In recent years, magnetic nanoparticles have attracted attention and been actively discussed for biomedical applications. Mg-Zn ferrite nanoparticles embedded in amorphous SiO2 were synthesized using the wet chemical method, and their magnetic properties and transverse relaxation for application as a medium for magnetic resonance imaging (MRI) were examined. We previously found that these Mg-Zn ferrite nanoparticles exhibited significant hyperthermia effect for human breast cancer cells 1. Namely, if this material shows function as a contrast agent for MRI, it is expected to be useful for both diagnosis and treatment as theranostics 2.
Image contrast in MRI is caused by the difference in MR signal due to the magnetic moment of the protons, which are hydrogen nuclei. That contrast depends on the proton density, T1 relaxation time, and T2 relaxation time. In this study, magnetic relaxation phenomena were analyzed by magnetization measurements and AC magnetic susceptibilities. The AC magnetic susceptibilities for various particle sizes of the Mg0.8Zn0.2Fe2O4 nanoparticles were measured in the range of 150–350 K under an AC magnetic field of 1 Oe, 100 Hz. The temperature corresponding to the peak of χ” shifted to higher values as the particle size increased. Relaxation phenomena were evaluated using Cole-Cole plot analysis, and these samples were found to follow the Debye single-relaxation phenomenon.
Spin-echo magnetic resonance measurements for Mg0.8Zn0.2Fe2O4 nanoparticles with particle sizes between 8 and 20 nm were performed using a 0.3-T MRI system. The particles exhibited a significant T2 shortening effect compared with that of agarose as a background control. All particles exhibited effective relaxivity, R2, which was five times higher than that of the intrinsic core of conventional iron oxide agents of ferucarbotrans. The results show that Mg-Zn ferrite nanoparticles embedded in amorphous SiO2 have the potential for theranostics applications.
1 Hamada, S., Aoki, K., Kodama, K., Nashimoto, and Ichiyanagi, Y., 2022. AC magnetic susceptibility and heat dissipation of Zn-doped Mg-ferrite nanoparticles. J. Magn. Magn. Mater. 559 p.169539.
2 S.S. Kelkar, T.M. Reineke, 2011. Theranostics: Combining imaging and therapy, Bioconjug. Chem. 22 (10) Pp.1879–1903.
Fig1. Imaginary parts of the AC magnetic susceptibilities of Mg0.8Zn0.2Fe2O4 for various particle sizes.
Fig.2 T2 relaxation curves of Mg0.8Zn0.2Fe2O4 nanoparticles nanoparticles. Iron oxides and agarose samples are shown for comparison.