PMA (propidium monoazide) is a high affinity photoreactive DNA binding dye invented by scientists at Biotium for viability PCR of bacteria and other organisms. The dye is weakly fluorescent by itself but becomes more fluorescent after binding to nucleic acids. It preferentially binds to dsDNA with high affinity. Upon photolysis, the dye covalently reacts with DNA, thus resulting in permanent DNA modification. The dye is cell membrane-impermeable, and thus can be selectively used to modify only exposed DNA from dead cells while leaving DNA from viable cells intact. This feature makes the dye highly useful in the selective detection of viable pathogenic cells by quantitative real-time PCR in the presence dead cells whose DNA has been PMA-modified and thus can not be amplified. Since Biotium first developed PMA dye, there have been numerous publications on the use of the dye in pathogenic bacterial detection related to food and water safety, medical diagnosis and biodefense. PMA dye is also available in solid form.    Molecular weight: 511  Abs = 464 nm (before photolysis)  Abs/Em = 510/610 nm (following photolysis and covalent attachment to DNA/RNA)  Dark red liquid  Store at 4°C and protect from light at all times     Note: Scientists at Biotium have recently invented a new and improved dye for viability PCR, called PMAxx™. PMAxx™ functions in a manner very similar to PMA, but has much greater activity and ability to distinguish between live and dead bacteria. PMAxx™ can be used as a replacement for PMA in any bacterial viability-PCR assay. We recommend that customers interested in using PMA try PMAxx™ instead, for improved detection of viable bacteria.   For viability PCR of gram-negative bacteria we highly recommend using our PMA Enhancer in conjunction with PMA. PMA Enhancer for Gram Negative Bacteria was designed to improve PMA-mediated discrimination between live and dead gram-negative bacteria. When a sequence from a gram-negative bacteria is amplified by PCR, samples pre-treated with Enhancer show a decrease in the signal from dead cells, with no change in the signal from live cells.   Biotium also provides strain-specific PMA Real-Time PCR Bacterial Viability kits with validated primers for selected pathogens.   For photoactivation of PMA, PMaxx™ or EMA dyes, 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.