Single‐Atom Gd Nanoprobes for Self‐Confirmative MRI with Robust Stability

Gadolinium (Gd)-based complexes are extensively utilized as contrast agents (CAs) in magnetic resonance imaging (MRI), yet, suffer from potential safety concerns and poor tumor targeting. Herein, as a mimic of Gd complex, single-atom Gd nanoprobes with r1 and r2 values of 34.2 and 80.1 mM-1 s-1 (far higher than that of commercial Gd CAs) at 3 T are constructed, which possessed T1 /T2 dual-mode MRI with excellent stability and good tumor targeting ability. Specifically, single-atom Gd is anchored on nitrogen-doped carbon matrix (Gd-Nx C) through spatial-confinement method, which is further subjected to controllable chemical etching to afford fully etched bowl-shape Gd-Nx C (feGd-Nx C) with hydrophilic properties and defined coordination structure, similar to commercial Gd complex. Such nanostructures not only maximized the Gd3+ site exposure, but also are suitable for self-confirmative diagnosis through one probe with dual-mode MRI. Moreover, the strong electron localization and interaction between Gd and N atoms afforded feGd-Nx C excellent kinetic inertness and thermal stability (no significant Gd3+ leaching is observed even incubated with Cu2+ and Zn2+ for two months), providing a creative design protocol for MRI CAs.