Ion-containing segmented polyurethanes exhibit unique morphology and physical properties due to synergistic interactions of electrostatic, hydrogen bonding, and hydrophobic interactions. A fundamental investigation on a series of well-defined ion-containing polyurethanes elucidated the influence of charge placement, charge density, and soft segment structure on physical properties, hydrogen bonding, and morphologies. An unprecedented comparison of poly(ethylene oxide)(PEO)-based sulfonated polyurethanes containing sulfonate anions either in the soft segments or hard segments revealed that sulfonate charge placement dramatically influenced microphase separation and physical properties of segmented polyurethanes, due to altered hydrogen bonding and thermodynamic immiscibility between soft and hard segments. Moreover, studies on sulfonated polyurethanes with identical sulfonated hard segments but different soft segment structures indicated that soft segment structure tailored sulfonated polyurethanes for a wide range of mechanical properties. Sulfonated polyurethanes incorporated with ammonium-functionalized multi-walled carbon nanotubes (MWCNTs) generated novel polyurethane nanocomposites with significantly enhanced mechanical performance. Modification of MWCNTs followed a dendritic strategy, which doubled the functionality by incorporating two ammonium cations per acid site. Complementary characterization demonstrated successful covalent functionalization and formation of surface-bound ammonium salts. Upon comparison with pristine MWCNTs, ammonium-functionalized MWCNTs exhibited significantly enhanced dispersibility in both DMF and sulfonated polyurethane matrices due to good solvation of ammonium cations and intermolecular ionic interactions between anionic polyurethanes and cationic MWCNTs. Segmented polyurethanes containing sulfonated PEO-based soft segments and nonionic hard segments were incorporated with various contents of room temperature ionic liquid, 1-ethyl-3-methylimidazolium ethylsulfate (EMIm ES), to investigate the influence of ionic liquid on physical properties, morphologies, and ionic conductivity. Results indicated that EMIm ES preferentially located in the sulfonated PEO soft phase, leading to significantly enhanced ionic conductivity and well-maintained mechanical properties. These properties are highly desirable for electromechanical transducer applications. Electromechanical actuators fabricated with sulfonated polyurethane/IL composite membranes exhibited effective response under a low applied voltage (4 V). However, in the case of an imidazolium-containing segmented polyurethane with imidazolium ionic hard segments and hydrophobic poly(tetramethylene oxide) (PTMO) soft segments, EMIm ES selectively located into the imidazolium ionic hard domains, as evidenced with a constant PTMO soft segment glass transition temperature (Tg) and systematically reduced imidazolium hard segment Tg. Dielectric relaxation spectroscopy demonstrated that ionic conductivity of imidazolium-containing segmented polyurethanes increased by five orders of magnitude upon incorporation of 30 wt% EMIm ES. Imidazolium-containing sulfonated pentablock copolymers were also investigated to elucidate the influence of imidazolium counter cation structures on solution rheology, morphology, and thermal and mechanical properties. Combination of living anionic polymerization and post functionalization strategies provided well-defined sulfonated pentablock copolymers containing structured imidazolium cations in sulfonated polystyrene middle block. Varying alkyl substitute length on imidazolium cations tailored physical properties and morphologies of sulfonated pentablock copolymers. Results indicated that long alkyl substitutes (octyl and dodecyl) on imidazolium cations significantly influenced solution rheological behavior, morphology, and water uptake properties of sulfonated pentablock copolymers due to the altered characteristic of imidazolium cations. Imidazolium-containing sulfonated pentablock copolymers exhibited systematically tailored mechanical properties due to the plasticizing effect of alkyl substitutes. In addition, incorporation of ionic liquids into sulfonated pentablock copolymers further tailored their mechanical properties and ionic conductivity, which made these materials suitable for electromechanical transducer applications. All sulfonated pentablock copolymers were successfully fabricated into actuator devices, which exhibited effective actuation under a low applied voltage (4 V). / Ph. D.

