As Syrian leader Bashar al-Assad has shown, chemical weapons are no longer on the forbidden fringe of warfare.

“Let’s be clear: Assad’s most recent use of poison gas against the people of Douma was not his first, second, third, or even 49th use of chemical weapons,” Ambassador Nikki Haley told the UN Security Council on April 13. “The United States estimates that Assad has used chemical weapons in the Syrian war at least 50 times. Public estimates are as high as 200.”

That evolution has breathed new urgency into U.S. military efforts to more effectively detect the use of chemical and other non-conventional arms. One project underway at the Navy Research Lab stands at the forefront of that effort.

Researchers in the Material Science and Technology Division are developing atomically-thin semiconductors to serve as sensors in emerging detection systems. The team published a 2017 paper in Scientific Reports and has two patent applications pending.

“We’re now in the applied phase of basic research. We’re going to start building prototypes that we can test in real world situations,” said Adam Friedman, the lead researcher on the team which includes at least seven physicists, chemists and engineers. “We’re looking for ways to build the technology that we can put into real sensors in the field.“

The military already has access to a range of portable sensors. The primary models detect based on electronic measurements, optical readings and ion mobility spectrometry. They’re good, but not good enough. The chief drawback is that sensors are specialized: chemical sensors look for chemicals but aren’t optimized to search for traces of radiation, for example. Most also have mechanical limitations.

“They can usually do only one thing, they tend to be dependent on things like temperature and humidity, and they also use a lot of power,” Friedman said.

Other military leaders have acknowledged the need for a more robust solution.

“As the threat of a chemical or biological attack on the United States homeland and military forces abroad continues to grow, the Department of Defense’s (DoD) sense of urgency to develop effective chemical and biological sensors to mitigate this threat also grows,” a DARPA document reads.

DARPA has its own effort underway. Its SIGMA+ program aims to combine sensors with sophisticated analytics as a means for detecting nuclear, chemical and other threats.

Atomic-scale sensing

The NRL effort aims to create a sensing mechanism that is literally three atoms thick, a sensor that virtually eliminates concerns about size, weight and power.

“We’re talking about putting the entire thing onto a watch battery,” Friedman said. “If you do that and add a few antennas and some measuring electronics, it would cost $10 per sensor and weight less than 5 grams. You’d probably get a week of batter life out of it.”

The physics is excruciating, but it basically comes down to this: all the major “nasty compounds” tend to shed electronics. Sarin gas, ammonia-based explosives, “they all have an excess amount of charge, and these [developmental] materials happen to be very good at accepting charge,” Friedman said.

“These films can sense a single electron. It is reflected in the film’s conductivity and reflected in its optical properties. The film becomes more conductive and we read that conductivity” in order to determine what happened, he said.

Scientists know what it looks like when toxic substances shed electrons. The material being developed by NRL will detect those minuscule electronic exchanges and rapidly determine what noxious substances are present.

Navy’s expeditionary forces have already expressed an interest in the technology, “You have lots of people and potentially lots of information about the battlefield,” Friedman said. With a fast and accurate detection tool, “you can put it all together to get a much better picture of what is going on.”

The NRL sensor could be incorporated into existing sensor platforms within five years. In the long term, scientists envision this becoming a standard piece of expeditionary equipment.

“My goal is to put a sensor on every single Marine or soldier in the field and to be able to integrate the information from all of those sensors to get an overall picture of the battlefield,” Friedman said.

“If you can make the sensors small and sensitive and wearable, and if everyone has one and they are interconnected, your platoon will be able to pinpoint buried explosives or the location of a chemical factory,” he said. “It would make the battlefield safer for soldiers who would have much more information, and it would make missions much more efficient if you are trying to locate something that could possibly be dangerous.”