Size-control synthesis of structure deficient truncated octahedral Fe3−δO4nanoparticles: high magnetization magnetites as effective hepatic contrast agents

Abstract

This study reports the size-controlled synthesis of truncated octahedral Fe_3−δO₄ nanoparticles varying from 5 to 22 nm in edge length. Size-dependent XRD spectra show that the iron oxide gradually shifted from magnetite toward maghemite as the size decreased. The nonstoichiometric Fe_3−δO₄ was expressed the resulting iron oxide nanoparticles. The smaller particle size resulted in larger δ value. The size dependence of the XRD, magnetization, and Raman measurements indicate that the 22 nm-sized particles formed magnetite nanoparticles. The saturation magnetization increased linearly as the particle size increased, eventually reaching 94 emu/g, which is comparable to bulk magnetite (92 emu/g). The magnetic behavior of Fe_3−δO₄ nanoparticles exhibited a transition from superparamagnetism to ferromagnetism when the particles reached 22 nm in size. The XRD, electron diffraction analysis, fast Fourier transform filtering analysis, and Ar ion beam etching results in this study indicate that the presence of metallic iron in the 22 nm-sized magnetite nanoparticles was responsible for their high magnetization. The high magnetization of the 22 nm-sized magnetite was achieved by different surface modification strategies using surfactant (CTAB) and a polymer (PSMA), generating hydrophilic properties. The chosen PSMA-coated magnetites have an r₂ relaxivity larger than 200 mM⁻¹ s⁻¹, whereas the commercial Resovist hepatic agent achieves only 91 mM⁻¹ s⁻¹. In an effort to develop highly effective hepatic contrast agents, the PSMA-coated magnetite was injected into BALB/C mice to evaluate the T₂* relaxation and image contrast. Results show a greater signal reduction in the liver than Resovist agent. The biodistribution profile of these iron oxide nanoparticles shows significant liver uptake, which is consistent with MRI observations.