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Smell that? DNA in the air might not let criminals get away so fast in the future

By Elizabeth Rayne

What if a fugitive could be detected just by testing the air from the crime scene?

Humans leave DNA everywhere. So do animals, even plants and fungi. Some species tend to be so elusive that it becomes nearly impossible to find them. Researchers wanted to see whether endangered or invasive species could be tracked just by the invisible trail left behind when skin cells and other micro-evidence they cast off ends up floating around, and vacuuming the air showed that it is sometimes possible to use “airDNA” to detect where an animal has been. They also hypothesize that their methods could be used to someday track criminals who have all but vanished.

When an organism sheds DNA into its environment, from land to water to anything it might touch, that genetic material is known as eDNA (environmental DNA), which becomes airDNA when airborne.

“Any biological material can be a source of eDNA,” ecologist Elizabeth Clare, who led a study recently published in PeerJ, told SYFY WIRE.

Future forensics aside, airDNA could be critical to saving endangered species before their time is up. It could even help discover species we never even knew existed—and undiscovered animals are thought to be mostly small creatures that have easily been able to hide from us for so long. Clare and her team saw airDNA in action with naked mole rats that had their own enclosure at an animal facility. They vacuumed the air with filters similar to a HEPA filter you may already have, which your DNA is probably trapped in. They might not be Godzilla, but they are still the first proof of airDNA coming from relatively large animals.

It wasn’t as easy as sucking up air. It was already a plus that the naked mole rats weren’t hanging out with other animals, because, as the researchers noted in their study, there were already enough issues with contamination from the DNA of humans who went inside to vacuum.

The researchers also ran into the problem of genetic material from the mole rats coming up as that of other species, such as another type of mole rat, which is difficult to differentiate even through samples of hair or any other source of DNA. Even distantly related species including dogs, cows and sheep, showed up in the results. Human DNA was all over.

Then there was the issue of DNA scattering all over the air. There was a better chance of detecting naked mole rats in a closed space than out in the open, where airDNA molecules would not only disperse further apart from each other but possibly get confused with DNA from other organisms in the area. There is also a possibility that wind can carry airDNA over from places that are not in the immediate vicinity of an area where scientists might be searching for an animal infamous for hiding. If naked mole rats were being searched for in the wild, it would probably be easier to find their DNA from sucking up air in an abandoned burrow. Clare and her team are currently working on finding out how to best detect airDNA with these obstacles.

“This is an area of active research,” she said. “One challenge outside will be the dilution. In larger spaces this may not be possible without really changing the technology involved. The other challenges will include how complex the sources are and how many species are contributing.”

Though Clare and her team have only theorized about what airDNA can do for forensics, and are not pursuing it any further themselves, forensic scientists are undoubtedly going to see this as a breakthrough. Current methods of detecting criminals through DNA are mostly limited to hair and bodily fluids left behind at the crime scene or on a trail otherwise gone cold. Combined with other detection techniques such as fingerprinting, airDNA could potentially help catch fugitives who would otherwise literally get away with murder. We might find out when further scientific investigations on this start turning into criminal investigations.

It is even possible that eDNA and airDNA could someday be used to detect life on other planets. Unknown species on Earth have a much better chance of being found with an air vacuum because there is are already extensive references that could connect something like a new type of lizard with species it is already related to. While it is much too early to tell, since we are still working on figuring out how to characterize the atmospheres of exoplanets without starlight getting in the way, it could happen.

“It’s fun to think about such ideas, but in a very science fiction way,” Clare admitted. “It would depend on whether some alien life even uses DNA the way we do and in the format we do. Assuming it exists, and that it does, the problem would be that these methods rely on having a well established reference database we can compare our ‘unknown’ to. Without the references we can’t learn very much—but it is still an interesting idea to consider.” 

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