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A novel metal-polymer composite is presented, comprised of a micron-sized nickel powder dispersed within a silicone polymer matrix. The composite is intrinsically electrically insulating, but displays a dramatic increase in conductivity under compression, tension and torsion. The electrical response to applied compression is characterised. Combined with electron microscopy, the large sensitivity to compression is shown to be due to the uniquely spiky morphology of the filler particles. Low mechanical energy mixing techniques are essential for retaining these sharp tips. In addition, wetting of the nickel particles by the silicone polymer is highly effective, resulting in negligible inter-particle contact between metallic grains even at very high loadings and compressions. Current-voltage characteristics are highly non-linear, displaying peaks, hysteresis, negative differential resistance, trap-filling and radio frequency emission. Evidence points towards an inter-particle conduction mechanism dominated by field emission and Fowler-Nordheim tunnelling, made possible by localised field enhancements at the sharp tips. A novel mechanism of grain charging and the 'pinching-off of conduction pathways is also suggested. Granular forms of the composite display dramatic increases in resistance when exposed to organic solvent vapours, transduced by a polymer swelling mechanism. Responses are dependent upon vapour concentration, and differential responses are obtained with other polymers, indicating excellent potential for applications in artificial olfactory devices (electronic noses). Polymer-solvent interactions follow both Fickian and anomalous diffusion characteristics, and follow basic trends predicted by solubility parameters.

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The subject of this thesis is the development of solid phase extraction (SPE) materials and miniaturised apparatus applicable for sample preparation in the analysis of transition elements from environmental matrices. It consists of five main chapters and a general conclusion. The first chapter is a general introduction. Considerable attention is given first to underlining the role of SPE as an efficient sample preparation approach in trace analysis. Subsequently the materials and techniques most frequently exploited for the synthesis of SPE materials specific for metals are discussed with the aid of various demonstrative examples from recent literature. Then the current research trends towards downscaled analytical systems and the efforts to integrate SPE apparatus within miniaturised devices are pointed out. Particular attention is paid to the fabrication techniques predominantly exploited to construct microfluidic devices, i.e., from glass and polymers. Given that the developed SPE systems in this thesis were coupled with various analytical detectors/instruments including atomic spectroscopy (i.e., ICP-OES, ICP-MS), optical absorption spectroscopy (in UV-Vis range) and electrochemical (amperometry) monitoring. the essential fundamentals of these detection techniques are presented. In the second chapter, the development of a rapid and an environmentally friendly chemical transformation, consisting of minimum steps in comparison with the traditional method, to immobilise oxins (i.e., 8-hydorxyquinoline (8-HQ)) on silica surfaces is reported. The produced chelating resin shows excellent performance as SPE materials for on-line sample preparation (preconcentration and matrix elimination) of some transition metals prior to their determination by ICP-OES. The applicability of this SPE material was tested by analysing Cu, Co, Zn, Ni and Pb in the range of 50-300 ng ml-1 from a synthesis matrices simulating sediment. The recovery values were ranged from 100% for Zn to 70% for Ni. The work in this chapter also presented a method to mask the environmentally abundant (major) transition metals (i.e., Fe, Al and Mn). The system used at its optimised parameters to analyse the studied ions from different sediments reference materials. The results show good agreement with the certified values. Chapter three describes methods to fabricate miniaturised SPE columns from monolithic materials. Short monolithic columns were fabricated from silica materials using a simple sol-gel method relaying on the hydrolysis of potassium silicate (21 % Si02, 9% K20) using formamide and/or acetamide, then functionalised with 8-HQ and L-cystiene via two different in situ procedures. The functionalised monolithic microcolumns encapsulated inside a house made connector, and thus easily incorporated within a FI manifold coupled with UV/Vis spectrometer allowing the eluted metals to be derivatised, with chromogenic reagents (i.e., PAR and ferrozine), and monitored on-line. The system has been characterised for Co, Cu and Fe (II). The microcolumns functionalised with L-cystiene operating at flow rate of 0.3 ml min-l for 4 minutes, the linear range for the Co, Cu and Fe (II) ions were 20-240, 10-200 and 5-180 ng ml-1 respectively. For those functionalised with 8-HQ, the linear range were 15-300, 10-250 and 5-250 ng ml-1 in the same order. In chapter four, downscaled SPE apparatus applicable for sample preparation prior to ICP-MS monitoring, have been constructed making use of the lab on a chip concept. Standard photolithography and wet etching were used to fabricate glass microfluidic devices accommodating three microchannels, each of them incorporating a defined section that could be packed with SPE resin. The microdevice interfaced with the ICP-MS instrument throughout a low flow rate concentric nebuliser using a Teflon connector, and coupled with FI delivering sample and reagents via a splitting valve. The feasibility of this miniaturised system to perform SPE of trace metals was proved by analysing trace metals, Cd, Co, and Ni, in seawater reference materials. Chapter five reports two designs to integrate microfluidic devices with electrochemical detection. In the first one, a microfabricated glass microfluidic device incorporating single microchannel with a packed section was coupled with a specially designed miniaturised electrochemical cell in a configuration that permits the working electrode to be mounted opposite to the channel outlet to facilitate end channel amperometric detection. The miniaturised electrochemical cell was made from three pieces of glassy carbon, silver and platinum rods of 2 cm length as working, reference and auxiliary electrodes respectively. These rods were assembled in a miniaturised Perspex block, stabilised with insulating epoxy resin and their ends were polished to mirror like discs. In the other design, the microfluidic devices were fabricated from PDMS by a simple casting and moulding techniques permitting the construction of three dimensional (3D) microchannels. The elastic characteristics of PDMS offer a great degree of flexibility for the placement of the microelectrodes inside the microchannel; thus, the monitoring is performed in-channel. To minimise variation in background current due to the pH change, the SPE process was carried out in buffer media i.e., the metals were loaded in acetate buffer of pH 4.8 and eluted with buffered solution of 50 nM Pyridine-2,6-dicarboxylic acid (PDCA) containing 50 mM of KCI as a supporting electrolyte to maintain a constant conductivity. The system shows good performance in the SPE and monitor Cu ion from standards solution in the range 100-400 ng ml-1 with LOD at 52 ng ml-1 In chapter six a general conclusion and a concise prospective for further work are presented.

