A smart T₁-weighted MRI contrast agent for uranyl cations based on a DNAzyme–gadolinium conjugate

Rational design of smart MRI contrast agents with high specificity for metal ions remains a challenge. Here, we report a general strategy for the design of smart MRI contrast agents for detecting metal ions based on conjugation of a DNAzyme with a gadolinium complex. The 39E DNAzyme, which has high selectivity for UO₂²⁺, was conjugated to Gd(III)–DOTA and streptavidin. The binding of UO₂²⁺ to its 39E DNAzyme resulted in the dissociation of Gd(III)–DOTA from the large streptavidin, leading to a decrease of the T₁ correlation time, and a change in the MRI signal.