Nanostructured materials play a vital role in almost all aspects of science and technology in the 21st century. The materials include nanoparticles, nanofilms, biological membranes etc. whose physicochemical properties are size-dependent. Thin films have wide range of applications in various branches of science. One of the efficient methods to form miniaturized structures for device applications is to fabricate nanostructured films on different substrates. Surfactant assembly on metallic and non-metallic surfaces based on self assembly and Langmuir-Blodgett technique offers a unique way to form thin films at molecular levels. The process of formation of unimolecular assemblies gives the flexibility of tuning the properties of underlying substrates for various applications including wetting characteristics, lubrication, passivation, mimicking biological phenomena etc. Towards this direction, self assembled monolayers (SAMs) of alkanethiols on gold and silver surfaces have been studied comprehensively for the past two decades. The reported literature on short chain length thiol-based monolayers is however, limited since the formation using conventional methods yield poor quality monolayers. The short chain length monolayers are useful in various applications like tribology, layer-by-layer assemblies, biosensors etc. Hence, it is essential to reproducibly form SAMs of various chain lengths and understand their properties. The present study is related to the formation of SAMs of alkanethiols and diselenides on gold and silver surfaces to form ordered and well-oriented monolayers. Monolayers of varying chain lengths (CH3(CH2)nSH where n = 3, 5, 7, 9, 11, 15) have been formed on gold and silver surfaces using different methods, (1) adsorption from neat thiols; (2) adsorption under electrochemical control and (3) adsorption from alcoholic solutions of the thiols. The characteristics features of the SAMs have been followed based on three different aspects, (i) structure and stability of the methylene groups (ii) interfacial characteristics involving the end group and the solvent and (iii) metal-head group interactions. The structure and stability of the monolayers have been followed based on vibrational spectroscopy and electrochemistry under different environment including thermal perturbations. The stability of the SAMs at different temperatures and subsequent changes associated with the orientation / packing has been monitored both in the dry state using reflection absorption infrared spectroscopy (RAIRS) and under electrochemical conditions using cyclic voltammetry and impedance analysis. Monolayers adsorbed from neat thiols show superior quality in terms of stability and structural arrangement. Short chain thiols with n = 3, 5, 7 show substantial stability when the adsorption is carried out from neat thiols. Figure 1 shows the RAIR spectra of hexanethiol SAM on gold adsorbed by three different procedures. Monolayers adsorbed under potential control behave very similar to the monolayers adsorbed from neat thiol as for as stability and structural orientation are concerned. Monolayers prepared using conventional methods of adsorption from alcoholic solutions are of inferior quality in terms of stability and arrangement especially for the short chain lengths. This is likely to be due to the fact that monolayers prepared using conventional methods may have intercalated solvent molecules within the monolayer assembly that degrade the integrity of the SAM leading to poor quality. The blocking characteristics of the monolayers for diffusing redox couple have been followed by determining the heterogeneous electron transfer rate constant using electrochemical techniques. The spectroscopic data and the electrochemical data follow similar trend indicating the superior quality of monolayer adsorbed from neat thiol in terms of stability as compared to conventionally prepared monolayers. Figure 1. RAIR spectra of hexanethiol-SAMs on Au(111) surface at 25C. The monolayers are formed by adsorption (A) from neat thiol (B) under potential control and (C) from alcoholic solution of the thiol. Wavenumber (cm-1) The interfacial characteristics of the monolayers (effect of end group functionality on the solvent properties) have been monitored on the basis of capacitance, contact angle and atomic force microscopy- measurements. Well-organized monolayers behave like good capacitors with relatively low values of double layer capacitance in presence of a liquid electrolyte as compared to the expected values based on known thickness and dielectric constant of the SAMs. This behavior can be explained by invoking the depletion of water density at the methyl terminated SAM-water interface where the solvent properties are different from that of bulk. Variation of one such property, dielectric constant, has been mapped using force measurement based on AFM. Dielectric constant of water changes from the bulk value of 78 to a low value as given in figure 2. This cross-over occurs within a span of 1-3 nm depending on the chain length of the thiol. Of the three procedures used, the ones based on the use of neat thiol and electrochemical adsorption result in well-oriented alkyl chains followed by highly oriented