Performance of Different Cotton and Nylon Swabs on DNA Recovery and Storage

Abstract

Touch DNA samples are routine yet challenging pieces of evidence that provide investigators with information that helps them solve crimes. However, this type of evidence can be easily lost if the correct collection method is not used. This problem could be overcome with an optimal method of collection that increases the amount of touch DNA collected from different types of surfaces. Better-quality touch DNA can increase the chances of getting a full genetic profile. This study was divided into two parts which aimed to assess whether the type of swab used on different surfaces will significantly increase DNA recovery, concentrations, and the DNA preservation during three different timeframes (24h, 1 month and 3 months). Two different cotton swabs and Nylon swabs were used to lift touch DNA on three different surfaces (glass, plastic and wood) to identify the most suitable method of collection across all three surfaces. A total of 72 samples were lifted (3 replicates from each swab on 3 different surfaces) from two different participants (Male and Female) which were left to dry for 14 days in room temperature prior to DNA extraction. DNA preservation of the swabs was observed while using three dilutions of blood sample which was prepared from one of the volunteers (1:1 – 1:10 – 1:20) where 10 uL of each dilution was pipetted onto the four types of swabs in three replicates (n=36) to observe the preservation over three different timeframes 24h storage, 1 Month and 3 Months with a total of 108 samples. The COPAN CLASSIQSwabsTM Dry swab showed an overall average result during the storage periods of 24h with (1:1) dilution by (2.694ng/μL), (1:10) dilution with (0.548ng/μL) and (1:20) dilution with (0.143ng/μL). Results for the period of 1 Month also showed an average of (1:1) dilution with (2.825ng/μL), (1:10) dilution with (0.361ng/μL) and (1:20) dilution with (0.156ng/μL). These findings can be helpful for laboratories and crime scene investigators to optimize DNA sample collection and preservation based on their workflow.