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

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 T-1 positive contrast with a longitudinal relaxivity (r(1)) of 0.23 mM(-1) s(-1) and a small ratio of r(1) to transversal relaxivity (r(2)) of 4.00. In the 4T1 xenograft mouse model, the tumor signal from T-1-weighted MRI was positively enhanced by similar to 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.