Conducting vertical nanopillar arrays can serve as three-dimensional nanostructured electrodes with improved performance for electrical recording and electrochemical sensing in bio-electronics applications. However, vertical nanopillar-array electrodes made of inorganic conducting materials by conventional nanofabrication approach still faces challenges in high manufacturing costs, poor scalability, and limited choice of carrier substrates. Here, we report a new type of conducting nanopillar arrays composed of multi-walled carbon nanotubes (MWCNTs) doped polymeric nanocomposites, which are manufactured over the wafer-scale on both rigid and flexible substrates by direct nanoimprinting of perfluoropolyether nanowell-array templates into uncured MWCNT/polymer mixtures. By controlling the MWCNT ratios and the annealing temperatures during the fabrication process, MWCNT/polymer nanopillar arrays can possess outstanding electrical properties with high DC conductivity (~4 S/m) and low AC electrochemical impedance (~104 Ω at 1000 Hz). Moreover, by electrochemical impedance spectroscopy (EIS) measurements and equivalent circuit modeling-analysis, we can decompose the overall impedance of MWCNT/polymer nanopillar arrays in the electrolyte into multiple bulk and interfacial circuit components, and thus can illustrate their different dependence on the MWCNT ratios and the annealing temperatures. In particular, we find that a proper annealing process can significantly reduce the anomalous ion diffusion impedance and improve the impedance properties of MWCNT/polymer nanopillars in the electrolyte. / Master of Science / Conducting vertical nanopillar arrays can serve as three-dimensional nanostructured electrodes with improved performance for electrical recording and electrochemical sensing in nano-bioelectronics applications. However, vertical nanopillar-array electrodes made of inorganic conducting materials by conventional nanofabrication approach still faces challenges in high manufacturing costs, poor scalability, and limited choice of carrier substrates. Compared to conventional nanofabrication approaches, nanoimprint lithography exhibits unique advantages for low-cost scalable manufacturing of nanostructures on both rigid and flexible substrates. Very few studies, however, have been conducted to achieve the scalable nanoimprinting fabrication of conducting nanopillar arrays made of MWCNT/polymer nanocomposites. Here, I'm reporting a new type of conducting nanopillar arrays composed of multi-walled carbon nanotubes (MWCNTs) doped polymeric nanocomposites, which can be manufactured over the wafer-scale on both rigid and flexible substrates by direct nanoimprinting of the perfluoropolyether nanowell-array template into uncured MWCNT/polymer mixtures. We find that the nanoimprinted conducting nanopillar arrays can possess appealing electrical properties with a high DC conductivity (~4 S/m) and a low AC electrochemical impedance (~104 Ω at 1000 Hz) in the physiologically relevant electrolyte solutions (1X PBS). Furthermore, I've conducted a systematic equivalent circuit modeling analysis of measured EIS results to understand the effects of the MWCNT ratios and the annealing temperatures on the impedance of different bulk and interfacial circuit components for MWCNT/polymer nanopillar arrays in the electrolyte.

Phosphonium ions readily compare to ammonium ions in regards to their aggregate characteristics, thermal stability, and antibacterial activity. Ionic aggregation in phosphonium-based polymers provides thermoreversible crosslinks, ideal for reversible self-assembly, self-healing, and smart response. In polymers, these ionic functionalities aggregate, providing improved moduli, and altering the size and structure of ionic aggregates regulates polymer melt processability. This dissertation highlights phosphonium-based chemistry for the synthesis of novel step-growth ionomers and structure-property relationships in ionic polymers. The synthesis of phosphonium endcapping reagents for melt polyester reactions afforded a thermally stable ionic functionality that controlled molecular weight. Weak association was present with phosphonium ions at low ion concentrations below 7.7 mole %. The use of novel ionic bisacetoacetate monomers in the formation of networks from Michael addition reactions led to the synthesis of ionic networks with increased and broadened glass transitions and improved tensile stresses at break and strains at break compared to those in the non-ionic networks. The first electrospun fibers from Michael addition crosslinking reactions are reported, and equilibrium ionic liquid uptake experimental results indicated that ionic functional networks absorb close to three times the amount of ionic liquid as non-ionic, poly(ethylene glycol)-based films. Chain-extending polyurethanes with a phosphonium diol and subsequently varying the hard segment content led to changes in ionic aggregation, crystallinity, and thermal transitions in the polymers. Additionally, novel phosphonium-based methacrylate monomers incorporated into diblock copolymers with styrene exhibited microphase separation. Overall, the inclusion of phosphonium ions pendant to or in the main chain of various types of polymers led to changes in morphology, improved tensile properties, enhanced moduli, broadened transitions, changes in crystalline melting points, changes in solubility, and appearance of ionic aggregation. / Ph. D.

