Numerical modeling and in situ small angle X-ray scattering characterization of ultra-small SPION magnetophoresis in a high field and gradient separator

Magnetic nanoparticles (MNPs) have recently gained significant attention in various fields, including chemical and biomedical applications, due to their exceptional properties. However, separating MNPs from solution via magnetophoresis is challenging when MNPs are smaller than 50 nm as Brownian forces become on the order of the magnetic forces. In this study, we successfully separated small MNPs (5-30 nm) by utilizing high magnetic fields and gradients generated by economical permanent magnets. In situ small angle X-ray scattering (SAXS) was used to investigate the time-dependent concentration changes in the ferrofluid, and the results validated that only the 30 nm particles experienced particle aggregation or agglomeration, indicating that dipole-dipole interactions did not play a discernable role in the separation process for particles smaller than ∼15 nm. However, numerical simulations have provided further validation that in the absence of particle-particle interactions, even MNPs with diameters less than 15 nm exhibited magnetophoresis that effectively counteracted the effects of Brownian motion.