An ultra-sensitive T ₂-weighted MR contrast agent based on Gd³⁺ ion chelated Fe₃O₄ nanoparticles

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.