No description available.

The demanding problem of lack of selectivity in semiconducting oxide gas sensors was addressed by the combination of different technologies: shape and size selective catalysts (zeolites), chromium-titanium oxide sensing material and multi-electrode sensor arrays. Sensor devices were fabricated with additional shape and size selective catalysts (zeolites) of three different types (ZSM-5, (3 and Y) either printed over the top of the sensing material or admixed with it. The shape and size selectivity of the zeolite sensors has been demonstrated in their ability to discriminate a range of volatile organic, flavour and fragrance compounds of different molecular size and shape. To promote the selective catalytic activity of the sensors the zeolites were catalytically modified (ion exchanged) by the controlled addition of chromium catalysts. The modification increased their catalytic activity in a controlled way allowing them to selectively crack longer species into smaller ones without resulting in complete combustion of the analytes. Arrays of these sensors have been used in an electronic nose with small number of sensors and a sufficiently large variance in the response for reliable and repeatable discrimination of gases. The discrimination was as good as, and in some cases better than, that achieved using much larger sensor arrays, while also allowing additional discrimination of gases on the basis of their reactivity. Investigation of different parameters such as the chromium loading of the zeolites, the thickness of the zeolite layer, and the sensor operating temperature, allowed further improvements in the discrimination between the different tested compounds. Computational simulations of the interactions of a range of volatile organic molecules with different zeolites were performed using a commercially available software to select promising zeolite catalyst materials for the construction of new sensors and to compare computational predictions with experimental results.

No description available.

A wide variety of silica based nanoparticles (NPs) were synthesised to engineer materials with properties for specific applications by manipulating the nanoparticle composition. These include luminescent core shell NPs and luminescent mesoporous silica which have been successfully synthesised. The particle size distribution and characteristics of the NPs were determined by photon correlation spectroscopy. The laser Doppler velocimetry was used to determine the NPs stability in suspension. Transmission and scanning electron microscopy analysis were used to assess morphology and size of the NPs. Diffuse reflectance infra-red Fourier transform spectroscopy was used to study the template removal to produce porous NPs. The particles were then utilized for assessing different applications. A novel dual oxygen (O2) and sulphur dioxide (SO2) gas sensor was produced by incorporating fluorophores within SiNPs. The fluorophore rhodamine B isothiocyanate (RBITC) was encapsulated within SiNPs (208±9 nm) to produce a nanosensor that is sensitive to SO2, while ruthenium-tris(4,7-diphenyl-1,10-phenanthroline) dichloride (Ru(dpp)3) was encapsulated within SiNPs (192±8 nm) to sense O2. The sensor utilises the fluorescence quenching phenomena as a detection mechanism and had high sensitivity for detection of low O2 gas concentrations (0.018 %). These novel nanosensors demonstrate potential to develop multisensor systems to capable of detecting multiple gasses simultaneously in a single matrix for a magnitude of future applications that require small robust gas sensing. Biocompatibility of SiNP number, size (smaller than 100 nm), and dye encapsulation on conduit arterial function, in vitro was assessed. Their effects on endothelial-dependent [acetylcholine (ACh); 0.01-200 M] and independent [sodium nitroprusside (SNP); 0.001-10 M] dilator responses were examined. When incubated with 1.96×1012 NP/ mL, both 30 nm, 70 nm SiNPs and RBITC encapsulated in silica nanoparticles (SiRBITC NPs) significantly reduced endothelium-dependent, but not independent vasodilation. Furthermore, attenuated dilation due to SiRBITC NPs, but not SiNPs, could be partially restored using superoxide dismutase. Our results suggest that the mechanism of attenuated dilation is different for SiNPs and SiRBITC NPs which has implications for the future fabrication of biocompatible nanoparticles for imaging diagnostics. Spherical mesoporous nanoparticles (MNP) and dye encapsulated MNP were synthesised via a sol-gel method in XXIII the presences of organic template. The template was removed using an acidic extraction. The average diameters of the MNP were 100 nm. The interior pores were loaded with SNP, these drug loaded MNP were placed in live tissue and release in real-time was observed, in vitro. We demonstrate that the initial instantaneous release is due to the surface adsorption of the drug followed by released from the pores. Furthermore, these drug loaded MNP were placed in live tissue and release in real-time was observed, in vitro.

