Amine-assisted catechol-based nanocoating on ultrasmall iron oxide nanoparticles for high-resolution T₁ angiography

Surface engineered iron oxide nanoparticles (IONPs) with catecholic ligands have been investigated as alternative T₁ 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 Fe³⁺ mediated ligand oxidation. Herein, we report highly stable and compact (∼10 nm) Fe³⁺ 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 T₁ 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.