methyl terminal groups. This is responsible for the high hydrophobic nature of the interface and the subsequent observation of interfacial water properties. The SAMs prepared from ethanol fail to show the hydrophobic effects. Hydrophilic monolayers (NH2 terminated monolayers) fail to show depletion of water density at the interface indicating the importance of end group functionality in altering the interfacial characteristics of the monolayer. Figure 2. Spatial variation of dielectric permittivity of water at the hexanethiol SAM - water interface. The SAM is formed on gold (111) surface; (a) from ethanolic solution of the thiol (b) under electrochemical control (c) from neat thiol. The origin on the x-axis is the position of the methyl groups of SAM and the direction towards right side is in to the bulk water. The well-oriented SAMs have been used to follow the adsorption of a biopolymer. Zein protein is a prolamine of maize and is projected to be a biocompatible coating for food products and food containers. Hence, it is essential to prepare impermeable coatings of zein with different surface wetting properties. The adsorption of zein on highly ordered SAMs with hydrophobic or hydrophilic end group functionality has been studied and the orientation of the protein followed using spectroscopy, microscopy and electrochemistry. It is observed that zein shows higher affinity towards hydrophilic than hydrophobic surfaces with small foot print size on the Figure 3. Orientation of zein protein on hydrophilic and hydrophobic SAM as deciphered from the experimental data. hydrophilic surface resulting in large surface coverage. Figure 3 shows the schematics of zein deposits on hydrophilic and hydrophobic SAM surfaces determined based on spectroscopy, quartz crystal microbalance and electrochemical studies. The AFM shows cylindrical, rod-like and disc-like features of zein on hydrophilic surfaces that form the base units for the growth of cylindrical structures of zein. The published literature on the studies on SAMs on silver surfaces reveals that there is no consensus on the structure of the monolayers on silver. This may be due to the difficulty in getting pristine oxide-free surfaces in the case of silver and this is likely to affect the monolayer quality. Hence, it is decided to prepare SAMs of alkanethiols on silver and study their characteristics. Subtle differences between the monolayers adsorbed from neat thiol and from alcoholic solutions of thiols have been observed in terms of stability and permeability. Atomic force microscopic studies illustrate the presence of depletion of water at the SAM-aqueous interface. Diselenide-based monolayers have been formed on gold to understand the head group-substrate interactions on the monolayer properties. The disorder observed on short chain diselenide-based monolayers formed from alcoholic solutions can be eliminated by adsorption from neat compounds as described for the thiols. A preliminary account on the stability of SAMs under hydrodynamic conditions has been given based on rotating disc electrode voltammetry. It is observed that the SAMs get well-ordered when the electrode is rotated at a fast rate leading to the hypothesis that the monolayer assembly gets annealed as a function of the rotation rate. The thesis is planned as follows: Chapter 1 gives general introduction about organic thin films with particular emphasis on self-assembled monolayers on gold and silver, their characteristics in terms of stability, interfacial properties and adsorption behaviour. Chapter 2 deals with the experimental methodologies and schematics used for the preparation and characterization of the monolayers. Chapter 3 is on the contribution of alkyl spacer to the stability of the monolayers studied using spectroscopy and electrochemistry. Chapter 4 deals with the interfacial properties of the SAMs in presence of aqueous medium. In order to emphasize the importance of the terminal functional groups, adsorption of zein has been demonstrated on surfaces of controlled wettablity. Chapter 5 explains the formation and stability of monolayers of short and long chain alkyl diselenides on gold surfaces. Chapter 6 gives the structural and interfacial characteristics of alkanethiol monolayers on silver surfaces. The stability and subsequent changes of alkanethiol monolayers under hydrodynamic conditions has been discussed in the appendix section.(For fig pl refer pdf file.)

Theoretical studies using the Kohn-Sham density functional formalism have been carried out to identify and investigate the stability of a variety of atomic clusters for their use in cluster assembled materials. The stable behavior found in a cluster system provides a way to classify inorganic clusters. The clusters in this study can be categorized in one of the following, jellium, all-metal aromatic, Zintl analogue or as a covalent metal-carbide. By understanding the electronic structure and ultimately the stable nature of a cluster first, it is proposed one can construct assemblies based on the stable cluster. The methodology presented is a viable way to design future nanomaterials with a variety of architectures and precise control over properties based on stable cluster motifs.

