Magnetic Particle Spectroscopy (MPS)-Based Bioassays

Magnetic Particle Spectroscopy (MPS) originates from Magnetic Particle Imaging (MPI) and was initially designed to assess the suitability of magnetic nanoparticle tracers for MPI applications. Since 2006, MPS has found application in bioassays. It relies on detecting the magnetic dynamics of magnetic nanoparticles in bioassay contexts. When exposed to an external sinusoidal magnetic drive field, magnetic nanoparticles exhibit magnetization relaxation, aligning their magnetic moments with the field direction through Brownian and Néel relaxations. Their nonlinear magnetization responses induce higher harmonics of the drive field frequency, revealing information about the nanoparticles' biological environment. Throughout its development, various MPS designs have been reported. Herein, I will cover the dynamic magnetization models of magnetic nanoparticles and the surface functionalization of these nanoparticles for MPS-based bioassays. In addition, different MPS platforms will be explored, including single- and dual-driving field designs and MPS assay mechanisms such as volumetric- and surface-based bioassays. The integration of MPS with lateral flow assays and microfluidic channels will also be discussed. Various examples of MPS-based bioassays for detecting viruses (e.g., influenza A virus, SARS-CoV-2) and foodborne pathogens/toxins will be showcased.