Sampling touch DNA from human skin following skin‐to‐skin contact in mock assault scenarios—A comparison of nine collection methods

Abstract

Collection of touch DNA from an offender on the victim's skin can provide relevant evidence for investigations of criminal cases. Therefore, the choice of the optimal sample collection method is crucial. In this study, we investigated the recovery of STR profiles from touch DNA on human skin by comparing nine different collection methods: the dry and wet cotton swabs in three different movements, the double-swab (wet-dry) method, the wet and dry Copan FLOQSwabs™, and the Scene Safe FAST™ minitapes. Mock assault scenarios were conducted with a male offender grasping the forearms of a female victim. Samples were collected from the assaulted area of the victim's skin, and the recovery of the offender's STR profile was evaluated. Our results indicate that the different swabs and swabbing techniques did not have a distinct impact on the STR recovery; however, the lowest STR recovery was achieved with Scene Safe FAST™ minitapes. In addition, we compared the double-swab method to the single-swab method by analyzing the DNA quantity of the wet and dry swabs separately. We found on average 13.7% more offender DNA using the double-swab method, but this did not translate into higher STR recovery. Our findings indicate that several methods perform equally well when collecting touch DNA from human skin, although SceneSafe FAST™ minitapes seem to be the least adequate for this purpose.

Indirect DNA Transfer and Forensic Implications: A Literature Review

“…The use of the double swab technique was justified by the experimental model: the main goal of each study was to focus on the secondary transfer generated after a touch. As reported in the literature and confirmed in this review, to sample skin cells, the single/double swab techniques, or adhesive tape, are the best methods to guarantee adequate cell recovery [16,71,72]. Moreover, the cutting-out technique could be applied in selected experimental models (i.e., garment sampling), considering that it may not always be used on hard surfaces.…”

“…In three cases, the authors did not indicate the extraction protocol, while in six cases an "in-house method" was used. In a recent research article [71], it has been demonstrated that swabs and direct PCR could positively influence the DNA profiling from a touched item, reducing the number of required cells.…”

“…techniques, or adhesive tape, are the best methods to guarantee adequate cell recovery [16,71,72]. Moreover, the cutting-out technique could be applied in selected experimental models (i.e., garment sampling), considering that it may not always be used on hard surfaces.…”

“…Quantifiler Duo DNA Quantification Kit (3), Investigator Quantiplex HYres (5), PowerQuant System (4), ALU assay (2), Plexor DNA Quantification Kit (2), QuantiBlot Kit (1), and Investigator Quantiplex Kit (5) were the other methods used. As previously described, modern techniques could improve profiling by applying direct PCR after swab sampling [71]. On the other hand, the use of quantification methods that may evaluate the quantification between male and female DNA, are very useful in the evaluation of activity level.…”

Touch DNA Sampling Methods: Efficacy Evaluation and Systematic Review

“…Barash et al [ 108 ] found that the tape collection of biological material simplifies sampling, is non-destructive, and is also highly effective in genotyping DNA from many previously untested items left at crime scenes. Another work evaluates nine collection methods in sampling touch DNA from human skin following skin-to-skin contact in mock assault scenarios [ 53 ]. The results express that the different tools did not have a distinct impact on the STR recovery even if adhesive tape seemed to be the least adequate for this purpose as it achieved the lowest DNA collection.…”