Influences of oils on the persistence and recovery of DNA

Trace DNA can be deposited onto a wide range of surface types which can include substrates with a coating of oil: examples being firearm components, power tools, and kitchen utensils. We report on the impacts of oil on DNA recovery and downstream DNA processing. Thumbprints were made on 60 separate glass slides, then stained with Diamond Dye and fluorescent cellular material counted as an estimation of the cells deposited. Aliquots of five different mineral oils, chosen due to their common uses and variation in viscosity, were spread across the entire deposited thumbprint. The thumbprints coated with one of the five oils were left at room temperature for either 1 day or 7 days. A swab was used to collect cellular material which was then processed manually through a DNA extraction process, quantified and STR alleles amplified using the VeriFiler™ Plus STR kit. It was observed that all five oils impacted the initial DNA recovery process by saturating the swab. The presence of oils also impacted the DNA extraction process by interacting with the magnetic resin. Oils with higher viscosity accentuated these observed effects during the DNA extraction process, as the presence of a white precipitate was seen to be carried over into the final eluate. A total of 56% of the 1-day samples and 72% of the 7-day samples resulted in DNA profiles comprised of 12 or more alleles. The results of this study highlighted the possible impacts of collecting samples with oils present on the surface.