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This thesis describes the development and application of hydrodynamic modulation voltammetric (HMV) techniques coupled to ultramicroelectrodes (UMEs) that possess intrinsically high mass transport rates in quiescent solutions. This study demonstrates that the well defined convective-diffusive conditions of the microjet electrode (MJE) arrangement allows mass transport to be enhanced by almost two orders of magnitude compared to a 25 mm diameter disc-shaped UME. The MJE comprises a nozzle which is used to deliver solution to a UME surface at high velocity. Scanning electrochemical microscopy (SECM) with small UMEs has been used to image the hydrodynamics of the jet system with high precision. Variations in local mass transport for both IrCl63- and Fe(CN)64- oxidation at a range of flow rates has been observed at various positions within the impinging jet and the stagnation zone has been thoroughly characterised under a variety of experimental conditions. Agreement has been found between experiment and theory for voltammetric data recorded with the nozzle and UME aligned in the stagnation zone, for a range of viscous solutions examined. By modulating the mass transport rate to the surface of an UME, in the MJE arrangement, by the introduction of a rotating blade between the end of the nozzle and the UME, it was possible to enhance the current sensitivity of the system. Trace level detection, to 2 x 10-7 mol dm-3 IrCl63- solution, was readily facilitated. This type of HMV experiment has utilised two methods to provide the reference signal for phase-sensitive detection of the current signal, involving either a dual-disc electrode or a single UME coupled to an LED detection system. Both HMV methods have been shown to work well.

The purpose of this work was to exploit the technology of flow injection (FI) analysis to develop fast, new and automated novel methods for the benefit of the pharmaceutical and consumer healthcare (CH) industry at GSK. Two (general) approaches for optimisation of the method variables have been applied in this work. Classical univariate optimisation, where one variable is altered at a time (whilst keeping all others constant) was applied for the early publications in this thesis. A more recent and efficient approach however, is multivariate optimisation, in which two or more variables are altered simultaneously using the structured statistical (chemometric) technique called design of experiments (DOE). DOE was employed for the majority of method development in latter work, to perform a rapid screening to select the most critical variables and variable interactions; and then optimising these by modelling the effects on the responses in more detail. Multivariate investigation and optimisation was found to offer significant benefits for the efficient development of new methods. Several methods employing reaction with OPA (ortho-phthalaldehyde), developed and applied by the author, were further investigated/optimised in conjunction with the University of Brussels via a consortium project named ChemoAc (chemometrics in analytical chemistry). In these joint publications the original GSK methods were externally subjected to DOE optimisation and advanced chemometric techniques; in the latter papers with the objective of providing a generic methodology. This work has succeeded in developing several new and novel analytical methods, described in a total of sixteen publications and supporting analytical methodology enclosed within this thesis. Reviews of the technique of FI and the principles behind multivariate DOE serve to highlight the context of the research.

