- •The M-Vac® was superior to double swabbing for DNA collection from brick surfaces.
- •Double swabbing collected more DNA than the M-Vac® on non-porous tiles.
- •Cell-free DNA is lost in the filtration step of M-Vac® processing.
- •The M-Vac® is a useful option for DNA collection when traditional methods fail.
Collecting sufficient template DNA from a crime scene sample is often challenging, especially with low quantity samples such as touch DNA (tDNA). Traditional DNA collection methods such as double swabbing have limitations, in particular when used on certain substrates which can be found at crime scenes, thus a better collection method is advantageous. Here, the effectiveness of the M-Vac® Wet-Vacuum System is evaluated as a method for DNA recovery on tiles and bricks. It was found that the M-Vac® recovered 75% more DNA than double swabbing on bricks. However, double swabbing collected significantly more DNA than the M-Vac® on tiles. Additionally, it was found that cell-free DNA is lost in the filtration step of M-Vac® collection. In terms of peak height and number of true alleles detected, no significant difference was found between the DNA profiles obtained through M-Vac® collection versus double swabbing of tDNA depositions from 12 volunteers on bricks. The results demonstrate that the M-Vac® has potential for DNA collection from porous surfaces such as bricks, but that alterations to the filter apparatus would be beneficial to increase the amount of genetic material collected for subsequent DNA profiling. These results are anticipated to be a starting point to validate the M-Vac® as a DNA collection device, providing an alternative method when DNA is present on a difficult substrate, or if traditional DNA collection methods have failed.
NOTE FROM M-VAC SYSTEMS: Although we have not obtained the raw data, methods used etc, we find these results very exciting as well as expected. Clearly the data is significant enough for the police in the UK and around the world to recognize how much they need this new forensic DNA collection capability. The fact that the double swab collected more DNA from the non-porous tiles is not surprising nor a revelation, especially if the DNA material was concentrated in a relatively small area. We rarely recommend using the M-Vac over the swab in that scenario. Also, cell-free DNA is far too small to be captured on the filter we commonly use (.45 and .20 micron PES filters) so that is not a surprise either. Most of the time the M-Vac collects enough cellular DNA that the free DNA is insignificant anyway and does not affect the quality of the DNA profile. The bottom line is the M-Vac has now been successfully tested by research universities in the US, the UK, Sweden, and more testing is going on in Australia and elsewhere by police agencies, crime labs and research facilities. And, once again, the M-Vac system has shown it is a valuable tool for generating DNA profiles where the other collection methods cannot!