This thesis explores the surface assembly of mechanically interlocked molecular architectures at gold surfaces for potential applications in molecular switches, anion sensing and stimuli (redox and optical) responsive molecular films. <b>Chapter One</b> introduces the field of mechanically interlocked molecules focusing on rotaxane and catenane surface assemblies in the form of single molecule thick self-assembled monolayers. A review of the surface-attached characteristics of mechanically interlocked molecules is given before exploring specific anion template directed strategies for their construction. The potential to incorporate both redox-active and optically-active functional groups within these mechanically interlocked molecules is also discussed. <b>Chapter Two</b> provides the experimental details and procedures employed in this thesis to characterise the molecular systems under investigation. <b>Chapter Three</b> introduces several surface characterisation techniques such as; ellipsometry, contact angle, X-ray reflectivity and X-ray photoelectron spectroscopy, with a particular focus of applying these tools to probe the surface co-conformation of switchable and interlocked molecules at surfaces. Electroanalytical techniques such as cyclic voltammetry, chronoamperometry and electrical impedance spectroscopy are also introduced. <b>Chapter Four</b> details the surface assembly of a series of ferrocene containing anion templated catenane self-assembled monolayers on gold. Detailed electrochemical and angle resolved X- ray photoelectron spectroscopy characterisation elucidates the co-conformation upon surface attachment. <b>Chapter Five</b> details the anion templated surface assembly of a redox-active rotaxane self- assembled monolayer on gold. Subsequent electroanalysis and X-ray photoelectron spectroscopy characterisation confirms the structural integrity of the film and a possible co- conformation at the surface is discussed. <b>Chapter Six</b> describes efforts towards constructing optically responsive hybrid d-f lanthanide containing mechanically interlocked molecules. Initial work focuses on switching characteristics of a redox switchable antennae and its ability to modulate the luminescence of a series of lanthanide complexes in solution. Subsequent surface attachment of the lanthanide complexes in the form of emissive self-assembled monolayers is also investigated.

Des récepteurs de barbiturates greffés avec des groupements anthracène photoactifs possédant différentes fonctions d’ancrage ont été synthétisés et caractérisés, en vue de transférer leurs propriétés de reconnaissance photocontrôlable à des substrats par diverses techniques de modification, comme la formation de liaisons amide, de liaisons thioacétate, ou par réaction click. Les propriétés photophysiques et photochimiques de ces récepteurs ont été étudiées en solution, et la fluorescence, la durée de vie et le rendement quantique ont été mesurés à différentes températures. Des surfaces d’or modifiées ont été fabriquées et caractérisées par ellipsométrie, mesure d’angle de contact, AFM et PM-IRRAS. Les résultats montrent qu’il est possible de moduler les propriétés de reconnaissance moléculaire des récepteurs de manière réversible via une combinaison d’irradiation lumineuse (365 nm) et de chaleur (80 °C). / Anthracene-appended photoactive barbiturate receptors possessing various anchoring groups are synthesized and characterized in view of transferring their photocontrolled binding properties onto substrates through various surface grafting techniques, such as amide bond formation, direct thioacetate linkage, or post click reaction modification. The photophysical and photochemical properties of the synthesized receptors were investigated in solution using variable temperature fluorescence, lifetime measurement and reaction quantum yield measurements. Receptor-modified gold substrates were characterized using ellipsometry, contact angle, AFM and PM-IRRAS experiments. The results showed that it is possible to reversibly modulate the binding properties of the anthracene-appended receptors through a combination of the irradiation with light (365nm) and heat (80℃).

M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology / A project investigating the behaviour of an assembled preloaded rotor was performed for an M-Tech qualification in the Mechanical Engineering Department. Pre-Stressing of mechanical structures is widely applied to improve their performance, and in this project the behaviour of an assembled preloaded rotor was investigated. An Impact Test was done on the structure to see if induced stresses originated by a set of bolts which keep the discs system together, would influence the natural dynamic response or the rotor. Tendencies in the natural response were investigated. Analytical models like the Finite Element Beam model and the Solid Finite Element model were studied in order to find a represntative description of this particular structure's dynamic behaviour after pre-tension. From the experimental results it was apparent that the slenderness of the pre-tensioned sector influences the natural frequency. The solid finite element model appears to be the most applicable model to present the assembled rotor-disk system as a continuous shaft. Furthermore, modelling and predictions for a typical rotor and similar assembled structures can be generated from the findings.

