Novel nanogel-based MRI Contrast Agents

We present here the preparation and properties of new Gd³⁺-containing nanogel-based contrast agents. These gel nanoparticles are prepared by simple ionotropic gelation from sodium alginate and Gd³⁺. The nanogels are 100-200 nm in diameter and have a high R₁ relaxivity of ≈ 30 mM^-1 s^-1 at 1 T, however, they have poor stability in high ionic strength media. Adding further covalent crosslinks with a suitable agent such as epichlorohydrin dramatically increased the relaxivity of the nanogels to ≈ 60 mM^-1 s^-1 at 1 T and provides a viable strategy to increases their stability against transmetallation.