PEGylation of Ni1-xZnxFe2O4 Nanoparticles with Heat Dissipation Based on Néel and Brownian Relaxation

Abstract

Ferrite nanoparticles (NPs) have demonstrated considerable potential for use in biomedical applications such as magnetic resonance imaging, magnetic particle imaging, and magnetic hyperthermia treatment (MHT)[1,2]. In the medical application of ferrite NPs, biocompatibility must be ensured. To enhance the biocompatibility, we modified the NPs by using polyethylene glycol (PEG), which is highly hydrophilic and biocompatible. Furthermore, in the heat dissipation of the magnetic NPs, caused by the relaxation mechanism, the imaginary part of the magnetic susceptibility χ’’ at the room temperature is a key parameter. Moreover, M–Zn ferrite NPs (M = Ni, Co, Mn, Fe) are multielement ferrites, whose magnetization can be increased by doping with nonmagnetic Zn ions . The purpose of this study was to develop a sample with improved biocompatibility by PEGylation, to clarify the change in magnetization characteristics due to the Zn doping effect, and to clarify the heat generation mechanism of the sample for MHT application.This study was focused on Ni-Zn ferrite NPs , and NPs with different contents of Zn ions were prepared. Ni1-xZnxFe2O4 (x = 0, 0.2, 0.5, 0.8) NPs coated with PEG were synthesized using our original method[2]. The crystal structures of these particles were examined through X-ray diffraction and X-ray absorption spectroscopy. The particle diameters were controlled to be between 5–20 nm by controlling the amount of water, and the samples with different Zn doping amounts were adjusted to have a particle size of 10 nm. PEGylation in the particles was confirmed through the Fourier-transform infrared spectrometry technique(Fig. 1) and by using a thermogravimeter-differential thermal analyzer.The magnetization curves of all the samples were obtained at 300 K in a ±10 kOe field. All the samples exhibited superparamagnetic behavior with no coercive force, and the magnetization values ranged between 39 and 43 emu g-1 with only a slight afference. The field-cooled/zero-field-cooled measurement showed that, in terms of the temperature dependence of the magnetization, the blocking temperature TB ranged between 105 and 150 K(Fig. 2). χ’’ exhibited a peak value in the x = 0.5 sample at room temperature, and the most effective temperature rise was expected in this composition because the heat dissipation of superparamagnetic particles depends on the value of χ’’ .Moreover, we measured the increase in the temperature in the AC magnetic field of 15 kHz, 130 Oe for all the samples. The temperature of the samples was measured using an optical fiber thermometer. The value of heat dissipation could be attributed to the Néel relaxation system. To clarify if the heat generation mechanism pertained to the Néel relaxation or Brownian relaxation, the heating effect in silicone oil and water was evaluated at a frequency of 210 kHz. It was noted that the Néel relaxation and Brownian relaxation were dominant for particle sizes of approximately 10 nm and more than 20 nm, respectively.Thus, we successfully developed highly biocompatible magnetic NPs and experimentally clarified the contribution of the Néel and Brownian relaxation depending on the particle size. **