O objetivo do presente trabalho é o desenvolvimento de nanocompósitos de silício poroso/azul de metileno (PS/MB) utilizando-se substratos de silício macroporoso e mesoporoso para sua aplicação no monitoramento de gases orgânicos. Foram estudados processos de formação de PS/MB usando PS macroporoso e controlando o pH da solução. Os resultados obtidos indicam que a acidez da solução compromete a adsorção eficiente das moléculas de MB, sendo necessário a utilização de uma solução tampão para elevar o nível do pH. A necessidade de controlar o nível de pH da solução deve-se principalmente à característica ácida da superfície de PS recém formada, já que a superfície está constituída principalmente de ligações do tipo Si-Hx que são altamente hidrofóbicas. Os resultados da emissão fotoluminescente (PL) das estruturas de PS/MB em substrato de PS oxidado mostraram que a intensidade de emissão PL das moléculas de MB é mais intensa se comparada com a emissão das moléculas de MB em solução aquosa de baixa concentração. Esse resultado evidencia que a interação entre os elétrons p e a superfície do filme de PS otimiza a recombinação radiativa, minimizando possíveis caminhos não radiativos do estado excitado da molécula de MB. Adicionalmente, o resultado mostrou que as moléculas de MB adsorvidas sobre substratos de PS oxidados preservam suas características moleculares, atuando em forma monomérica. No caso de moléculas MB adsorvidas em substratos de PS não oxidados, os espectros de emissão PL mostraram que as moléculas de MB perderam sua identidade molecular formando, possivelmente, complexos na superfície do PS. Os resultados dos ensaios de adsorção das moléculas de MB em substratos de silício mesoporoso demonstraram ser mais eficientes quando o solvente utilizado foi o etanol, em condição de pH neutro. A monitoração de ambientes de vapores orgânicos foi efetuada através da resposta PL de uma estrutura de silício mesoporoso oxidado com moléculas de MB adsorvidas (Ox- PS/MB). Os resultados da emissão PL da estrutura Ox-PS/MB para os diferentes ambientes orgânicos apresentaram sinais de PL característicos para cada tipo de gás. Esses resultados mostraram o grande potencial de aplicação da estrutura Ox- PS/MB em um sistema de nariz óptico. / The objective of the present work is the porous silicon/methylene-blue (PS/MB) nanocomposite fabrication by using the macro-porous and mesoporous silicon substrate in order to be applied for organic solvent detection. The PS/MB formation process was studied PS/MB by using the macroporous silicon substrate by the pH value controlling of the solution moieties. The results showed that the acid condition of the solution compromises the efficiency of the MB adsorption wherever it was necessary to use the buffer in order to control the pH level of the solution. This additional process was a necessary condition because the fresh PS surface had had acid feature because the surface moieties at fresh PS are formed for the highly hydrophobic Si-Hx bonds. The PL spectra results from the PS/MB formed at oxidized PS substrate showed that the PL emission from the adsorbed MB molecules is more intense than the emission from the MB molecules in low concentrated solution. These results suggest that the PS surface and electrons p (in the MB) interaction minimizes the non-radioactive path for the excited state recombination of the MB molecules. Additionally this result showed that the adsorbed MB molecules preserved their molecular identity aging as a monomer moiety. In the case of the MB adsorbed at non-oxidized PS substrate, the PL spectra showed that the MB molecules lost their identity forming possible complex moieties at PS surface. The experimental results of the MB adsorption at the mesoporous silicon surface showed to be more efficient when the solution was ethanol at neutral pH value. The organic vapor ambient monitoring was made throughout the PL emission response of the Ox-PS/MB structure. These results showed that the PL emission had had the characteristic feature for each type of gas used in the experiment. These results showed the high potential application of the Ox-PS/MB structure in the optical nose system.

