Friday, December 02, 2016

Learning to Sniff from Man’s Best Friend

They sniff out drugs, cadavers, missing people, explosives, and even cancer. Dogs are more than man’s best friend, they are some of the best chemical detectors in existence. They are so good that by modifying a commercially available explosives detector to act like a dog’s nose, researchers were able to make the detector much more effective. That’s great news for most of us, not-so-great news for drug smugglers.

Military working dog, Falco, sniffs for hidden narcotics during competition, March 19, 2014. Falco’s handler is Pfc. Jeremiah Hogue, 69th Military Police Detachment, 759th MP Battalion.
Image Credit: Fort Carson. Photo by Andrea Stone (CC BY 2.0).

To find contraband, a detector (dog or otherwise) needs to sniff out odor molecules released by the substance. This involves sucking air into intake valve (or nose), and then sensing odor molecules of interest. New and improved sensing technologies have led to rapid advancements in the second part of this process, sensing molecules of interest, but the first part has been more or less neglected. The problem is that no matter how sensitive you are to the presence of an odor, if your intake valve (or nose) doesn’t draw in the odor molecules, you won’t find the goods.

Traditional vapor samplers collect samples in one of two ways—by standing still and waiting for air to pass into them, or by sucking in air continuously. Could there be a better way? Inspired by the way air moves in and out of a dog’s nose, researchers from the National Institute for Standards and Technology, MIT Lincoln Laboratory, and the United States Food and Drug Administration aimed to find out. Their results were published yesterday in the journal Scientific Reports.

Using a 3D printer, the researchers created a model of dog’s nose that mimics the way dogs sniff. Unlike manmade detectors, dogs are active sniffers. They suck in air, but they also send it back out. This cycle repeats about five times every second. The way the air leaves a dog’s nose was particularly interesting to the team. It doesn’t just go straight out, like air does when we breath out, it leaves the nostrils in jets that point down and to the side.

From an aerodynamics point of view, sending expired air down and to the side disturbs the air. Imagine sending a jet of air angled down at your TV stand. If your TV stand is like mine, the jet will kick up dust that settled there long ago and send it back into sneeze-inducing range. Similarly, the jets from a dog’s nose mix up the air and send some new stuff its way. They create movement that enables a dog to draw in air that would normally be beyond its reach.

After creating the model, the researchers did some experiments that let them visualize the air flowing in and out of the model. They compared the aerodynamics of their model to the results of past studies on live dogs to make sure that they matched, and to get a better understanding of exactly what was happening. With a good model in hand, it was on to the next phase—testing how the in-and-out system inspired by our canine friends compares to a suction only system.

The model was configured for two sampling methods. One configuration actively sniffed, like a dog, and the other pulled in samples through continuous suction. The researchers compared the two methods by placing an odorous material near the nose, running the nose in each mode, and then comparing the amount of odor molecules collected in each case. In both cases the results were impressive—the dog-inspired method drew in several times as many odor molecules as the suction only method.

Next, the team created a custom inlet for a handheld, commercially-available vapor detector that is used to find explosives. The inlet wasn’t a dog’s nose, per se, but it was designed to mimic the same external aerodynamics, sucking in and then expelling jets down and to the side. Even though the same amount of air was analyzed in experiments with and without the expelled jets, active sniffing led to a 16-fold improvement in the detection of TNT vapor! This was true when the source was at various distances from the detector, with the exception of when the source was directly beneath the inlet. In that case, the jets disturbed the concentrated source of odor molecules already in its path.

This work is likely to inspire a new generation of vapor samplers that help keep us and our loved ones safer. There could be more to come too. The researchers are exploring whether the fact that the jets are warmer than the surrounding air might have an impact on sniffing, and what we can learn from how dogs align their sniffing patterns with the direction of the expired jets. So the next time you see a dog aimlessly sniffing, take a minute to appreciate all that is happening in the moment, and maybe give the pup a quick pat of thanks.

Kendra Redmond

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