The most commonly used viability PCR reagents include Propidium monoazide (PMA), Ethidium Monoazide (EMA), and PMAXX. All three reagents are membrane-impermeable, DNA-binding dyes that belong to the phenanthridine family. They selectively penetrate dead cells with compromised membranes, covalently binding to DNA on exposure to strong light and preventing DNA amplification during PCR. This allows for selective detection of viable cells.