Resources Hub

Note: Do not remove the cover or introduce liquids to the interior of the PMA-Lite.

1. Thoroughly wipe all exposed PMA-Lite surfaces and the inner rims of the tube holes with 10% bleach in water (household bleach diluted at a ratio of 1 part bleach to 9 parts water).
2. Let the bleach sit on the unit for 10 minutes.
3. Thoroughly wipe the surfaces with dH2O.
4. Wipe the surfaces with 70% ethanol and allow to air dry.

PMA is stable after dilution to 0.2 mM in water as long as it is protected from light and can be stored in the same way as the 20 mM stock solution.

Each tube position on the PMA-Lite™ is illuminated by the three LED bulbs. We haven't tested positional variability, but it is likely that the illumination varies slightly between positions and between devices. However, the illumination at each position is exceedingly bright, far in excess to what is required for photocrosslinking of the viability dyes EMA, PMA or PMAxx™ to nucleic acids, so any variability should not significantly affect the vPCR results.

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.

Viability PCR originally used EMA (ethidium monoazide) to inactivate dead cell DNA. Biotium developed PMA (propidium monoazide) in collaboration with investigators at Montana State University (Nocker et al. 2006). PMA is more selective for dead cells than EMA, and became widely used for selective detection of viable microbes and viruses. PMAxx™ is Biotium's newest viability PCR dye, designed to be more effective than PMA at eliminating PCR amplification of dead cell DNA. Therefore it provides the best discrimination between live and dead bacteria.

Learn more about PMA and PMAxx™ for viability PCR.

The LEDs in the PMA-Lite™ and PMA-Lite™ 2.0 have a wavelength that is 465-475 nm and a brightness of approximately 600-800 millicandela (mcd). These are nominal values provided for reference use only, individual LED wavelength and brightness are not a calibrated specifications for the device.

There are three LEDs in each well (one bottom, two side) that provide illumination around each sample tube for efficient photoactivation.

The illumination in each well on the PMA-Lite far exceeds what is required for photocrosslinking of the viability dyes EMA, PMA, or PMAxx™ to nucleic acids. Therefore, any variability in brightness of the PMA-Lite LEDs should not significantly affect the v-PCR results. If performance verification is required, we recommend doing a functional PMA-PCR assay to verify that PMA-treated samples photoactivated in the device give qPCR results within an acceptable range. Mixing the samples during photoactivation and using longer illumination times may be necessary if the samples are complex and not fully transparent to light.

For other related FAQs, see Is illumination even across all positions in the PMA-Lite™ device? and Can I use PMA or PMAxx™ with environmental samples?