Sensitive Contrast-Enhanced Magnetic Resonance Imaging of Orthotopic and Metastatic Hepatic Tumors by Ultralow Doses of Zinc Ferrite Octapods

Contrast ability of magnetic nanoparticles (MNPs) is critical for the sensitive and accurate diagnosis of cancer with magnetic resonance imaging (MRI). However, the low sensitivity of current contrast agents (CAs) remains a major limitation to meet clinical needs. Shape and composition engineering are two important means for improving the contrast ability of MNPs. Herein, we report a facile method incorporating both approaches to manufacture zinc ferrite octapods with a large effective radius and various Zn doping ratios. The saturated magnetizations and T2 relaxivities of these engineered octapods both show an interesting trend with ascending zinc doping level. Particularly, the r2 value of ZnxFe3–xO4 (x = 0.44) octapods at 7.0 T is 989.1 mM–1s–1, and the highest T2 relaxivity ever reported, which is 10.2 times higher than the commercial sample, Feraheme. With the aid of this octapod sample, contrast-enhanced MRI (CE-MRI) for detecting orthotopic and metastatic hepatic tumors could be accomplished even at a dose of as low as 0.2 mg/kg, which is 1/10 of the regular dose for commercial CAs. These ZnxFe3–xO4 octapods hold great potential for sensitive CE-MRI in detecting early hepatic tumors and tiny metastatic tumors with less dosages and side effects in clinic.