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 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.