Dual-Fluorophore and Dual-Site Multifunctional Fluorescence Sensor for Visualizing the Metabolic Process of GHS to SO₂ and the SO₂ Toxicological Mechanism by Two-Photon Imaging

As a momentous gas signal molecule, sulfur dioxide (SO₂) participates in diverse physiological activities. Excess SO₂ will cause an apparent decrease in the level of intracellular glutathione (GSH), thereby damaging the body’s antioxidant defense system. In addition, endogenous SO₂ can be generated from GSH by reacting with thiosulfate (S₂O₃^2–) and enzymatically reduced to cysteine (Cys), a synthetic precursor of GSH. In view of their close correlation, a two-photon (TP) mitochondria-targeted multifunctional fluorescence sensor Mito-Na-BP was rationally designed and synthesized for detecting SO₂ and GSH simultaneously. Under single-wavelength excitation, the sensor responded to GSH-SO₂ and SO₂-GSH continuously with blue-shifted and green fluorescence-enhanced signal modes, respectively, not just to GSH (enhanced) and SO₂ (quenched) at 638 nm with a completely converse response tendency. Given its favorable spectral performance (high sensitivity, superior selectivity, and fast response rate) at physiological pH, Mito-Na-BP has been successfully applied in monitoring the level fluctuation of GSH affected from high-dose SO₂ and visualizing in real time the metabolic process of GSH to SO₂ by TP imaging. It is expected that this research will provide a convenient and efficient tool for elucidating intricate relationships of GSH and SO₂ and facilitate further exploration of their functions in biomedicine.