Transfer of picked-up DNA to cotton plates

DNA is readily transferred to a knife handle by hands during a stabbing action and DNA existing on the handled knife-handle is readily picked-up during the action and transferred to a subsequently handled object. We repeated a part of an earlier study where instead of placing a handprint on five DNA-free glass plates post handling of a knife-handle, participants placed handprints on five consecutive cotton plates. Less DNA was collected from the cotton plates than from the glass plates. This appears to be due to less efficient recovery from cotton plates. DNA from the previous handler(s) of the knife was observable on some subsequently touched cotton plates. Sometimes not on the initially touched plates but on those touched later in the sequence, pointing to potential impacts of different manners of contact. The proportion of this relative to the depositor's DNA was on average < 10%. Where there were multiple previous handlers of the knife, DNA of the most recent handler(s) tended to be more prominent than earlier handlers, within the profiles derived from the cotton plates. As per prints left on glass plates, the total and transferred amounts of DNA tended to decrease as more cotton plates were touched subsequent to picking-up foreign DNA from previously touched knife handles. The substrate of the item contacted impacts on the yield and detectability of transferred DNA. More studies are required to increase our understanding of the impacts different substrates have on DNA transfer, persistence, prevalence and recovery.