O estudo de sistemas voltados para a detecção e discriminação de compostos e substâncias gasosas tem se destacado nas áreas da nanociência e da nanotecnologia devido ao grande interesse no controle de odores e aromas presentes em alimentos, cosméticos e no meio ambiente. Dentre os diversos tipos de sensores matriciais de gases, conhecidos como narizes eletrônicos, os feitos à base de polímeros vêm se destacando devido ao baixo custo, fácil processabilidade, operação em temperatura ambiente e boa resposta sensorial. O presente trabalho mostra a confecção e análise de sensores poliméricos e um nariz eletrônico de pequenas dimensões, portátil e de baixo custo baseado em polímeros condutivos. Como materiais ativos dos sensores foram estudados materiais pertencentes à classe das polianilinas, politiofenos, polipirrol e ftalocianina de níquel, depositados por duas técnicas diferentes: spin coating e automontagem. As análises da espessura, reprodutibilidade e estabilidade elétrica mostraram diferenças em relação aos materiais empregados e a técnicas escolhidas, em que a uniformidade superficial não está associada diretamente com a estabilidade elétrica. Sensores que empregam PAni e POMA sofrem variação da resistência elétrica em função do tempo, o que está relacionado com a perda de dopagem desses materiais. O projeto e desenvolvimento de uma câmara de medidas são relatados com simulações que mostraram o perfil adequado para o posicionamento dos sensores. Para nortear a concepção do nariz, foi realizado um comparativo entre resistência e capacitância elétricas como parâmetros de interrogação mostrando resultados similares na discriminação, mas com diferenças de 100 vezes em valor relativo, o que resultou na escolha da resistência elétrica. O nariz eletrônico concebido apresenta poder de discriminação não só comparável ao da técnica de cromatografia gasosa, como também permite discriminar diversos tipos de analitos: perfumes, álcool etílico puro e adulterado, sucos de maçã, vinhos, cachaças e cachaças adulteradas e mel, tanto através da técnica de PCA quanto por redes neurais artificiais. O emprego de uma elipsóide como selecionador da região das classes facilitou o processo de visualização e análise dos dados enquanto que o uso de redes neurais mostrou classificações corretas próximas a 100% para praticamente todos os analitos. / The study of sensors for detection and discrimination of gaseous substances and compounds have been gaining much attention in areas such as nanocience and nanotechnology due to the great motivation in control of odors and substances associated with food, cosmetics and environment. Within several types of gas sensor arrays, known as electronic noses, polymeric-made ones distinguishes due to good sensory response, can be utilized at ambient temperature, are able to be easily processed and are of potential low cost. This work shows the fabrication and analysis of polymeric sensors and a small size, low cost and portable electronic nose. Polymeric materials belonging to polyaniline, polythiophene and polypyrrole classes and nickel phtalocyanines, deposited by two different techniques (spin coating and self assembly) were studied as active materials for the sensors. Analysis of thickness, reproducibility and electrical stability were performed and they showed differences among the studied materials and deposition techniques, where superficial uniformity is not associated directly with electrical stability. Sensors with PAni and POMA showed an electrical resistance variation in function of time which is related to dopant loss. Project and development of an analysis chamber are reported with simulations that showed an adequate profile for sensor positioning. A comparison between resistance and capacitance was performed aiming the electronic nose conceptualization. Both parameters showed similar discrimination capability but a 100 times difference in relative variation, leading to the choice of the electrical resistance. The conceived electronic nose shows a discrimination capability similar to gas chromatography and also allows the discrimination of many different analyte types: perfumes, pure and adulterated ethanol, apple juices, wines, pure and adulterated cachaças and honey, either with PCA technique or as well with artificial neural networks. The use of an ellipsoid to envelop class regions ease the visualization process and data analysis from PCA results while neural networks showed correct classifications near to 100% for almost all analytes.

