A MOF-based portable fluorescent sensing platform for visualization assay of thiamethoxam via hydrogen bond-induced...

Turn-on metal-organic framework (MOF) fluorescence sensors based on hydrogen bonding-induced intramolecular charge transfer (ICT) are novel fluorescent sensing materials. These sensors enhance the ICT effect through intermolecular hydrogen bonding, enabling highly sensitive detection of specific molecules. However, fluorescence quenching induced by electron-withdrawing targets (EWT) significantly inhibits the ICT process, negatively impacting the signal-to-noise ratio and sensitivity of ICT fluorophores for accurate sensing. Here, we present a MOF probe (UiO-66-Cou) based on 7-(diethylamino)-2-oxo-2H-chromene-3-carboxaldehyde (Cou) and UiO-66-NH₂ (based on the Schiff base reaction), which can be used for the "turn-on" sensing of thiamethoxam (TH) in aqueous environments with an extremely low detection limit (0.588 fmol/L) and high fluorescence turn-on efficiency. UiO-66-Cou detected TH and reversed the fluorescence quenching induced by TH (EWT) by facilitating fluorescence turn-on through weak hydrogen bonding interactions between the molecules. The specific hydrogen bond (CH⋯O) effectively prevents the rotation of the CN bond, thus enabling fluorescence turn-on. More importantly, for this MOF with low fluorescence emission efficiency, subsequent modification by integrating ICT fluorophores significantly enhances its fluorescence performance and functionality. Additionally, UiO-66-Cou was integrated into polymethylmethacrylate (PMMA) (UiO-66-Cou@PMMA) to prepare a portable detection device for the rapid and reliable detection of TH in vegetable and fruit samples. This post-modification strategy based on hydrogen bond enhanced ICT fluorophores is not only applicable to UiO-66-Cou, but can also be extended to other MOF based fluorescent probe systems with lower luminescence efficiency. By introducing suitable ICT fluorophores and hydrogen bond interactions, its fluorescence recognizability and sensing sensitivity can be significantly enhanced. In summary, this work provides an effective and scalable strategy for enhancing ICT fluorophores via hydrogen bonding.