Navy-funded researchers have discovered that a locust’s sensitive “horns” can distinguish between the scents of TNT and other explosives — a development that one day could herald the deployment of bomb-sniffing, electronically augmented bug swarms.
The research by a team from Washington University in St. Louis, published this month in the science journal “Biosensors and Biolectronics: X,” is the first proof of concept for a system that aims to tap into the antennae and brainpower of garden-variety bugs to create an advanced bomb-detection sensor.
The work is funded by two Office of Naval Research grants totaling more than $1.1 million, and biomedical engineering professor Barani Raman believes it has the potential to produce a biorobotic sniffer that would be leaps ahead of entirely man-made “electronic noses.”
Locusts, which differ from ordinary grasshoppers in their tendency to swarm — sometimes in biblical proportions — have had about 250 million years to refine their sensory organs. A single antenna, or horn, has 50,000 neurons of some 50 different types, researchers say.
That makes for far more “perfected” and complex sensing organs than systems developed by engineers, said Raman, whose doctoral research focused on electronic noses. For the past four years, his lab has studied how those advanced biological sensors could be hijacked and coupled with modern computing power.
A critical question was whether the bugs actually could detect compounds that don’t typically play a role in their lives — unlike, for example, the chemicals that give green leaves their scent, Raman said.
“What we did not know was, again, something like a TNT and DNT, which has no meaning to the insects, you would not expect them to have sensors for that,” Raman said. “But it turns out … the insects do have sensors for them and very exquisite sensors … because they can pick up some of these odors at extremely low concentrations — of parts per billion and below.”
The new, peer-reviewed study found that the tiny herbivores can distinguish not only between the vapors from explosive chemicals like TNT, DNT, RDX, PETN and ammonium nitrate, they can do so within a fraction of a second and can sense where the scent is coming from.
The American locusts used in the study appear to work better as bomb sniffers when in a swarm. Data from a group of seven bugs gave accurate results about 80% of the time, compared with about 60%, on average, for lone bugs, the researchers found.
The study relied on techniques the researchers had developed previously to tap into the bugs’ brains to decode neural reactions to various stimuli. Bug brains are relatively simple, allowing for implants that record their electrical activity and algorithms that can be trained to figure out what they’re smelling, Raman said.
While dogs’ noses remain the gold standard for bomb detection, locusts offer several advantages: they’re cheap, abundant and don’t require expensive behavioral conditioning. Reading their neural activity also means that the bomb-detection capability isn’t dependent on things like a dog’s desire to please its handler, he said.
Another advantage locusts have is that they can carry relatively large loads. The research team is still developing other elements of the system, such as tiny “backpacks” to carry the electronics needed to record neural activity.
As part of the study, engineering professors Shantanu Chakrabartty and Srikanth Singamaneni helped improve the system for transmitting the locusts’ brain activity. The team also developed a new surgical procedure to attach electrodes to the brains so that the locusts could move and feed, while allowing sensory data to be recorded for up to a few days.
Those advancements mean the bugs can be transported once sealed up after surgery, Raman said. One day, they might be placed onto a remote-controlled device and transported to collect readings.
The study was a “necessary step,” Raman said, but more work will need to be done, including taking the locusts out of a lab to see how they fare in the real world, with shifting winds, temperatures and other factors.
“When the rubber hits the road, we need more rigorous testing,” he said.
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