Preliminary evaluation of three swabs and three wetting agents for the collection of forensic DNA samples from biological fluid stains on a non-porous surface

Collection of DNA samples from biological fluid stains using swabs is a fundamental technique utilized by forensic analysts at crime scenes and laboratories worldwide. A wide range of swabs and wetting agents are used by forensic agencies globally; however, gaps remain in our understanding of the efficiency of swabs and wetting agents for collecting DNA. This study aimed to assess the performance of three different swabs (cotton, rayon, viscose) and wetting agents (water, 70% ethanol, 100% isopropanol) commonly used by forensic agencies, in all combinations, for collecting DNA from dilute blood and saliva stains on a rigid plastic substrate. The results demonstrated that using water as the wetting agent had a significant detrimental effect on DNA yield and STR profiling, whereas 70% ethanol and 100% isopropanol both performed significantly better than water. There was no significant difference between swab materials; however, there was a non-significant trend of rayon and viscose producing better results than cotton overall. Taken together, these data supported 70% ethanol and 100% isopropanol as potentially suitable swab wetting agents for collecting DNA from biological fluid stains on non-porous surfaces. These results should prompt further research on a wider range of biological fluids/sources, substrates and other influencing factors.