Water-soluble superparamagnetic manganese ferrite nanoparticles for magnetic resonance imaging.

We report here a thermal decomposition approach to the synthesis of water-soluble superparamagnetic manganese ferrite (MnFe(2)O(4)) nanoparticles (NPs) for magnetic resonance (MR) imaging applications. In this approach, tetraethylene glycol was utilized as a coordination and stabilization agent, rendering the NPs water-soluble and stable. The formed NPs had a diameter of 7 nm with a narrow size distribution, and were superparamagnetic with a saturated magnetization (Ms) of 39 emu/g. In vitro cytotoxicity test revealed that the MnFe(2)O(4) NPs were biocompatible at a particle concentration below 200 microg/mL. The transverse relaxivity of MnFe(2)O(4) NPs in water and cells after incubation were determined to be 189.3mm(-1)s(-1) and 36.8mm(-1)s(-1) based on iron concentration, respectively. In vivo MR imaging studies in conjunction with inductively coupled plasma-atomic emission spectroscopy showed that the MnFe(2)O(4) NPs were preferentially accumulated in liver after intravenous injection for 4h. This suggests that the developed MnFe(2)O(4) NPs can serve as a sensitive MR imaging contrast agent for liver imaging. By appropriately modifying or functionalizing the surface of the NPs, these particles may be used for MR detection of other diseases.