Hydroethidine (HE) operates effectively as a probe for measurement of O2-. The dye enters cells freely and is dehydrogenated to ethidium bromide. A major advantage of this probe is its ability to distinguish between O2- and H2O2. Studies have been performed using neutrophils and endothelial cells as well as HL60 cells and macrophages. The probe has been used extensively with NK cell and as a vital dye for identification of proliferation and hypoxic cells in tumors. Fluorescence emission occurs at around 600 nm.
