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No description available.

This thesis describes the development of three integrated solid-state electrochemical (amperometric) sensors for glucose measurement in a disposable format. This work envisages a sensor that measures glucose in biological samples e.g. whole blood. All three sensors were constructed based on using the enzyme glucose oxidase as the analyte-selective agent, which was immobilized on carbon electrode by physically entrapped in a PVA-Nafion™ polymer composite membrane. The first sensor system (described in Chapter 3) uses insoluble ammonium salts of hexacyanoferrate as a mediator for measuring hydrogen peroxide (in cathodic mode, working at ea -400mV vs. Ag-AgCI» produced from the reaction between glucose and glucose oxidase. Hydrogen peroxide sensing with these waterinsoluble ferricyanide modified electrodes were first studied. Tetrahexyl ammonium ferricyanide (THAF) was used as the model compound to investigate glucose sensing. The glucose sensors functioned well in static solution. For flow analysis, the sensors were found to perform better when operating in anodic mode at ca 200mV vs. Ag-AgCI, where the ferricyanide worked as a mediator for GOx. Chapter 4 describes the investigation of a second mediator system, the waterinsoluble benzoquinone derivatives. These mediators have lower reduction potential than benzoquinone and minimise the effects of common interferents in biological samples. 2,6-dimethylbenzoquinone based glucose sensors operate at potentials around 200mV vs. Ag-AgCI. Common interferents at biological concentrations did not cause any problems for the optimised sensor that used a Nafion™ membrane to exclude anionic species. However, an approach that used a comparator sensor to compensate for interference has been developed. Chapter 5 reports the synthesis and investigation of a novel mediator Nmethylphenazinium iron tetrachloride (NMPITC). It was found that the compound was able to oxidise reduced GOX and reduced hydrogen peroxide at different potentials. The performance as electron mediator for GOX in solution and in solidstate sensor was investigated. The sensor constructed with this mediator operated at low potentials (ca lOOmV vs. Ag-AgCl) that minimized the effects of common interferents.

Blood gas exchange across synthetic membranes is primarily used in blood oxygenators for short-term (1-3 hours) cardiopulmonary bypass procedures. Long term applications (6 hours - i4 days) of membrane oxygenators include treatment of acute respiratory failure or acute liver failure. There are several types of membranes used in these devices: (1) microporous membranes which have high gas permeabilities but have problems of pore wetting if employed in long-term therapies and (2) homogeneous membranes, e.g. silicone rubber which have lower permeability characteristics but are non-wettable and (3) composite membranes which a very thin homogeneous membrane is mechanically supported by a micro porous layer.

Glucose absorbs electromagnetic energy in the near infrared (NIR) spectrum at characteristic wavelengths. An NIR beam is transmitted and as it passes through a solution this absorbance causes detectable spectral changes. The amount of spectral absorbance can be correlated to the concentration of glucose in the solution. In this study we used NIR Spectroscopy and micro sensors and detectors in order to detect glucose in small volume samples with economic instrumentation. The goal was to accurately measure the concentration of glucose in a solution held in a glass capillary vessel.

The nature of a biomaterial surface will influence interactions that will occur thereon. specifically, the chemical composition and topography will dictate the availability of sites of reactivity thereby determining the interfacial response. At the biological level, it is this surface mediated response that indicates the biocompatibility of the material. Hence, understanding and controlling the causative elements of the interfacial response will allow for the engineering of specific cell-biomaterial interactions.

Photochemical control of cell adhesion onto surfaces, a process commonly achieved with caged molecules, has become an important technique in the fabrication of cellular assemblies for biosensors, tissue engineering applications, and studies for cell-cell and cell-substrate interactions. The ability to study cell behaviour at a biomaterial surface requires control of material surface chemistry. In this study the RGD (Arg-Gly-Asp) and RGE (Arg-Gly- Glu) peptide motifs were immobilized by conjugation to surface bound azides to afford cell-receptive modified surfaces. The peptides were synthesized using Frnoc- solid phase peptide synthesis (SPPS) and purified and characterized by high performance liquid chromatography (HPLC). The modified surfaces were characterized using X-ray photoelectron spectroscopy (XPS) and the effect of these surfaces on fibroblast adhesion and spreading were examined at several time points. Our results demonstrate a higher degree of cell attachment and spreading on RGD modified surfaces compared to unmodified and control surfaces. Dynamic control over the interactions between the cells and artificial substrate was investigated by protecting the side chain of the aspartate residue in the RGD peptide with a photolabile protecting group. Combination of the immobilisation techniques, described alongside in situ uncaging (UV light 365nm) has allowed us to develop a photo-addressable surface that will facilitate surface patterning of cell adhesion.