A l’échelle micro-nanométrique, la fiabilité et la durée de vie des microsystèmes (MEMS),généralement réalisés en silicium, sont fortement affectées par les effets de frottement, d’adhesion,d’usure... L’objectif de ce travail est d’étudier les mécanismes de frottement et d’usure sur deswafers de silicium. Le comportement micro-nanotribologique de monocouches auto-assemblées(SAMs) d’alkyltrichlorosilane, déposées sur des wafers de silicium de différentes orientationscristallographiques – i.e, Si(100), Si(111) et Si(110), a été étudié à l’aide d’un nanotribomètre. Lesparamètres modifiés au cours de l’étude sont les suivants : la longueur de la chaîne, les paramètrestribologiques (charge normale, vitesse de glissement, distance de glissement, taux d’humidité relativeet température du substrat) et les propriétés de surface du silicium (orientation cristallographique,topographie). Les résultats expérimentaux montrent que le comportement nanotribologique desmonocouches greffées sur des substrat polis est influencé par l’homogénéité du film et la fractiond’aire qu’il couvre. Ces deux paramètres étant contrôlés par le temps d’immersion et l’orientationcristallographique du substrat. La topographie du silicium a également été modifiée de manièreà créer des motifs périodiques (microstructure par DRIE). Le comportement tribologique de cessurfaces revêtues d’OTS est contrôlé par les variations des propriétés physico-chimiques dessurfaces et la fragilité de la microstructure. Pour s’affranchir des problèmes de fragilité, des motifsstructurés à l’échelle nanométrique sont réalisés par nano-impression. / At micro and nanoscale, fiability and durability of micromechanical devices (MEMS), usuallymanufactured of silicon, are strongly affected by the friction effects, adhesion, wear... The aim ofthis work is to study the mechanisms of friction and wear of silicon wafers. Micro/nanotribologicalstudy of self-assembled monolayers (SAMs) derived from n-alkyltrichlorosilanes deposited on siliconwafers displaying various crystallographic orientations – i.e, Si (100), Si (111) and Si (110) – hasbeen conducted using a nanotribometer (ball-on-disc). The parameters that have been varied are: the alkyl chain length, the tribological parameters (normal load, sliding velocity, sliding distance,relative humidity level and substrat’s temperature) and surface characteristics of the silicon substrates(crystallographic orientation, roughness). On smooth silicon substrats, experimental results show thatthe tribological behaviour of SAMs is control by the film’s homogeneity and the surface coverageof the monolayer in connection with the time immersion and the crystallographic orientation of thesubstrate. The topography of silicon was also modified by changing the microstructure by DRIE inorder to create periodic patterns. The tribological behavior of OTS SAM grafted on microstructuredsurfaces was controlled by the changes in physico-chemical properties and the fragility of thepatterns. To overcome the problems of fragility of these surfaces, patterns at the nanoscale areachieved by nanoimprint.

