Cu/Zn ion exchange strategy for directed structural evolution of water-unstable Zn-MOF: A bifunctional sensing platform for sulfide colorimetric detection and glutathione fluorescence turn-on assay.

Abstract

Metal-organic framework (MOF) holds great application potential in sensing fields thanks to their tailorable structures, high specific surface areas and abundant active sites. Nevertheless, most one-pot synthesized MOF are limited by insufficient water stability and monotonous functionality, which greatly restrict their applications in multi-scenario detection of complex environmental and biological matrices. In this work, a water-unstable Zn-based MOF functionalized with the aggregation-induced emission (AIE)-active ligand 1,1,2,2-tetrakis (4-carboxyphenyl)ethylene (H4TCPE) is employed as an organic ligand, and directional evolution of material structure and function is realized through precise regulation of Cu/Zn ion exchange degree. Partial ion exchange in anhydrous ethanol yields bimetallic Zn/Cu-MOF that retains the original framework and introduces Cu2+ active sites, while complete ion exchange in aqueous phase triggers structural reconstruction to form water-stable Cu-MOF with fluorescence-free. Accordingly, two sensing platforms are constructed: a colorimetric system for sulfide (S2-) detection with a limit of detection of 0.25 μM, and a fluorescent system for glutathione (GSH) detection with a limit of detection of 1.23 μM. Both deliver favorable accuracy and anti-interference capacity in real samples including tap water, beer and serum. This work clarifies the structure-activity relationship among ion exchange degree, material properties and sensing performance, providing a new paradigm for functional modification of water-unstable MOF.

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