Magnetoelastic Resonators for Highly Specific Chemical and Biological Detection: A Critical Study

We have developed a detection system made of an amorphous ferromagnetic ribbon of composition Fe
₆₄
Co
₁₇
Si
_6.6
B
_12.4
, with excellent magnetoelastic properties as a saturation magnetostriction of 23 ppm and a ΔE effect of 27%. The resonators were coated with polystyrene (PS). Consecutive depositions were applied by dip coating from 10 to 100 μM solution in tetrahydrofuran. The mass increment after each deposition was accurately measured with a high precision (0, 1 μg) balance and was compared with the corresponding resonant frequency. We have tested resonators with L = 3, 2, and 1 cm length. As theory predicts, we have observed a decrease in the resonant frequency as the PS mass increases, reaching a maximum sensitivity of S = Δf/Δm = 52.4 Hz/μg (that corresponds to 19 ng detection for 1 Hz resolution), for the 1 cm length resonator. Nevertheless, our measurements show even better results than theoretically predicted by the common resonator model. Bearing this in mind, here, we present a critical study on the conditions for optimum performance of such resonance-based sensing devices, both from the point of view of the magnetoelastic resonance conditions and from the layer deposition procedure.