Melanie Anderson pulls aside a small curtain in a dark closet. A dim red bulb is the only light.
“This might take a while because I want to grab male moths,” she says, reaching into the cage behind the curtain.
She pulls out a mottled brown Manduca sexta, sometimes called the Carolina sphinx moth. It’s big — larger than her palm.
“That looks like a female. It has slightly smaller antennae,” she says. “So I’m going to put it back.”
For this University of Washington engineer, the antennae are the key.
Anderson reaches once, then twice more into the fluttering mass of insects in the cage. She finally snags a male.
“I tell people ‘moth antenna’ and they’re like, ‘What does ‘MOTH’ stand for?’ And I’m like, ‘No, no, no. The insect,’ Anderson explains. “We actually use a live biologic component of the moth — the antenna — and we put it on an electrical circuit to read signals from it.”
But Smellicopter is more than just cutting-edge bio-hybrid technology, it’s an innovation that could make us safer in the face of accidents and disasters.
A moth’s antennae are an evolutionary masterpiece of smell. They can pick up the faintest of scents.
“Biology can detect chemicals at a level that far exceeds anything that’s synthetic — not by a factor of a 1000 or 10,000 or 100,000 or even a million factors. Even greater than that,” said University of Washington biologist Tom Daniel. “So, we use the extreme sensitivity of odor detection in living systems and asked, ‘How could we integrate it into synthetic systems?’”
Daniel, who’s head of a consortium of researchers looking at nature-inspired flight systems, asked Anderson this question, and she’s gotten her Ph.D. answering it.
Anderson and her research partner Joseph Sullivan have created a drone that taps into the extraordinary sensory power of a moth’s antenna.
“You can have it in a chemical plant to be able to survey that area and find the source of an odor leak or a gas leak very quickly before it gets out of hand,” Anderson said. “It can be used to replace search dogs or search and rescue workers in dangerous situations. So it can really save lives.”
It works by bringing biology, robotics, coding, aerodynamics and a host of other disciplines together to create one device.
After cutting the antenna off an anesthetized moth, Anderson uses tweezers to thread the hollow structure onto a hair-like wire of a circuit.
“She can manipulate that antenna and get that tiny silver wire inside of it. And she doesn’t need a table or anything — I cannot,” Sullivan says, watching Anderson’s steady hands.
“Give it a couple more months of Warhammer painting and you’ll have the same dexterity,” Anderson quips back.
She bends the antenna over to tread the other end onto the opposite wire. The loop of the antenna completes the circuit.
When the moth antenna encounters certain odors, it reacts, creating faint signals running between the two wires.
“We’re measuring electrical activity in the antenna, which is very, very faint,” Sullivan says.
Some moths eat flower nectar, so their antennae are highly tuned to those smells.
“Especially if I just showered, then sometimes it’ll react to my shampoo or conditioner,” she said.
The reaction can be seen on a line graph on her computer. In the ambient air, the line is fairly steady. But when Anderson puffs some floral scent across the antenna, it spikes. These spikes are what signal to the drone that the source of the odor is near.
“Electroantennogram” odor sensors like this have been around for a while — but mounting them on a drone for use in disaster areas is new.
Inspired by Nature
The idea for Smellicopter came out of the U.S. Air Force Center of Excellence on Nature-Inspired Flight Technologies and Ideas. The group was comprised of scientists and engineers from several universities.
“We’re not very good at making odor sensors that will interface with a flying machine,” said Mark Willis, a biologist who studies moths at Case Western Reserve University in Ohio. “If you think about it, flight is a kind of locomotion where everything is happening fast … If you can’t make quick adaptations, you’re gonna smack into something.”
Willis is a member of the Center for Excellence but wasn’t directly involved in the creation of Smellicopter.
He said artificial odor sensors currently can’t respond quickly enough to meet the demands of flight. But a moth’s antenna is ideal because it can react in quick succession to odors in the environment with just under 100 milliseconds between responses.
“Smellicopter is actually a great example of a beginning step while we’re busy trying to come up with a synthetic odor detector that will clear itself as quickly as a biological odor detector. We can just take the biological odor detector and slam it onto the robot,” Willis said.
Smellicopter’s connection to the natural world goes even further than its living antenna. Anderson’s drone also looks to moths to inspire how the drone flies.
“The moths, when they smell odor… they will surge upwind. And then when they lose the odor, like if the wind shifts or they get a little off course, then they cast back and forth crosswind until they find the odor again. And then they surge upwind again,” she said.
In a small wind tunnel on campus, the cast and surge strategy of Smellicopter is put to the test. Anderson places a drop of the floral scent at the head of the tunnel and launches the small drone.
Smellicopter flies back and forth searching for the trail. It locks in and surges toward the scent.
“That time it went straight to the source. It had a lot of hits right at that last surge,” Anderson tells Sullivan.
“Yeah, I see that. Peak. Peak. Peak. Peak.”
Smellicopter’s next evolution
If gas leaks, buried disaster victims and explosive devices all smelled like flowers, Smellicopter would be in business.
But they don’t. And that’s the next big step in Smellicopter’s evolution.
“We are working towards genetically engineering the moth’s antenna so that they can sense different chemicals … Amplify the antenna’s sensitivity to things like bomb scents and then kind of remove the sensitivity to things that we don’t want — like the floral scent and the moth pheromone,” Anderson said.
This work is underway now, as part of Anderson’s postdoctoral position at UW. She’s also working on a cell phone-mounted electroantennogram that could be used as a handheld sensor.
Smellicopter hovers at the intersection of emerging technologies.
“We have device technologies, which is robotics, and neural recording technologies. We have gene editing. That’s crazy, contemporary technology,” said Tom Daniel.
And it also offers a glimpse of what could be possible if you add artificial intelligence into the mix — the possibility of listening in on not just one signal coming from the moth’s antenna, but all of them at once.
“There are many cells in the antenna circuit coming into the animal, each one signaling different chemicals. Could we use machine learning to discern between ‘Is that Tom?’ or ‘Is that you?’ I know my dog can smell the difference between us,” Daniel said.
“So can we combine gene editing, device technology and AI to make a sommelier?”
And if we could make an artificial sensor that sophisticated, there’s no limit to where our new noses could take us next.