Cette thèse traite de la modification de surface des nanotubes de carbone avec des polymères Le chapitre I présente l'état de l'art des matériaux hybrides associant des liquides ioniques avec des nanotubes de carbone (NTC) ou du graphenes. Le chapitre II commence par un aperçu général de l'adsorption non-covalente de polymères sur la surface de NTC, suivi d'une description détaillée de l'étude réalisée sur la fonctionnalisation non covalente des nanotubes de carbone avec divers liquides ioniques polymérisable (LIP) à base d'imidazolium. Dans ce cadre, nous avons comparé deux méthodes expérimentales: la polymérisation in situ et le mélange en solution. Une des applications les plus importantes des NTC se situe dans le domaine des nanocomposites polymères/NTC. Le chapitre III décrit la formation de composites polyetherimide/NTC à partir des NTC-LIP obtenue dans la chapitre II. La préparation des composites en utilisant la méthode dite « solvent casting » est détaillée. Les NTC bruts, oxydés à l'acide nitrique et fonctionnalisé par le LIP ont été comparés. Des mesures mécaniques, thermiques et électriques de ces composées ont été aussi réalisées. Le dernier chapitre, divisé en deux sections, traite de la fonctionnalisation covalente des nanotubes de carbone avec une variété de polymères en utilisant deux approches différentes: "grafting from" et "grafting to". En utilisant la première approche, nous avons réalisé la croissance de chaînes de polyamide (PA) à partir de la surface de nanotubes de carbone fonctionnalisés avec le caprolactame par polymérisation anionique par ouverture de cycle. Les propriétés de traction des composites à base de PA ainsi préparées ont été étudiées. La polymérisation radicalaire de monomères vinyliques à base de LI de type imidazolium greffés à la surface de NTC est également présentée dans cette partie. Dans la deuxième partie du chapitre IV, nous présentons plusieurs stratégies de fonctionnalisation, y compris l'addition radicalaire et le greffage sur les défauts de NTC, pour la préparation des NTC fonctionnalisés de manière covalente avec des polymères compatibles avec des matrices époxy / This thesis deals with the surface modification of multi-walled carbon nanotubes with polymers with the aim to achieve a high level of dispersion in polymer matrices. Chapter I gives a comprehensive review of the state of the art of hybrids of ionic liquids with carbon nanomaterials, particularly, nanotubes and more recently, graphene. Chapter II starts with a general overview of the non-covalent adsorption of polymers onto the CNT surfaces followed by a detailed description of the study carried out on the non-covalent functionalization of CNTs with various imidazolium based polymerized ionic liquids (PIL). For this purpose, we further compare the two experimental methods: in situ polymerization and solution mixing. One of the most important applications of CNT is in polymer/CNT composites. Chapter III describes the formation of polyetherimide/CNT composites starting from PIL-CNT hybrids obtained in Chapter II. The preparation and characterization of composites using solvent casting methods have been detailed. Pristine, acid oxidized and PIL functionalized CNTs have been compared. Mechanical, thermal and electrical property measurements on these composites have also been described. The last chapter – Chapter IV, divided into two sections, discusses the covalent functionalization of CNTs with a variety of polymers using two main approaches: “grafting from” and “grafting to”. Using the first approach we have grown polyamide (PA) chains from the surface of caprolactam grafted CNTs by anionic ring opening polymerization. The tensile properties of the PA based composites prepared therefrom containing pristine, amine- and PA-functionalized CNTs have been investigated. The radical polymerization of vinyl imidazolium based IL monomers attached to the activated CNT surface is also given in this section. In the second part of Chapter IV, we have reported several “grafting to” functionalization strategies including radical addition and “defect site” grafting used for the preparation of CNTs covalently attached with polymers intended to blend well with epoxy matrices

Electrically conductive adhesives (ECA) are an alternative to tin/lead solders for attaching Surface Mount Devices (SMD) in electronic assemblies. ECAs are mixtures of a polymer binder (for adhesion) and conductive filler (for electrical conductivity). They bring more conductivity, higher strength, less weight and longer durability than metal alloys. ECAs can offer numerous advantages such as fewer processing steps, lower processing temperature and fine pitch capability. Multi walled carbon nanotubes (MWCNT) were used as conductive fillers in this research because of their novel electronic and mechanical properties. The high aspect ratio of the nanotubes makes it possible to percolate at low loadings to obtain good electrical and mechanical properties. Replacing the metal filler with CNTs in the adhesive made the ECA light weight, corrosion resistant, reduced processing temperature, lead free, electrically conductive and high mechanical strength. The MWCNTs at different loadings were mixed with epoxy and epoxy: heloxy to form a composite mixture. Different loadings, additives and mixing methods were used to obtain good electrical and mechanical properties and pot life. Pressure dispensing, screen and stencil printing were the processing techniques used for making the samples. The volume resistivity, contact resistance, die shear and lap shear tests were conducted on different surface finished Printed Circuit Boards (PCB) like silver, tin and Electro less Nickel Immersion Gold (ENIG). The results are summarized and compared with traditional methods.

