Fabrication of a dual-emitting dye-encapsulated metal-organic framework as a stable fluorescent sensor for metal ion detection.

Dye-loaded metal organic frameworks (MOFs) are regarded as one of the most fascinating luminescent materials for selective chemical sensing. Herein, a facile two-step synthesis procedure is reported for the successful encapsulation of fluorescein dye into porous zinc-adenine metal-organic framework (bio-MOF-1) crystals, and thus the aggregation-caused quenching of dye molecules can be eliminated in the confined MOF structure to further create dual emission centers. The as-prepared solid state fluorescein@bio-MOF-1 composite exhibits both the characteristic emissions of the fluorescein dye and bio-MOF-1, and host-guest energy transfer also occurs. Particularly, depending on the variety of the luminescence intensities of different metal ions incorporated in fluorescein@bio-MOF-1, such a host-guest system could be used for high-sensitive sensing of metal cations, especially for the drastic luminescence quenching of Fe ions. The quenching effect coefficient (K) for every metal ion detected is calculated, and the largest K value for Fe ions is determined to be 5072 M. Such an encapsulation strategy can be widely adopted to design new dye@MOF composites with multiple luminescent centers for metal cation sensing.