Plasmon sensors to put bomb-sniffing canines out of work
Led by Xiang Zhang, UC Berkeley professor of mechanical engineering, the researchers has found a way to dramatically increase the sensitivity of a light-based plasmon sensor to detect incredibly minute concentrations of explosives. They noted that the sensor could potentially be used to sniff out a hard-to-detect explosive popular among terrorists.
The sensors were put to test with various explosives—including 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. One part per billion would be akin to a blade of grass on a football field. They noted that these results are much more sensitive than those published to date for other optical sensors.
The plasmon laser sensor is shown in this scanning electron microscope image. Source: Ren-Min Ma and Sadao Ota, UC Berkeley
"Optical explosive sensors are very sensitive and compact," said Zhang, who is also director of the Materials Science Division at the Lawrence Berkeley National Laboratory and director of the National Science Foundation Nanoscale Science and Engineering Centre at UC Berkeley. "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."
Latest generation of plasmon sensors
The nanoscale plasmon sensor used in the lab experiments is much smaller than other explosive detectors on the market. 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.
In designing the device, the researchers took advantage of the chemical makeup of many explosives, particularly nitro-compounds such as DNT and its more well-known relative, TNT. Not only do the unstable nitro groups make the chemicals more explosive, they also are characteristically electron deficient, the researchers said. This quality increases the interaction of the molecules with natural surface defects on the semiconductor. The device works by detecting the increased intensity in the light signal that occurs as a result of this interaction.
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