Move over, sniffer dogs: now there’s bomb-sensing grasshoppers. Barani Raman and colleagues at Washington University in St. Louis in Missouri have tapped into the olfactory senses of the American grasshopper, Schistocerca americana, to create biological bomb sniffers.
In insects, olfactory receptor neurons in the antennae detect the presence of chemical odours in the air. In turn, they send electrical signals to a part of the insect brain known as the antennal lobe. Each grasshopper antenna has approximately 50,000 of these neurons.
The team puffed vapours of different explosive materials onto grasshopper antennae, including vapours of trinitrotoluene (TNT) and its precursor 2,4-dinitrotoluene (DNT). They used non-explosive controls such as hot air and benzaldehyde, the primary component in the oil of bitter almonds.
By implanting electrodes into the antennal lobes of grasshoppers, the team found that different groups of neurons were activated upon exposure to the explosives. They analysed the electrical signals and were able to distinguish the explosive vapours apart from non-explosives, as well as from each other.
The team fit grasshoppers with tiny lightweight sensor backpacks that were able to record and wirelessly transmit the electrical activity almost instantaneously to a computer.
The grasshoppers’ brains continued to successfully detect explosives up to seven hours after the researchers implanted the electrodes, before they became fatigued and ultimately died.
The process immobilised the grasshoppers, so the researchers then put them on a wheeled, remote controlled platform to test their ability to sense explosives at different locations. The grasshoppers were able to detect where the highest concentration of explosives was when the team moved the platform to different locations.
The project was funded by the US Office of Naval Research and the researchers believe the grasshoppers could be used for homeland security purposes.
They also tested the effect of combining sensory information from multiple grasshoppers, given that in the real world chemicals might be dispersed by environmental factors including wind.
Taking neural activity from seven grasshoppers yielded an average accuracy of 80 per cent, compared to 60 per cent for a single grasshopper.
A limitation of the study was that it did not test the grasshoppers’ explosives-detecting ability when multiple odours were present at the same time.