| This dissertation focuses on the theoretics and applications of the wireless magnetoelastic microorganism sensors. The wireless magnetoelastic technique is based on magnetoelastic principle, the sensor platforms consist of a magnetoelastic sensor and an exciting/a receiving coil. In response to a time varying magnetic field, the magnetoelastic sensor efficiently couples and translates magnetic energy to mechanical energy. The elastic energy mechanically deforms the sensor, causing it mechanically vibrate along its length. When the frequency of the ac field is equal to the mechanical resonance frequency of the sensor, the vibration amplitude is maximum, and the sensor vibrates at its characteristic resonance frequency that shifts in response to change of liquid properties (such as viscosity or density) or mass loading. Since the sensor material is also magnetostrictive, the mechanical oscillation in turn generates magnetic flux that can be remotely detected using a pick-up coil. The sensor is totally passive. No physical connections between the sensor and the detection system are required for signal telemetry, nor does the sensor require any internal power sources. The wireless nature of the magnetoelastic sensor makes it a powerful candidate for in situ and in vivo analysis. In this dissertation, three kinds of magnetoelastic biosensors were developed:(1) The development of wireless magnetoelastic (ME) Escherichia coli O157:H7 (E. coli O157:H7) sensor: Fabricate the wireless magnetoelastic E. coli O157:H7 sensor; research on the sensor in response to the change of liquid properties (viscosity, density, etc.) of the test solution and bacteria adhesion to the sensor, and investigate the effect of gentamycin sulfate injection (GSI) on proliferation of the bacteria, it can be used to availably evaluate the medicament effect of antibiotic. The growth and reproduction of E. coli O157:H7 decreases the solution viscosity, and in turn the resonance frequency of the magnetoelastic sensor increases, the bacteria adhesion reversely results in the decrease of the resonance frequency, change of solution properties and bacteria adhesion affect the resonance frequency together. Using the described sensor we are able to directly quantify E. coli O157:H7 concentrations of 2×10~2 to 3×10~6 cells/ml.(2) The development of wireless magnetoelastic sensor for early determination of Staphylococcus aureus (S. aureus) in different liquid medium: Fabricate the wireless magnetoelastic S. aureus sensor; investigate the sensor in response to the change of liquid properties of the test solution (culture medium or milk), and compare the sensor in response to different bacteria in milk, it can be used for predictive indication of milk spoilage. The S. aureus growth results in the change of viscosity, so the resonance frequency of the sensor changes. In liquid medium, decrease of viscosity causes the increase of resonance frequency; in milk, the viscosity firstly decreases and afterwards increases, so the resonance frequency firstly increases and then decreases. We are able to directly quantify S. aureus concentrations of 3×10~3 to 2×10~7 cells/ml in culture medium or 10~4 to 10~7 cells/ml in milk.(3) The development of wireless magnetoelastic sensor to rapidly monitor Staphylococcus epidermidis (S. epidermidis): Fabricate the wireless magnetoelastic S. epidermidis sensor; investigate the sensor in response to the change of mass loading which caused by the liquefaction of solid nutrient gelatine medium film. S. epidermidis proliferation liquefies the solid film, and the film liquefaction causes the decrease of mass loading, so the resonance frequency increases, the sensor can be used to determine S. epidermidis concentrations ranging from 3×10~3 to 2×10~7 cells/ml; investigate liquefaction ability of different kinds of bacteria, it is fast for detection of different microorganisms.
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