Ce mémoire est consacré à l'élaboration, au greffage chimique de macrocycles azotés sur des surfaces, le développement des procédés d'élaboration de surfaces sensibles aux ions, l'évaluation de leurs propriétés et la réalisation de prototypes de capteurs chimiques sensibles aux ions. Les macrocycles azotés sont des cyclames sensibles aux ions de métaux de transition et des terpyridines sensibles aux lanthanides. Un capteur sensible à l'ion Fer (III) est réalisé par fonctionnalisation d'un ISFET et de structures de nitrure de silicium/silicium au moyen du greffage de macrocycles azotés de type cyclames sur la surface du dispositif. Un agent de couplage poly(méthylhydrosiloxane) (PMHS) permet cette immobilisation avec une grande efficacité. L'immobilisation d'un dérivé du cyclame (naphtyl-cyclam) sur des surfaces d'or a permis la préparation de capteurs chimiques sensibles aux ions. Les molécules de cyclame ont été déposées sur des électrodes en or par des interactions fortes entre le groupe de naphtyle et la surface d'or. Le film obtenu a été caractérisé en termes de composition, morphologie et propriétés électriques. La conductivité protonique du film naphtyl-cyclam a été mise en évidence par la spectroscopie d'impédance électrochimique (EIS) et la voltampérométrie cyclique (CV). Nous avons montré que l'immobilisation de dérivé de phényl-terpyridine sur des surfaces d'or a permis la préparation des capteurs chimiques sensibles aux ions Gadolinium (III). Les molécules de terpyridine ont été auto-assemblées sur des électrodes en or par des interactions fortes (greffage chimique) avec groupement thiol terminal. Les propriétés électriques de ces interfaces films sensibles/électrolyte sont décrites et des modèles théoriques sont proposés d'après les résultats expérimentaux obtenus par la spectroscopie d'impédance électrochimique / This dissertation is devoted to the elaboration, the chemical grafting of aminated macrocycles on surfaces, the development of elaboration processes of surfaces sensitive to the ions, the evaluation of their properties and the fabrication of prototypes of chemical sensors sensitive to the ions. The aminated macrocycles are cyclames, sensitive to transition metal ions and terpyridines sensitive to lanthanides. A chemical sensor sensitive to iron (III) ion is fabricated by means of the functionalization of an ISFET and of silicon nitride/silicon structures through grafting of aminated macrocycles of the cyclam type on to the surface of the device. The coupling agent poly(methylhydrosiloxane) (PMHS) allows such an immobilization with a high efficiency. The immobilization of a derivative of cyclam (naphtyl-cyclam) on gold surfaces allowed the preparation of chemical sensors sensitive to the ions. The molecule of cyclam was deposited on gold electrodes by strong interactions between the naphtyl group and the gold surface. The film obtained was characterized in terms of composition, morphology and electrical properties. The proton conductivity of the N-MNC film was brought out, for the first time, by electrochemical impedance spectroscopy (EIS) and by cyclic voltammetry (CV). We showed that the immobilization of the phenyl-terpyridine derived on gold surfaces allowed the preparation of the chemical sensors sensitive to gadolinium (III) ions. The molecules of terpyridine were self-assembled on gold electrodes by strong interactions (chemical grafting) with a final thiol group. The electrical properties of these sensitive films/electrolyte are described and theoretical models are proposed from the experimental results obtained by the electrochemical impedance spectroscopy

De nos jours, les biocapteurs électrochimiques constituent des outils rapides, fiables, rentables et sans marquage pour la détection sur site des polluants environnementaux et l’évaluation des critères de sécurité alimentaire et pour la détection des résidus militaires sur le terrain. Nous avons développé des biocapteurs d’affinité basés sur des récepteurs biologiques pour la détection électrochimique de l'estradiol dans des échantillons environnementaux et de molécules odorantes dans l'adultération de viande de porc. Des biocapteurs sensibles, sélectifs, rapides, simples reproductible, stables et efficaces ont été élaborés. En outre, une autre stratégie basée sur des nanomatériaux intégrés a été employée pour élaborer un capteur biomimétique pour la détection d’explosifs, qui a montré de bonnes qualités dans la protection de l'environnement. A la fin du manuscrit, certaines perspectives sont discutées / Nowadays, electrochemical biosensors are rapid, reliable, cost-effective and label-free tools for in field monitoring of environmental pollutants, for assessing the food safety criterion and for detection of the territory military residues. We developed biological receptors based affinity biosensors for electrochemical detection of estradiol in environment samples and odorant molecules in pork meat adulteration. The sensitive, selective, rapid, simple, repetitive, stable and effective biosensors were produced. In addition, another strategy entrapment based on integrated nano-material was used to produce a biomimetic sensor for explosives detection, which has shown good valuable in environmental protection and homeland security. In the end, certain significant prospective are discussed