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Browsing Cranfield Health by Course name "PhD"
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Item Open Access Advanced manufacturing processes for the production of biosensors(Cranfield University, 1998-08) Newman, Jeff D.; Turner, Anthony P.F.Biosensors were first described over thirty five years ago, but commercialisation did not occur until the early 1970s. Interest was subsequently sparked by the market for large numbers of disposable devices required for self-testing of blood glucose levels by diabetic patients. The introduction of automated production technology, for the manufacture of the millions of devices required, became a necessity. Screen printing has been the most successful of these technologies to date, but there are many other techniques which could be applicable to biosensor production. This thesis reviews the main technologies used in sensor construction and describes the manufacture of some devices using a range of these processes. The construction of transducers and subsequent chemically- and biologically-sensitive layers, as well as membrane structures are considered. Most of the work presented here concerns the manufacture of electrochemical devices, but many of the techniques described would be equally applicable to certain aspects of the production of other classes of biosensors.Item Open Access Ecological factors affecting growth and ochratoxin A production of Aspergillus section Nigri species on grapes(2006-05) Mitchell, D.; Magan, NareshThis study investigated the effects of interacting environmental factors on the ecophysiology of Aspergillus carbonarius and ochratoxin A (OTA) production, to facilitate the building of a database of knowledge for risk prevention. Spore germination and germ tube extension was faster on grape flesh than in vitro on grape- based media, or grape skin. Under optimum conditions (25-35°C; 0.90-0.99 water activity (aw)) 50% of conidia germinated in < 4.5 hours. Two dimensional profiles in relation to aw x temperature were constructed for rate of germination and germ tube extension for the first time. Mycelial growth was also influenced by aw, temperature, pH and modified atmospheres. Two dimensional temporal profiles of growth and OTA production were constructed based on information on strains from four different European countries. This showed that the optimum aw and temperature, and range were 0.98 aw, 30°C and 0.99-0.88 aw and 15-40°C, respectively. In contrast, for OTA production these were 0.95 aw, 15-20°C, and 0.99-0.93 aw and 15-35°C respectively. Environmental factors also influenced mycelial interactions between A. carbonarius and nine other common grape fungi. An Index of Dominance showed that A. carbonarius was very competitive against these species over a range of aw levels and temperatures. OTA production was generally suppressed by interactions at 0.95 aw with some inhibition of OTA production at 30°C at 0.99 and 0.95 aw. At 0.99 and 20°C all strains except two species produced a stimulation in OTA production. The efficacy of fungicides (5) and anti-oxidants (2) on growth and OTA production was limited at the concentration used. The only two fungicides that did suppress growth were Switch (cyprodinil and fludioxonil) and carbendazim. OTA production was stimulated at sub-optimal concentrations regardless of aw level used. Anti-oxidants were ineffective under all conditions tested. Modified atmospheres (0.03, 25 and 50% CO2) at different aw levels showed that there was very little long term effect on spore germination and germ tube extension, even at 50% CO2. Regardless of aW) OTA production was influenced more by the aw itself than CO2 concentrations. The efficacy of Sodium metabisulphite (NaMBS) at different aw levels (0.99, 0.97, 0.93 aw) on grape juice-based media at 25°C on germination and germ tube extension showed inhibition by >500 mg kg' 1 of NaMBS. Low concentrations (100, 250 mg kg'1) stimulated growth and OTA production. LD50 and LD90 ranges were determined for both growth and OTA production for the first time. Field sampling found that black aspergill! were present on grapes from setting to harvest with a significant increase in the population with grape ripening, and higher temperatures. The most commonly isolated OTA species from grapes was A. carbonarius with no Pénicillium verrucosum and only a few Aspergillus ochraceus isolated. In all the field sampling found no OTA present in any of the grape musts.Item Open Access Extraction of genetic network from microarray data using Bayesian framework(2007-04) Kumuthini, Judit; Bessant, Conrad; Setford, S.The aim of the work described in this thesis was to develop novel methods for the extraction of gene regulatory networks (GRN) from gene expression data, and use these methods to capture previously unknown relationships between genes in specific biological applications. This has been accomplished through the application of Bayesian Networks (BN) through minimum description length (MDL) and taboo search for parameter and structure learning respectively to three large scale microarray datasets from Saccharomyeces cerevisae, Escherichia coli and human stem cells. The application of BNs for modelling the well characterised yeast cell cycle demonstrated the efficacy of the techniques employed. Using the cDNA microarray data from the yeast cell cycle project by Spellman et a l (1998), this study succeeded in extracting many biologically plausible genetic relationships, which were supported by evidence from publicly available genome and literature databases. Two novel