Evaluating the global thiols redox state in living cells using a reducing sulfur species responsive fluorescence switching platform

Redox dyshomeostasis is a critical factor in the initiation of numerous diseases, making the accurate evaluation of the redox status of the cellular environment an important aspect of physiological research. However, maintaining redox homeostasis relies on a complex and dynamic physiological system involving multiple substrate-enzyme interactions, so its accurately detection remains a challenge. With this research, we developed an activable fluorescence switching platform by incorporating different conjugate acceptors to a fluorophore using ester bonds and resulting in fluorescence quenching due to donor-excited photo-induced electron transfer (d-PeT), which was confirmed through density functional theory calculations. The reaction-based probe was deployed for recognizing all major intracellular reducing sulfur species (RSS), including H₂S, cysteine (Cys), homocysteine (Hcy), glutathione (GSH), and protein free thiols. The quenched fluorescence was significantly recovered by RSS, through releasing the fluorophore and diminishing the d-PeT effect. Furthermore, the fluorescent probe was used for the sensing and imaging RSS in living cells, demonstrating good cell-permeability, low cytotoxicity, and negative correlation with reactive oxygen species content, enabling the evaluating of global thiols redox state in HepG2 cellular lines during ferroptosis processes.