A adulteração de combustíveis é uma grande preocupação no Brasil. A agência reguladora nacional (ANP) detecta anualmente de 1 a 3% de adulterações nas amostras coletadas, o que é um índice alto considerando o tamanho do mercado brasileiro. As alternativas de adulteração são vastas e muito dinâmicas, por isso os arranjos de sensores baseados no conceito de seletividade global parecem os mais adequados para detectar falsificação de combustíveis. O conceito de seletividade global leva em conta a sensibilidade cruzada de sensores químicos não específicos e o uso de métodos de análise multivariada de dados para encontrar padrões para amostras de diferentes composições químicas. Os sensores químicos podem ser obtidos de uma variedade de materiais sensoativos, cujas respostas elétricas variam de acordo com as propriedades físico-químicas do meio em que se encontra. Os polímeros condutores são excelentes materiais sensoativos, pois sua condutividade elétrica é grandemente influenciada pelas condições ambientais e podem ser processados na forma de filmes finos através várias técnicas. No presente trabalho, filmes de poli(3-metiltiofeno) (PMTh) e poli(3-hexiltiofeno) são depositados por cronopotenciometria e cronoamperometria sobre microeletrodos interdigitados e são caracterizados por espectroscopia de impedância. Os dados são analisados por redes neurais artificiais do tipo multilayer perceptron e bons resultados são obtidos na detecção de adulteração de gasolina. O mesmo estudo também pode ser aplicado na detecção de adulteração de álcool etílico combustível com um desempenho um pouco pior. / Fuel adulteration is a major concern in Brazil. The local governmental agency detects from 1 to 3% of problematic samples yearly, which is a lot considering Brazils market size. The myriad of adulteration possibilities is vast and it is very dynamic, thus array of sensors based on global selectivity concept seems to be more suitable methodology to detect problems in fuel. The global selectivity concept encompasses the cross-sensitivity of non-specific chemical sensors and the use of multivariated data analysis methods as a way to provide fingerprints for samples of different chemical composition. The chemical sensors can employ different types of sensoactive materials, whose electrical responses are dependent on the physicochemical characteristics of the media they get in contact with. Conducting polymers (CP) are per excellence suitable sensoactive materials, since their electrical conductivity is highly influenced by the environmental conditions and they can be easily processed in the thin film form by different techniques. In the present work films of poly(3-methylthiophene) (PMTh) and poly(3-hexylthiophene) (PHTh) are deposited by chronopotenciometry and chronoamperometry onto interdigitated microelectrodes and characterized through Impedance Spectroscopy. This data was analyzed with Multilayer perceptron neural networks and a very good performance is found in gasoline adulteration detection. A less great performance was also achieved in the investigation vehicular ethanol adulteration.

Les propriétés physiques et chimiques exceptionnelles du matériau diamant ont suscité l'intérêt des chercheurs pour le développement d'applications industrielles, comme par exemple dans les domaines de la dissipation thermique ou de l'électronique de puissance. En particulier, les propriétés mécaniques remarquables de ce matériau peuvent être exploitées avantageusement pour la conception de résonateurs MEMS (Micro-Electro-Mechanical Systems). Même si certains dispositifs MEMS à base de diamant avaient été décrits dans la littérature, les propriétés mécaniques de ce matériau n'avaient jamais été associées à ses propriétés chimiques pour la réalisation de transducteurs chimiques ou biochimiques à base de résonateurs MEMS. Ainsi, l'objectif cette thèse a été de démontrer l'intérêt de ce matériau innovant pour la fabrication de ces capteurs. Les MEMS offrent la possibilité de faire de la détection en temps réel de manière directe (sans marqueur), rapide et sensible, sur de faibles quantités d'analytes. De plus ils permettent d'adresser des cibles non électro-actives qui ne peuvent pas être détectées par des capteurs électrochimiques. Dans cette étude, nous avons développé dans un premier temps des procédés de micro-structuration spécifiques du diamant. Ces procédés entièrement compatibles avec des techniques de salle blanche ont permis d'aboutir à la réalisation de nombreux transducteurs à base de micro-leviers en diamant sur des substrats en silicium de 4 pouces. De plus les approches développées permettent d'éviter la gravure fastidieuse du matériau diamant. Leur caractérisation mécanique en régime dynamique a permis de caractériser le module d'Young E du matériau diamant synthétisé en fonction des conditions de croissance. Dans le meilleur cas une valeur de E très élevée de l'ordre de 1100 GPa a été obtenue, ce qui est très proche de la valeur du diamant monocristallin (1200GPa). Par ailleurs, nous avons pu vérifier que les propriétés de résonance (fréquence de résonance et facteur de qualité) des structures en diamant réalisées étaient supérieures à celles de structures identiques en silicium. En particulier, cela rend ces résonateurs plus aptes à être exploités en milieux liquides. Nous avons montré que dans de tels milieux les micro-leviers en diamant étaient très peu sensibles à une variation massique. En revanche leur sensibilité à une