Successful STR amplification of post-blast IED samples by fluorescent visualisation and direct PCR

Abstract

Improvised explosive devices (IEDs) present a number of challenges in terms of the generation of forensically relevant information. Inhibition to PCR from sub-optimal sample types as well as from specific substrates has historically meant that extraction prior to PCR has been required. Improvements to STR kit buffers lead to the successful introduction of direct PCR to the analysis of IED-relevant samples, however none of these samples have been exposed to detonations. This study presents data to support the use of direct PCR in the analysis of IED components post-detonation. VeriFiler™ Plus generated informative profiles, containing ≥ 12 autosomal alleles, from samples touched for a maximum of 15 s that were then exposed to a detonation from plastic explosive placed as close as 100 mm. Of the 37 recovered touched items or fragments, 28 contained autosomal alleles from the donor with 18 (49 %) presenting informative profiles that matched the DNA donor. This compared with results following STR PCR post-extraction with one of 11 amplified post-detonation touch DNA samples being informative. The use of Diamond™ Nucleic Acid Dye (DD) staining and visualisation before and after detonation allowed for analysis as to cell loss or damage as a result of the detonation itself and aided in the triaging of samples to be selected for DNA profiling. This is the first record of cellular visualisation and comparison before and after detonation with accompanying STR results on a range of sample types typical of IED constituents. Following comparison of DD visualised cells and STR amplification success, chemical analysis of plastic and electrical tape samples supported substrate-specific inhibition. These data represent the first instance of informative DNA profiles being produced from post-detonation samples using direct PCR, as close as 100 mm from the charge.