Abstract
The performance of magneto-impedance sensors to detect the presence and concentration of magnetic nanoparticles is investigated, using finite element calculations to directly solve Maxwell’s equations. In the case of superparamagnetic particles that are not sufficiently magnetized by an external field, it is assumed that the sensitivity of the magneto-impedance sensor to the presence of magnetic nanoparticles comes from the influence of their magnetic permeability on the sensor impedance, and not from the stray magnetic field that the particles produce. The results obtained not only justify this hypothesis, but also provide an explanation for the discrepancies found in the literature about the response of magneto-impedance sensors to the presence of magnetic nanoparticles, where some authors report an increasing magneto-impedance signal when the concentration of magnetic nanoparticles is increased, while others report a decreasing tendency. Additionally, it is demonstrated that sensors with lower magneto-impedance response display larger sensitivities to the presence of magnetic nanoparticles, indicating that the use of plain, nonmagnetic conductors as sensing materials can be beneficial, at least in the case of superparamagnetic particles insufficiently magnetized in an external magnetic field.
Highlights
Magnetic nanoparticles (MNPs) are used in numerous biomedical applications, both for diagnosis and therapy [1]
We aim to evaluate the response of a magneto-impedance sensor in the presence of a sample containing superparamagnetic particles
The assumption is made that the sensitivity to MNPs comes from their magnetic permeability, and not from the stray magnetic field that they produce
Summary
Magnetic nanoparticles (MNPs) are used in numerous biomedical applications, both for diagnosis and therapy [1]. The fact, contradicting results are reported, usually do not provide a satisfactory explanation regarding the is that superparamagnetic particles do not display remanence, and do not produce physical origin of the MI effect’s sensitivity to the presence of magnetic nanoparticles. It is assumed external magnetic fields unless magnetized by an appropriate biasing field. The sensing mechanism is very simple: the presence of a high permeability medium in the proximity of the MI sensor modifies the distribution of the electromagnetic field associated with the alternating current flowing in the sensor This produces a variation of the sensor’s impedance, but it is not related to the intrinsic sensitivity of the MI to low magnetic fields. The results from the numerical solution of Maxwell’s equations confirm that our assumption qualitatively reproduces the experimental results, and help to explain the discrepancies reported in the literature compiled in [16], about the MI behavior when detecting magnetic nanoparticles
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