Scientists at MIT have developed a technique for using fluorescent carbon nanotubes and proteins from bee venom to detect the presence of explosives. The new device can sense single molecules of compounds of explosives and pesticides, in real-time, with high sensitivity, at room temperature and atmospheric pressure.
The study, published in the journal Proceedings of the National Academy of Sciences [Heller et al., PNAS (2011) doi:10.1073/pnas.1005512108], involved coating carbon nanotubes with protein fragments called bombolitins that are found in bee venom, and which have never been shown to detect explosive molecules before.
Team leader, Michael Strano, had previously developed carbon nanotube sensors for a range of molecules using the natural fluorescence of the nanotubes, by joining them to a molecule that binds to a particular target. In this study, however, the target binds to the bee venom proteins that coat the nanotubes, altering the wavelength of the fluorescent light rather than its intensity.
As Strano points out, “Compounds such as TNT decompose in the environment, creating other molecule types, and those derivatives could also be identified with this type of sensor. 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.”
With each combination of nanotube peptide reacting differently to different nitro-aromatic compounds, the use of a range of nanotubes coated in different bombolitins can identify the unique characteristics of each explosive. With traditional detectors using spectrometry to analyze charged particles in the air, it is hoped the greater sensitivity of the new device could lead to a major breakthrough.
The team was initially interested in detecting biologically important molecules using the carbon nanotube-based sensors they had developed. They showed an interaction with a pesticide compound, and as pesticides have a similar chemical structure to explosives, they started to investigate them as well. The ability to detect a single molecule of an explosive, as well as employ the fluorescence of a nanomaterial to detect changes in peptide structure due to a molecular binding interaction, has practical potential in both biology and medicine.
The study showed that a whole class of compounds can be detected and identified with very high sensitivity, with this detection occurring through several different types of mechanisms. There is apparently already some interest for commercial and military applications, and in airports of course; also, as the nanotubes can detect two pesticides that are also nitro-aromatic compounds, they could be developed as environmental sensors.
However, to be commercially viable, the sensor would have to be coupled with a concentrator that would ensure any molecules in the air came into contact with the carbon nanotubes; also, the color change can currently only be seen using a certain type of microscope, so more research is needed before commercial applications are viable.
Laurie Donaldson