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|Title:||Printing, Stabilization and Optimization of Odour-Generating Sensors|
|Abstract:||This thesis describes the development, production, optimization and use of two types of odour-generating sensors, which in the presence of specific targets release odorous molecules that are easily detectable by the human nose. The first sensor was based on our previous work using an enzyme-based odour-generating system. This sensor consists of two enzymes, pyridoxal kinase and tryptophanase, that when combined lead to the generation of methyl mercaptan (easily detectable by the human nose) in a manner that is proportional to the presence of the target, adenosine triphosphate (ATP). In this thesis, I took three steps towards making this sensor more relevant from an application point of view. Our previous sensor was solution-based, a format that is not useful from a practical point of view – it is much more appealing to have the sensor in a solid support. My first contribution was to inkjet-print a fully functional sensor on a paper surface to create, what we call “Smell-Tell” paper or swab. Paper is an attractive support for biosensors because it is inexpensive, readily available and can be discarded after use. Inkjet printing is a scalable technology that will allow producing these sensors in large-scale. Printing the sensor on paper is an important step improving sensor usability. The printed paper sensors were active for at least 48 days when stored in the fridge (4°C). Keeping the sensors refrigerated to preserve activity is a substantial drawback towards usability of these sensors. My second contribution was to demonstrate that the enzymes and substrates needed for the “Smell-Tell” paper could be preserved at room temperature, with minimal loss of activity, when immobilized in a pullulan film. Pullulan is a readily water-soluble nonionic polysaccharide and our group has previously reported the ability of this material to preserve the activity of enzymes and other molecules at room temperature. I have shown that it is also possible to prepare “Smell-Tell” pullulan tablets, which provide an instrument-free one step assay for on-site detection of ATP, and that the tablets are stable for at least 2 months when stored at room temperature. The two-enzyme system used is quite complex and no previous effort had been made to optimize the conditions under which it works best, with minimum use of reagents. Fractional factorial design, a statistical method, was used to optimize the system and to investigate the influence of different variables including enzyme concentration, reaction duration, temperature, etc. Based on human smell tests and a designed scoring system, the conditions were optimized in an efficient manner. I found that the most important factor affecting the ability to detect the target (ATP) was the time of reaction (the longest time provided lower detection levels). Using this statistical method, it was possible to decrease the amount of enzymes used by 30% without sacrificing the detection limit. The second odour-reporting sensor described in this thesis is a dual-signaling sensor that reports the presence of water (as little as 50 µL) through the generation of both odour and colour signals. This type of sensor can be used to report intrusion of water into difficult to reach electrical panels, or to detect and report water leakage in individual boxes stored in large containers (such as those used to ship meat in trucks). In addition to experimentally validating the approach, we used modeling to simulate the evaporation and diffusion of the odorous signal and the results demonstrated the possibility of using an odour signal as the reporting signal even in a large room. Proof-of-concept was therefore obtained for instrument-free multi-sensory reporters employing odorous signals.|
|Appears in Collections:||Open Access Dissertations and Theses|
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