An ultra-sensitive T 2-weighted MR imaging contrast agent was prepared based on Fe3O4 nanoparticles and Gd3+ ions (Fe3O4@Gd). Amino modified Fe3O4 nanoparticles were conjugated to diethylenetriamine pentaacetic acid, and finally coordinated with Gd3+ ions. The nanoparticles had a uniform morphology with a size of 100 nm and a Gd/Fe mass ratio of 1/110. The r 2 (transverse relaxivity) of the Fe3O4 nanoparticles increased from 131.89 mM-1 s-1 to 202.06 mM-1 s-1 after coordination with Gd3+ ions. MR measurements showed that the aqueous dispersion of Fe3O4@Gd nanoparticles had an obvious concentration-dependent negative contrast enhancement. Hepatoma cells were selected to test the cytotoxicity and MR imaging effect. The application of Fe3O4@Gd nanoparticles as contrast agents was also exploited in vivo for T 2-weighted MR imaging of rat livers. All the results showed the effectiveness of the nanoparticles in MR diagnosis.
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