Carbon nanotubes (CNTs) are well known as excellent electrical conductors. However, their transport properties are limited by electrical breakdown in ambient. Moreover, the electronic properties can further be modulated by doping. Devices such as Schottky diodes, transistors and logic gates based on un-doped and doped CNT junctions have been realized. Recently, nitrogen doped CNTs show potential application in replacing platinum cathode catalyst in fuel cell technology. We synthesize pristine, nitrogen-doped and nitrogen-doped:pristine CNT intratubular junctions by one-step co-pyrolysis and explore them for different applications. We show that the position of electrical breakdown can be predicted which is essential to know for high current applications. Among other applications, we show that individual CNT intratubular junction exhibits rectifying characteristics. Further investigation indicates the intratubular junction behaves like Schottky diode. Lastly, the potential replacement of platinum by nitrogen doped CNTs in direct methanol fuel cell has been explored.

Cette thèse s’inscrit dans le cadre du développement de nouveaux matériaux composites multifonctionnels, permettant de remplacer l’aluminium en tant qu’élément constituant le packaging de l’électronique embarquée dans les avions, afin de rendre ces derniers plus légers. L’association d’un polymère mécaniquement résistant avec des nano-charges conductrices est une alternative prometteuse. Cette thèse concerne l’étude du procédé de Dépôt Chimique à partir d’une phase Vapeur (CVD) en lit fluidisé pour déposer des métaux conducteurs, tels que le fer et le cuivre, à la surface de nanotubes de carbone multi-parois (MWCNTs) produits industriellement (Arkema Graphistrength®C100), enchevêtrés en pelotes poreuses de 388 μm de diamètre. Tout d’abord, afin d’augmenter la réactivité de surface des nanotubes, un procédé d’oxydation en lit fluidisé a été étudié à température ambiante, à partir de plusieurs mélanges gazeux à base d’ozone. Les diverses analyses réalisées (MET, spectroscopie IR, XPS,..) montrent que des groupements chimiques de type hydroxyl, acide carboxylique, éther, … sont greffés de façon uniforme sur toute la surface externe des MWCNTs et que leurs parois externes sont aussi gravées de façon modérée et localisée. Au final, il apparait que les défauts créés et les fonctions oxygénées greffées ont permis d’accroitre le nombre de sites de nucléation sur la surface des nanotubes et donc la masse de métal déposé. Le dépôt de fer à partir de ferrocène Fe(C5H5)2 a été étudié à haute température (entre 400 et 650°C), sous différentes ambiances gazeuses (azote, hydrogène, air, vapeur d’eau). Les analyses réalisées (MEB-FEG, DRX, MET, ICP-MS, ...) montrent un dépôt uniforme du bord jusqu’au coeur des pelotes, de nanoparticules à base de carbure de fer Fe3C prisonnières de l’enchevêtrement des nanotubes. La présence d’hydrogène a permis de minimiser la formation parasite de nano-objets (tubes et fibres). Le dépôt de cuivre à partir d’acétylacétonate de cuivre (II) Cu(C5H7O2)2 a été étudié entre 250 et 280°C sous hydrogène. Les caractérisations réalisées indiquent que des nanoparticules de Cu pur ont été déposées sur l’ensemble des parois externes des MWCNTs, du bord au coeur des pelotes. L’ensemble des résultats obtenus démontre que le procédé de CVD en lit fluidisé est capable de déposer de façon uniforme des métaux à la surface de nanotubes de carbone enchevêtrés en pelotes poreuses, pour des conditions opératoires spécifiquement choisies. / This Ph.D project is part of the development of new composite multi-functional materials allowing replacing aluminum in the on-board electronic packaging of airplanes, to make them lighter. The combination of a polymer mechanically resistant with conductive nano-fillers is a promising alternative. The thesis concerns the study of the Fluidized Bed Chemical Vapor Deposition (CVD) process of conductive metals, such as iron and copper, on the surface of industrial multi-walled carbon nanotubes (MWCNTs, Arkema Graphistrength®C100) tangled in porous balls of 388 μm in diameter. First, in order to increase the surface reactivity of nanotubes, an oxidation process in fluidized bed has been studied at room temperature, from several gaseous mixtures