Hydroethidine operates effectively as a probe for measurement of reactive oxygen species. The dye enters cells freely and is dehydrogenated to ethidium bromide. The probe has been used extensively with NK cell and as a vital dye for identification of proliferation and hypoxic cells in tumors. Studies have been performed using neutrophils and endothelial cells as well as HL60 cells and macrophages. A major advantage of this probe is its ability to distinguish between superoxide and H2O2. Fluorescence emission occurs at around 600 nm. Redox indicator. Blue fluorescence until oxidized to ethidium
