Bombs and explosives leave a telltale chemical trace in the air around them. To detect these tiny amounts of airborne volatile chemical explosives, alert squads at airports and elsewhere rely on the olfactory talents of sniffer dogs. But as dependable as Fido and his friends may be, canine bomb detectors are expensive to train and tire out easily. And when they get tired on the job, disaster can strike.
A new, less cuddly method to detect airborne traces of explosives like TNT takes inspiration from one of nature’s other super sniffers. This new detecting technique is modeled on the architecture of the silk moth antenna, the plush appendages that fan outwards from the head of the males of the species.
The antenna serves a crucial role and is essential for the species’ survival—it’s the part of the moth that detects single molecules of pheromones in the air, leading a male moth to its mate. The antennae bristle with fine hairs that are continuously vibrating at a regular frequency. When a pheromone molecule lands on a hair, the vibration changes, tipping off a sensory alarm.
The architecture of the bomb detectors are based on this same principle. They’re coated with nanotubes made of titanium dioxide which is selectively sticky for TNT molecules. Like the hairs on the silk moth antennae, they’re supported on a stalk at one end, and continuously quiver, sort of like a steadily oscillating diving board.
All that changes when there’s a tiny amount of TNT in the air at close range. When a TNT molecule lands on a swaying nanotube, it changes the frequency at which it moves. That change is fed back into the sensory system of the detector, indicating the presence of an explosive nearby.
Taken together, the titanium dioxide coating and the vibrating nanopores give the system its unique sensitivity, up to one part per trillion. "The system answers in real time so you can put the sensors in luggage rooms at the airport," Denis Spitzer, who built the system says. His research is funded in part by a French defense agency, and Spitzer is also gunning for military applications for the sensors.
Future versions of this setup will have different classes of bristles picking up different molecules—a single stalk will be able to detect more than one kind of explosive. "A first step will be to make it even more sensitive than it is now," says Spitzer.
A clear advantage to this is that the device can carry out a detection in real time, though, Spitzer says they have yet to test if the system can measure explosives from far away. A version of the detector made with different materials could detect tiny amounts of chemicals in water as well, Spitzer says.