variation de masse volumique du liquide est de l'ordre de 3Hz.kg-1.m3 et donc significative. Par ailleurs, en fonctionnalisant des micro-leviers en diamant par de l'acide caproïque, nous avons mis en évidence que des variations de densité de charges à la surface des micro-leviers pouvaient induire des variations de fréquence de résonance de plusieurs dizaines de Hz dans le cas de structures vibrant à quelques kHz. Ceci a permis de mettre en évidence la grande sensibilité de nos transducteurs en diamant à des interactions moléculaires. Dans ce contexte nous avons pu réaliser un capteur d'ADN permettant la reconnaissance spécifique en temps réel de brins d'ADN cibles de 24 paires de bases sans marqueur. En parallèle de ces travaux, des structures d'actionnement et de lecture ont été intégrées et évalué sur des dispositifs résonants à base de diamant. Ceci a permis de les interfacer à un premier prototype de système d'acquisition électronique portable dédié réalisé au cours de cette thèse / Diamond material is very promising for future technological applications due to its outstanding physical and chemical properties. In particular, its remarkable mechanical features may be used advantageously for MEMS (Micro-Electro-Mechanical Systems) devices development. However, even though several diamond-based MEMS devices have been reported in the literature, the mechanical properties of this material have never been combined to its chemical properties for developing resonating MEMS-based biochemical transducers. Thus, the purpose of this study was to demonstrate the interest of such diamond transducers for chemical or biochemical sensing applications. MEMS devices are indeed attractive because they allow fast, label free and sensitive detection in real time on small volumes due to their miniaturized size. Moreover they offer the possibility to address non electroactive target species which are undetectable using classical electrochemical methods. In this study, we developed specific clean room compatible processes for diamond micro-structuring. The bottom-up approaches undertaken here were based on diamond patterns growth. Hence they avoid time consuming diamond etching steps. These processes allowed fabricating several diamond micro-cantilever transducers over 4-inches substrates. The mechanical characterization of the cantilevers in oscillating regime was performed in order to extract the material Young's modulus E when the structures were made of different polycrystalline diamond qualities. In the best case, a value of E as high as 1100 GPa and very close to the Young's modulus of monocrystalline diamond (1200 GPa) was achieved. In parallel, we verified that both cantilevers resonance frequency and Q-factor were significantly higher than those of identical silicon structures (on average twice higher). This makes diamond mechanical structures more suitable for use in liquid media. In such damping media a very poor sensitivity to mass changes was determined. Nevertheless, their sensitivity to liquid density changes was found to be significant (-3Hz.kg-1.m3). More importantly, by functionalizing diamond micro-cantilevers with caproic acid, an evidence of these transducers high sensitivity to surface molecular interactions was shown. Especially, when charge density variations occurs several tens Hz changes were measured on kHz-range oscillating cantilevers. In this context, a label free DNA sensor was achieved and allowed the specific detection of 24-mer target DNA in real time. In parallel to this work, actuation and boron doped diamond-based readout gauges were integrated to the resonant cantilevers and characterized. They allowed interfacing the cantilevers to a dedicated acquisition electronic prototype developed in the course of this study

The detection of volatile organic compounds in liquid is of interest for applications in public health, workplace safety and environmental monitoring. Traditionally, water samples were taken and analyzed in the laboratory using classical laboratory instrumentation. Current trends target real-time measurements using e.g. chemical microsensors built with microfabrication technologies. Among these, mass-sensitive chemical sensors, based on cantilever beams or surface acoustic devices, have shown substantial promise in gas-phase applications. In a liquid environment, the resonant microstructures typically suffer from high damping, which negatively affects the sensor resolution. In this work, a novel disk-type resonator developed at Georgia Tech was investigated as chemical microsensor for liquid-phase applications. The micromachined resonator vibrates in a rotational in-plane mode shape, reducing damping in a liquid environment. As part of the present research, a measurement setup with a custom-made flow cell for liquid-phase chemical measurements and a coating system to locally deposit polymer sensitive films onto the resonators were developed. To improve the film adhesion on the resonator surface in liquid, physical and chemical binding techniques were developed and tested on wafer samples. Polymers such as poly(4-vinylpyrrolidone), poly(ethylene-co-propylene) and poly(styrene-co-butadiene) were deposited using the custom-designed coating system onto the disk-type resonators. Liquid-phase measurements using tetrachloroethylene as the chemical analyte were performed. The experimental results are discussed, sources of problems are identified and recommendations for future research are made.

