PMA and PMAxx™ are membrane-impermeant dyes that selectively modify DNA in dead cells with damaged membranes. Therefore, samples should not be frozen before PMA treatment, because this will permeabilize live cell membranes to the dye, and live/dead discrimination will be lost.
After PMA treatment and photolysis, PMA or PMAxx™ becomes covalently linked to dead cell DNA, and any excess dye in solution should be photolyzed and rendered non-reactive. Cells can be frozen at this point for storage before DNA extraction and PCR. For full cell recovery, we would recommend pelleting the cells and removing the supernatant before freezing.← FAQs