Mn( ii ) chelate-coated superparamagnetic iron oxide nanocrystals as high-efficiency magnetic resonance imaging contrast agents

In this communication, a paramagnetic bifunctional manganese (II) chelate ([Mn(Dopa-EDTA)]2-) containing a catechol group is designed and synthesized. The catechol can bind iron ion on the surface of superparamagnetic iron oxide (SPIO) nanocrystals to form core-shell nanoparticles. Both 4 and 7 nm SPIO@[Mn(Dopa-EDTA)]2- show good water solubility, single-crystal dispersion, and low cytotoxicity. The study of the interplay between the longitudinal and transverse relaxation revealed that 4 nm SPIO@[Mn(Dopa-EDTA)]2- with lower r2/r1 = 1.75 at 0.5 T tends to be a perfect T1 contrast agent while 7 nm SPIO@[Mn(Dopa-EDTA)]2- with a higher r2/r1 = 15.0 at 3.0 T tends to be a T2 contrast agent. Interestingly, 4 nm SPIO@[Mn(Dopa-EDTA)]2- with an intermediate value of r2/r1 = 5.26 at 3.0 T could act as T1-T2 dual-modal contrast agent. In vivo imaging with the 4 nm SPIO@[Mn(Dopa-EDTA)]2- nanoparticle show unique imaging features: (1) the long-acting vascular imaging and different signal intensity changes between liver parenchyma and blood vessels with CEMRA sequence; (2) the synergistic contrast enhancement of hepatic imaging with T1WI and T2WI sequence. In summary, these Fe/Mn hybrids core-shell nanoparticles, with its easy to synthesis, good biocompatibility, and synergistic contrast enhancement ability, may provide a useful way for tissue and vascular MR imaging.