Strong magnetic interaction potentially favors smaller particles in MPS

Magnetic nanoparticles (MNPs) are pivotal in biomedical applications such as imaging, hyperthermia, and biosensing due to their distinct relaxation dynamics under alternating magnetic fields (AMF). In vivo, MNPs are gradually internalized into cellular and tissue environments, where decreasing interparticle distances – resulting from aggregation, target binding, and dense packing – alter their magnetic response to AMF. These changes amplify magnetic dipole particle-particle interactions (pp-IA) among MNP, notably impacting their relaxation behavior. In this work, we investigate the effect of pp-IA on magnetic particle spectroscopy (MPS) via stochastic simulations coupling Néel and Brownian relaxation mechanisms. Our preliminary results provide evidence that at average interparticle distances below ~50 nm, MNPs with smaller core size (16 nm) yield stronger MPS signals than larger cores (20–28 nm).