Dyes and Fluorophores 

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. 

Spectral Properties:

λabs = 464 nm (before photolysis)

λabs /λem = ~510/~610 nm (following photolysis and reaction with DNA/RNA)