Evaluation of nickel ferrite nanoparticles coated with oleylamine by NMR relaxation measurements and magnetic hyperthermia

Abstract

Nickel ferrite nanoparticles were synthesized via a facile solvothermal approach. Oleylamine (OAm) was used in all synthetic procedures as a stabilizing agent and solvent. By varying the polarity of the solvents, hydrophobic NiFe₂O₄ nanoparticles coated with OAm of relatively similar sizes (9–11.7 nm) and in a range of magnetization values (32.0–53.5 emu g⁻¹) were obtained. The as-prepared hydrophobic nanoparticles were characterized by XRD, TEM, SEM, TGA and VSM and converted to hydrophilic by two different approaches. The addition of a positively charged ligand (cetyltrimethyl ammonium bromide, CTAB) and the ligand exchange procedure (2,3-dimercaptosuccinic acid, DMSA) have been successfully applied. The aqueous suspensions of NiFe₂O₄@CTAB and NiFe₂O₄@DMSA showed good colloidal stability after a long period of time. The different surface modification affected both the NMR relaxometric measurements and the hyperthermia effects. In both techniques CTAB modification demonstrated higher r₂ relaxivity (278.9 s⁻¹ mM⁻¹ in an NMR spectrometer at 11.7 T) and SAR values (423.4 W g⁻¹ at an applied AC field with a particle concentration of 0.5 mg mL⁻¹). The results indicate that a coating with a larger molecule as CTAB under the same size, shape and magnetization of NiFe₂O₄ NPs gave rise to NMR relaxometric properties and heating efficacy.