knowledge extraction techniques were applied; Target Node (TN) analysis and learning through simulation. Further, it was demonstrated how the addition of prior knowledge to the extracted network can improve the network structure extracted purely from experimental data. The second part of this thesis demonstrated how the BN approach could be adapted to a data set of very high dimensionality, specifically data from a 54,634 probe array used to monitor human adipose tissue. Genetic networks extracted included insulin receptor (IR) and Fatty acid binding proteins (FABP) families that play key roles in fatty acid uptake, transport, and metabolism In the final part of this thesis, the genome-wide GRNs of a prokaryotic expression system were extracted from novel oligo cDNA microarray data from E-coli K12 to identify metabolic stress responsive genes during recombinant protein production. Also, detailed analysis of known metabolic stress related genes and the genes that are directly or indirectly associated in the GRN were used to establish possible markers for host system exhaustion. In conclusion, the BN methods developed proved to be a powerful and effective means of extracting GRNs in a variety of applications.Item Open Access An investigation into the effects of bacterial fermentation in autism(2006-11) Bilbao Montoya, Maria Pilar; Ritchie, Laurie; Hunter, John O.Gastrointestinal symptoms have been observed to be present very often in autistic children. These symptoms are very similar to those observed in Irritable Bowel Syndrome (IBS). An investigation to investigate whether there is a similar cause for autism as well as IBS was done. Methods for the analysis of breath VOCs and urine organic acids were developed to be applied afterwards in the research of biomarkers of autism and IBS. Bacterial metabolites in urine and breath were identified by restricting the diets of healthy volunteers to each of two enteral feeds. The way enteral feeds work in the treatment of Crohn’s disease (CD) was investigated. Enteral feeds work by reducing bacterial activity in the gut, measurably reducing their metabolic products. The urine of IBS patients was analysed and bacterial compounds investigated. Some gastrointestinal symptoms are frequently misdiagnosed as IBS. According to the symptoms and treatment that is successful for these different groups of patients three subgroups can be made: “retention and overflow”, “musculoskeletal” and “abnormal fermentation” IBS. When the urine of these subgroups was observed, different biomarkers for the various subgroups could be identified. Patients with abnormal fermentation IBS have increased bacterial products in urine, suggesting an increase in bacterial activity in the colon. These biomarkers decreased after an exclusion or fibre-free diet and symptoms improved. In a further study, potential biomarkers for autism were identified. The origin of the majority of these compounds is unknown, although some of them are of known bacterial origin. A conclusion of this is that autistic children may exhibit abnormal fermentation since GI symptoms manifest at almost the same time as the autistic behavioural symptoms start and may be present from birth. Autistic children share many symptoms with IBS patients, although the biomarkers are different, showing that the GI symptoms observed in autistic children are not IBS in the children studied. More research needs to be done to determine the origin of the autism biomarkers discovered in urine.Item Open Access Towards the development of an electrochemical immunosensor for the identification of transient ischemic attack via the labeless detection of biomedical markers.(2006) Barton, Andrew Charles; Higson, Seamus P. J.The thesis describes the development of generic platforms for labeless transduction of binding events. A particular application of the project is the labeless detection of biochemical markers for stroke, specifically transient ischemic attack, to facilitate rapid diagnosis and subsequent introduction of appropriate therapy within the required three-hour time frame. Novel biocomponents are under development for detection of these biochemical markers, and further demonstration of the generic nature of the technologies being developed will be realised via the use of a library of monoclonal antibodies as capture biocomponents. This work forms part of an investigation into labeless affinity immunosensor detection via impedimetric transduction utilising the technique of electrochemical impedance spectroscopy (EIS). Novel microelectrode arrays were fabricated by the sonochemical ablation of a homogeneous insulating layer of poly(o-phenylenediamine) exposing discrete areas of an underlying screen-printed conductive substrate. The receptor biocomponents are then subsequently coupled to the transducer by either electropolymerised entrapment or non-covalent affinity within and/or at the surface of conducting polymer ‘mushroom’ shaped protrusions for site-specific immobilisation. Upon exposure to a range of concentrations of antigen analyte solution, complex plane impedance analyses are used to relate the differing redox states of the polymer to possible charge transfer and / or related mechanisms between the immobilised antibody / antigen analyte and the polymer. Results show that signal differentiations were obtained, for a number of antibody / antigen species over a range of concentrations of clinical relevance (ng-pg/mf1), suggesting that the techniques employed offer a viable approach towards the labeless quantification of biochemical markers of transient ischemic attack (TIA).