Synthesis of Water-soluble Fe3O4 Nanocrystals with a Phase-transfer Method

Hydrophobic Fe3O4 nanocrystals with superparamagnetic behavior were synthesized in an or- ganic solvent. High quality water-soluble Fe3O4 nanocrystals were then prepared by a phase transfer method, in which amphiphilic oligomers (polymaleic acid aliphatic amine ester) was used as surface coating agents. The obtained aqueous Fe3O4 nanocrystals were characterized with transmission electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and dynamic light scattering. A solution of Fe3O4 nanocrystals in water showed expected superparamagnetic behavior when subjected to an external magnetic field. We found that hydrophobic ester chain length of the amphiphilic oligomer can dramatically affect the phase transfer efficiency, which was explained by the impact of local hydrophobic environment on the stability of nanocrystals in water. A biocompatible test showed that the water-soluble Fe3O4 were very stable in various physiological conditions without particle aggregation.