Bomb-sniffing dogs are wonderful things, but they have their drawbacks: They can be distracted. They require food to live. They poop. Thankfully, UC Berkeley researchers are developing technology that could supplement dogs, if not make them obsolete: They’re working on a super-sensitive light-based plasmon sensor to detect incredibly minute concentrations of explosives.

“Optical explosive sensors are very sensitive and compact,” said Xiang Zhang, UC Berkeley professor of mechanical engineering. “The ability to magnify such a small trace of an explosive to create a detectable signal is a major development in plasmonsensor technology, which is one of the most powerful tools we have today.”

The engineers put the sensor to the test with various explosives – 2,4-dinitrotoluene (DNT), ammonium nitrate and nitrobenzene – and found that the device successfully detected the airborne chemicals at concentrations of 0.67 parts per billion, 0.4 parts per billion and 7.2 parts per million, respectively. For reference, one part per billion would be akin to a blade of grass on a football field. It’s really that sensitive.

Not only is the nanoscale plasmon sensor among the most sensitive explosive detection methods ever produced, it’s also one of the smallest. That’s because there’s not much to it – It consists of a layer of cadmium sulfide, a semiconductor, that is laid on top of a sheet of silver with a layer of magnesium fluoride in the middle. Explosives like DNT and TNT rely on nitro-unstable, electron deficient chemical compounds in order to work properly. Those same qualities create interactions with defects on the surface of the semiconductor layer, and so the device works by detecting the increased intensity in the light signal that occurs as a result of this interaction.

Hopefully, similar devices will soon be used to detect even trace amounts of otherwise undetectable explosives, thanks to the powerful signal produced.

“The difference in intensity is similar to going from a light bulb for a table lamp to a laser pointer,” Zhang said. “We create a sharper signal, which makes it easier to detect even smaller changes for tiny traces of explosives in the air.”