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

Abstract

We have developed a detection system made of an amorphous ferromagnetic ribbon of composition Fe64Co17Si6.6B12.4, with excellent magnetoelastic properties as a saturation magnetostriction of 23 ppm and a $\Delta E$ effect of 27%. The resonators were coated with polystyrene (PS). Consecutive depositions were applied by dip coating from 10 to $100~\mu \text{M}$ solution in tetrahydrofuran. The mass increment after each deposition was accurately measured with a high precision (0, $1~\mu \text{g}$ ) 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 $S = \Delta f/\Delta m = 52.4$ Hz/ $\mu \text{g}$ (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.