In Depth

Bomb-sniffing grasshoppers: the next frontier for public security?

Scientists ‘hijack’ insects’ brains to detect chemical explosives

Bomb-sniffing cyborg grasshoppers have been created by scientists to detect explosives such as TNT.

Academics at Washington University in Missouri tapped into the insects’ minds to monitor whether they were smelling explosives, and if so, what kind they were detecting. Or as the researchers put it, the “bio-hacked” grasshoppers play a similar role to a “canary in a coal mine”.

How does the science work?

The scientists essentially “hijack” the insect’s sense of smell, by implanting electrodes into their brains that can pick up electrical signals triggered when olfactory receptor neurons in their antennae detect chemical odours in the air. 

The signals are then transmitted wirelessly to the scientists’ computer from a “backpack” attached to the grasshopper, says New Scientist.

This gives the researchers a baseline reading of which parts of the grasshopper’s brain are activated when the insect smells chemical explosives.

When the grasshoppers then smell a new substance, the scientists can compare the new signal reading with the baseline reading.

If the same part of the brain that lit up for smelling chemical explosives subsequently lights up again, the likelihood is that the grasshopper is smelling chemical explosives.

Indeed, the scientists found that the groups of neurones activated by different smells were distinct enough to identify specific sets activated by specific explosives.

A total of seven grasshoppers were tested, and as a unit correctly identified chemical explosives with 80% accuracy.

In a paper outlining their research, the scientists conclude: “Our study provides the first demonstration of how biological olfactory systems [sense of smell] can be hijacked to develop a cyborg chemical sensing approach.”

Why grasshoppers?

Machines engineered to smell out explosives “have limited capacity compared to the broad-spectrum abilities of the biological” sense of smell, say the study authors.

“Despite decades of efforts, these machines do not match the capability of their biological counterparts in terms of range sensitivity and range,” they add.

According to the research paper, the grasshopper was chosen because: 

  • they are sturdy and can recover from surgeries to implant electrodes
  • their olfactory system has been well studied
  • they have “non-spiking local neurons in the antennal lobe, therefore, signals from projection neurons alone can be monitored”
  • they can be trained to recognise aromas using classical conditioning procedures
  • they can carry heavy payloads
  • they can function in both solitary and group conditions.

However, the process “was not without harm to the insects”, which as well as having wires attached to their brains, “were also immobilised, meaning they had to be carried into the test chamber on a wheeled remote-controlled platform”, reports The Telegraph.

The grasshoppers could successfully detect explosives for up to seven hours after the electrodes were implanted but then became fatigued and ultimately died.

The project was funded by the US Office of Naval Research, and the researchers believe the grasshoppers could be used for national security purposes.

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