Smartphone-integrated luminescent Europium-organic framework sensor for on-off ratiometric identification of...

Benefiting from the intrinsic luminescence of levofloxacin (LEV), a ratiometric sensing strategy based on lanthanide metal-organic frameworks (Ln-MOFs) has been developed, enabling dynamic luminescence behavior and superior ratiometric identification and differentiation performance. In this work, a 3D Eu(III)-MOF {[Eu(NBC) (HCOO)]}_n (denoted as Eu-NBC, where H₂NBC = 2,6-naphthalenedicarboxylic acid) was successfully synthesized as a ratiometric luminescence sensor for LEV identification and differentiation. The Eu-NBC material displays remarkable thermal stability, confirmed by in situ variable temperature PXRD and exceptional luminescence characteristics with good water/pH stability that facilitate visual, quantitative, and ratiometric LEV identification and differentiation. Owing to the intrinsic emission of LEV and competitive absorption effects, Eu-NBC exhibits dual emission bands originating from LEV and Eu³⁺ ions, which endows Eu-NBC with outstanding on-off ratiometric capabilities-including a high quenching constant of 5.82 × 10³ M^-1 (0-40 μM in aqueous solution) and 6.05 × 10³ M^-1 (0-28 μM in HEPES), a low detection limit of 0.2 μM and 0.165 μM, respectively, and a rapid response time within 1 min. Furthermore, a distinct colorimetric transition from red to blue under UV irradiation enables naked-eye identification and differentiation of LEV, supporting the fabrication of portable Eu-NBC hydrogels suitable for real-time monitoring. A smartphone-integrated platform utilizing RGB color analysis was also developed to facilitate on-site quantitative identification and differentiation, while a flexible Eu-NBC@PU film was engineered for practical visual trace analysis. Notably, Eu-NBC achieved excellent recovery rates of 96.2-108.3 % in tap water and 93.1-106.7 % in pasteurized milk for LEV identification, confirming its reliability in real-world applications.