Secondary DNA transfer of biological substances under varying test conditions.

This research investigates factors that may influence the secondary transfer of DNA. These include the type of biological substance deposited, the nature of the primary and secondary substrate, moisture content of the deposit and type of contact between the surfaces. Results showed that secondary transfer is significantly affected by both the type of primary substrate and the moisture (wetness) of the biological sample. Porous substrates and/or dry samples diminished transfer (with on average only 0.36% of biological material being transferred from one site to another), whereas non-porous substrates and/or wet samples facilitated transfer events (approximately 50-95% of biological material was transferred from one site to another). Further, the type of secondary substrate also influenced transfer rate, with porous surfaces, absorbing transferred biological substances more readily than non-porous ones. No significant differences were observed among the biological substances tested (pure DNA, blood and saliva). Friction contact between the two substrates significantly enhanced secondary transfer compared to either passive or pressure contact. These preliminary results will assist in developing general assumptions when estimating probability of a secondary DNA transfer event under simple conditions.