Source: Army photoK9 officers, trained to detect everything from missing persons and explosives to narcotics, are generally expensive, not to mention overtaxed. Duke University researchers have been developing an artificial robot nose that might help law enforcement sniff out concealed narcotics, explosives and missing persons in the absence of trained K9s.

A prototype of the device includes odor receptors grown from mice genes, which respond to target odors, such as the scent of cocaine or explosives.

"This idea of an artificial nose has been present for a long time," said senior study author Hiroaki Matsunami, a professor of molecular genetics and microbiology in the Duke School of Medicine. "The receptors were identified in the 1990s, but there are significant technical hurdles to produce all these receptors and monitor the activity so that we can use that in an artificial device."

"E-noses" that exist now use various chemical compounds to detect smells instead of receptor stem cells, Matsunami said, calling those devices "not as good as a trained dog."

"The idea is that by using the actual, living receptors, maybe we can develop a device similar to animals," Matsunami said. "Nobody has achieved that yet, but this study is moving toward that goal."

Roughly 20,000 genes containing instructions for creating proteins that taste, smell, feel and move are present in human, mouse and dog genomes. Roughly 5% of mouse genes contain the instructions for making odor receptors. Conversely, just 2% of human genes are used to create odor receptors.

"These animals invest a lot of resources for this purpose," Matsunami said. "Mice and rats are very good smellers; we just don't use mice for detecting explosives in real life. There are some practical problems to do that."

To begin, researchers first set out to identify the best odor receptors to react to target odors such as marijuana and cocaine. Then the researchers developed a liquid medium primed with molecules that light up to signal a reaction. Following that, the researchers copied roughly 80% of the mouse odor receptors, mixing them with seven target odor chemicals in the medium.

The resulting luminescence was measured and researchers selected the best-performing odor receptors for the second portion of the study, which involved monitored receptor activation in real time.

Taking into consideration the presence of mucus in the human nose and the fact that humans don’t typically submerge their noses into liquid baths of odor chemicals, the team mimicked how the human nose works in their study, exposing odorants to vapor and a handful of enzymes.

For the purpose of this study, researchers tested the receptors against just two odor vapors.

"We only tested two of them in the paper, but it's showing the proof of principle of how it can be used," Matsunami said.

Eventually, the researchers hope to modify the device so that it can be used to test all of the receptors against a variety of smells.

"We have a panel of receptors so we can monitor how different receptors respond differently to various smells, including ones that are similar to each other in chemical structure or ones that might be related to real-world use, like something associated to explosives or drugs," Matsunami said.

The team also tested different enzymes that might be found in mucus to see how they assisted or prevented reactions. This demonstration proved more true-to-life than the vapor molecules interacting with odor receptors.

"You'd think when we smell a chemical, the chemical would bind to the chemical receptor in the nose, but actually it's not so simple," Matsunami said. "When the chemical dissolves in the nasal mucus before binding to the receptor, it might be converted to another chemical by enzymes in the nasal mucus."

Because mucus is an unknown factor in understanding how we smell, mimicking the key components of nasal mucus might be the next step toward constructing an artificial nose, according to researchers.

"It's not like our paper will be immediately applied to a portable device used in the airport soon, but this is an important step forward to show that it is possible," Matsunami said. "We can more clearly see what kind of hurdles to pass in order for the community to create such a device."

The study is published in the journal Nature Communications.