A highly sensitive turn-off fluorescent probe based on 2D Eu(III)-MOFs nanosheets for glutathione in vitro and living cells

Glutathione (GSH) is generally used as an effective and sensitive tumor marker because its abnormal levels are associated with high free radical level in tumor. In this work, GSH could be easily detected by a kind of designed Eu-based metal–organic frameworks (Eu-MOFs, named Eu(DTBA)) fluorescent sensor. Due to the “antenna effect” of 4,4′-dithiobenzoic acid (4,4′-DTBA) ligands on Eu³⁺, Eu(DTBA) emits the strong characteristic red light of Eu³⁺ under ultraviolet excitation. Moreover, the emission intensity strongly depends on GSH concentrations. Thus, Eu(DTBA) can serve as a turn-off fluorescent switch of GSH because its framework structure can easily be destroyed by GSH that leads to the fluorescence quenching. Remarkably, during sensing GSH, Eu(DTBA) has shown many appealing performances, such as broad a response window (0–20 mM), fast response (3 min), high sensitivity (LOD = 0.35 µM), and excellent anti-interference ability. The real bioimaging application has demonstrated that the reported Eu(DTBA) can be used as an excellent bioimaging agent to successfully distinguish tumor cells from normal cells in clinical diagnosis.