Crime scene DNA sampling by wet-vacuum applying M-Vac

Abstract

A possible alternative to conventional stain recovery by swabbing, taping or cutting, is the M-Vac wet-vacuum instrument (M-Vac Systems Inc.). We have evaluated M-Vac for sampling of dried saliva on porous and non-porous surfaces, shed cells on clothes and touch DNA. M-Vac gave significantly higher DNA yields for dried saliva stains on laminated wood, compared with cotton swabs (average DNA concentrations 1.14 vs. 0.57 ng/μL, p = 0.02). For stains on glass, M-Vac and cotton swabs gave comparable DNA yields. Additionally, M-Vac retrieved three times as much DNA from saliva stains on cotton fabric (T-shirt) compared with saliva on towels (terry cloth), showing that the absorption properties of the surface affect wet-vacuum sampling. M-Vac was also applied for retrieving wearer DNA from clothes, enabling generation of complete DNA profiles from denim jeans, leggings and cotton T-shirt. A mixed DNA profile was retrieved from an “aggressor” pressing a hand against the shoulder area of a worn T-shirt. Since the major component of the obtained mixed DNA profile was from the wearer, M-Vac may not be ideal for touch DNA sampling of clothes. Wet-vacuum sampling requires a fairly large instrument, trained users and DNA extraction procedures handling large sample volumes. The complexity of M-Vac sampling prevents it from being extensively used, but in specific and important cases it can be a valuable sampling tool.