The M-Vac® is a swab-free collection system that retrieves particles from substrates and concentrates them onto a filter. This wet vacuum system collects DNA by directly spraying a DNA free solution onto a surface. It creates a 'mini hurricane' to loosen present DNA material, followed by concentration onto a filter that is subjected to DNA analysis. The M-Vac® is able to collect DNA from large areas as well as textured, porous, and rough substrates that typically present themselves as challenges during routine casework.
Four (4) different substrates were prepared and processed with both a traditional DNA collection technique (scraping and/or swabbing) and the M-Vac® System. Each substrate was designed to mimic true evidence that laboratory personnel encounter during routine casework. Each substrate was divided into two equal parts, the left side subjected to a traditional collection technique and the right side subjected to the M-Vac®. All samples subsequently underwent extraction (Qiagen® EZ1 DNA Investigator Kit), quantitation (Investigator® Quantiplex HYres Quantitation Kit), amplification (Promega® PowerPlex Fusion), and capillary electrophoresis for separation and detection. The prepared substrates are listed as below:
Item 1: Saliva
A 1:10 saliva dilution was created and evenly distributed (~20 strokes) across the front of the shirt with a sterile swab.
Item 2: Touch
An individual forcibly grabbed and pulled shirt up around the collar, on the front, and under the arms after wearing nitrile gloves for several minutes.
Item 3: Negative control
A new, clean t-shirt directly out of a Hanes® plastic package.
Item 4: Touch
A brick was held for approximately 5 minutes prior to being forcibly thrown.
The M-Vac® retrieved higher concentrations of DNA from items 1, 3, and 4 than the traditional DNA collection technique (Table 1). The concentration from the M-Vac® collection for item 2 was lower than the traditional method, however the M-Vac® sampling yielded a more informative DNA profile. Item 2 yielded an additional male profile in conjunction with the expected female profile generating a mixture. The negative controls exhibited one allele from the scraping/swabbing collection technique and nine alleles with the M-Vac® sampling technique; however, both results are too weak to be reliably interpreted. The amount of DNA recovered from item 4 using the M-Vac® was approximately 30x times more than the traditional collection techniques and yielded a full DNA profile whereas the traditional collection method only yielded two alleles (Table 2). The M-Vac® consistently retrieved more DNA versus the traditional methods and is therefore a sufficient DNA collection system for porous, textured or rough substrates.
Courtesy of Richland County Sheriff's Department. The validation was developed, conducted, analyzed and written by Richland County Sheriff's Department Crime Lab personnel.