Ethidium monoazide is a fluorescent photoafinity label nucleic acid stain, after photolysis, which binds covalently to nucleic acids both in solution and in cells that have compromised membranes.?Ethidium monoazide bromide is relatively impermeant to live cells, it selectively labels DNA in dead cells in a mixed population of live and dead cells. The fluorescence of ethidium monoazide is weak, but the intensity increases ~15-fold upon binding to DNA with excitation/emission maxima of ~504/600 nm.