Highly water-dispersible PEG surface modified ultra small superparamagnetic iron oxide nanoparticles useful for target-specific biomedical applications

For the application of superparamagnetic iron oxide nanoparticles in biomedical fields for target-specific purposes, they should be ultra small in diameter. We developed a simple one-step synthesis of surface modified ultra small superparamagnetic iron oxide nanoparticles (USPIONs) with an average particle diameter of 1.7 nm in a polar organic solvent. Polyethylene glycol diacid (PEG) surface modified USPIONs synthesized in triethylene glycol were nearly monodisperse in diameter and highly water-dispersible. The PEG surface modified USPIONs were tested for use as magnetic resonance (MR) contrast agents. They had a low r₂/r₁ relaxivity ratio of 3.4 (r ₁ = 4.46 and r₂ = 15.01 mM^-1 s^-1) and showed clear dose-dependent T₁ and T₂ map images, indicating that they will be useful as both target-specific T₁ and T₂ MR contrast agents due to their ultra small size.