Aimée Rose and her colleagues at the Massachusetts Institute of Technology used a type of compound known as a semiconducting organic polymer (SOP) in their design. When exposed to laser light, this type of compound subsequently produces its own additional laser light--a process called lasing. Molecules of explosives such as trinitrotoluene (TNT) are deficient in electrons and are attracted to the electron-rich polymer. When they stick to the surface, they interfere with the lasing and the SOP's light output decreases as a result. By measuring the change in lasing, the scientists were able to detect TNT at concentrations as low as five parts per billion. The team also successfully identified dinitrotoluene (DNT) at 100 parts per billion in just one second of detection time.
The detector is relatively immune to interference, the researchers report, noting no response was recorded in the presence of molecules such as benzene or naphthalene. SOPs had previously been used to locate buried land mines; the new design, however, offers a 30-fold increase in sensitivity over previous ones.