A wireless magnetoelastic biosensor for convenient and sensitive detection of acid phosphatase

This paper describes a wireless and low-cost biosensor for the sensitive detection of acid phosphatase (ACP) 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 enzymatic hydrolysis of 5-bromo-4-chloro-3-indolyl phosphate (BCIP), producing a dimer 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 ACP concentration ranging from 1.5 to 15 U/l, with a detection limit of 1.5 U/l at a noise level of ∼20 Hz. The sensitivity achieved is comparable to spectrometry and surface acoustic wave sensors. The effect of substrate concentration and BSA immobilization are detailed.