Encapsulating GSH-Au/Ag NCs in ZIF-8 with improved fluorescence for the specific identification and detection of 4-nitrophenol utilizing inner filter effect

Considering the severe hazard to health posed by nitrophenol (NP) isomers, especially 4-NP, reliable and selective detection strategies are urgently challenged. In this study, a fluorescence platform based on glutathione-stabilized gold/silver nanoclusters (GSH-Au/Ag NCs) and zeolite imidazolate framework material (ZIF-8) was developed for 4-NP detection. The synergistic effect of gold and silver makes the bimetallic nanoclusters (GSH-Au/Ag NCs) much better in optical properties than gold nanoclusters. Subsequently, GSH-Au/Ag NCs with aggregation-induced emission (AIE) effect was encapsulated into ZIF-8 to obtain GSH-Au/Ag NCs@ZIF-8 nanocomposite. Compared with GSH-Au NCs, the fluorescence signal was efficiently further improved nearly 7 times through the confinement effect of ZIF-8, and the fluorescence lifetime was increased from 1.2 μs to 6.9 μs. The addition of 4-NP effectively quenched the fluorescence emission peak of GSH-Au/Ag NCs@ZIF-8 at 600 nm, and the assay exhibited highly sensitivity to 4-NP with the detection limit of 1.11 μM from 2.0 μM to 35 μM. Especially, results showed that 4-NP could be easily discriminated from nitrophenol isomers (3-NP and 2-NP). The mechanism research demonstrated that the absorption curve of GSH-Au/Ag NCs@ZIF-8 + 4-NP overlapped greatly with the fluorescence excitation spectrum of GSH-Au/Ag NCs@ZIF-8, and the fluorescence lifetime of GSH-Au/Ag NCs@ZIF-8 did not change when 4-NP was present or not. Therefore, the mechanism of GSH-Au/Ag NCs@ZIF-8 for 4-NP detection was mainly attributed to the inner filter effect (IFE). Furthermore, the developed detection assay was applied to water sample with satisfactory recovery results, demonstrating its high potential in monitoring 4-NP in environment.