  Nowadays, there is a growing interest in the field of magnetic particle
spectroscopy (MPS)-based bioassays. MPS monitors the dynamic magnetic response
of surface-functionalized magnetic nanoparticles (MNPs) upon excitation by an
alternating magnetic field (AMF) to detect various target analytes. This
technology has flourished in the past decade due to its low cost, low
background magnetic noise interference from biomatrix, and fast response time.
A large number of MPS variants have been reported by different groups around
the world, with applications ranging from disease diagnosis to foodborne
pathogen detection, and virus detection. However, there is an urgent need for
guidance on how to optimize the sensitivity of MPS detection by choosing
different types of MNPs, AMF modalities, and MPS assay strategies (i.e.,
volume- and surface-based assays). In this work, we systematically study the
effect of AMF frequencies and amplitudes on the responses of single- and
multi-core MNPs under two extreme conditions, namely, the bound and unbound
states. Our results show that some modalities such as dual-frequency MPS
utilizing multicore MNPs are more suitable for surface-based bioassay
applications, whereas, single-frequency MPS systems using single- or multi-core
MNPs are better suited for volumetric bioassay applications. Furthermore, the
bioassay sensitivities for these modalities can be further improved by careful
selection of AMF frequencies and amplitudes.
