Ferromagnetic Resonance Heating of Magnetic Nanoparticles Resovist for Biomedical Applications

Ferromagnetic resonance (FMR)-based magnetic energy dissipation potentially generates effective heating for cancer therapy in magnetic hyperthermia. We demonstrated the FMR characteristics of normal/customized Resovist (particle sizes of 60 and 16 nm) for biomedical applications and revealed the bias magnetic field-dependent FMR spectrum in the range of 1–10 GHz under 0–2000 Oe. Moreover, an improvement in heating power was observed under the FMR condition. The maximum temperature increment rate was 2.5 °C/s, which is tenfold greater than that of conventional magnetic hyperthermia with a frequency range of several hundreds of kilohertz. Our results indicate that magnetic hyperthermia by utilizing FMR enables the progressive study of cancer treatment.

I. Introduction

Magnetic hyperthermia enables selective treatment of cancer cells [1], [2] using temperature variations with minimal interference in healthy tissues [3], [4]. The injection of magnetic nanoparticles (MNPs) into an animal/human body enables local treatment owing to heat generation based on magnetic relaxation (magnetic energy dissipation). Generally, the increase in temperature originates from magnetic energy dissipation based on Neel and/or Brownian relaxation [5] under the application of alternating magnetic fields in the frequency range of 100–1000 kHz, and the heating efficiency is typically 100 W/g for iron oxide nanoparticles. Due to the lack of heating efficiency, medical devices for magnetic hyperthermia are large in size and require considerable power to apply to medical sites. For effective heating, the waveforms of the applied alternating magnetic field have been optimized, and over 100 W/g was achieved [6], [7], [8]. However, the mechanism of magnetic energy dissipation is still based on magnetic relaxation processes, indicating a limited heating effectiveness.