No description available.

Microelectrodes offer a number of advantages for exploitation as electrochemical sensors such as imparting stir-independence to sensor responses and allowing lower limits of detection to be minimised. Microelectrode arrays offer an attractive route for increasing the current responses of microelectrodes, whilst still retaining their advantageous properties. Despite this, no commercial sensors, to date, have successfully employed microelectrode arrays, largely due to conventional fabrication routes proving too costly to be economically viable for the production of disposable sensing devices. Previous work carried out by this research group has described a novel and patented procedure for the fabrication of microelectrode arrays via the sonochemical ablation of insulating polymer films electrochemically deposited upon conductive surfaces. This format lends itself to mass fabrication due to the simplicity and inexpensiveness of the approach. This thesis describes work focussed towards the optimisation of each of the individual components involved in the formation of sonochemically fabricated microelectrode arrays. In particular, factors and techniques that may facilitate the commercial exploitation and mass fabrication of such arrays as generic sensing templates are described. Screen printed carbon has been investigated for its suitability as a host electrode. The comparative use of a number of possible activation methods to increase amperometric current responses at such electrodes is also described. Homogeneous poly(o-phenylenediamine) films of -40 nm thickness formed at the surfaces of screen printed carbon electrodes via the anodic electropolymerisation of o-phenylenediamine are shown to serve as effective diffusional barriers, thus insulating the underlying carbon electrodes. Microelectrode arrays formed by the sonochemical ablation of such films to expose microscopic areas of the underlying conductive substrates are seen to possess electrode element populations of -7.3 x 104 cm 2. Over 400 such sensors are shown to be able to be fabricated simultaneously with reproducibility of responses <4% relative standard deviation. Amperometric and cyclic voltammetric characterisations of the thus produced microelectrode arrays performed in model redox systems are shown to agree with accepted theoretical microelectrode behaviour, demonstrating sigmoidal shaped voltammograms, fluctuations in steady-state current responses of <10% with convection, scan rate independence and fast attainment (<20 seconds) of steady-state responses. Arrays of this type are also demonstrated to be suitable for exploitation within aqueous chlorine sensing devices, offering detection limits of <0.005 mg/l free chlorine, representing an order of magnitude lower than those obtainable via contemporary optical wet chemistry based approaches. In order to demonstrate further the applicability of this approach to the mass fabrication of disposable devices, methods for the deposition of a chemical modifying layer are also investigated, to avoid the need for additional reagents.

The electrochemistry of oxygen and methanol at solid polymer electrolyte (SPE)-based amperometric sensors, fabricated according to an all-planar design concept, has been investigated. The solid protonic conductors used were Nafion®-117 membranes and Polybenzimidazole (PBI) films. The working and counter electrodes were non-porous gold and/or platinum layers (300-1500 nm thick), sputtered on the same face of the solid electrolyte, separated by a gap of the ionic conductor (10-1 mm wide) and in contact with the gas sample. Such all-planar solid-state devices could offer potential advantages over sandwich-type gas sensors namely, reduction in precious metal electrode area and simplified fabrication. Sensors based on both materials exhibited near-linear response to oxygen concentration changes (in the 0.1-21% v/v range) and response times comparable to those of commercially available sensors, irrespective to sample relative humidity, but the magnitude of the signal did depend on the latter even after ohmic correction or at low currents. A systematic study of the effect of humidity on oxygen reduction and gold surface electrochemistry reveals, that the fall in the oxygen signal with decreasing humidity cannot be explained simply in terms of decreasing membrane conductivity and increased ohmic losses, but is related to the effect of water on the number of electro active sites, their catalytic activity and oxygen reduction mechanism in general. The latter is further supported by the unusually high Tafel slopes obtained both on gold and platinum electrodes with decreasing levels of test gas humidification. The shape of the oxygen reduction current-potential curves observed at open all-planar gold-based devices and the magnitude of current at both gold-and platinum-based ones, when compared to those of sandwich-and capillary-type arrangements, point to high mass transport rates and a thin or porous mass transport barrier. Current distribution considerations supported by surface electrochemistry estimates suggest that parts of the deposit closer to the reference and counter electrodes contribute more to the observed currents. Further experimentation by varying the deposit thickness and progressive masking of working electrode areas, revealed that the test gas reacted both at the line formed by the gas/solid electrolyte/metal layer interface (diffusion from the gas phase) and underneath the deposit (diffusion from the back of the sensor and through the Nafion® membrane), but not through the metal layer. For monitoring of dissolved methanol (0.5-3 M) in acidic solutions using bare platinum micro disc electrodes and of methanol vapours (in eqUilibrium with 2-10% w/w or ca. 0.6-3 M aqueous solutions of methanol) using Nafion®-based all-planar platinum sensors, a simple amperometric method was developed. For both types of sensors a clear voltarnmetric picture was obtained with a good separation of methanol oxidation and oxygen reduction curves. The amperometric response could be correlated to the variations in methanol concentration, demonstrating the suitability of the method for crude monitoring of dissolved methanol levels in a range applicable to the feed of direct methanol fuel cells.

