|dc.description.abstract||There is an urgent need for the detection technologies that can rapidly detect/monitor the presence of pathogens in food. Various detection technologies have recently been developed and investigated. Among these technologies, magnetostrictive particle (MSP)-based technology provides many unique advantages over others. For example, MSP is a great candidate for in-field tests. This technology is based on a mechanical resonator, whose resonance frequency changes with the binding of pathogens onto its surface. This resonator is actuated by use of the magnetostrictive effect and its vibration is sensed using a magnetic signal. The surface of an MSP is coated with a sensing element that reacts with the target of interest with a strong specificity. Phage based MSP biosensors for the detection of B. anthracis and S. typhimurium have been developed.
In this research, all aspects of the MSP detection technology are studied to fully develop the technology. First of all, a fundamental study was carried out to determine the influence of the size/dimension of an MSP on its resonance behavior. To use the widely exploited and accepted antibodies, a methodology is here introduced to effectively immobilize antibodies onto the surfaces of MSPs. Sensors for the detection of different pathogenic bacteria are developed using antibodies as a sensing element. To develop the MSP technology for in-field detection, handheld interrogation devices are here studied. Finally, to increase the sensitivity of the MSP sensors, MSPs in micro/nano-size
including bar- and tube-shapes have been fabricated.
It is found in the resonance behavior study that the apparent acoustic velocity of the MSP is dependent on the length and length to width ratio rather than a constant. It hasalso been found that although the medium has a very complicated influence on the resonance behavior, the resonance frequency of an MSP is still linearly dependent on the inverse length of the MSP. However, the apparent acoustic velocity changes with the length and length/width ratio. A new method based on using the resonance frequencies of an MSP at different harmonic modes is introduced here to determine the surface roughness of the MSP.
Thiol groups were introduced onto antibodies after modification. The modified antibodies for E. coli, S. aureus, and L. monocytogenes were successfully immobilized onto the gold-coated MSPs. These antibody-immobilized MSPs exhibited great performance as biosensors. For example, the biosensors using an MSP the size of 1.0 mm x 0.3 mm x 30 µm shows a detection limit of less than 102 cfu/ml for detection of the pathogenic bacteria in water. In the experiments, a reference sensor was used to monitor the non-specific binding, and a way to reduce the non-specific binding was studied by using different block agents.
Both frequency-domain and time-domain technologies were exploited in the development of handheld interrogation device. An indirect approach was introduced in the frequency-domain technology. Based on its principle, a circuitry was designed and a circuit was built. The circuit was examined using the MSPs with different sizes. The results show that this indirect approach works well in the characterization of MSP sensors. Additionally, a method to further enhance the signal was introduced. All of the numerical simulation results were consistent with the experimental results. Regarding the time-domain technology, a pulse was used to actuate an MSP resonator, and the response of the MSP was analyzed using fast Fourier transform (FFT) to determine the resonance frequency. It was also experimentally proved that handheld interrogation devices based on either frequency-domain or time-domain technologies can be used for the characterization of multiple MSP-sensors simultaneously. Both devices were validated by using them to characterize the MSP sensors for the detection of pathogenic bacteria in water.
For the fabrication of the micro/nano-sized MSPs, a Co-Fe-B alloy was selected. Amorphous Co-Fe-B in the form of thin films as well as nano-bars and nano-tubes were fabricated using an electrochemical deposition method.||en