Efficiencies of recovery and extraction of trace DNA from non-porous surfaces

Abstract

13DNA recovery and extraction efficiencies are key considerations for trace DNA 14 interpretation in casework, but prior studies have tended to focus on assessing these 15 for body fluids rather than trace DNA. This study therefore examined the recovery and 16 extraction of trace DNA using different collection methods from a range of non-porous 17 surfaces relevant to crimes including homicides, terror attacks, and wildlife poaching. 18 Direct extraction of DNA from solutions of a known concentration revealed absolute 19 extraction efficiencies of ~82 %. When DNA was extracted from swabs seeded with 20 the DNA solution, a similarly high efficiency of ~85 % was achieved from nylon-flocked 21 swabs, with a lower efficiency of ~55 % from cotton swabs. However, when DNA was 22 recovered from non-porous surfaces with swabs, ~55 % of DNA was still recovered 23 from plastic knife handles, but lower efficiencies were achieved from the other 24 substrates, particularly metal cable. Varied and poor recovery was observed using 25 mini-tapes and requires further investigation. These results demonstrate that >50 % 26 recovery efficiency of trace DNA is achievable with both swab types, although recovery 27 rates may be affected by surface type and/or practitioner experience.

DNA transfer in forensic science: A review

“…The main methodologies applied are swabbing, tape lifting or direct extraction via excision [7,211]. There are however many types of swabs and tape-lifts, and means of their application, with significant differences in retrieval rates [7,[212][213][214][215][216][217][218][219][220][221]. Some other methods are available such as a wet-vacuum system [222] or sampling of individual skin flakes [167], but these are less commonly utilised.…”

The efficiency of DNA extraction kit and the efficiency of recovery techniques to release DNA using flow cytometry

“…In Wood et al [4], an extraction efficiency around 81% was reported, using QIAamp® DNA Investigator Kit (QIAGEN). This is higher than those reported in this paper: 23% and 63%, using respectively, QIAshredder-QIAamp DNA Mini kit and Investigator® Lyse&Spin Basket-QIAamp DNA Mini kit.…”

“…Besides, the direct comparison between them has its limits. Indeed in Wood et al [4], acellular DNA was used whereas keratinocyte cells were used in this study. DNA traces, obtained when touching a surface may be the results of a mix between acellular DNA, and cells [13].…”

“…Only a few studies dealt with the efficiency of extraction kits for traces of low levels of DNA [3,4]. In Browlow et al [3] the obtained measure of extraction efficiency jointly considered the type of surface and the efficiency of the swab used to collect and then release the cells and DNA; however, the sole efficiency of the extraction kit alone remains unknown because DNA traces were deposited on a surface.…”

“…In Browlow et al [3] the obtained measure of extraction efficiency jointly considered the type of surface and the efficiency of the swab used to collect and then release the cells and DNA; however, the sole efficiency of the extraction kit alone remains unknown because DNA traces were deposited on a surface. In Wood et al [4], the efficiency of recovery techniques was evaluated from recovery up to the release of cells and DNA. While this considers the ability of the DNA swabs to release cells and DNA, which is a variable that affects the overall efficiency of the DNA extraction process, the efficiency of the extraction kit itself remains unknown since it combines the extraction efficiency of the kit and that of the release of cells and DNA.…”