Rhodamine B-encapsulated MOF@boric acid-modified COF for adsorption and ratiometric fluorescence detection of baicalin

Efficient adsorption and sensitive detection of baicalin (BAI) are essential for maximizing its medical value. In this work, a rhodamine B (Rb)-encapsulated metal–organic framework (MOF)@boric acid–modified covalent organic framework (COF) composite material (Rb-MOF@COF-BA) was designed for high-capacity adsorption and high-sensitivity detection of BAI. Specifically, the Zr-based MOF of UiO-66 was prepared with Zr 4+ and 2-aminoterephthalic acid, during which Rb was encapsulated, resulting in strong red fluorescence. The –NH 2 group on the Rb-MOF surface then reacted with 2,5-dimethoxyterephthalaldehyde and coupled with the ligand 1,3,5-tris(4-aminophenyl)benzene to integrate the COF. Subsequently, to enhance the recognition of cis -diol-containing BAI through boron affinity, Rb-MOF@COF was functionalized with (4-ethynylphenyl)boronic acid via aza-Diels–Alder cyclization, obtaining the Rb-MOF@COF-BA composite with blue fluorescence. For BAI, Rb-MOF@COF-BA demonstrated a high adsorption capacity of 114.2 mg g −1 and reached equilibrium within 200 min. Additionally, the Rb-MOF@COF-BA composite displayed dual emissions at 440 and 580 nm, enabling its use as a ratiometric fluorescence sensor for BAI detection, accompanied by a visible blue-to-red spectral transition. The resulting radiometric fluorescence method demonstrated linear ranges of 0.2−3.0 and 3.0−20.0 μmol L −1 with a low detection limit of 0.0173 μmol L −1 for BAI. This analytical method was employed to identify and quantify BAI in Yinhuang oral solution, yielding favorable results that confirmed the potential of this ratiometric detection for practical applications. Graphical