Selective Cation Exchange Enabled Growth of Lanthanide Core/Shell Nanoparticles with Dissimilar Structure

Core/shell nanostructure is versatile for improving or integrating diverse functions, yet it is still limited to homeomorphism with isomorphic core and shell structure. Here, we delineate a selective cation exchange strategy to construct lanthanide core/shell nanoparticles with dissimilar structure. Hexagonal NaLnF₄, a typical photon conversion material, was selected to grow cubic CaF₂ shell to protect surface exposed Ln³⁺. Preferential cation exchange between Ca²⁺ and Na⁺ triggered the surface hexagonal-to-cubic structure evolution, which remediated the large barrier for heteroepitaxy of monocrystalline CaF₂ shell. The heterostructured CaF₂ shell leads to greatly enhanced upconversion emission with increased absolute quantum yield from 0.2% to 3.7%. Moreover, it is advantageous in suppressing the interfacial diffusion of Ln³⁺, as well as the leakage of Ln³⁺ from nanoparticle to aqueous system. These findings open up a new avenue for fabricating heterostructured core/shell nanoparticles, and are instructive for modulating various properties

Gd-Dots with Strong Ligand–Water Interaction for Ultrasensitive Magnetic Resonance Renography

Magnetic resonance imaging contrast agents with both significantly enhanced relaxivity and minimal safety risk are of great importance for sensitive clinical diagnosis, but have rarely been reported. Herein, we present a simple strategy to improve relaxivity by introducing surface ligands with strong interaction to water molecules. As a proof of concept, NaGdF₄ nanoparticles (NPs) capped by poly­(acrylic acid) (PAA) show superior relaxivity to those capped by polyethylenimine and polyethylene glycol, which is attributed to the strong hydrogen-bond capacity of PAA to water molecules as revealed by theoretical calculation. Furthermore, benefiting from PAA and ultrasmall particle size, Gd-dots, namely PAA-capped GdOF NPs (2.1 ± 0.2 nm), are developed as a high-performance contrast agent, with a remarkable ionic relaxivity of ∼75 mM^–1 s^–1 in albumin solution at 0.5 T. These Gd-dots also exhibit efficient renal clearance with <3% of injected amount left 12 h post-injection. Ultrasensitive MR renography achieved with Gd-dots strongly suggests their great potential for practical applications