The purpose of this work is the development of MEMS-based resonant sensors for liquid-phase biochemical sensing applications. Specifically, the sensors developed here are aimed at embedded or point-of-sampling applications: (1) when there is not enough time to send a sample to a lab for analysis, (2) in resource-poor settings, (3) when collecting analyte and shipping it to a lab would damage the sample, or (4) for in-situ monitoring. To this end, a bulk micromachined resonant cantilever sensor and a surface micromachined sensor based on the spring-softening effect are investigated as transducer elements. The developed cantilever resonators are operated in an in-plane vibration mode to reduce fluid damping and mass loading by the surrounding fluid. The surface of the resonator is either coated with a chemically sensitive polymer film for chemical sensing or with a layer of protein or antibody for biosensor testing. Chemical tests for sensing volatile organic compounds using polymer-coated in-plane resonators in the liquid-phase give estimated limits of detection below 100 ppb. In addition, biosensor tests for the detection of anti-IgG yield estimated limits of detection around 100 ng/ml. In an attempt to further improve sensor reliability and to further lower the limits of detection, a second sensing concept has been investigated. The presented sensing scheme is capacitive with a resonator acting as an analog-to-digital converter. The resonator and the sensing capacitors are coupled via the spring softening effect. Through this mechanism a change in capacitance causes a shift in resonant frequency. Extensive device modeling has been performed and a process has been developed allowing for fabrication and on-chip packaging of these sensor structures. Initial mechanical characterization data show that the resonators do in fact vibrate.

Chemical sensors are generally used as one-dimensional devices, where one measures the sensor’s response at a fixed setting, e.g., infrared absorption at a specific wavelength, or conductivity of a solid-state sensor at a specific operating temperature. In many cases, additional information can be extracted by modulating some internal property (e.g., temperature, voltage) of the sensor. However, this additional information comes at a cost (e.g., sensing times, power consumption), so offline optimization techniques (such as feature-subset selection) are commonly used to identify a subset of the most informative sensor tunings. An alternative to offline techniques is active sensing, where the sensor tunings are adapted in real-time based on the information obtained from previous measurements. Prior work in domains such as vision, robotics, and target tracking has shown that active sensing can schedule agile sensors to manage their sensing resources more efficiently than passive sensing, and also balance between sensing costs and performance. Inspired from the history of active sensing, in this dissertation, we developed active sensing algorithms that address three different computational problems in chemical sensing. First, we consider the problem of classification with a single tunable chemical sensor. We formulate the classification problem as a partially observable Markov decision process, and solve it with a myopic algorithm. At each step, the algorithm estimates the utility of each sensing configuration as the difference between expected reduction in Bayesian risk and sensing cost, and selects the configuration with maximum utility. We evaluated this approach on simulated Fabry-Perot interferometers (FPI), and experimentally validated on metal-oxide (MOX) sensors. Our results show that the active sensing method obtains better classification performance than passive sensing methods, and also is more robust to additive Gaussian noise in sensor measurements. Second, we consider the problem of estimating concentrations of the constituents in a gas mixture using a tunable sensor. We formulate this multicomponent-analysis problem as that of probabilistic state estimation, where each state represents a different concentration profile. We maintain a belief distribution that assigns a probability to each profile, and update the distribution by incorporating the latest sensor measurements. To select the sensor’s next operating configuration, we use a myopic algorithm that chooses the operating configuration expected to best reduce the uncertainty in the future belief distribution. We validated this approach on both simulated and real MOX sensors. The results again demonstrate improved estimation performance and robustness to noise. Lastly, we present an algorithm that extends active sensing to sensor arrays. This algorithm borrows concepts from feature subset selection to enable an array of tunable sensors operate collaboratively for the classification of gas samples. The algorithm constructs an optimized action vector at each sensing step, which contains separate operating configurations for each sensor in the array. When dealing with sensor arrays, one needs to account for the correlation among sensors. To this end, we developed two objective functions: weighted Fisher scores, and dynamic mutual information, which can quantify the discriminatory information and redundancy of a given action vector with respect to the measurements already acquired. Once again, we validated the approach on simulated FPI arrays and experimentally tested it on an array of MOX sensors. The results show improved classification performance and robustness to additive noise.

