Reduced Glutathione (GSH) is the predominant intracellular antioxidant thiol, playing critical roles in antioxidation, protein thiol protection, and amino acid transmembrane transport. The ratio of reduced to oxidized glutathione (GSH/GSSG) serves as a key dynamic indicator of cellular redox status. Therefore, quantifying intracellular GSH and GSSG levels, as well as the GSH/GSSG ratio, provides a reliable assessment of the cellular redox state. DTNB reacts with GSH to form a colored complex, exhibiting a characteristic absorption peak at 412 nm; the absorbance is directly proportional to the GSH concentration.