Used primarily as a fluorescent probe to detect superoxide radicals in biological systems. It penetrates live cells and, upon reaction with superoxide, is oxidized to ethidium, which intercalates into DNA and emits strong red fluorescence. This property makes it valuable in flow cytometry, fluorescence microscopy, and assays for measuring oxidative stress in cells and tissues. Commonly applied in research related to inflammation, neurodegenerative diseases, cardiovascular disorders, and aging, where superoxide production plays a key role. Its selectivity for superoxide over other reactive oxygen species enhances its utility in studying redox signaling and oxidative damage.