Genetically Modified Mice Could Be Tiny Landmine-Sniffing Heroes

A Belgian organization called APOPO already uses giant African pouched rats as a cheaper way to sniff out landmines. The rats are not genetically modified, but their sense of smell is sharp enough to detect TNT. The bomb-sniffing rats are taught to scratch the ground when they detect a hidden mine (fortunately, they are small enough not to set off the explosives). While the furry minesweepers are effective (with two handlers, they can cover a field in one hour that would take two full days for metal detectors), they need nine months of training to become reliable, a process that costs around 6,000 euros per rat.

The genetically engineered mice, however, are so sensitive to TNT that encountering the molecule is likely to change their behavior involuntarily, so they would need little to no training. Charlotte D’Hulst, a molecular neurobiologist at Hunter College who presented her work at a meeting of the Society for Neuroscience, used genetic modification to ensure that the mice have 10,000 to 1,000,000 odor-sensing neurons with a TNT-detecting receptor compared with only 4,000 in a normal animal, “possibly amplifying the detection limit for this odor 500-fold,” she says. Each odor-sensing neuron in a mouse’s nose is spotted with one kind of odor receptor. Usually, each specific receptor is found in one out of every thousand odor-sensing neurons, but about half the scent-detecting neurons in D’Hulst’s mice have the TNT-detecting receptor.

This particular odorant receptor was originally identified by Danny Dhanasekaran, a molecular biologist at the University of Oklahoma College of Medicine. Dhanasekaran says that a given odor is usually detected by a handful of different kinds of odorant receptors, which helps natural noses more easily and accurately discern smells. However, by engineering a great abundance of one receptor that detects TNT, D’Hulst and colleagues “could enhance the sensitivity of the system so it can be easily used in operations to detect landmines,” says Dhanasekaran, who is continuing to look for other TNT-type receptors.

D’Hulst hopes this overwhelming dedication to just one odor will provide an easy way to know whether or not the engineered mice have encountered TNT. Recent research suggests that sudden and intense stimulation of the olfactory system will trigger seizures, she says. “We can only hope that our mice will show a seizure behavior … upon detecting landmines. We won’t have to work with food rewards; we will probably use some radio signaling system. A chip implant may track, report, and record their behaviors.” The researchers still need to test the mice in behavioral studies.

Roger Hess, director of field operations for Golden West Humanitarian Foundation, a charity that develops technologies to aid landmine removal, says that while this mine-sniffing method could show promise, it would still depend on detection of trace vapors from the mine. The release of the odor from the ground can depend on soil and water conditions, and the trace of an explosive could be several meters away from where the mine is actually buried, he says. The technique will also not work for mines that have no gaps for the scent of explosives to escape.

“Due to the risk of missing an item, a secondary method would need to be employed,” he says.