Detection of Salmonella Typhimurium on Environmental Surfaces Using Magnetoelastic/magnetostrictive (ME) Biosensors.
Type of DegreePhD Dissertation
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Food products can be contaminated by Salmonella anywhere along the food supply chain, so that serious foodborne illnesses, hospitalizations, and even death are caused. The conflict between the fast food-supply requirement and the long-time sample preparing process of the conventional Salmonella detection method cannot be settled. A wireless Salmonella sensing technique based on magnetoelastic/magnetostrictive (ME) biosensors was developed to provide a low-cost, portable, label-free, on-site detection to ensure the safety of our food. In this dissertation, utilizing the newly developed planar spiral coil, fast detections of Salmonella Typhimurium on sample surfaces were demonstrated. At first, a methodology for the rapid and sensitive detection of Salmonella on plastic food processing plates using ME biosensors was developed. With the application of the microfabricated planar spiral coil and 1 mm long ME sensors, real-time and in-situ detection of S. Typhimurium on plastic surface without sample preparation and/or enrichment in the testing process was achieved with a sensitivity lower than 150 CFU/mm2. Based on this direct surface measurement method, a new approach to monitor the Salmonella in a large volume of water using a membrane filter was also developed. By passing the Salmonella suspension through a membrane filter, almost all target cells were isolated on the filter surface. With this method, a detection of bacteria in liquid was transformed into a surface detection. The concentration efficiency of bacteria on the membrane filter was almost 100%, and the limit of detection of this measurement system was found at 54 CFU. Furthermore, swabs and gelatin are also employed and compared as new large-scale surface sampling technologies. Widely used in hospitals, labs, and food supply chains, the swab is an essential sampling tool for microorganisms. However, for the surface detection, it only covers a small area. Gelatin is a translucent, colorless, flavorless food additive that was derived from collagen obtained from various animal body parts. Gelatin solution was directly sprayed onto a surface of interest to form a solid film that could be peeled off from the surface and removed the bacterial cells from the surface. Therefore, the gelatin can be used to cover a large area. The gelatin film with target bacterial cells was then dissolved in water so that the technologies for detecting bacterial cells in water could be used to detect the bacteria cells. It was experimentally demonstrated both swabs and gelatin are great candidates for bacteria sampling from sample surfaces. In this research, the detection methods by using the ME sensing system was demonstrated.