Comparing Touch DNA Sample Collection Methods for Enhancing the Recovery of Single Source Profiles

Touch or contact DNA is the transfer of DNA as a result of physical contact between an individual and an item.  Therefore, individuals’ actions may be recorded by the biological traces they leave behind.  Detection of the last individual to handle or wear an item is often an important determination in forensic science.   We would like to broaden the knowledge pertaining to touch DNA by investigating various methods for its collection.  We are testing a new collection method using Gel-Pak ‘0’ that has been shown to recover the top layer of loose particulate.  The goal of this study is to compare the two current collection methods of swabbing and scraping with the Gel-Pak ‘0’ method, and determine if one is better for obtaining a DNA profile from the most recent wearer of an item.   We hypothesized that Gel-Pak ‘0’ will be more effective in detecting the last wearer.  To test this hypothesis, DNA analysis was performed on samples collected by the three methods from items worn by more than one person.  Preliminary data revealed that all three methods resulted in DNA mixtures.  Gel-Pak ‘0’ collected equal to or slightly less DNA than the other two methods.  The last wearer was more discernable with Gel-Pak ‘0’ and swabbing while scraping had a tendency to recover more DNA from the habitual wearer than the last wearer.  Further research may reveal how to most effectively collect wearer DNA in forensic investigations.