PMA is a high affinity photoreactive DNA binding dye developed by Biotium for viability PCR. PMAxx™ is Biotium's new and improved viability PCR dye. The dyes are weakly fluorescent by themselves but become highly fluorescent upon binding to nucleic acids. Upon photolysis, the dye forms a stable covalent bond with the DNA, thus resulting in permanent DNA modification. The dye is cell membrane-impermeable and thus can be used to selectively modify DNA from dead cells with compromised membrane integrity, while leaving DNA from viable cells intact. PMA and PMAxx™