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

Abstract 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‐N_xC) through spatial‐confinement method, which is further subjected to controllable chemical etching to afford fully etched bowl‐shape Gd‐N_xC (feGd‐N_xC) 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‐N_xC 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.