Effect of interparticle and inter-cluster dipole–dipole interactions on dynamic behavior of superparamagnetic iron oxide nanoparticles modified with citric acid

This paper describes the hydrodynamic behavior of superparamagnetic iron oxide nanoparticles modified with citric acid (CA-SPIONs) in suspension under alternating current magnetic fields given interparticle and inter-cluster dipole–dipole interactions. The cluster size of the CA-SPIONs is modulated to control interparticle interactions, and the ionic concentration of the CA-SPION suspension is varied to control inter-cluster interactions. Dynamic magnetic susceptibility (DMS) measurements of the CA-SPION suspensions under alternating current magnetic fields indicate that the interparticle interaction by clustering and the inter-cluster interaction by increasing the ionic concentration cause frequency spectra modulation, such as their broadening in the low-frequency region and a decrease in the Brownian relaxation frequency. The experimentally obtained DMS spectra differ from the spectra numerically calculated from the hydrodynamic size distribution of CA-SPIONs using the Debye relaxation model without considering the magnetic interactions; the differences are attributed to the interparticle and inter-cluster dipole–dipole interactions. These insights contribute to a deeper understanding of dynamics of superparamagnetic iron oxide nanoparticles and facilitate nanoparticle parameter optimization for tailored applications in the biomedical field, particularly for their efficacy and precision in liquid-phase biosensing and imaging.