Ethidium monoazide bromide (EMA) is a fluorescent nucleic acid stain with a photoaffinity label. The dye, after photolysis, binds covalently to nucleic acids.The dye has been used to footprint drug binding sites on DNA, to modify plasmid DNA, and for labeling yeast cells for leukocyte phagocytosis assays. A particularly useful application of the dye is to label dead cells in a mixed population of live and dead cells. Because EMA is relatively impermeant to live cells, it selectively binds DNA in dead cells. Photolysis renders the dead cell DNA covalently labeled with the dye. One can then wash and fix the cell preparation for analysis by microscopy, fluorescence plate reader or flow cytometry. The major advantage of this method is that researchers can avoid extensive manipulation of live pathogenic organisms. EMA also has been used to differentiate between viable and dead bacteria by 5'-nuclease PCR.  Ex (pH 3) = 458 nm  &lamba;Ex/&lamba;Em (after photocrosslinking to nucleic acid) = 510/600 nm6  Orange solid soluble in DMF, or ethanol  Store desiccated at 4oC or -20oC and protect from light, especially in solution  C21H18BrN5  MW: 420  [58880-05-0]     For viability PCR applications, Biotium also offers propidium monoazide iodide (PMA), as well as our new and improved viability PCR dye, PMAxx™. PMA and PMAxx™ are less membrane permeant than EMA and therefore more selective for dead cell labeling for qPCR quantitation of viable bacteria.    For photoactivation of PMA, PMAxx™ or EMA dye, we recommend the use of Biotium's PMA-Lite™ LED Photolysis Device (for tubes) or Glo-Plate™ Blue LED Illuminator (for plates), which are designed to conduct photolysis under controlled conditions.