A ratiometric fluorescent, colorimetric, and paper sensor for sequential detection of Cu2+and glutathione in food: AIEE and reversible piezofluorochromic activity

A new Schiff base 2 was rationally synthesized that exhibited aggregation induced emission enhancement (AIEE) and unique reversible piezofluorochromic properties. Probe 2 displayed a distinguished ratiometric fluorescent and colorimetric recognition of Cu2+ and further acted as a probe for the selective detection of glutathione (GSH) based on its 2-Cu2+ complex. Firstly, probe 2 showed a highly selective fluorescence quenching response towards Cu2+ over its competing ions that was attributed to the intermolecular charge transfer (ICT) to paramagnetic Cu2+. Based on ratiometric fluorescence titration, the limit of detection (LOD) of probe 2 for Cu2+ was calculated as 2.13 nM. The complexation mode of probe 2 for Cu2+ was confirmed through H-1 NMR titration, Job plot, computational, and DLS studies. Subsequently, the addition of GSH to probe 2-Cu2+ complex immediately enhanced its fluorescence, and the emission of probe 2 was recovered which was ascribed to the displacement of Cu2+ by GSH and release of probe 2. The developed strategy for the identification of GSH was confirmed through 1H NMR titration experiments. Advantageously, probe 2 and probe 2-Cu2+ complex coated paper sensors were successfully developed for the nanoscale sensing of Cu2+ and GSH in food samples. The detection of Cu(2+ )and GSH in food and actual water samples was adequately accomplished through a very effective dip-coating method. Finally, a sequential detection strategy was used to design logic circuits.

Automated summary

A new compound with aggregation induced emission enhancement (AIEE) and reversible piezofluorochromic properties was synthesized. It can selectively detect copper ions and glutathione, and has been successfully applied for nanoscale sensing in food samples using a dip-coating method. Additionally, a sequential detection strategy was designed.