Assessing passive and active collection of airborne DNA for forensic applications

Advancements in DNA profiling sensitivity have facilitated the generation of informative profiles from as little as a few cells. However, recovering profiles from trace and touch DNA samples remains challenging due to difficulties in visualising sampling areas and offenders' efforts to remove contact traces. Collection of environmental DNA (eDNA), which is the genetic material shed by organisms into their surroundings, presents a novel approach to bypass these challenges. While passive sampling (relying on airborne material naturally settling onto collection surfaces) and active sampling (use of devices that deliberately draw in air for sampling) have been effectively employed to detect genetic material from various species and pathogens in ecological and epidemiological research, the application of these techniques in forensic investigations remains in its early stages. Therefore, the recovery of human DNA from air presents a promising new evidence source of forensic relevance. To explore this potential, the extent to which regular occupants as well as short-term visitors in different environments can be detected within the air and on collection plates was investigated. Further, the influence of air disturbance on air DNA quantity was examined. The findings of this research shed light on DNA presence in the air over various periods of time, revealing the potential for DNA traces to be left behind in environments after brief occupancy. These observations inform our understanding of evidence deposition at crime scenes through airborne mechanisms and demonstrate the utility of air disturbance as a means to enhance DNA recovery and detection. Air disturbance increased the amount of DNA recovered from both passive plates and active air sampling. However, aerosolised DNA began to settle within 30 min and approached pre-disturbance levels after one hour, thus suggesting that analysing air samples (particularly within an hour of an individual having occupied a space or post-disturbance) may be helpful to identify recent occupants and past visitors, even if they have not directly touched surfaces. With further optimisation, this type of sampling could prove particularly valuable in cases where traditional means of sampling are limited or insufficient.