Aggregation induced emission fluorescent probes based on covalent organic frameworks for the detection of glutathione

Developing covalent organic frameworks (COFs) with excellent detection performance remains challenging. Here, (3-aminopropyl) triethoxysilane (APTES)-functionalized COF-1 was synthesized to obtain COF-1 nanosheets, and the molecule with aggregation induced emission (AIE) characteristic such as 4,4',4″,4″'-(Ethene-1,1,2,2-tetrayl)tetrabenzoic acid(H₄tcpe) or 4',4″',4″"',4″""'-(Ethene-1,1,2,2-tetrakis)tetrakis([1,1'-biphenyl]-4-carboxylic acid)(H₄tcbpe) was adsorbed onto the surface of COF-1 via π-π interaction to construct a fluorescent probe. Owing to the distinctive long-chain, dicarboxyl, and multi-point coordination structure of GSH, the addition of GSH into the COF-1&H₄tcpe/H₄tcbpe probe solution enables its flexible framework to modulate the electron cloud density of the probe leading to block the ICT effect and suppress the rotation of H₄tcpe/H₄tcbpe molecules, leading to fluorescence enhancement. Thus, COF-1&H₄tcpe and COF-1&H₄tcbpe can be used as a probe for the detection of GSH. Compared with COF-1&H₄tcpbe, the COF-1&H₄tcpe probe showed more excellent detection performance, which presented a wider linear range of 0.3-400 μM for GSH, and the detection limit (LOD) for GSH was as low as 0.10 μM. This work provides a new strategy for designing highly fluorescent COF composites with affinity and structural selectivity.