Legionella pneumophila peut causer une pneumonie fatale chez l’Homme dite maladie des légionnaires. L. pneumophila peut résister aux stress environnementaux en entrant dans un état VBNC (Viable mais non cultivable). La détection de L. pneumophila dans les milieux environnementaux est basée sur l’utilisation de méthodes normalisées : la culture (AFNOR T90-431, ISO 11731) et la PCR (AFNOR T90-471, ISO 12869). Mais, la culture ne détecte pas les formes VBNC et la PCR ne peut pas différencier les formes viables des mortes de la bactérie. Le premier objectif de notre étude était l’élaboration d’un immunocapteur pour la détection de L. pneumophila dans les échantillons artificiels. Notre immunocapteur a été obtenu par l’immobilisation d’un anticorps monoclonal anti-L. pneumophila (MAb) sur une électrode d’indium-tin oxyde (ITO), par la méthode de monocouches auto-assemblées d’époxysilane. Dans le second objectif, l’orientation des Mabs a été étudiée pour réduire la concentration à utiliser sans affecter sa sensibilité. Les Mabs ont été immobilisés sur l’ITO à l’aide des SAMs d’aminosilane pour la détection des formes VBNC. Les deux immunocapteurs ont été caractérisés par la mouillabilité (mesure de l’angle de contact), microscopie à force atomique (AFM), microscopie confocale à balayage laser (CLSM) et spectroscopie d’impédance électrochimique (EIS). Une limite de détection de 10 bactéries a été déterminée dans les échantillons artificiels. La performance de l’immunocapteur ITO-APTES a été évaluée sur des échantillons réels. Les deux méthodes de l’électrochimie et la culture ont été comparées, et les résultats suggèrent une sensibilité plus élevée par la méthode électrochimique. / Legionella pneumophila, may cause a fatal pneumonia in humans named Legionnaires’ disease. The strategies of L. pneumophila to resist to stressful environmental conditions include the ability to enter into a VBNC (Viable But Not ulturable) state. Detection of L. pneumophila in environmental samples benefit from the use of standardized methods: culture (AFNOR T90-431, ISO 11731) and PCR (AFNOR T90-471, ISO 12869). Culture is hampered by its inability to detect VBNC forms. PCR cannot discriminate between live and dead bacteria. The first objective of our study was the elaboration of an immunosensor for the detection of L. pneumophila in artificial samples. Our immunosensor was obtained by immobilization of a onoclonal anti-L. pneumophila antibody (MAb), on an indium-tin oxide (ITO) electrode – by Self Assembled Monolayers (SAMs) method using an epoxysilane. In the second objective, orientation of antibodies was studied for redusing the concentration of MAb used without affecting its sensitivity. Anti-L. pneumophila antibodies were immobilized into an ITO electrode modified by SAMs of aminosilane for the detection of VBNC. Tow immunosensors elaborated were characterized by wettability (contact angle measurement), atomic force microscopy (AFM), confocal laser scanning microscopy (CLSM) and electrochemical impedance spectroscopy (EIS). A detection limit of 10 bacteria was observed on artificial samples. The performance of the last immunosensor ITO-aminosilane electrode was evaluated in term of the bacteria detection in environmental samples. Electrochemical and culture methods were compared, and results suggest that the electochemical methods is more sensitive.

Purpose – The purpose of this study is to increase knowledge regarding sustainable product-service systems (SPSS) barriers and solutions for non-assembled products. To answer this purpose, we developed the following research questions: (1) what barriers do providers face when utilizing SPSS in a non-assembled product context and (2) what solutions can be used to overcome these barriers? Method – This study was conducted as an abductive case study within SPSS in the renewable energy industry. We interviewed a total of 20 respondents from 16 different companies operating in China, Cyprus, and Sweden. Each respondent was chosen based on their experience and knowledge within the area. Findings – The findings are summarized in a framework that links the identified barriers with specific solutions. In brief, finding stakeholders for large and long-term investments was identified as a major barrier while educating stakeholders was suggested as a common solution. Theoretical and practical implications – The results disqualify two of the barriers in the existing literature while suggesting that varying market conditions is a new barrier. Furthermore, the study provides new insights to the existing literature and presents a framework that managers can use to matchmake SPSS-barriers with solutions. Limitations and future research – The study is limited to a case study focused on barriers and solutions for SPSS-providers. As a result, future research is suggested to validate the findings in another context and among other stakeholders.

