DNA transfer: The role of temperature and drying time.

It has previously been shown, and reconfirmed here, that biological material on a substrate will transfer readily upon contact with another substrate when wet but hardly when dry. There is however a paucity of data regarding the speed at which body fluids dry and how this may affect its transfer upon contact. Here we conduct transfer experiments at 4°C, 22°C and 40°C at multiple time points during the drying process. The speed at which blood dries is dependent on the temperature, with the drying process complete within 15-60min. The percentage of deposited DNA transferred upon contact follows an exponential pattern of decline from soon after deposition, decreasing until the sample is dry. There are no differences in transfer rates upon contact among the different temperature conditions within the first 5min or after 60min since deposit, but significant variation occurs between these time points. When considering the likelihood of a proposed scenario that incorporates one or more contact situations it is important to consider the timing of the potential transfer event(s) relative to when the biological sample in question was initially deposited. The results of this study will assist the interpretation and evaluation of alternative scenarios involving transfer of biological substances.