The impact of substrate characteristics on the collection and persistence of biological materials, and their implications for forensic casework

This study assessed the level of nucleic acid persistence on the substrate pre-, and post-swabbing, in order to assess whether biological materials (touch, saliva, semen, and blood) are collected differently depending on the substrate characteristics. A total of 48 samples per deposit and substrate variety (n = 384) were assessed by tracking the persistence of nucleic acid using Diamond™ Nucleic Acid Dye (DD) staining and Polilight photography. The number of DD nucleic acid fluorescent complexes formed post-staining were counted (fluorescent count) and in conjunction with the fluorescence signal intensity (DD nucleic acid complex accumulation) used to estimate the level of nucleic acid persistence on substrates. Touch deposits have shown to be the most persistent deposit with strong adhesion capabilities on both substrate verities. Saliva displayed a higher persistence than semen and/or blood. Semen displayed a high collection efficiency as well as a high fluorescence signal intensity. Blood displayed a low persistence on both substrates with a superior collection efficiency that may also indicate a higher probability to become dislodged from surfaces given a particular activity. Our research has shown that the persistence and recovery of biological deposits is not only measurable but more importantly, may have the potential to be estimated, as such, may build an understanding that can provide valuable guidance for collection efficiency evaluations, and the assessing of the probability of particular profiles, given alternate propositions of means of transfer occurring