Neste trabalho, aplicamos técnicas de óptica não-linear de segunda ordem, em particular a Espectroscopia por Geração de Soma de Freqüências (SFG) e a Geração de Segundo Harmônico (SHG), para investigar a adsorção e o ordenamento molecular de filmes automontados de polieletrólitos variando-se os parâmetros que influenciam a adsorção (pH, força iônica, densidade de carga), além de investigar a estabilidade térmica e possíveis transições de fases nesses filmes multicamadas como função do pH das soluções e o do número de camadas. A espectroscopia SFG de filmes dos polieletrólitos poly(allylamine hydrochloride) (PAH) e poly(styrene sulfonate) (PSS) permitiu acompanhar a adsorção das camadas pelo monitoramento do campo elétrico na interface (substrato+filme adsorvido)/solução. As medidas de fase do sinal SFG confirmaram a supercompensação de cargas em todos os valores de pH estudados, exceto a pH 12, onde a adsorção foi possível devido a interações eletrostáticas locais. Os filmes secos mostraram grande ordenamento e homogeneidade quando a secagem era espontânea (sem a ação de jato de N2), independentemente do pH. Nestes filmes, observou-se pela primeira vez que as camadas adsorvidas podem alterar o ordenamento e a conformação das cadeias previamente adsorvidas. A espectroscopia SFG também apontou para a redução da densidade de carga e do ordenamento molecular quando a força iônica era aumentada, devido ao efeito de blindagem eletrostática. Os filmes tornaram-se mais inomogêneos e desordenados em virtude da compensação extrínseca. O efeito da força iônica foi o de reduzir a densidade de carga e assim o ordenamento molecular, mesmo se a secagem fosse espontânea. A técnica de SHG foi aplicada a filmes automontados de PAH e PS-119 para confirmar sua estabilidade térmica em função do pH e do número de camadas, além de verificar o ordenamento molecular antes e após o tratamento térmico. Os resultados mostraram que os filmes não são termicamente estáveis: o sinal é completamente destruído à temperatura de 150oC aproximadamente, ao contrário do que relata a literatura. As medidas SHG também confirmaram a isotropia dos filmes no plano das amostras, independente do pH ou do número de camadas. Comparando-se o sinal SHG antes e depois do aquecimento, comprovou-se que após o resfriamento lento, o sinal era restituído a quase o mesmo valor que antes, mostrando que o processo de desordem térmica é reversível. Entretanto, nenhuma transição de fase foi observada, pois a redução do sinal SHG foi lenta e gradual, sem nenhuma variação brusca que caracterizasse uma transição vítrea. Enfim, nossas medidas do sinal SHG em função do número de camadas também discordaram dos resultados da literatura, pois a susceptibilidade de segunda ordem não cresceu linearmente com o número de bicamadas. Isso indica que as moléculas não adsorvem com mesmo ordenamento em cada bicamada. Desse modo, podemos concluir que as técnicas SFG e SHG fornecem informação a nível microscópico que podem levar ao aprimoramento das aplicações dos filmes automontados, e que seriam difíceis de obter com técnicas tradicionais. / In this study, we have applied second-order nonlinear optical techniques, in particular Sum-Frequency Generation (SFG) and Second-Harmonic Generation (SHG), to investigate the adsorption and the molecular ordering of self-assembled polyelectrolyte films varying the parameters which are relevant to polyelectrolyte adsorption (pH, ionic strength, charge density), besides investigating the thermal stability and possible phase transistions in these multilayer films as function of pH of the solutions and of the number of layers. SFG spectroscopy of films fabricated with the polyelectrolytes PAH and PSS allowed us to monitor the adsorption of each layer by the electric field at the (substrate+adsorbed film)/solution interface. Phase-measurements of the SFG signal confirmed that charge supercompensation occurred at all pH values investigated, except at pH 12, where the adsorption was possible by local electrostatic interactions. Dry films have shown great order and homogeneity if the drying was spontaneous (without blow-drying with N2), independently of pH. In these films, it was observed for the first time that layer adsorption can modify the order and the conformation of previously adsorbed chains. SFG spectroscopy also pointed to the reduction of the charge density and of the molecular order if the ionic strength was increased, due to the electrostatic screening effect. The films were more inhomogeneous and disordered due to extrinsic charge compensation. The effect of the ionic strength was to reduce the charge density and the molecular order, even if the drying were slow (spontaneous). The SHG technique was applied to LBL films of PAH and PS-119 to confirm their thermal stability as a function of pH of the solutions and the number of layers, besides comparing the molecular order before and after the thermal treatment. The results have shown that the films are not thermally stable, with the SHG signal nearly vanished if the temperature of 150 oC is reached, in contrast of what is reported in the literature. SHG measurements have also confirmed that the films are isotropic in the plan of the samples, independent of pH or the number of layers. Comparing the SHG signal before and after heating, it was found that the SHG signal was considerably reduced at high temperatures, but after slow cooling it was recovered to almost the same value as before heating, showing that the thermal disorder is reversible. However, no phase transistion was observed, since the SHG signal reduction was slow and gradual, without any sudden change that would characterize a glass transition. At last, our SHG measurements as a function of the number of layers also disagreed with results in the literature, therefore the second order susceptibility did not grow linearly with the number of bilayers. This indicates that the molecules do not adsorb with same order in each bilayer. Therefore, we can conclude that SFG and SHG techniques provide information on the film arrangement at the microscopic level which could be difficult to get with traditional techniques and could also lead to the improvement of applications of LBL films.

