Gram-Scale Preparation of Iron Oxide Nanoparticles with Renal Clearance Properties for Enhanced -Weighted Magnetic Resonance Imaging.

Extremely small-sized iron oxide nanoparticles (ESIONs) have been accepted as a potential alternative to gadolinium-based contrast agents for enhanced -weighted MR imaging. Recently developed zwitterion-coated ESIONs showed a high contrast power and efficient renal clearing ability, but the tedious preparation steps that required high-cost, unfriendly experimental conditions and a sophisticated phase transition process would likely hinder their clinical translation. Herein, we present a one-pot gram-scale synthesis of zwitterion-capped ultrasmall iron oxide nanoparticles (ZUIONs). The nanoparticles have a core size as small as 3.7 nm and display high colloidal stability in various buffers. The relaxivity of 2.4 mM s and / ratio as low as 2.2 at 1.0 T guarantee their application as effective MRI contrast agents. In vivo studies showed that ZUIONs could induce a significant contrast enhancement in blood pool and be eliminated from the body mainly through the renal excretion pathway. The combined advantageous features including facile preparation, excellent biocompatibility, strong MRI contrast effect, appropriate circulation time, and renal clearable property would render ZUIONs attractive for practical applications.