Dans cette thèse, deux applications de nanomatériaux sont présentées : la première concerne l’utilisation de la technique LSPR pour la détection d’interactions moléculaires et la seconde est consacrée à l’utilisation de surfaces semi-conductrices de TiO2 et de ZnO pour la photo-catalyse pour la dépollution environnementale. D’abord, nous avons présenté la préparation et la caractérisation d’interfaces plasmoniques d’ITO/Au NSs/ITO. Celles-ci montrent des signaux optiques aussi bien pour des couches minces qu’épaisses d’ITO. Elles permettent une détection LSPR à courte et à longue portée. La chimie « click » a été utilisée pour greffer le CBPQT4+ fonctionnalisé alcynyl sur une interface ITO/Au NSs/ITO terminée « azide ». Les interfaces obtenues ont été utilisées pour démontrer la possibilité d’enregistrer la formation et la rupture de complexes « hôte-invité » (CBPQT+4/TTF) utilisant la technique LSPR. Dans la seconde partie, consacrée à la photocatalyse, nous nous sommes intéressés à deux types de traitements de TiO2 et de ZnO dans le but d’améliorer leur efficacité photocatalytique sous irradiation visible. Nous avons, préparé et caractérisé des lames de quartz recouvertes d’une couche mince de TiO2 de différentes épaisseurs avec et sans nanostructures d’or sous la couche mince de TiO2. La performance photocatalytique de ces interfaces n’est pas exceptionnelle pour la dégradation de la rhodamine B mais elles sont très stables. La dernière partie de la thèse concerne la préparation et la caractérisation de nanostructures de ZnO et de ZnO dopé à l’iode. La substitution des ions d’oxygène par des ions d’iode introduit des niveaux donneurs dans la bande interdite de ZnO qui sont suffisamment superficiels à température ambiante. L’activation d’une transition, dans la bande interdite dans le cas des substrats de ZnO dopé à l’iode, explique les meilleures performances photocatalytiques de ces substrats de la rhodamine B sous irradiation visible. Ces résultats sont très prometteurs pour diverses applications photocatalytiques des substrats à base de ZnO. / In this thesis, two applications of nanomaterials are presented: the first concerns the use of the LSPR for the detection of molecular interactions and the second is devoted to the use of TiO2 and ZnO semi-conductive surfaces for photocatalysis in view of environmental remediation. The first part concerns the fabrication and characterization of plasmonic interfaces of ITO/Au NSs/ITO. These surfaces showed optical signals for thin as well as for thick ITO films. These interfaces allowed short and long-range LSPR sensing. The “click” chemistry was used to covalently link an alkynyl-functionalized CBPQT4+ unit to an azide-terminated LSPR interface. Tetrathiafulvalene was used as a model guest molecule to demonstrate the possibility to follow the complexation/decomplexation events by monitoring the change in the LSPR signal. The second part is devoted to photocatalysis. It is focused on the investigation of the effect of two different treatments of TiO2 and ZnO on their photocatalytic efficiency under visible light irradiation. We have first prepared and characterized quartz slides coated with a thin layer of TiO2 with different thicknesses with and without gold nanostructures under the thin layer of TiO2. The photocatalytic performance of these interfaces is not exceptional for the degradation of rhodamine B under visible light irradiation but these interfaces have the advantage of being very stable. The last part of the thesis consists on the preparation of ZnO and iodine-doped ZnO substrates by a hydrothermal chemical deposition, and evaluation of their photocatalytic performance. The substitution of oxygen ions by iodine ions introduces donor levels in the bandgap of ZnO, which are sufficiently shallow at room temperature. The activation of a sub-band gap transition in iodine-doped ZnO nanostructured substrates explains the better performance of these substrates for the photodegradation of rhodamine B under visible light irradiation. These results are very promising in view of various photocatalytic applications of the ZnO-based substrates.