containing ozone. The various analyses (TEM, IR spectroscopy, XPS, …) show that hydroxyl, carboxylic acid, ether, … chemical bonds are grafted uniformly on all the outer surface of MWCNTs and that their outer walls are locally and moderately etched. At the end, it appears that the created defects and the oxygen containing bonds have allowed to increase the number of nucleation sites on the nanotubes surface and then the weight of the deposited metal. The iron deposit from ferrocene Fe(C5H5)2 has been studied at high temperature (between 400 and 650°C) under different gaseous atmospheres (nitrogen, hydrogen, air, water vapor). The analyses (FEG SEM, XRD, TEM, ICP-MS, ...) show a uniform deposit from the outer part to the center of the balls, of nanoparticles containing iron carbide Fe3C. The presence of hydrogen has allowed minimizing the parasitic formation of nano-objects (tubes and fibers). The copper deposition from copper (II) acetylacetonate Cu(C5H7O2)2 has been studied at 250-280°C under hydrogen. The characterizations indicate that nanoparticles of pure copper have been deposited on all the MWCNT outer walls, from the outer part to the center of the balls. The whole results obtained prove that the Fluidized Bed CVD process is able to deposit uniformly metals on the outer surface of MWCNTs tangled in porous balls, for specifically chosen operating conditions.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The present work describes the synthesis of a new catalyst of palladium nanoparticles supported on multi-walled carbon nanotubes containing nitrogen (Pd@CNxNCPM) 1 and its use in carbon-carbon coupling reactions (Suzuki and Heck) as well as reactions catalytic hydrogenation (reduction of double C-C bonds and nitro compounds reduction). The synthetic strategy employed afforded the simple way to obtain the catalyst with reaction in a short time and efficiently. To this was employed as the palladium precursor, the salt potassium hexacloropalladate IV and hydrazine monohydrate as the reducing agent, without the need for stabilizing agents for the control of nucleation and size of nanoparticle. The catalyst system was characterized as its morphology: dispersion, size and shape of nanoparticles by scanning electron microscopy. Also the catalyst was performed Raman spectroscopy and determination of amount of palladium. After characterization the catalyst, it was tested for coupling reactions of carbon-carbon: Suzuki and Heck leading to the formation of their products with 70-> 95% for Suzuki coupling and 75-> 95% for Heck. For the synthesis in question were used 0.5 mol% of catalyst (based amount of palladium) for Suzuki and 10 mol% for Heck. It should be noted that the catalyst shown stable in the reaction conditions tested, and observed the possibility of reuse of this system for additional reaction cycles without loss of efficiency for the Suzuki coupling. Also, the catalyst was efficient and chemoselectiv for catalytic hydrogenations of unsaturated carbon-carbon bonds and nitro compounds leading to their products in good yields. Thus, the synthesized catalyst proved versatile and can be used in reactions of carbon-carbon coupling well as in catalytic reduction may also be recovered and reused, which provides an environmentally friendly at the same characteristic. / O presente trabalho apresenta a síntese de um novo catalisador de nanopartículas de paládio suportadas em nanotubos de carbono de paredes múltiplas contendo nitrogênio (Pd@CNxNCPM) 1 e sua utilização em reações de acoplamento carbono-carbono (Suzuki e Heck) bem como em reações de Hidrogenações catalíticas (reduções de duplas ligações C-C e redução de nitrocompostos). A estratégia sintética utilizada permitiu a obtenção do catalisador de maneira simples, em curto tempo reacional e de maneira eficiente e sem a presença de agentes estabilizantes externos. Para isso foi empregado como precursor de paládio o sal hexacloropaladato IV de potássio e como agente redutor, hidrazina monohidratada sem a necessidade de agentes estabilizantes para o controle da nucleação e tamanho de nanopartículas. O sistema catalítico foi caracterizado quanto sua morfologia: dispersão, tamanho e forma de nanopartículas através de microscopia eletrônica de varredura. Também foi realizada