Dihydroethidium is a cell-permeable blue fluorescent dye that upon entering cells interacts with superoxide to form oxyethidium, which intercalates with nucleic acids and emits a red fluorescence detectable qualitatively by fluorescent microscopy or quantitatively by HPLC. This selective and sensitive probe has been used to detect reactive oxygen species during the phagocytic respiratory burst and for the detection of intracellular superoxide in cultured cells.
