Rationally Trapped Polycrystalline Perovskite in Lanthanide MOF Cages for Ammonia‐Mediated Nucleic Acid Intelligent Visualization

Abstract Perovskites nanoparticles (PNPs), promising materials in fluorescence biosensing, have has their practical applications stymied by poor stability in polar solvents. Integrating PNPs into metal–organic frameworks (MOFs) offers a solution by enhancing their compatibility with various environments. Lanthanide MOFs (Ln‐MOFs) are particularly advantageous due to their customizable structure, enhanced stability, and intrinsic fluorescence. Herein, the mechanism by which hybrid materials achieve a balance between physical and fluorescence properties is elucidated. Through theoretical calculations, 2,2'‐bipyridine‐5,5'‐dicarboxylic acid is selected as the ligand to sensitize Eu ³⁺ and facilitate Pb ²⁺ chemisorption. In addition, 4‐bromobutyric acid is not only employed to create hierarchical Eu‐MOFs and optimize the framework for in situ growth of polycrystalline perovskites but also utilized to generate zwitterionic ligands through an S _N 2 reaction with MOF cages restricted n‐octylamine, ensuring the stable dispersion of hybrid materials in ethyl acetate (polar solvent). The prepared PNPs@Ln‐MOF exhibits significantly enhanced fluorescence lifetime (50‐fold) and stability in polar solvents. Besides, the highly sensitive fluorescence color shift of PNPs@Ln‐MOF in response to ammonia offers a generalizable strategy for ammonia‐mediated biosensing device. Supported by CRISPR/Cas technology, this device allows for precise on‐site nucleic acid assay (LOD = 200 fM), pioneering advanced applications of perovskite‐based hybrid materials in biosensing.