In the 1950s, German biologist Dietrich Schneider first attempted to decipher the mechanism behind insects' powerful sense of smell by attaching electrodes to moth antennae. These tiny insect noses, Schneider found, continue to process and report the presence of scent for up to an hour after being severed from the moth.
Today, Penn State entomologist Tom Baker is taking Schneider's work further by hooking moth antennae to a complex computer algorithm that not only identifies odors, but also locates their sources. Baker calls the device—designed by research assistant Andrew Myrick—an olfactory biosensor.
The possible uses for such a device are numerous, explains Baker. It could detect drugs and explosives at sea or in airports; smell landmines or chemical factories in towns near the battlefield; or locate bodies for search and rescue operations. Some experts believe that insects are better suited to such tasks than dogs, as they are more machine-like in their behavior and don't become distracted by hunger, boredom, or a different human handler. Using insects would also eliminate the ethical and emotional issues felt by handlers when sending their dogs into dangerous environments such as minefields.
"Another possible application could be food safety," notes Baker, referring to studies showing that insects display distinct nerve responses when they detect trace volatiles present in deteriorating fish and fruit. "However, first I think it's going to be useful as a research tool."
Despite looking so unlike our noses, moths' antennae function in a very similar way, explains Baker. Covered with tens of thousands of tiny odor-sensitive hairs, the moth's sniffers are constantly being bombarded by odor particles, select types of which are allowed to penetrate through a hair's outer surface and strike delicate sensors within called dendrites. Upon impact, the dendrite becomes excited and an electrical pulse travels down the antenna, Baker explains. "By attaching electrodes to the antennae, we make use of the electronic reports that they produce naturally."
Organized, grape-bunch-like clusters of neurons at the base of the antennae called glomeruli sort these pulses into their different odorant classes, says Baker, but this physiology is far too complicated to tap into. So to create his own sorting method, he attached four different species of moth antennae to his device—each tuned to slightly differentsets of odors. The result, he says, is the aptly named Quadro-Probe.
"This is still in the 'proof of concept' stage," Baker comments. "Our ability to discriminate among odors is clearly the huge limitation. Right now the device mainly finds specific odors set up in advance"—but it does so in real time, with 80 to 100 percent accuracy. Says Baker: "It shows the principles we're shooting for."
Tom Baker, Ph.D., is professor of entomology in the College of Agricultural Sciences; tcb10@psu.edu. Baker presented a talk on the work described here at CrossOver 2005, a symposium held at University Park in October 2005 to explore the interface of life sciences and materials at Penn State. His work was supported by the Defense Advanced Research Projects Agency in 1998-2003 and the Keystone Alliance in 2004-2005, and is currently supported by the Office of Naval Research.
