The Research Of Wireless Magnetoelastic Microorganism Sensors

This dissertation is focused on the theoretics and the 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) Micrococcus luteus (M. luteus) sensor: Fabricate the wireless magnetoelastic M. luteus 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 as an application of the sensor the salt tolerability of M. luteus was also investigated. Bacteria consume nutrients from the culture medium in growing and reproducing process, and produces small molecules, with a corresponding decrease in viscosity of the culture medium, and in turn the resonance frequency of the magnetoelastic sensor increases, Using the described sensor we are able to directly quantify M. luteus concentrations of 103 to 107 cells ml–1.(2) The development of wireless magnetoelastic sensor for early determination of Lactic acid bacteria (LAB) (Lactobacillusdel brueckiissp. bulgaricus and Streptococcus thermophilus co-existing) in different liquid medium: Fabricate the wireless magnetoelastic LAB sensor; investigate the sensor in response to the change of liquid properties of the test solution (culture medium or milk), and compare the existing of bacteria other than LAB results in different response profiles,. it offers a way to detect other bacteria during milk zymolysis and can be used for predictive indication of milk spoilage. The LAB 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 LAB concentrations of 103 to 107 cells ml–1 in culture medium or 102 to 107 cells ml–1 in milk.(3) A new wireless magnetoelastic sensor technique was proposed for studying the effect of surfactants on the growth of Pseudomonas aeruginosa (P. aeruginosa) in media. The influence of the concentration and ion type of surfactants (cationic, anion and nonionic surfactants), on the growth of bacteria was investigated in detail. The growth and reproduction of P. aeruginosa decreases the solution viscosity, and in turn the resonance frequency of the magnetoelastic sensor increases, the frequency shift curves under different growth conditions were obtained and compared with each other. This paper has great meaning to application and study of surfactants.