Hydrophobic-to-Hydrophilic Transition of Fe₃O₄ Nanorods for Magnetically Induced Hyperthermia

Magnetically induced hyperthermia employing iron oxide nanoparticles is an effectual alternative to the conventional cancer therapeutic modalities. However, colloidal instability, heterogeneous heat distribution in polydispersed nanostructures, and nonspecific targeted delivery still pose major challenges hampering clinical translation. Due to a larger surface area, enhanced blood circulation time, and prolonged retention in tumors, one-dimensional nanostructured materials are of interest of research. Here, we report monodisperse oleate-coated magnetite nanorods (average length of ∼74 ± 13 nm) synthesized using an iron oleate precursor via thermal decomposition. The formation of rod-shape morphology is primarily ascribed to the selective growth along the (110) direction resulting from the preferential adsorption of oleate to (111) facets of Fe3O4. The nanorods are single domain particles with a saturation magnetization of 72 emu/g, which possess negligible coercivity and magnetic dipolar interactions. Hydrophobic-to-hydrophilic phase transition of oleate-coated magnetite nanorods was achieved using an amphiphilic surfactant tetramethylammonium 11-aminoundecanoate, suitable for hyperthermia and biological studies. Distinctive heating responses in various nonaqueous, aqueous, and physiological media evidenced the highest SAR of ∼376 W/g under an alternating current magnetic field of 500 Oe and 315 kHz, which is primarily attributed to effective relaxation losses. Hyperthermia studies conducted in simulated body fluid exhibited an improved heating efficiency (∼369 W/g) compared to water (∼252 W/g). Our results pinpoint the significance of the dispersion stability of magnetite nanorods on the heating performance in varying viscous fluids. In vitro assessment of hydrophilic magnetite nanorods against MCF-7 breast cancer cell lines demonstrated anticancer activity. Moreover, the nanorods induced minimal damage against erythrocytes, resulting in reduced hemolysis. These results indicate the potential use of magnetite nanorods as targeted nanoheating agents for hyperthermia applications.