Investigating the effects of residual illicit substances on DNA recovery and analysis

Due to preconceived notions held by forensic bodies around the world, the idea of collecting and analysing DNA recovered from drug residues or surfaces bearing drug residues is yet to be investigated with the fear of the drugs inhibiting analytical protocols or compromising DNA integrity, of which this study aims to investigate.<br><br>Drugs analysed within this study included codeine, morphine, oxycodone, ketamine, and synthetic cannabinoids. Parameters relating to forensic usefulness, such as absolute amount of DNA recovered (ng) and quality analysis of the DNA profile (peak height and number of alleles present in the profile) were examined. The integrity of the DNA sample was investigated using statistics such as degradation index (DI) and PCR cycles required for the IPC to reach threshold (Ct).<br><br>Preliminary research revealed that a pre-extracted “naked” DNA solution could be recovered from drug residues, prompting comparisons of the quality and quantity of DNA recovered when using cellular or naked DNA. Cellular DNA, which is more real-world applicable, was identified as generating the most forensically useful profiles. Different sampling methods were then compared to determine the optimal way of collecting DNA from drug residues, finding that analysing a whole tablet was ideal for powdered drug residues, and swabbing techniques were ideal when sampling synthetic cannabinoids and ketamine. A degradation study was completed to investigate whether DNA degrades when deposited on drug residues over time, identifying that the DNA may begin to degrade after 28 days. Qualitative chemical analysis was completed on the final DNA extracts obtained, finding that trace amounts of the drug residues remained in the extract, but no noticeable impact on the quality or quantity of the DNA profiles generated form these samples was observed.<br>