MIT's developed a new explosives detector so sensitive that it can pick up a single molecule of an explosive such as TNT.
The team coated carbon nanotubes with protein fragments normally found in bee venom, bombolitins, which they have found to react to nitro-aromatic compounds such as TNT. Such sensors, they say, would be far more sensitive than existing explosives detectors, which use spectrometry to analyze charged particles as they move through the air.
"Ion mobility spectrometers are widely deployed because they are inexpensive and very reliable. However, this next generation of nanosensors can improve upon this by having the ultimate detection limit, [detecting] single molecules of explosives at room temperature and atmospheric pressure," says professor Michael Strano.
The detector takes advantage of carbon nanotubes' natural fluorescence. When the target binds to the bee-venom proteins coating the nanotubes, it shifts the fluorescent light's wavelength. A new type of microscope reads the signal, which can't be seen with the naked eye.
Each nanotube-peptide combination reacts differently to different nitro-aromatic compounds. By using several different nanotubes coated in different bombolitins, the researchers can identify a unique 'fingerprint' for each explosive - and even for their breakdown products.
"Compounds such as TNT decompose in the environment, creating other
molecule types, and those derivatives could also be identified with this type of sensor," Strano says. "Because molecules in the environment are constantly changing into other chemicals, we need sensor platforms that can detect the entire network and classes of chemicals, instead of just one type."
The technology has already drawn commercial and military interest, Strano says. For it to become truly practical, it would have to be used with a concentrator that would bring any molecules floating in the air in contact with the carbon nanotubes.
"It doesn't mean that we are ready to put these onto a subway and detect explosives immediately. But it does mean that now the sensor itself is no longer the bottleneck," Strano says. "If there's one molecule in a sample, and if you can get it to the sensor, you can now detect and quantify it."