Visualization of Cysteine-Mediated Redox Imbalance under Environmental Exposures via π-Bridge-Tailored Fluorescent Probes

Disturbance of cellular redox homeostasis is often accompanied by aberrant fluctuations in cysteine (Cys) and reactive oxygen species (ROS) levels, and simultaneous monitoring of their fluctuations provides critical insights into redox imbalance mechanisms. However, precise monitoring of such redox disorders under environmental stress remains largely underexplored, limiting understanding of stress-induced physiological disorders and related toxicological mechanisms. Herein, two Cys-activated fluorescent probes featuring furan and thiophene π-bridge modifications, Afd-Cys and Atd-Cys, were designed to evaluate redox imbalance induced by thiol-chelating pollutants (Cd 2+ /Hg 2+ ) and nonthiol-chelating stress (high salt, glucose, and poly(methyl methacrylate)). Two probes show large Stokes shifts (129 and 138 nm) and high sensitivity (LOD = 32.8 and 56.6 nM). Afd-Cys exhibits more distinct changes in fluorescence quantum yield and lifetime, with its sensing mechanism verified by MS and DFT calculations. Furthermore, Afd-Cys enables Cys imaging under exogenous stimulation in multiple cell lines. It was also applied to monitor redox imbalance fluctuations in HepG2 cells, cockscomb flowers, and zebrafish under diverse environmental exposures, revealing corresponding redox responses, and elucidate the molecular mechanisms underlying redox imbalance induced by thiol-chelating environmental stress. This work provides original insights for Cys-mediated redox imbalance under typical environmental stress.