Amine-assisted catechol-based nanocoating on ultrasmall iron oxide nanoparticles for high-resolution T 1 angiography.

Surface engineered iron oxide nanoparticles (IONPs) with catecholic ligands have been investigated as alternative T 1 contrast agents. However, complex oxidative chemistry of catechol during IONP ligand exchange causes surface etching, heterogeneous hydrodynamic size distribution, and low colloidal stability because of Fe 3+ mediated ligand oxidation. Herein, we report highly stable and compact (∼10 nm) Fe 3+ rich ultrasmall IONPs functionalized with a multidentate catechol-based polyethylene glycol polymer ligand through amine-assisted catecholic nanocoating. The IONPs exhibit excellent stability over a broad range of pHs and low nonspecific binding in vitro . We also demonstrate that the resultant NPs have a long circulation time (∼80 min), enabling high resolution T 1 magnetic resonance angiography in vivo . These results suggest that the amine assisted catechol-based nanocoating opens a new potential of metal oxide NPs to take a step forward in exquisite bio-application fields.