  Magnetic particle spectroscopy (MPS) is a technology that derives from
magnetic particle imaging (MPI) and thrives as a standalone platform for many
biological and biomedical applications, benefiting from the facile preparation
and chemical modification of magnetic nanoparticles (MNPs). In recent years,
MPS has been reported in extensive literatures as a versatile platform for
different bioassay purposes using artificially designed MNPs, where the MNPs
serve as magnetic tracers, the surface functionalized reagents (e.g.,
antibodies, aptamers, peptides, etc.) and tiny probes capturing target analytes
from biofluid samples. The biochemical complexes on MNP surfaces can be
tailored for different bioassay requirements, while the design of MNPs are of
less attention for MPS-based bioassays. For MNPs in most bioassay applications,
superparamagnetism is prerequisite to avoid agglomerates and false magnetic
signals. Single- and multi-core superparamagnetic nanoparticles (SPMNPs) are
prevalently used in MPS-based bioassays. In this mini review, we compared the
pros & cons of different MPS platforms realizing volumetric- and surface-based
bioassays with single- and multi-core nanoparticles, respectively.
