The Research On Wireless Magnetoelastic Biosensors: The Fabrication And Applications

We focus on the development and applications of wireless magnetoelastic sensor platforms which consist of an exciting coil, a receiving coil, a magnetoelastic sensor, and electronics. 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 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, 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. In this paper, the applications of the magnetoelastic sensor in biochemical analysis were studied. The detailed research work was listed as follows:(1) Acid phosphatase (ACP) assay with a wireless magnetoelastic (ME) biosensor. The sensor was fabricated by applying a magnetoelastic ribbon with a layer of pH-sensitive polymer and upon it a sensing film containing bovine serum albumin (BSA) and adenosine-5′-monophosphate (5′-AMP). The ACP-catalyzed hydrolysis of 5′-AMP decreases the solution pH, resulting in the polymer shrinking and consequently the resonance frequency of the magnetoelastic sensor increasing. The kinetic parameters were measured to be 1.64×10-3 mol/l (Michaelis constant) and 130 Hz/min (maximum initial rate). The proposed sensor can determine 0.2 to 1.2 U/ml of ACP.(2) A wireless magnetoelastic glucose biosensor is fabricated by co-immobilizing glucose oxidase (GOx) and catalase onto a pH-sensitive polymer coated magnetoelastic sensor with chitosan as a supporting substrate. The GOx-catalyzed hydrolyzation of glucose produces gluconic acid, resulting in shrinking and corresponding mass decrease in the pH-responsive polymer, and consequently the resonance frequency of the magnetoelastic sensor increasing. The glucose biosensor is applied to measurement of glucose concentration in urine samples; the shift in resonance frequency is found proportional to the glucose concentration, with a linear response between 1 mmol/l and 15 mmol/l. The presence of acetaminophen, lactose, saccharose and galactose do not significantly interfere with glucose detection; ascorbic acid does, as expected, however its effect can be eliminated through cross-correlation with a pH-responsive magnetoelastic reference sensor. A L9 (34) orthogonal array based on the Taguchi method was used to optimize the sensor fabrication process and to determine the key factors that affect sensor performance. Assays of 15 clinical urine samples give glucose levels that are identical to the results by a clinical instrument, showing the proposed sensor can be applied for glucose assay in urine.(3) Kinetic study on the reaction of BSA and tannin. This paper describes a wireless and low-cost biosensor for the sensitive detection of tannin using a thick-film magnetoelastic transducer. In response to an externally applied time-varying magnetic field, the magnetoelastic ribbon-like sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the attached film. As the ribbon material is magnetostrictive, the mechanical vibrations of the sensor launch magnetic flux as a return signal that can be detected remotely using a pickup coil. The measurement is based on the interaction of tannin with bovine serum albumin (BSA) modified on the magnetoelastic biosensor, producing a insoluble tannin-BSA complex, which binds tightly to the sensor surface, resulting in a change in the sensor resonance frequency. The biosensor demonstrates a linear shift in resonance frequency with tannin concentration ranging from 0.60 to 1.08 mmol/l, with a detection limit of 0.60 mmol/l. The effect of the different methods of immobilization BSA, BSA concentration, and the value of pH are detailed. The kinetic reaction of BSA and tannin has been investigated.