| This sensor is to be a precursor to the application of acoustic wave technology to the detection of food-borne pathogens. The aim is to develop a low cost, fast responding, sensitive, specific, and selective biosensor, for the detection of food-borne pathogens. The focus of this work is on the detection of Salmonella typhimurium, which generally enters the gastrointestinal tract through contaminated food.; The thickness shear mode (TSM) resonator was selected for the construction of the biosensor. The sensor consists of a disc shaped AT-cut quartz crystal sandwiched between two gold electrodes, one acting as the sensing surface and the other for interfacing with relevant electronics.; The hypothesis tested in this work is that ‘bacteria in PBS and fat free milk can be detected by a TSM resonator coated with a specific antibody with affinity for that antigen’. The interaction of the bacteria with the antibody results in the change in the area mass density of the crystal. Since the crystal is a mass-frequency transducer, there is a change in the resonant frequency. This frequency change is proportional to the concentration of cells in the suspension, as has been demonstrated using the Sauerbrey Equation. This project is part of the efforts of the Auburn University Detection and Food Safety (AUDFS) Program, whose mission with overall objective is: “To improve the safety of the U.S. food system by developing the Science and Engineering required to rapidly identify, pinpoint, and characterize problems that arise in the food supply chain, through the integration of Sensor and Information systems technology”.; The TSM resonator was coated with polyclonal Salmonella typhimurium antibody using the Langmuir-Blodgett method. This biosensor is driven by a Maxtek PLO-10 oscillator connected to an TIP Frequency Counter and the setup interfaced with a Personal Computer for data acquisition. The biosensor was tested with Salmonella typhimurium bacteria cultures in PBS and fat free milk. From this work, we see that the piezoelectric quartz crystal sensor is able to detect microbes in PBS and milk. The characteristics of the sensor are given in the body of this text. This work also includes SEM images. This is the first time in the literature, that the SEM pictures have been used to visualize how the Salmonella bacteria cells actually attach to the sensor surface. This has enabled us to perform point counts leading to an estimation of the number of bacteria attached to the surface and hence calculated values of anticipated frequency shift. It has been observed that there is a disparity between the real-time data and the calculated values from the Sauerbrey Equation, especially in the lower concentration region. At the high concentration end, the equation breaks down again. The first case is attributable to density-viscosity effects and the latter is due to the occupation of all binding sites or epitopes. After all epitopes have been occupied on the sensor surface, any addition of mass/cells does not result in a frequency change. From this work the TSM resonator has been proved to hold the potential for real-time sensor for pathogen detection. (Abstract shortened by UMI.)... |
