Air conditioners may help catch criminals, by snagging their DNA

Even if a criminal wears gloves, their cast-off DNA may still be present in a room’s air after they leave. A new study suggests that if such telltale material gets sucked up by an air conditioner, it could let forensic investigators know if a suspect has or has not been in a certain room.

Throughout their lives, animals disperse DNA into the environment via their feces, sloughed skin, and other genetic material. Therefore, by seeing what types of this “environmental DNA” (eDNA) are present in water, soil or air samples, scientists can determine which species are present in the region.

Among many other applications, we’ve recently seen eDNA analysis used to check for great white sharks near beaches, document a frozen prehistoric ecosystem, and even search for the Loch Ness monster.

Being members of the animal kingdom ourselves, us humans also leave eDNA wherever we go. The substance can even stay airborne for a while, in the form of tiny exhaled saliva droplets or minuscule flakes of skin. What’s more, before that eDNA has a chance to settle and get wiped up by a careful alcohol-cloth-wielding culprit, it may get sucked up by a room’s air conditioning system.

With this fact in mind, scientists from Australia’s Flinders University set out to see if human eDNA could be obtained from a room’s air conditioner. It’s important to note that air conditioners work by recirculating the air in a room, not by drawing air in from outside.

After cleaning the air conditioners in four offices and four homes – thus removing any existing DNA – the researchers left the occupants to live their regular lives for four weeks. When samples were then taken from the inside of those air conditioners, eDNA that could be matched to the occupants was found in all but one sample.

In fact, in a separate batch of experiments, it was found that airborne eDNA could even be filtered directly from the air – no air conditioner required. That said, this technique is limited to detecting the eDNA of people who have been in the room recently. By contrast, the air conditioner eDNA can identify people who have been in the room some time ago.

Further studies will now focus on the pros and cons of different eDNA collection methods.

“It is very unlikely that an average offender, even with forensic awareness, could totally prevent their DNA from being released into the environment,” says the lead scientist, Dr. Mariya Goray.

A paper on the research was recently published in the journal Electrophoresis.

Source: Flinders University via Scimex