Molecularly imprinted polymers (MIPs) are biomimetic sensing elements that combine the accuracy and highly specific binding affinity of a biosensor, with the robustness and reusability associated with artificial electrochemical sensors. This thesis investigates the application of a MIP sensor to address the challenge of phosphate detection in precision agriculture. Traditional chemical sensing approaches using portable electrochemical sensors display a significant cross-interference between inorganic phosphate and other nutrient ions. This is due to the low position of phosphate in the Hofmeister Selectivity Series for anions, its high electronegativity and its pH dependent structure, resulting in a molecule that is very difficult to detect. To address this challenge, a sensor was created by spin coating a phosphate selective MIP onto a substrate containing a series of electrodes. These electrode devices allowed for electrical measurements to be taken using an inductance, capacitance and resistance (LCR) testing station, and to observe the change in the materials dielectric constant as the binding sites become occupied by the target analyte. The devices underwent several design reiterations to produce an optimised setup consisting of 100 interdigitated chrome electrodes with a width of 1 μm and a separation distance of 1 μm on a quartz substrate. The final electrode design was used to carry out a nutrient cross-interference study across several polymer permutations. The purpose of this was to develop an optimised MIP formulation for binding specifically to inorganic phosphate ions. From this study, an optimal phosphate selective MIP was identified, based upon a binding site constructed from methacrylic acid around a diphenyl phosphate template molecule. During capacitance measurements, this MIP formulation demonstrated a clear preferential response to phosphate (1610 pF) over the average capacitance results observed following exposure to the competing nitrate (1286 pF) and sulphate (1212 pF) nutrients tested in the cross-interference study.

O objetivo do presente trabalho é o desenvolvimento de nanocompósitos de silício poroso/azul de metileno (PS/MB) utilizando-se substratos de silício macroporoso e mesoporoso para sua aplicação no monitoramento de gases orgânicos. Foram estudados processos de formação de PS/MB usando PS macroporoso e controlando o pH da solução. Os resultados obtidos indicam que a acidez da solução compromete a adsorção eficiente das moléculas de MB, sendo necessário a utilização de uma solução tampão para elevar o nível do pH. A necessidade de controlar o nível de pH da solução deve-se principalmente à característica ácida da superfície de PS recém formada, já que a superfície está constituída principalmente de ligações do tipo Si-Hx que são altamente hidrofóbicas. Os resultados da emissão fotoluminescente (PL) das estruturas de PS/MB em substrato de PS oxidado mostraram que a intensidade de emissão PL das moléculas de MB é mais intensa se comparada com a emissão das moléculas de MB em solução aquosa de baixa concentração. Esse resultado evidencia que a interação entre os elétrons p e a superfície do filme de PS otimiza a recombinação radiativa, minimizando possíveis caminhos não radiativos do estado excitado da molécula de MB. Adicionalmente, o resultado mostrou que as moléculas de MB adsorvidas sobre substratos de PS oxidados preservam suas características moleculares, atuando em forma monomérica. No caso de moléculas MB adsorvidas em substratos de PS não oxidados, os espectros de emissão PL mostraram que as moléculas de MB perderam sua identidade molecular formando, possivelmente, complexos na superfície do PS. Os resultados dos ensaios de adsorção das moléculas de MB em substratos de silício mesoporoso demonstraram ser mais eficientes quando o solvente utilizado foi o etanol, em condição de pH neutro. A monitoração de ambientes de vapores orgânicos foi efetuada através da resposta PL de uma estrutura de silício mesoporoso oxidado com moléculas de MB adsorvidas (Ox- PS/MB). Os resultados da emissão PL da estrutura Ox-PS/MB para os diferentes ambientes orgânicos apresentaram sinais de PL característicos para cada tipo de gás. Esses resultados mostraram o grande potencial de aplicação da estrutura Ox- PS/MB em um sistema de nariz óptico. / The objective of the present work is the porous silicon/methylene-blue (PS/MB) nanocomposite fabrication by using the macro-porous and mesoporous silicon substrate in order to be applied for organic solvent detection. The PS/MB formation process was studied PS/MB by using the macroporous silicon substrate by the pH value controlling of the solution moieties. The