Duncan Taylor

1. Contact force (or pressure) is rarely a controlled variable in DNA transfer studies, including shedder tests, even though it is generally accepted that higher pressure increases DNA transfer1–4....

Background: The presence or absence of saliva and saliva-derived DNA may be relevant to a range of different crime types, including sexual assault and homicide offences, where allegations of saliva transfer to the skin of a victim or offender from actions such as biting, kissing, licking or sucking are relevant. The interpretation of skin samples following allegations of biting, kissing, licking or sucking requires an awareness of the prevalence, transfer and persistence of saliva, and its DNA composition, including self- and non-self DNA, with and without such activities occurring. The matter of persistence is especially important given that the examinations of suspects or victims do not often occur immediately after the offence. Methods: This study investigates the transfer of saliva onto human skin and its persistence following actions of biting, kissing, licking and sucking. Seven male–female couples were asked to shower and then bite, kiss, lick and suck separate defined areas of both of their partner’s arms. Following these different actions, one arm was sampled immediately, and the other arm was sampled 6 h later. Background (prior to shower) and control (post-shower but before deposition) samples were also obtained. For participants who wore long-sleeve clothing post-activity, the inner sleeves were also sampled along with the tested skin areas at 6 h sample collection. Presumptive saliva tests were carried out on all background, control, 6 h experimental and clothing samples collected, using the RSID-Saliva immunological test kits. All recovered samples (immediate, persistence, clothing, background and control) underwent DNA extraction and quantification, and all background, 6 h and clothing samples were STR-amplified, generating DNA profiles. Results: The results were considered with the questionnaire data provided by participants, to assess what factors may have influenced the presence or absence of any saliva, self (donor), partner or foreign DNA detected. Comparisons of the DNA quantities recovered from the immediate samples and 6 h samples were made. Furthermore, saliva detection rates of 6 h samples and DNA profile data were compared between all samples generated from the four different actions which resulted in saliva transfer to skin. Concussions: This research will assist forensic investigators when interpreting saliva DNA evidence recovered from the skin of victims or suspects after a prolonged period of time between the offence and collection.

Swabs are commonly used in forensic contexts to recover biological material from surfaces. Previous investigations have shown that there is no single best swab and wetting agent combination for DNA recovery. Touch DNA is often present in low quality and quantity, and the recovery and processing methods used during casework can result in DNA loss, therefore even small improvements in recovery could influence successful detection. Therefore, a DNA recovery method tailored for a touch DNA workflow is fundamental to effective forensic casework. In this study, combinations of five swabs (viscose, cotton, nylon, foam and polyester) and three wetting agents (water, 100% isopropanol (IPA) and 2% sodium dodecyl sulphate (SDS)) were used to collect samples of synthetically and naturally derived touch DNA from a polypropylene surface. Surfaces were swabbed using a single systematic swabbing method and extracted using the DNA IQ™ system. Interactions between the swabs and wetting agents had the greatest effect on DNA recovery, and polyester swabs moistened with SDS were among the combinations with the highest DNA yield under these experimental conditions. The worst-performing swabs differed by DNA type sampled. Polyester, viscose and cotton swabs moistened with water were amongst the combinations yielding the lowest DNA recovery for the synthetic touch deposits, whereas foam and nylon swabs moistened with IPA had the lowest yield for natural touch deposits. This research aims to contribute towards the development of a standardised touch DNA recovery method applicable to the sampling of polypropylene surfaces and other relevant touch DNA collection related objectives, such as investigations into DNA transfer and shedder testing.

Airborne environmental DNA (eDNA) is emerging as a valuable tool in forensic genetics to support individual identification in cases where other biological traces are limited or absent. Here, we investigate the potential of human airborne eDNA as a source of forensic evidence by evaluating its recovery following simulated residential burglaries.A total of 391 eDNA samples were collected from air, dust, and surfaces in 22 households by two laboratories. Samples were recovered under two conditions: immediately after residents vacated the premises and following a 15‑minute simulated burglary. Resulting DNA profiles were compared against reference databases of residents and intruders.Under normal occupancy, air samples detected regular occupants, whereas airborne eDNA collected 30 minutes after simulated burglaries identified intruders in 82% of cases in one laboratory and 36% in the other. When combined with dust and surface samples, airborne eDNA provided additional evidence for detecting legitimate occupants, including past visitors. Variation in eDNA recovery across households and laboratories likely reflects differences in occupancy patterns, shedding abilities, cleaning and environmental conditions.This study demonstrates that, under controlled short-delay conditions, airborne eDNA can recover intruder-associated DNA profiles after brief occupancy, supporting its potential as a complementary source of forensic information.

DNA present within the air represents one form of environmental DNA (eDNA) 1,2. Air DNA collection constitutes a new and promising method for forensic trace DNA analysis in circumstances where trad...

Background/Objectives: DNA profiling can fail, or produce poor results, when naturally occurring materials are present during the amplification step. This study demonstrates that simple modifications to the reaction setup can overcome this obstacle. PCR inhibition is caused by a range of compounds including haem, humic acid and dyes. Various strategies to overcome this inhibitory effect have been explored, such as improving extraction methods to remove these compounds, diluting samples to reduce inhibitor concentration, or using inhibitor-tolerant DNA polymerases. In this study, we evaluate whether modified setups can help mitigate the effects of humic acid, a common inhibitor that induces various inhibition mechanisms. Methods: We combined the GlobalFiler STR kit with Investigator Quantiplex Pro into a single reaction. Supplementing the amplification GlobalFiler with additional reagents creates altered amplification environments that use additional DNA polymerase and reaction buffer. Results: The modified setups outperformed the standard GlobalFiler protocol, even at the highest concentration of humic acid tested. The STR reactions supplemented with qPCR reagents produced higher-quality profiles with improved allele amplification and an even peak balance, indicating that a dual-DNA polymerase system offers a more robust and inhibitor-tolerant environment for STR amplification. In addition to demonstrating the value of this combined approach, these data provide a comprehensive dataset characterising the impact of increasing humic acid concentrations on profile quality from an ideal DNA input. Conclusions: For PCR inhibitors with similar mechanisms this approach offers broader applicability in forensic casework and a promising step toward more reliable and robust profiling of inhibited samples.