Renal-clearable zwitterionic conjugated hollow ultrasmall Fe3O4 nanoparticles for T1-weighted MR imaging in vivo

Abstract

Monodispersed hollow Fe₃O₄ nanoparticles with the diameters of 7 and 10 nm were prepared via a high-temperature pyrolysis method and the Kirkendall effect by regulating the ratio of oleylamine to oleic acid. The water solubility was studied by zwitterionic dopamine sulfonate (ZDS) to obtain ZDS-conjugated Fe₃O₄ nanoparticles (Fe₃O₄@ZDS NPs). The 7 nm Fe₃O₄@ZDS NPs exhibited a good T₁ positive contrast with a longitudinal relaxivity (r₁) of 0.23 mM^-1 s^-1 and a small ratio of r₁ to transversal relaxivity (r₂) of 4.00. In the 4T1 xenograft mouse model, the tumor signal from T₁-weighted MRI was positively enhanced by ∼23% after the intravenous injection of 7-Fe₃O₄@ZDS NPs (40 mg kg^-1). More importantly, 7-Fe₃O₄@ZDS NPs can be partially metabolized by the kidney, which is an important step for the use of MRI contrast agents in clinic.