Study Of A Wireless Magnetoelastic Chem/Biosensor And Its Application

This dissertation is devoted to the fabrication of wireless magnetoelastic bio/chemical sensors and their applications in bio/chemical analysis. In response to a time-varying AC magnetic field, a magnetoelastic ribbon efficiently couples and converts magnetic energy into mechanical energy. The elastic energy mechanically deforms the sensor, causing it mechanically vibrate along its length. When the frequency of the applied AC magnetic field is equal to the mechanical resonance frequency of the ribbon, the vibration amplitude is maximal and the sensor vibrates at its characteristic resonance frequency that shifts in response to mass loading. Since the magnetoelastic material is magnetostrictive, the vibration of the sensor in turn generates a time varying magnetic flux, which can be remotely measured with a set of pick-up coils. The excitation and transmission of signals of magnetoelastic sensor are carried out remotely by magnetic field. No direct physical connections between the sensor and the detection system are required, nor is any internal power required. The wireless nature of the magnetoelastic sensor makes it a powerful candidate for in situ and in vivo analysis. The details of work are summarized as follows:(1) A wireless magnetoelastic sensor for determination of body fluid acidity is developed. The magnetoelastic pH sensor was fabricated by coating a layer of pH-sensitive polymer on a magnetostrictive ribbon, which pre-coated with a layer of polyurethane film. The effects of composition of pH-sensitive polymer on sensor stability and sensitivity, and the interferents existing in physiological fluid on sensors responses were investigated. The sensor transduction signal is derived from the pH-polymer mass differences between its relatively shrunken state in acidic solution and relatively swollen state in alkaline solution. The shift in the resonant frequency of magnetoelastic pH sensor is linear and reversible between pH 5 and 8 with a sensitivity of 200 Hz/pH and a measurement resolution of 0.1 pH. The proposed magnetoelastic pH sensor platform offers a great opportunity for developing a useful in vivo and in situ physiological pH measurement technology.(2) A wireless magnetoelastic glucose biosensor in blood is developed. The glucose biosensor was fabricated based on magnetoelastic pH sensor (pH-polymer used as sensing film). The magnetoelastic biosensor was fabricated by coating the ribbon-like, magnetoelastic sensor with a pH-sensitive polymer and a biolayer of glucose oxidase (GOD) and catalase. pH-sensitive polymer is used as a sensing film to amplify the mass change associated with enzyme biocatalytic reaction and to increase the sensor sensitivity. The GOD-catalyzed oxidation of glucose produces gluconic acid, inducing the pH-responsive polymer to shrink, which in turn decreases the sensor mass loading and increases the resonant frequency. At glucose concentration range of 2.5 ~ 20.0 mM, the biosensor responses are reversible and linear, with a detection limit of 1.2 mM. The proposed magnetoelastic glucose biosensor can potentially be used as a planted sensor and applied to in vivo and in situ measurement of glucose concentrations in body blood.(3) A wireless magnetoelastic bienzyme glucose biosensor is described. The bienzyme biosensor was fabricated by first coating the magnetoelastic-ribbon with horseradish peroxidase (HRP) and upon it a layer of glucose oxidase (GOD). Sensor sensitivity is increased by amplifying the mass change associated with enzyme reaction by biocatalytic precipitation. The GOD catalyzed oxidation of glucose produces gluconic acid and H2O2, and the generated H2O2 biocatalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to insoluble product in the presence of HRP. The insoluble product accumulated on the sensor surface, which resulted in the increasing in sensor mass loading and decreasing in resonant frequency. And the extent of resulting sensor resonant frequency changing, correlated with the amount of glucose. The biosensor response is linear in the range of glucose concentrations of 5 ~ 50 mM, with a detection limit of 2 mM. The biosensor is applied to determine glucose concentration in urine sample.(4) A wireless magnetoleastic microorganism sensor is developed for the early diagnosis and rapid detection of bacteria. The microorganism sensor is fabricated by coating a magnetoelastic-ribbon with a polyurethane protecting film. Bacteria consume nutrients from the culture medium in growing and reproducing process, and produces small molecules, with a corresponding change in viscosity of culture medium. The resonant frequency changes of magnetoelastic sensor resulted from the properties changes of a liquid culture medium and bacteria adhesion to the sensor surface. The bacteria concentration can be quantified based on the changes in resonant frequency and amplitude during culture course. Pseudomonas aeruginosa (P. aeruginosa) and Mycobacterium Tuberculosis (M. Tuberculosis) were selected for the analytical objects. Bacteria can be identified from their characteristic growth curve since different microorganisms show different response profiles to their culture medium. The effects of change in culture medium properties and bacteria adhesion on sensor resonant frequency were investigated with quartz crystal microbalance (QCM), microscopy imaging. The drug-resistance on bacteria growth in culture medium was evaluated based on this proposed method. Using the described technique we are able to directly quantify P. aeruginosa and M. Tuberculosis concentrations in the range of 103 to 108 and 104 to 109 cells/mL, and with a detection limit of 103 and 104 cells/mL, respectively.(5) A wireless, passive magnetoelastic sensing device is presented for the in situ, continuous, and real-time evaluation of the formation of Pseudomonas aeruginosa (P. aeruginosa) biofilms. The polyurethane-coated magnetoelastic-ribbon is used as a transducer for monitoring of P. aeruginosa biofilm formation. In a flowing system, both the resonant frequency and amplitude of the sensor are wirelessly monitored through magnetic field telemetry. Changes in the resonant characteristics of the sensor provide information on the biofilm growth characteristics. The adhesion strength of the biofilm was evaluated by increasing the applied excitation voltage, showing that a tightly attached film was formed.