Sensitive Ratiometric Detection of Vitamin B₂ by a Zn(II)-MOF with Tetranuclear Clusters

Vitamin B₂ (VB₂) is an essential nutrient for the human body and plays important roles in human health. Therefore, the construction of an efficient sensor for VB₂ detection is required. Here, a fluorescent Zn(II)-MOF of 1,2-bis(benzimidazol-1-ylmethyl)benzene (1,2-bbix), {[Zn(1,2-bbix)(OH)](NO₃)·0.5H₂O}_2n (MOF 1), was prepared for the ratiometric detection of VB₂. MOF 1 displays an interesting 2-fold interpenetrated dia network based on tetranuclear Zn₄ clusters. MOF 1 emitted blue fluorescence at 409 nm, which was quenched after adding VB₂, while a new and enhanced emission at 537 nm associated with VB₂ was clearly observed, thereby establishing an effective ratiometric fluorescence method for VB₂ detection. MOF 1 can selectively detect VB₂ in aqueous media with the limit of detection being 0.11 μM. MOF 1 can also detect VB₂ in real food and pharmaceutical samples (milk and VB₂ tablets) with recoveries of 93.5-103.8%. The ratiometric sensing mechanism was investigated via powder X-ray diffraction (PXRD), IR, ultraviolet-visible (UV-vis), fluorescence lifetimes, X-ray photoelectron spectroscopy (XPS), and theoretical calculations. Additionally, a simple smartphone-assisted RGB method was developed for the visual detection of VB₂. The present work provides an effective on-off ratiometric fluorescence sensor for VB₂ detection, which has great potential application in the food and pharmaceutical fields.