Stable and Biocompatible Colloidal Dispersions of Superparamagnetic Iron Oxide Nanoparticles with Minimum Aggregation for Biomedical Applications

In this article, a simple and scalable method for preparing well-defined and highly stable colloidal dispersions of superparamagnetic iron oxide nanoparticles (IONPs) is reported. The IONPs with narrow size distribution were synthesized by polyol process. Nonhazardous sodium tripolyphosphate (STPP) was immobilized on the surface of IONPs via effective ligand exchange in aqueous phase. Then the STPP-capped IONPs were purified by tangential flow ultrafitration. The polyanionic nature of STPP and its strong coordination capability to iron oxide warrant the IONPs long-term colloidal stability even in phosphate-buffer saline. Because the ligand exchange and purification process did not involve repeated precipitation by organic solvents, the unwanted irreversible aggregation and organic impurities were avoided to the utmost extent. The absence of aggregation renders the IONPs well-defined magnetic behaviors and optimized relaxometric properties for T₁-weighted magnetic resonance imaging. The in vitro cytotoxicity test suggests that the STPP-capped IONPs possess little toxicity. In vivo MRI experiment carried out with a mouse model demonstrates the excellent T₁-weighted MR contrast enhancement capability of the IONPs. This new kind of IONPs is expected to be applicable in various biomedical applications.