espectroscopia Raman do catalisador bem como determinação do teor de paládio. Após devidamente analisado o catalisador, o mesmo foi testado para reações de acoplamento carbono-carbono de Suzuki e Heck levando a formação dos respectivos produtos com rendimentos de 70-> 95% para os acoplamentos de Suzuki e 75-> 95% para Heck. Para as sínteses em questão foram usados 0,5 mol% de catalisador (baseados na massa de paládio) para Suzuki e 10 mol% para Heck. Cabe salientar que o catalisador se mostra estável nas condições reacionais testadas, sendo observada a possibilidade de reuso deste sistema por ciclos reacionais adicionais, sem perdas de eficiência para o acoplamento de Suzuki. Ainda, o catalisador se mostrou eficiente para hidrogenações catalíticas quimiosseletivas de ligações de carbono-carbono insaturadas e nitrocompostos levando aos respectivos produtos em bons rendimentos. Dessa forma o catalisador sintetizado se mostrou versátil, sendo possível ser utilizado em reações de acoplamento carbono-carbono bem como em reduções catalíticas, também pode ser recuperado e reutilizado, o que confere ao mesmo uma característica ambientalmente correta.

<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

Philosophiae Doctor - PhD / Immunosensors are affinity ligand-based biosensor solid-state devices in which the immunochemical reaction is coupled to a transducer. The specificity of the molecular recognition of antigens by antibodies to form a stable complex is the basis of the immunosensor on the electrode. The development of such a sensor requires a better design and preparation of an optimum interface between the biomolecules and the detector material. The immunosensors were developed based on Polyaniline derivative composite. Novel water soluble PdTe quantum dots (QD) was synthesized and characterized by different physical techniques such as UV-Visible (UV-VIS), Fluorescence Spectroscopy (PL), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). The electroactivity of such synthesized quantum dots was studied by cyclic voltammetry in aqueous media. The synthesis of poly(2,5- dimethoxyaniline)-multi wall 'carbon nanotubes nanocomposite was carried out by electropolymerization in situ of 2,5-dimethoxyaniline - multi wall carbon nanotubes (PDMA-MWCNT) from aqueous dispersion containing acid-treated multi wall carbon nanotubes (MWCNT) and 2,5-dimethoxyaniline subsequently modifying a glassy carbon electrode in acid media. An undoped PDMA was also prepared for control. The composite for this work, consists of layer-by-layer method to form a multilayer film of QDs and PDMA-MWCNT. The method used was as follows; the drop coating of quantum dots followed by electrodeposition of poly(2,5- dimethoxyaniline )-carbon nanotubes onto surface of glassy carbon. The PDMA-CNT was characterized by UV-Visible (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The electrochemical characterisation of PDMA-CNT was carried out using cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The composite (QDs-PDMA-MWCNT) was also characterized using above mentioned techniques. The electrochemical immunosensor for fumonisin a mycotoxin was prepared by dropcoating of mycotoxins antibody onto the composite modified glassy carbon electrode. The response profiles of fumonisins sensors system were obtained from electrochemical impedance spectroscopy (EIS) measurements. The fumonisin immunosensor was used for the detection of fumonisins in certified com reference materials. For comparison reasons, analysis of such mycotoxins was carried out by using conventional analytical method enzyme-linked immunosorbent assay (ELISA). The EIS response of FBI immunosensor (GCEIPT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L-I and the corresponding sensitivity and detection limits were 0.0162 ka L ng-I and 0.46 pg L-I, respectively. Hence the limit of detection of GCEIPT-PDMA-MWCNT immunosensor for fumonisins in com certified material was calculated to 0.014 and 0.011 ppm for FBI, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FBI, FB2, and FB3) established by the Joint FAO / WHO expert committee on food additives and contaminants of 2 ug kg" and the maximum level recommended by the U.S. Food and Drug Administration (FDA) for protection of human consumption (2-4 mg L-I).