Touch DNA sampling with SceneSafe Fast™ minitapes.

To achieve optimal results in the forensic analysis of trace DNA, choosing the right collection technique is crucial. Three common approaches are currently well-established for DNA retrieval from items of clothing, notably cutting, swabbing and tape-lifting. The latter two are non-destructive and therefore preferable on items of value. Even though the most recently established technique of DNA retrieval by adhesive tapes is widely used since quite some years now, little information has been published so far on how well it performs compared to other methods. Even more important, when it comes to choosing the right DNA extraction method for forensic lifting-tapes, the available information one can rely on as a forensic geneticist is quite scarce. In our study we compared the two widely used, commercially available and automation suitable magnetic bead-based extraction methods "iPrep Forensic Kit" and "PrepFiler Express BTA™ Kit" to conventional organic solvent extraction. The results demonstrate that DNA extraction from standardized saliva samples applied to SceneSafe Fast™ minitapes is most efficient with phenol-chloroform. We also provide evidence that SceneSafe Fast™ minitapes perform better than wet cotton swabs in the sampling of touch DNA from cotton fabric. Applying the tape only once in every spot on the tissue is thereby sufficient for a considerably better collection performance of the tapes compared to swabbing.

Electrostatic sampling of trace DNA from clothing.

During acts of physical aggression, offenders frequently come into contact with clothes of the victim, thereby leaving traces of DNA-bearing biological material on the garments. Since tape-lifting and swabbing, the currently established methods for non-destructive trace DNA sampling from clothing, both have their shortcomings in collection efficiency and handling, we thought about a new collection method for these challenging samples. Testing two readily available electrostatic devices for their potential to sample biological material from garments made of different fabrics, we found one of them, the electrostatic dust print lifter (DPL), to perform comparable to well-established sampling with wet cotton swabs. In simulated aggression scenarios, we had the same success rate for the establishment of single aggressor profiles, suitable for database submission, with both the DPL and wet swabbing. However, we lost a substantial amount of information with electrostatic sampling, since almost no mixed aggressor-victim profiles suitable for database entry could be established, compared to conventional swabbing. This study serves as a proof of principle for electrostatic DNA sampling from items of clothing. The technique still requires optimization before it might be used in real casework. But we are confident that in the future it could be an efficient and convenient contribution to the toolbox of forensic practitioners.