We have performed a study of the magnetic, magnetoelastic, and corrosion resistance properties of seven different composition magnetoelastic-resonant platforms. For some applications, such as structural health monitoring, these materials must have not only good magnetomechanical properties, but also a high corrosion resistance. In the fabricated metallic glasses of composition ${\mathrm{Fe}}_{73-x}{\mathrm{Ni}}_x{\mathrm{Cr}}_5{\mathrm{Si}}_{10}{\mathrm{B}}_{12}$ , the Fe/Ni ratio was varied (Fe + Ni = 73% at.) thus changing the magnetic and magnetoelastic properties. A small amount of chromium $\left({\mathrm{Cr}}_5\right)$ was added in order to achieve the desired good corrosion resistance. As expected, all the studied properties change with the composition of the samples. Alloys containing a higher amount of $\mathrm{Ni}$ than $\mathrm{Fe}$ do not show magnetic behavior at room temperature, while iron-rich alloys have demonstrated not only good magnetic properties, but also good magnetoelastic ones, with magnetoelastic coupling coefficient as high as $0.41$ for $x=0$ in the ${\mathrm{Fe}}_{73}{\mathrm{Ni}}_0{\mathrm{Cr}}_5{\mathrm{Si}}_{10}{\mathrm{B}}_{12}$ (the sample containing only $\mathrm{Fe}$ but not $\mathrm{Ni}$ ). Concerning corrosion resistance, we have found a continuous degradation of these properties as the $\mathrm{Ni}$ content increases in the composition. Thus, the corrosion potential decreases monotonously from 46.74 mV for the $x=0$ , composition ${\mathrm{Fe}}_{73}{\mathrm{Ni}}_0{\mathrm{Cr}}_5{\mathrm{Si}}_{10}{\mathrm{B}}_{12}$ to −239.47 mV for the $x=73$ , composition ${\mathrm{Fe}}_0{\mathrm{Ni}}_{73}{\mathrm{Cr}}_5{\mathrm{Si}}_{10}{\mathrm{B}}_{12}$ .

We report the fabrication by melt spinning, the magnetic and magnetoelastic characterization and corrosion behaviour study (by potentiodynamic methods) of an Fe-based, Fe-Ni-Cr-Si-B metallic glass to be used as resonant platform for biological and chemical detection purposes. The same study has been performed in Fe-Co-Si-B (with excellent magnetoelastic properties) and Fe-Ni-B (with good corrosion properties due to the substitution of Co by Ni) composition amorphous alloys. The well-known, commercial metallic glass with high corrosion resistance Metglas 2826MB®(Fe₄₀Ni₃₈Mo₄B₁₈), widely used for such biological and chemical detection purposes, has been also fully characterized and used as reference. For our Fe-Ni-Cr-Si-B alloy, we have measured values of magnetization (1.22 T), magnetostriction (11.5 ppm) and ΔE effect (6.8 %) values, as well as corrosion potential (-0.25 V), current density (2.54 A/m²), and polarization resistance (56.22 Ω.cm²) that make this composition very promising for the desired biosensing applications. The obtained parameters from our exhaustive characterization are compared with the values obtained for the other different composition metallic glasses and discussed in terms of Ni and Cr content.

The main parameters of magnetoelastic resonators in the detection of chemical (i.e., salts, gases, etc.) or biological (i.e., bacteria, phages, etc.) agents are the sensitivity $S$ (or external agent change magnitude per Hz change in the resonance frequency) and the quality factor $Q$ of the resonance. We present an extensive study on the experimental determination of the $Q$ factor in such magnetoelastic resonant platforms, using three different strategies: (a) analyzing the real and imaginary components of the susceptibility at resonance; (b) numerical fitting of the modulus of the susceptibility; (c) using an exact mathematical expression for the real part of the susceptibility. $Q$ values obtained by the three methods are analyzed and discussed, aiming to establish the most adequate one to accurately determine the quality factor of the magnetoelastic resonance.

In the present work, a nanostructured ZnO layer was synthesized onto a Metglas magnetoelastic ribbon to immobilize hemoglobin (Hb) on it and study the Hb’s electrochemical behavior towards hydrogen peroxide. Hb oxidation by H₂O₂ was monitored simultaneously by two different techniques: Cyclic Voltammetry (CV) and Magnetoelastic Resonance (MR). The Metglas/ZnO/Hb system was simultaneously used as a working electrode for the CV scans and as a magnetoelastic sensor excited by external coils, which drive it to resonance and interrogate it. The ZnO nanoparticles for the ZnO layer were grown hydrothermally and fully characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and photoluminescence (PL). Additionally, the ZnO layer’s elastic modulus was measured using a new method, which makes use of the Metglas substrate. For the detection experiments, the electrochemical cell was performed with a glass vial, where the three electrodes (working, counter and reference) were immersed into PBS (Phosphate Buffer Solution) solution and small H₂O₂ drops were added, one at a time. CV scans were taken every 30 s and 5 min after the addition of each drop and meanwhile a magnetoelastic measurement was taken by the external coils. The CV plots reveal direct electrochemical behavior of Hb and display good electrocatalytic response to the reduction of H₂O₂. The measured catalysis currents increase linearly with the H₂O₂ concentration in a wide range of 25–350 μM with a correlation coefficient 0.99. The detection limit is 25–50 μM. Moreover, the Metglas/ZnO/Hb electrode displays rapid response (30 s) to H₂O₂, and exhibits good stability and reproducibility of the measurements. On the other hand, the magnetoelastic measurements show a small linear mass increase versus the H₂O₂ concentration with a slope of 152 ng/μM, which is probably due to H₂O₂ adsorption in ZnO during the electrochemical reaction. No such effects were detected during the control experiment when only PBS solution was present for a long time.