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Title: Influence of vapours on the electrical properties of ceramic and polymer films, in relation to rapid detection of fruit and vegetable rots.
Author: De Lacy Costello, Benjamin Paul John.
Awarding Body: University of the West of England at Bristol
Current Institution: University of the West of England, Bristol
Date of Award: 2000
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When foodstuffs are subject to microbial infection a range of volatile organic compounds (VOCs) are released which can be indicative of both the type and severity of the infection. The bacterium Erwinia carotovora, the primary cause of soft rot, is a major problem in the bulk storage of potato tubers. A number of classes of VOCs have been identified above E. carotovora infected potato tubers, but no disease specific marker has been identified. A number of studies have concluded that the best marker of E. carotovora infection is a substantial increase in the concentration of VOCs in the headspace above the tubers. Chemical sensors which are sensitive to low levels of the VOCs identified in the headspace above infected tubers have been developed. The aim was to use these sensors as the basis of a system for the early detection of soft rot in stored potato tubers. The sensors developed fall into two main categories: those which required heating to elevated temperatures, and those which were operated at ambient temperatures. The sensors operated at ambient temperatures included composites of tin dioxide and chemically prepared polypyrroles. The composites exhibited a high sensitivity to a range of organic vapours (1-100 vpm) and were more sensitive than either tin dioxide or polypyrrole at room temperature. Composites of chemically prepared polypyrroles with various thermoplastics were fabricated and were found to exhibit a high sensitivity to a range of volatile amines. Further studies incorporated chemically prepared polypyrroles into a printing ink vehicle, and sensors constructed from these films displayed good sensitivity, high stability and high mechanical strength. The sensors operated at elevated temperatures included a range of evaporated tin oxide films doped with Pt, CuO and ZnO, plus a range of thick film sensors based on tin dioxide, zinc oxide and mixtures of the two materials. The thick film sensors exhibited the highest sensitivity to the vapours of interest and also gave superior reproducibility of fabrication when compared to the sensors based on evaporated thin films. A synergistic effect appeared to be in operation where tin dioxide and zinc oxide were mixed, with sensors incorporating composites of the two materials exhibiting higher sensitivities than either tin dioxide or zinc oxide alone. A GC-MS study to elucidate the surface reactions occuring on exposure to the vapour, suggested that the synergistic effect was in part due to differences in the catalytic activities/pathways of the two materials. A prototype device was produced based on two evaporated tin dioxide film sensors and one thick film tin dioxidelzinc oxide (50/50 mlm) sensor. The device was tested to various quantities of sound tubers with an infected tuber added. The prototype device was capable of detecting one infected tuber amongst 100kg of sound tubers in a simulated storage crate.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Gas sensing; Plant pathogens; Chemical sensors