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

Abstract

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 ions 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 <i>r</i> ₂/<i>r</i> ₁ = 1.75 at 0.5 T tends to be a perfect <i>T</i> ₁ contrast agent while 7 nm SPIO@[Mn(Dopa-EDTA)]^2- with a higher <i>r</i> ₂/<i>r</i> ₁ = 15.0 at 3.0 T tends to be a <i>T</i> ₂ contrast agent. Interestingly, 4 nm SPIO@[Mn(Dopa-EDTA)]^2- with an intermediate value of <i>r</i> ₂/<i>r</i> ₁ = 5.26 at 3.0 T could act as <i>T</i> ₁-<i>T</i> ₂ dual-modal contrast agent. <i>In vivo</i> imaging with the 4 nm SPIO@[Mn(Dopa-EDTA)]^2- nanoparticle shows unique imaging features: (1) long-acting vascular imaging and different signal intensity changes between the liver parenchyma and blood vessels with the CEMRA sequence; (2) the synergistic contrast enhancement of hepatic imaging with the <i>T</i> ₁WI and <i>T</i> ₂WI sequence. In summary, these Fe/Mn hybrid core-shell nanoparticles, with their ease of synthesis, good biocompatibility, and synergistic contrast enhancement ability, may provide a useful method for tissue and vascular MR imaging.