Octahedral-Shaped Fe3O4 Nanoparticles With Enhanced Specific Absorption Rate and Relaxivity

Herein, we have synthesized citric acid functionalized monodisperse (6-12 nm) octahedral-shaped Fe₃O₄ nanoparticles (NPs). The as-prepared octahedral-shaped Fe₃O₄ NPs exhibit a bulk-like magnetization (~92 emu/g) value due to lesser surface spin disorder. In addition, compared with spherical morphology, these octahedral NPs (Oct-NPs) exhibit much higher specific absorption rate (SAR) value as a potential candidate for hyperthermia treatment and higher R₂ value as an efficient contrast agent for magnetic resonance imaging. The enhanced R₂ relaxivity and SAR values are attributed to the higher saturation magnetization (MS) value and a larger surface area of Oct-NPs. The R₂ value of 12 nm-sized Oct-NPs suspension is 353 mM^-1s^-1, which is 3.5 times higher than that of the commercial contrast agent. With increase in size (6-12 nm), the R₂ value gradually increases from 198 to 353 mM^-1s^-1; this increase is a consequence of the MS enhancement as well as the surface area.