BATTLEFIELDS strewn with mines are one of the nastiest legacies of war. They ensure that, long after a conflict has ceased, people continue to be killed and maimed by its aftermath. In 1999, the year the Ottawa Mine Ban Treaty came into force, there were more than 9,000 such casualties, most of them civilians. Though this number had fallen below 4,000 by 2014 it is, according to the Landmine and Cluster Munition Monitor, an international research group, rising again as a consequence of conflicts in Libya, Syria, Ukraine and Yemen.

These days most mines have cases made from plastic. Only the firing mechanisms include any metal. That means mines are hard to find with metal detectors. Many ingenious ways to locate and destroy them have been developed, ranging from armour-plated machines that flail the land, via robots equipped with ground-penetrating radar, to specially trained rats that can smell the explosives a mine contains. Such methods have, though, met with mixed success—and can also be expensive. Flails, for instance, scatter shrapnel and explosive residue around a minefield, making it hard to confirm that no undetonated devices remain. Minehunting rats, meanwhile, cost around $8,000 each to train. Often, therefore, mine detection boils down to rows of nervous people wearing blast-resistant clothing and creeping laboriously across a field, prodding the ground ahead to check for buried objects.

Shimshon Belkin, Aharon Agranat and Amos Nussinovitch of the Hebrew University of Jerusalem reckon they have a better approach. They have created a form of Escherichia coli, a bacterium widely studied by geneticists, that synthesises a fluorescent protein in response to traces of vapour given off by a mine’s explosives. As they report in Nature Biotechnology, they have now tested their invention’s effectiveness as a mine-hunter.

To turn their bacteria into a mine-detection system, they encapsulated them in beads of alginate, a material derived from seaweed that is permeable to vapours from explosives. They then scattered the beads across an area in which real mines had been buried and left them for a day, to give the vapours from the mines time to stimulate fluorescent-protein production in those beads that had landed above mines. That done, they used a laser to scan the field from a distance. The laser beam stimulated any fluorescent protein it hit to light up, indicating the location of a mine.

The result was a qualified success. The mines being sought had been buried either in one of two sorts of sand or in garden soil. The bugs detected all six sand-covered mines, and also places where flakes of explosive had been buried uncased, but were not fooled by an explosive-free dummy buried in the same material. They did not, though, detect either of the mines buried in garden soil, or flakes of explosive so buried. Whether this was because the researchers had not allowed enough time for vapour evaporating from the explosives to penetrate the soil (they had buried the targets only five days before the tests) or because those vapours cannot penetrate such soil well enough for the bacteria to detect them is a subject for a further test.

Even if it can be used only in sand, though, the approach Drs Belkin, Agranat and Nussinovitch have come up with may be useful. They hope to turn it into a working mine-detection system within three years. They think they can improve the bugs’ sensitivity to vapours from explosives and plan to test other ways of encapsulating and dispersing them. For safety’s sake, the E. coli they use are engineered not to be pathogenic. They also require a special nutrient, contained within the bead. Once this is exhausted the bugs die rapidly.

Besides improving their bacteria, the group would also like to speed up the laser-scanning system, so that it can cover the ground faster. What they use at the moment could be operated from a vehicle, but if it were made compact and light enough, it might also be mounted on a light aircraft or drone. If all that can be done, the world may, at last, have a cheap and effective mine-detection system.