Efficiencies of recovery and extraction of trace DNA from non-porous surfaces

DNA recovery and extraction efficiencies are key considerations for trace DNA interpretation in casework, but prior studies have tended to focus on assessing these for body fluids rather than trace DNA. This study therefore examined the recovery and extraction of trace DNA using different collection methods from a range of non-porous surfaces relevant to crimes including homicides, terror attacks, and wildlife poaching. Direct extraction of DNA from solutions of a known concentration revealed absolute extraction efficiencies of ∼82%. When DNA was extracted from swabs seeded with the DNA solution, a similarly high efficiency of ∼85% was achieved from nylon-flocked swabs, with a lower efficiency of ∼55% from cotton swabs. However, when DNA was recovered from non-porous surfaces with swabs, ∼55% of DNA was still recovered from plastic knife handles, but lower efficiencies were achieved from the other substrates, particularly metal cable. Varied and poor recovery was observed using mini-tapes and requires further investigation. These results demonstrate that > 50% recovery efficiency of trace DNA is achievable with both swab types, although recovery rates may be affected by surface type and/or practitioner experience