O transistor de efeito de campo de porta estendida e separada (SEGFET) é um dispositivo alternativo ao tradicional transistor de efeito de campo seletivo a íons (ISFET). A grande vantagem desse dispositivo se refere ao seu fácil processamento, ou seja, se restringe somente a manipulação do eletrodo de porta, evitando processos convencionais de microeletrônica. Neste sentido, sensores iônicos e biossensores podem ser facilmente implementados combinando materiais de reconhecimento químico e/ou biológico. Por sua vez, a técnica de fabricação de filmes finos camada por camada (layer-by-layer, LbL) se mostra versátil para manipulação de diversos tipos de materiais em nível molecular. Materiais orgânicos e inorgânicos podem ser automontados em substratos sólidos por meio da simples adsorção eletrostática formando compósitos com propriedades únicas com o objetivo de serem aplicados em sensores ou biossensores. Neste trabalho, o conceito de dispositivo SEGFET foi combinado com a técnica LbL por meio da manipulação de materiais orgânicos (polieletrólitos, dendrímeros e polianilina) e inorgânicos (TiO2 e V2O5) nanoparticulados a fim de se obter novos sensores de pH e biossensores para a detecção de glicose e uréia, dois importantes analitos de interesse clínico. Numa primeira etapa, diferentes filmes LbL foram produzidos, caracterizados e testados como camada sensível (porta estendida) em dispositivos SEGFETs. Todos os sistemas estudados se mostraram promissores como sensores de pH, ou seja, com uma sensibilidade próxima do valor teórico sugerido pela equação de Nernst (59,15 mV.pH-1). Esses resultados podem ser atribuídos à natureza anfotérica do material da última camada no filme LbL. Numa segunda etapa, as enzima glicose oxidase (GOx) e urease foram convenientemente imobilizadas nos filmes LbL. Pelo fato dessas enzimas gerarem ou consumirem prótons durante a catálise da reação, os filmes LbL modificados enzimaticamente foram utilizados em biossensores de glicose e uréia, apresentando eficiente detecção. Assim, a união de dispositivos SEGFET com a técnica de automontagem se mostrou promissora para construção de sensores e biossensores eficientes e de baixo custo. / Separative extended gate field-effect transistor (SEGFET) device is an alternative to the conventional ion-sensitive field-effect transistor (ISFET). The great advantage of SEGFET refers to its easy processing, i.e., it is limited under only manipulation of the gate electrode, avoiding the conventional microelectronic processes. In this way, ion sensors and biosensors can be easily implemented combining chemical and/or biological recognition materials. In turn, the layer-by-layer (LbL) technique shows be versatile for handling various types of materials at molecular level. In this thesis, the concept of SEGFET device was combined with the LbL technique through the manipulation of organic (polyelectrolytes, dendrimers and poly (aniline)) and inorganic materials (TiO2 and V2O5 nanoparticles) in order to get new pH sensors and biosensors for the detection of glucose and urea, two important analytes of clinical interest. In a first step, different LbL films were produced, characterized and tested as the sensitive layer (extended gate) in SEGFETs devices. All studied systems were promissing as pH sensors, i.e., with a sensitivity close to the theoretical value suggested by Nernst equation (59.15 mV.pH-1). These results can be attributed to the amphoteric nature of the material in the last layer of the LbL films. In a second step, glucose oxidase (GOx) and urease enzymes were conveniently immobilized onto LbL films. Because these enzymes generate or consume protons during catalysis of the reaction, the enzymatically modified LbL films were used in biosensors for glucose and urea, with efficient detection. Thus, the union of SEGFET devices with the LbL technique is promising to building up efficient and low-cost sensors and biosensors.