New Perspective on Planar Inductive Sensors: Radio-Frequency Refractometry for Highly Sensitive Quantification of Magnetic Nanoparticles

Abstract

We demonstrate how resonant planar coils may be used as sensors to detect and quantify magnetic nanoparticles reliably. A coil’s resonant frequency depends on the adjacent materials’ magnetic permeability and electric permittivity. A small number of nanoparticles dispersed on a supporting matrix on top of a planar coil circuit may thus be quantified. Such nanoparticle detection has application detection to create new devices to assess biomedicine, food quality assurance, and environmental control challenges. We developed a mathematical model for the inductive sensor response at radio frequencies to obtain the nanoparticles’ mass from the self-resonance frequency of the coil. In the model, the calibration parameters only depend on the refraction index of the material around the coil, not on the separate magnetic permeability and electric permittivity. The model compares favourably with three-dimensional electromagnetic simulations and independent experimental measurements. The sensor can be scaled and automated in portable devices to measure small quantities of nanoparticles at a low cost. The resonant sensor combined with the mathematical model is a significant improvement over simple inductive sensors, which operate at smaller frequencies and do not have the required sensitivity, and oscillator-based inductive sensors, which focus on just magnetic permeability.

Mn-ferrite nanoparticles as promising magnetic tags for radiofrequency inductive detection and quantification in lateral flow assays

“…Atomic magnetometers have also been used to achieve high sensitivity in LFAs quantication. 20 Other inductive strategies based on magnetic ux, 21 magnetic permeability 14,[22][23][24] and non-linear magnetization 25 have been developed to be low-cost and easily miniaturized while achieving high sensitivities for the detection of several biomarkers. 14 In the case of inductive sensors based on magnetic permeability, a copper coil applies an alternating magnetic eld to adjacent superparamagnetic particles.…”

“…Atomic magnetometers have also been used to achieve high sensitivity in LFAs quantification. 20 Other inductive strategies based on magnetic flux, 21 magnetic permeability 14,22–24 and non-linear magnetization 25 have been developed to be low-cost and easily miniaturized while achieving high sensitivities for the detection of several biomarkers. 14…”

Flexible & transparent breath sensor and conducting electrodes based on a highly interconnected Au nanoparticle network

“…[14][15][16] Current technology immensely demands wearable breath sensors with high sensitivity and selectivity besides being visibly transparent and with excellent mechanical flexibility as they have the potential to monitor our routine healthcare with great aesthetic appeal. 17 Transparent and robust breath sensors signify a vital connection between nanotechnology and healthcare, and they are demanded in scenarios where seethrough devices are required. 18 Diverse materials have been extensively studied to develop robust breath-sensing devices with ultra-sensitivity, long-term stability, and rapid response and recovery capabilities.…”