results showed that the acid condition of the solution compromises the efficiency of the MB adsorption wherever it was necessary to use the buffer in order to control the pH level of the solution. This additional process was a necessary condition because the fresh PS surface had had acid feature because the surface moieties at fresh PS are formed for the highly hydrophobic Si-Hx bonds. The PL spectra results from the PS/MB formed at oxidized PS substrate showed that the PL emission from the adsorbed MB molecules is more intense than the emission from the MB molecules in low concentrated solution. These results suggest that the PS surface and electrons p (in the MB) interaction minimizes the non-radioactive path for the excited state recombination of the MB molecules. Additionally this result showed that the adsorbed MB molecules preserved their molecular identity aging as a monomer moiety. In the case of the MB adsorbed at non-oxidized PS substrate, the PL spectra showed that the MB molecules lost their identity forming possible complex moieties at PS surface. The experimental results of the MB adsorption at the mesoporous silicon surface showed to be more efficient when the solution was ethanol at neutral pH value. The organic vapor ambient monitoring was made throughout the PL emission response of the Ox-PS/MB structure. These results showed that the PL emission had had the characteristic feature for each type of gas used in the experiment. These results showed the high potential application of the Ox-PS/MB structure in the optical nose system.

A adulteração de combustíveis é uma grande preocupação no Brasil. A agência reguladora nacional (ANP) detecta anualmente de 1 a 3% de adulterações nas amostras coletadas, o que é um índice alto considerando o tamanho do mercado brasileiro. As alternativas de adulteração são vastas e muito dinâmicas, por isso os arranjos de sensores baseados no conceito de seletividade global parecem os mais adequados para detectar falsificação de combustíveis. O conceito de seletividade global leva em conta a sensibilidade cruzada de sensores químicos não específicos e o uso de métodos de análise multivariada de dados para encontrar padrões para amostras de diferentes composições químicas. Os sensores químicos podem ser obtidos de uma variedade de materiais sensoativos, cujas respostas elétricas variam de acordo com as propriedades físico-químicas do meio em que se encontra. Os polímeros condutores são excelentes materiais sensoativos, pois sua condutividade elétrica é grandemente influenciada pelas condições ambientais e podem ser processados na forma de filmes finos através várias técnicas. No presente trabalho, filmes de poli(3-metiltiofeno) (PMTh) e poli(3-hexiltiofeno) são depositados por cronopotenciometria e cronoamperometria sobre microeletrodos interdigitados e são caracterizados por espectroscopia de impedância. Os dados são analisados por redes neurais artificiais do tipo multilayer perceptron e bons resultados são obtidos na detecção de adulteração de gasolina. O mesmo estudo também pode ser aplicado na detecção de adulteração de álcool etílico combustível com um desempenho um pouco pior. / Fuel adulteration is a major concern in Brazil. The local governmental agency detects from 1 to 3% of problematic samples yearly, which is a lot considering Brazils market size. The myriad of adulteration possibilities is vast and it is very dynamic, thus array of sensors based on global selectivity concept seems to be more suitable methodology to detect problems in fuel. The global selectivity concept encompasses the cross-sensitivity of non-specific chemical sensors and the use of multivariated data analysis methods as a way to provide fingerprints for samples of different chemical composition. The chemical sensors can employ different types of sensoactive materials, whose electrical responses are dependent on the physicochemical characteristics of the media they get in contact with. Conducting polymers (CP) are per excellence suitable sensoactive materials, since their electrical conductivity is highly influenced by the environmental conditions and they can be easily processed in the thin film form by different techniques. In the present work films of poly(3-methylthiophene) (PMTh) and poly(3-hexylthiophene) (PHTh) are deposited by chronopotenciometry and chronoamperometry onto interdigitated microelectrodes and characterized through Impedance Spectroscopy. This data was analyzed with Multilayer perceptron neural networks and a very good performance is found in gasoline adulteration detection. A less great performance was also achieved in the investigation vehicular ethanol adulteration.