Stable water-soluble iron oxide nanoparticles using Tiron

Success in biological and nanomaterial applications that rely on magnetic iron oxide nanoparticles (IONPs) often depends on monodispersity, size, and aqueous stability of the synthesized particles. Here we report a simple and efficient strategy to prepare monodisperse, ultrasmall, water dispersible superparamagnetic IONPs. Monodisperse IONPs are initially synthesized in organic solvents using oleic acid as a dispersant. The subsequent ligand exchange of oleic acid for dopamine and Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) allows for superior colloidal stability in aqueous media. Zeta potential measurements confirm the stability of the nanoparticles upon redispersal in water or biologically relevant buffers. The synthesized particles also preserve their general shape, size, and crystallinity after ligand exchange as evidenced by TEM and SAED measurements. Magnetic properties are also maintained after the ligand exchange as verified by magnetometry and magnetic force microscopy (MFM). An analysis of potential issues regarding this and other prior ligand exchanges is also highlighted, which may aid others in future investigations.