intégrée a permis d’atteindre une consommation de l’ordre du μW pour chaque voie de mesure. Enfin, pour compléter la chaîne de lecture, plusieurs architectures de convertisseurs ont été étudiées et réalisées pour fonctionner à des fréquences déchantillonnage proches du Hz. Les consommations obtenues pour les convertisseurs sont limitées avec comme ordre de grandeur la centaine de nW. / In order to realize an innovative product for pollutants in the atmosphere, SVS@CAP company started in 2009 the EUREBUS project in collaboration with the "Laboratoire de Physique Corpusculaire". The aim of this project is to design a wireless equipement to measure gas concentrations. The key issues of this project are concerning the autonomy as well as the small size of the product. In consequence an integrated and low power electronics remains essential. From a first study of the existing technologies to detect gaz concentrations, electrochemical sensors were selected because of their low power consumption. For each of the target gas, an electrical model was determined. From those models, a specific architecture was designed. A special effort was made on the energy consumption thanks to the use of the gm/id methodology which was necessary to achieve and exceed the specifications. The final order of the power consumption of the front-end developped and realized is around the μW. Finally, in order to complete the chain of acquisition, some architectures of analog to digital converter were studied, developped and realized with sample frequencies close to the Hz. The power consumptions of the converters developped are limited to the order of the hundreds of nW.

<p>Iron oxide nanoparticles were prepared using co-precipitation method in the presence and absence of beta-cyclodextrin (&beta / -CD). Such materials were characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The TEM shows that the surface morphology has no difference between nanoparticles prepared in the presence and absence of beta-cyclodextrin (&beta / -CD), amorphous particles with high surface area and dimensions of about 100 nm by 500 nm. The amorphous states of nanoparticles are confirmed further by XRD. The ATR-FTIR analysis confirms inclusion complex between &beta / -CD and nanoparticles.</p>

<p>Iron oxide nanoparticles were prepared using co-precipitation method in the presence and absence of beta-cyclodextrin (&beta / -CD). Such materials were characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The TEM shows that the surface morphology has no difference between nanoparticles prepared in the presence and absence of beta-cyclodextrin (&beta / -CD), amorphous particles with high surface area and dimensions of about 100 nm by 500 nm. The amorphous states of nanoparticles are confirmed further by XRD. The ATR-FTIR analysis confirms inclusion complex between &beta / -CD and nanoparticles.</p>

Magister Scientiae - MSc / Iron oxide nanoparticles were prepared using co-precipitation method in the presence and absence of beta-cyclodextrin β-CD). Such materials were characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), attenuated total reflection Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The TEM shows that the surface morphology has no difference between nanoparticles prepared in the presence and absence of beta-cyclodextrin β-CD), amorphous particles with high surface area and dimensions of about 100 nm by 500 nm. The amorphous states of nanoparticles are confirmed further by XRD. The ATR-FTIR analysis confirms inclusion complex between β-CD and nanoparticles. The nanoparticles synthesized were used to develop an electrochemical sensor for phenolic endocrine disruptors by modifying the surface area of glassy carbon electrode (GCE). Electrochemical characterization of the iron oxide β-CD nano-composites, studied in 0.1 M potassium chloride (KCl) using chronoamperometry,showed that the surface concentration of the adsorbed composite material was 8.5 x 10-8 mol/cm2. Sensor analysis of bisphenol A (BPA) was carried out using cyclic voltammetry (CV) and square wave voltammetry (SWV) based on amperometric techniques which gave a linear range of 0.50 × 10-6 M to 50 × 10-6 M; limit of detection of 0.156 x 10-6 M and order of magnitude of linearity of 2.03. Hence, the sensor was further used to study 4-tert-octylphenol (TOP); the results showed that the sensitivity and the limit of detection were 11.31 nA L/mol and 0.249 x 10-6 M, respectively and order of magnitude of linearity of 2.00. / South Africa