A systematic investigation of the electrochemical behaviour of two sets of microelectrode arrays, fabricated by standard photolithographic and reactive-ion etching techniques, is presented. The first set of microelectrode arrays had a constant relative centre-centre spacing of 10r (where r is the electrode radius). As a value of r was decreased, the cyclic voltammograms recorded from the array became increasingly peak-shaped, due to merging of the diffusion fields of the individual electrodes. Furthermore, it was shown that the peak current densities obtained were largest for the arrays with the smallest individual electrodes, as were the signal-to-noise ratios (SNRs). Electroplating the individuals electrodes with platinum black was also shown to increase the peak currents and the SNRs, due to an increase in the effective surface area. Sigmoidal voltammograms, which are indicative of radial diffusion, were obtained for an individual electrode radius of 25 mm but not for arrays with smaller electrodes. To obtain radial diffusion for an array of 2.5 mm electrodes, it was shown (using a second set of microelectrode arrays) that a minimum relative centre-centre spacing of 40r is required. Further enhancement of the peak current densities were obtained by decreasing the size of the individual electrodes. A series of nanoelectrode arrays were fabricated using electron-beam lithography (EBL). The voltammograms obtained from these arrays exhibited a continual increase in the recorded peak current as the individual electrodes radius was decreased to a value of 110 nm. Since EBL is a slow and costly technique, nanoimprint lithography (NIL) was investigated as an alternative method of fabricating nanoelectrode arrays and comparable results were obtained from arrays produced by EBL and NIL. A dissolved oxygen and temperature sensor incorporating a working microelectrode array was also designed and fabricated. The sector comprised a densely packed array of 2.5 mm radius electrodes and a micro-reference electrode, both of which were covered with an agarose electrolyte gel enclosed in an SU8 chamber. A thermal resistor was included for temperature compensation of the dissolved oxygen measurements. The Ag|AgCl micro-reference electrode was found to be stable for approximately 80 hours in 0.1 M KCl, with 100 nA of current passing through it. Linear calibration curves were obtained from both temperature and dissolved oxygen measurements

Nous avons synthétisé avec succès ces nano-composés (rGO/Arg-Ag NPs, rGO-Ni NPs and rGO-Co3O4NPs) et les avons caractérisés par de nombreuses techniques, XPS, SEM, TEM, FTIR, Raman, UV-Vis et TGA. Les analyses montrent que ces nano-composés à base de graphène ont des propriétés excellentes et une grande stabilité. Utilisés comme catalyseurs dans des applications environnementales, ils réduisent efficacement le 4-nitrophenol en 4-aminophenol ainsi que les colorants à forte adsorption et le chrome (VI) présents dans les eaux usées. / We successfully obtained these nanocomposites (rGO/Arg-Ag NPs, rGO-Ni NPs and rGO-Co3O4NPs).The resulting rGO-based nanocomposites were characterized by a variety of different techniques, including XPS, SEM, TEM, FTIR, Raman, UV-Vis and TGA. These analysis shows that these graphene-based nanocomposites have excellent properties and stability. The rGO-based nanocomposites, applied as a catalyst in environmental applications and shows good catalytic performance for reduction of 4nitrophenol to 4aminophenol and high adsorption dyes and Cr (VI) from wastewater.