Boosting ratiometric fluorescence detection via dual-antenna and bi-ligand strategies in a dual-emission Eu-MOF probe

Abstract

The development of a dual-emitting fluorophore with strong fluorescence intensity and long-term stability is essential for innovative, efficient, and user-friendly sensing platforms in bioanalysis, enabling precise detection and broad applicability in real-world scenarios. In this study, a dual-antenna effect was successfully integrated into a single dual-ligand europium-based metal-organic framework (BiL-MOF), which was both designed and systematically investigated. Upon excitation at 250 nm, the BiL-MOF exhibited two distinct emissions: a blue emission at 365 nm and the characteristic red emission peaks of Eu3+ ions. The use of two different ligands enabled efficient energy transfer from the excited states of the ligands to the 5D₀ state of Eu3+ ions, facilitating the dual-antenna effect. This phenomenon, along with the sensitization of Eu3+, was confirmed through both experimental studies and theoretical analysis. The dual-antenna design significantly improved the fluorescence quantum yield, from 2 % and 10 % in mono-ligand MOFs, to 42 % in the BiL-MOF, while also enhancing structural stability. Additionally, a red shift in absorption and an associated hyperchromic effect were observed, contributing to its potential utility in a variety of sensing applications. Interestingly, folic acid (FA) simultaneously quenched both emission peaks, a behavior attributed to the inner filter effect. This dual-response mechanism enabled the development of a highly sensitive and reliable ratiometric probe for FA detection using both conventional fluorometry and smartphone-based visual readouts. The fluorometric method achieved a detection limit of approximately 0.12 μM, with a linear response range from 5.0 to 165.0 μM. The smartphone-based visual approach also demonstrated excellent performance in analyzing pharmaceutical samples, delivering recovery rates between 98.1 % and 102.2 %, with outstanding reproducibility (RSD < 1 %, n = 4), underscoring its promise for real-world applications.