An Investigation of Touch DNA Collection Methods from Clothing: Traditional Cutting Techniques Versus a Wet Vacuum System

This study explored an innovative method for recovering a male offender's touch DNA deposited on the external side of a cotton t-shirt worn by a female. Traditional cutting procedures were compared, in parallel, to a novel wet vacuum system, called the M-VacRTM. This investigation compared these two collection methods to discover which method resulted in a higher yield of DNA, and also examined the relative amounts of male and female DNA obtained from clothing worn by a female and grabbed by a male, with the intent of mimicking an assault. The collected DNA was extracted and then quantified using the QuantifilerRTM Duo DNA Quantification Kit. STR profiles were analyzed using the AmpFISTRRTM Identifiler RTM PCR Amplification Kit. The average yield of male DNA obtained after a male grabbed the shirt with dry hands was 1.5 ng and 14 ng for cuttings and M-Vac samples, respectively. Compared to cuttings, this demonstrated a 9.7 fold increase (p = 0.0079) of male DNA when the M-Vac was employed for collection. Another variable explored was the impact sweat may have on the amount of touch DNA deposited. The average yield of male DNA obtained after a male grabbed the shirt with sweaty hands was 4.5 ng and 25 ng for cuttings and M-Vac samples, respectively. Compared to cuttings, a 5.8 fold increase (p = 0.0042) of male DNA was observed when the M-Vac was used for sample collection. In this study, the M-Vac was significantly more effective at obtaining touch DNA than fabric cuttings, thus warranting further investigation. The M-Vac could be useful for recovering touch DNA as evidence in the forensic science field.