Magnetic nanoparticle detection based on nonlinear Faraday rotation

TL;DR

This paper introduces a nonlinear Faraday rotation model for magnetic nanoparticles, demonstrating real-time detection of higher harmonics that correlate linearly with concentration, enabling potential high-resolution in vivo imaging.

Contribution

The study develops a novel model and detection method for magnetic nanoparticles using nonlinear Faraday rotation, improving sensitivity and specificity in contrast agent applications.

Findings

Detection sensitivity as low as 2e-7 rad rotation angle

Higher harmonics avoid background interference

Linear relationship between harmonics and concentration

Abstract

Magnetic nanoparticle (MNP) has attracted interest in various research fields due to its special superparamagnetic and strong magneto-optical effects, especially as contrast agents to enhance the contrast of medical imaging. By introducing the interaction coefficient, we propose a model of the nonlinear Faraday rotation of MNP under the excitation of an external alternating magnetic field. In our homemade device (which can detect the rotation angle as low as about 2e-7 rad), it has been verified that the higher harmonics of the Faraday rotation can avoid the interference of paramagnetic and diamagnetic background at lower concentrations. What's more, the higher harmonics of the Faraday rotation of MNP can be detected in real time and they have a linear relationship with concentration. In the future, it is expected to use MNP as a magneto-optical contrast agent to achieve high-resolution imaging in vivo.