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Abstract: 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 15U/l, with a detection limit of 1.5U/l at a noise level of ∼20Hz. The sensitivity achieved is comparable to spectrometry and surface acoustic wave sensors. The effect of substrate concentration and BSA immobilization are detailed. [Copyright &y& Elsevier]

A wireless remote‐query disposable magnetoelastic biosensor is developed for the assay of acid phosphatase (ACP). The sensor was fabricated by applying a layer of pH‐sensitive polymer to a magnetoelastic ribbon and, on top of it, a sensing film containing bovine serum albumin and adenosine‐5′‐monophosphate (5′‐AMP), the substrate of ACP. In response to an externally applied time‐varying magnetic field, the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent on the mass of the attached film. Because the magnetoelastic sensor is magnetostrictive, the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely from the sensor using a pick‐up coil. 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 experimental condition was optimized to be 37°C, in 2.5 mM sodium citrate buffer solution (pH 6.5). Using citrate as buffer can enhance the ACP activity, partly offsetting the effect of the buffer capacity on the sensitivity. The kinetic parameter were measured to be: 1.64×10–3 M (Michaelis constant) and 130 Hz/min (maximum initial rate). This work provides a remote enzymatic assay of ACP. The relative standard deviation in the measurements of six sensors in parallel is 3.4%. The proposed sensor can determine 0.2∼⃒1.2 U/ml of ACP. [ABSTRACT FROM AUTHOR]

Abstract: A remote query, inexpensive and hence readily disposable α-amylase biosensor is described. The sensor is fabricated by immobilizing a layer of starch gel on a thick-film ribbon-like magnetoelastic sensor. In response to an ac magnetic field the magnetoelastic sensor replies with a return magnetic field, the characteristic resonance frequency of which is inversely dependent upon the attached mass load of the sensor. When exposed to α-amylase the resonance frequency of the starch gel-immobilized sensor increases in proportion to the starch hydrolyzation by α-amylase allowing for its quantification. The starch-immobilized sensor can also be used for the detection of urea and methamidophos based on the inhibition of urea and methamidophos to α-amylase. The sensor described here can detect 75 to 125U/ml α-amylase, as well as 0.02–0.2% methamidophos, and 0.3–8mmol/l urea. [Copyright &y& Elsevier]