Encapsulation of Fluorophores within the Lanthanide Metal-Organic Framework for Regulating the Ratiometric Dynamic...

Derived from the photoluminescence of fluorophores and Ln³⁺, an encapsulation of fluorophores within lanthanide metal-organic frameworks (Ln-MOFs) is fabricated, facilitating Ln-MOFs with fascinating ratiometric luminescence sensing performance. Herein, a 3D Eu (III) MOF {[(CH₃)₂NH₂]₂[Eu₂(TPTC)₂·(H₂O)₂]·2DMF·8H₂O}_n (Eu-MOF, H₄TPTC = terphenyl-3,3″,5,5″-tetracarboxylicacid) and its acriflavine (ACF)-encapsulated derivative (ACF⊂Eu-MOF) are synthesized as promising ratiometric luminescence sensors for serotonin (5-HT) detection. Due to incomplete sensitization process, competitive absorption, and host-guest interactions, luminescence of H₄TPTC and Eu³⁺ in Eu-MOF is influenced by 5-HT, thus realizing ratiometric dynamic luminescence of 5-HT detection with high selectivity (K_SV = 1.88 × 10^-3 M^-1), low detection limit (LOD = 0.213 μM), and excellent reversibility (≥5 times). Specifically, ACF⊂Eu-MOF emits an additional luminescence of ACF except for Eu-MOF, achieving luminescence sensing performance with selectivity (K_SV = 4.71 × 10^-3 M^-1) and sensitivity (LOD = 0.086 μM). Additionally, Eu-MOF and ACF⊂Eu-MOF demonstrate naked-eye observation with increasing 5-HT concentrations, and portable luminescent hydrogels are fabricated for visual 5-HT detection in response to their color changes. A smartphone platform is achieved for intelligent 5-HT detection, thus facilitating practical application of Eu-MOF and ACF⊂Eu-MOF in real-time trace of 5-HT. Most importantly, ACF⊂Eu-MOF emits diverse luminescence under different illuminations, thereby enabling ACF⊂Eu-MOF for potential anticounterfeiting applications.