The amazing dog nose: can you smell me now?

By Carol Beuchat PhD
The amazing olfactory abilities of the dog are well-known to any dog owner. With a sniff of the door jamb, my dog knows who is on the other side of the front door before I open it, he can locate one of his toys hidden in a drawer, and he heads straight for the person with treats in their pocket when we go to the dog park. We have made good use of this portable detection system to find lost children, locate bombs, detect cancer, and many, many other things. The dog's nose is truly remarkable.
Just as amazing as its sensitivity to odor is its design, which is much more complex that it might first appear. Inside the muzzle is a complex system of passages, the turbinates, that both humidify the air and also direct it to the olfactory organ for scent detection. This design much accomplish both respiration and scenting as breathing and sniffing, respectively.
Some new studies reveal that the nose itself is much more complicated than might be expected from its simple design. There are two front-facing nostrils, or nares, as well as slits along the bottom on each side. With some very clever experiments, researchers have shown that this design is no accident. They have been able to reveal how air flows in and out of the canine nose, and how a simple design improves scent detection. In fact, engineers can improve the effectiveness of our chemical sensing technology by learning a few things from the dog.
Although dogs usually make very willing research participants, to achieve enough control to do replicate experiments, the researchers used the information from high-resolution magnetic resonance imaging (MRI) to fabricate a model nose using a 3D printer. Inside, a cylinder with a a piston was used to move air into and out of the nostrils to mimic inhalation and exhalation. They also used a hot-wire anemometer to sense the air flow rate that could detect changes with a resolution of 1 millisecond. The flow characteristics of the nose model were similar to those of a Labrador Retriever.
To determine the sensitivity of scent detection, they placed a "smell" source, a chemical called 2,4-dinitrotoluene (DNT) in a small tin with holes in the side to allow vapor to escape. They used sophisticated chemical sensors (ambient ion mass spectroscopy) to document scent detection.
Finally, to visualize the flows of air, they used high speed video and "schlieren imaging", which uses optical techniques to photograph density gradients in air flow, as well as "theater fog" for some demonstrations.

Staymates et al 2016


Staymates et al 2016​

What they found is fascinating. When the dog exhales, air is directed downwards and outwards. When the dog is sniffing a surface, the airflow from exhalation actually draws the odor from the object being scented towards the nose. This effectively extends the "aerodynamic reach" of the nose. The inspiration-expiration cycle during scent detection is repeated very quickly, about 5 times per second.

Staymates et al 2016


Staymates et al 2016​

The air flow patterns that result from the simple design of the dog's nose increase the efficiency of scent detection by 8 times over that for the steady "inspiration" used in scent detection devices. This is achieved simply by directing the exhaled air away from the source of the odor in a way that draws the scent towards the nose. In fact, the farther away the scent, the greater the advantage of the dog's nose over a commercial device with continuous inspiration; in one set of experiments, the dog's nose was 4 times better than the detector at a distance of 10 cm from the source of the scent, and 18 times better at a distance of 20 cm.
Using what they learned from the dog, these researchers were able to construct a "bioinspired" scent detector that "sniffs" instead of continuously drawing in air and directs the exhaled air in a way that draws in scent from the source to the intake. When the air intake was directly above the source of the scent (distance = 0 in the graph below), continuous "inspiration" was as good or better than sniffing. But as the scent source moved away, the advantage of sniffing got better and better.

Staymates et al 2016​

Needless, to say, the results of this study should be of great interest to the military and in situations where efficient odor detection is critical. A simple alteration in the design of odor detection devices can result in spectacular improvements in efficiency. Now why didn't we think of that?

Check out the really cool videos below that show the airflow patterns during odor detection by the dog (all videos are from Staymates et al 2016).
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