AC Magnetic-Field-Induced Heating and Physical Properties of Ferrite Nanoparticles for a Hyperthermia Agent in Medicine

AC magnetic-field-induced heating, cytotoxicity, and bio-related physical properties of two kinds of spinel ferrite nanoparticles, soft (NiFe₂O₄) and hard (CoFe₂O₄), with different mean particle sizes were investigated in this paper to confirm the effectiveness for an in vivo magnetic nanoparticle hyperthermia agent in biomedicine. AC magnetically induced heating temperature of the nanoparticles measured both in a solid and an agar state at different applied magnetic fields and frequencies clarified that the maximum heating temperature of NiFe₂O₄ nanoparticles is much higher than that of CoFe₂O₄ nanoparticles. In addition, it was demonstrated that solid-state NiFe₂O₄ nanoparticles with 24.8 and 35 nm mean particle size exhibited a promisingly high heating temperature (21.5degC-45degC) for a hyperthermia agent in the physiologically tolerable range of the ac magnetic field with less than 50 kHz of applied frequency. According to the magnetic and physical analysis results, the superior ac magnetically induced heating performance of NiFe₂O₄ nanoparticles was primarily due to their higher magnetic susceptibility (permeability) that directly induces a larger magnetic minor hysteresis loop area at the low magnetic field. Cytotoxicity test results, quantitatively estimated by methylthiazol tetrazolium bromide test method, verified that uncoated NiFe₂O₄, chitosan-coated NiFe₂O₄, and CoFe₂O₄ showed a noncytotoxicity, which is clinically suitable for a hyperthermia agent application.