Enhanced Magnetic Nanoparticle Detection Sensitivity in Non-Linear Magnetoimpedance-Based Sensor

Abstract

The capacity to detect magnetic nanoparticles (MNPs) of a sensor based on non-linear giant magnetoimpedance effect has been addressed. A meander type sensor was designed with four nearly zero magnetostrictive ribbons connected in series. Different amounts of MNPs, in aqueous solutions, were cumulatively added to the sensor surface. The associated evolution of magnetoinductive voltage of first ( $V_{Z}$ ) and second harmonic ( $V_{2f}$ ) was analyzed as a function of external magnetic field $H $ (maximum value, $H_{\text {MAX}} = 4.4$ kA/m) and as a function of exciting frequency, $f $ (100 kHz–3 MHz). Both harmonics exhibited optimal detection ratios at $H_{\text {MAX}}$ due to the effect of MNPs stray fields on the transverse permeability of the sensing ribbons. Further analysis with frequency was performed to quantify the amount of MNPs. Different parameters were respectively defined, $m_{\text {LF}} $ and ${m}_{\text {HF}}^{2}$ (proportional to permeability) and $R_{0}$ revealing the highest sensitivity of second harmonic for the detection of MNPs. In order to further confirm the role of stray fields in MNPs detection, a comparative study was performed employing diamagnetic gold nanoparticles.