Researchers at the Hebrew University of Jerusalem have developed a sensor that can rapidly locate buried explosives with the help of genetically engineered, bioluminescent E. coli bacteria, allowing field workers to search for dangerous buried ordnance from afar.

The sensor, described in an April 15 Biosensors and Bioelectronics paper, may offer a safe and relatively inexpensive method for detecting the roughly 110 million mines and explosive materials that are currently dispersed across 78 countries, potentially providing an alternative to previous approaches for buried explosive detection that relied on chemical analysis or animals trained to sniff them out.

Buried explosives present an urgent public health problem, leading to the deaths of between 15,000 and 20,000 people each year — and most of those killed are women, children and elderly people, according to the United Nations. Explosives come from a variety of sources, including military conflicts, training missions and accidental abandonment. Undetonated explosives, including those from World War I, can pose a risk decades after they are left behind. Conventional bomb removal remains a highly dangerous profession, with one death and two injuries recorded for every 5,000 bombs removed in the field. That stark reality drove the need for these researchers' innovation.

The team genetically engineered bacteria to detect trace amounts of dinitrotoluene, a derivative of trinitrotoluene, which is found in around 80% of buried mines. Both DNT and TNT vapors can rise through fissures in buried explosive devices, eventually reaching the earth's crust. But the researchers chose to track the presence of DNT, in particular, since it often produces a stronger vapor signature. 

Although biomarkers are sensitive to the materials they've been engineered to detect, researchers are still working to develop an ideal system for them to thrive under harsh conditions. "We [use] live bacteria," Aharon J. Agranat, a professor of applied physics at the Hebrew University of Jerusalem and a lead author on the paper, told The Academic Times. "They need to be in a wet environment. They eat food. They have to be in a certain temperature range, and they don't have an on-off switch."

Prototypes of the scanner — a sort of "miniscule chemical laboratory," as the researchers refer to it — were highly accurate in a controlled environment, detecting as little as 0.25 milligrams of DNT per kilogram of soil. The results were achieved by engineering two sets of genes within the bacteria: "promoter genes," which identify the DNT, and "reporting genes," which light up to locate the presence of an explosive substance. An electronic device can then spot those bioluminescent signatures and deliver a readout that displays possible bomb locations to investigators.

The breakthrough allows surveyors to locate mines from a safe distance so that they can receive an overview of bomb locations before they put themselves in harm's way. Previous strategies for locating explosives have involved animals — from dogs to elephants to giant African pouched rats — trained to sniff for explosive material, an often time-consuming and dangerous task.

Agranat sees his team's bioluminescent device as part of a larger trend to rethink the role of sensors in the scientific community. "If you spoke to someone about sensors 50 years ago, it would be [about] some device that measures a physical quantity and translates it to something that is displayed, like a thermometer" Agranat said. "Nowadays, sensors are something entirely different. There is a merger that is happening between the physical surroundings and cyberspace."

In other words, physical detection and virtual analytical systems can now be integrated to help scientists learn about the environment in real time. And biosensors like the kind developed by the Hebrew University team may one day be used as separate nodes in a larger platform capable of analyzing large surface areas.

Alternatively, bioluminescent bacteria could be placed in tiny beads and dispersed across a landscape to detect mines — a technique that the researchers explored in a 2017 paper. That system isn't perfect: The beads had to be analyzed at night for better optical fidelity and relied on an expensive scanning apparatus that may not yet be practical on a larger scale. Still, the researchers said that the innovation provides new tools that engineers can use as the basis for future mine-detection technologies.

Real-time analysis is especially important for the field of explosive detection, since older chemical detection methods often involved lengthy lab examinations — with weeks separating the collection date and the date at which results could be yielded. This long delay meant that field personnel tasked with dismantling buried devices had less time to locate and remove mines once they had been located.

The researchers tested their nodes in lab conditions that were ideal for bacterial bioluminescence, but how they would perform in more challenging terrains, temperatures and weather conditions remains unclear. Additionally, although this device was created to detect the presence of DNT, its current iteration would still overlook other potential signs of explosive materials in the environment.

But the researchers say that the system, while not without its flaws, has great potential. For instance, the biosensors can also be easily reprogrammed to detect other dangerous compounds, allowing researchers to use the bomb-detection infrastructure for finding pollutants or other unwanted materials in the environment. 

"[Bioluminescent bacteria] are very versatile. You can genetically engineer them for practically any type of material, and the reporting mechanism is the same," Agranat explained. "So we developed the option. But it has to be taken forward to become a viable technology, and I hope it happens in years to come."

The paper "An autonomous bioluminescent bacterial biosensor module for outdoor sensor networks, and its application for the detection of buried explosives" published April 15 in Biosensors and Bioelectronics, was authored by Aharon J. Agranat, Yossef Kabessa, Benjamin Shemer, Etai Shpigel, Offer Schwartsglass, Loay Atamneh, Yonatan Uziel, Meir Ejzenberg, Yosef Mizrachi, Yehudit Garcia, Galina Perepelitsa and Shimshon Belkin, Hebrew University of Jerusalem.