A Modular Core–Shell Nanoparticle Platform for Dual‐Modal MRI–Luminescence With High Relaxivity

ABSTRACT Bimodal imaging agents that combine MRI and optical signals can improve imaging and diagnostic precision by providing complementary anatomical and molecular information. Macromolecular MRI agents can deliver higher relaxivities than small‐molecule analogues by using controlled architectures that slow rotational motion and enhance Gd(III)–water interactions. The combination of bimodal functionality with macromolecular designs represents a highly promising route to new imaging agents, but its potential has not yet been realized due to safety concerns over possible unchelated metals and difficulties in achieving reproducible large‐scale production. Here, we present a simple, reproducible method to directly incorporate isostructural Gd(III) and Tb(III) complexes into amphiphilic core–shell block copolymer nanoparticles using a single macrocyclic methacrylate ligand. This modular design enables controlled spatial positioning of each MRI‐ and luminescence agent, achieving high relaxivity up to 30.2 mM ⁻¹ s ⁻¹ per Gd(III) and long‐lived (>1.30 ms) luminescence, providing a tunable platform for dual‐modal MRI–luminescence applications.