Renal-clearable zwitterionic conjugated hollow ultrasmall FeO nanoparticles for T-weighted MR imaging in vivo.

Monodispersed hollow FeO 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 FeO nanoparticles (FeO@ZDS NPs). The 7 nm FeO@ZDS NPs exhibited a good T positive contrast with a longitudinal relaxivity (r) of 0.23 mM s and a small ratio of r to transversal relaxivity (r) of 4.00. In the 4T1 xenograft mouse model, the tumor signal from T-weighted MRI was positively enhanced by ∼23% after the intravenous injection of 7-FeO@ZDS NPs (40 mg kg). More importantly, 7-FeO@ZDS NPs can be partially metabolized by the kidney, which is an important step for the use of MRI contrast agents in clinic.