An efficient and eco-friendly workflow for dual fingermark processing and STR profiling

Since its discovery in 1997, DNA retrieved from touched or handled items (touch DNA) has been increasingly used in criminal casework. Depending on the nature of the substrate examined, numerous techniques are being used for fingermark (FM) collection and development, however, it has been shown that FM processing may impede or even prevent the dual analysis of FMs and DNA. In search for a possible solution, we have recently established a novel workflow for a non-destructive collection and eco-friendly visualization of latent FMs using white BVDA gel-lifters and black Wetwop® solution. In the present study, the scope and limitations of the proposed protocol were thoroughly examined for DNA recovery and genotyping in relation to substrate type (porous and non-porous), time elapsed after the deposition (1, 7 and 14 days) and donor's gender. The study included 120 developed FMs of 20 donors (10 males and 10 females, aged 25-50 years), from which 240 DNA samples were recovered and quantified. The independent analysis of two DNA samples recovered from each FM, one - from the adhesive surface of the gel-lifter and the other - from its imprint on the protecting acetate cover, allowed us not only to increase the total number of the identified donors, but also to achieve a higher level of confidence per FM. Though this approach appeared to be more efficient on non-porous substrates (up to 65% on car tin), it is noteworthy that forensically useful DNA profiles (with at least 8 full STR loci) were generated from poor-quality FMs on the porous substrate, drywall (25% and 15% in males and females, respectively). Finally, the integration of the results of touch DNA analysis and that of FM visual inspection allowed us to increase by more than half the number of personal identifications and to strengthen the chain of forensic evidence.