New chemical sensor eases search for landmines and buried IEDs
03 August 2012
A chemical sensing system developed by engineers at the University of Connecticut is believed to be the first of its kind capable of detecting vapours from buried landmines and other explosive devices with the naked eye.
The key to the system is a fluorescent nanofiberous film that can detect ultra-trace levels of explosive vapours and buried explosives when applied to an area where explosives are suspected. A chemical reaction marking the location of the explosive device occurs when the film is exposed to handheld ultraviolet light.
The system can detect nitroaromatics such as those found in TNT and 2,4-DNT (the military's primary explosive and the principle components in landmines) as well as the elements used in harder to detect plastic explosives such as HMX, RDX, Tetryl, and PETN. The ultra-sensitive system can detect elements at levels as low as 10 parts per billion (TNT), 74 parts per trillion (Tetryl), 5 ppt (RDX), 7 ppt (PETN) and 0.1 ppt (HMX) released from one billionth of a gram of explosive residue.
If there is no explosive vapour present, the recyclable film retains a bright fluorescent cyan blue colour when exposed to ultraviolet light. If explosive molecules are present, the fluorescence is quenched and a dark circle identifying the threat forms on the film within minutes.
"Our initial results have been very promising," says UConn Dr. Ying Wang, who developed the system as a chemical engineering doctoral student working under the supervision of UConn Associate Engineering Professor Yu Lei. "We are now in the process of arranging a large-scale field test in Sweden."
Rather than using sophisticated chemical modifications or costly synthetic polymers in preparing the sensing material, UConn scientists prepared their ultra-thin film by simply electrospinning pyrene with polystyrene in the presence of an organic salt (tetrabutylammonium hexafluorophosphate or TBAH). This resulted in a highly porous nanofiberous membrane that absorbs explosive vapours at ultra-trace levels quickly and reliably. The film also has excellent sensitivity against common interferences such as ammonium nitrate and inorganic nitrates. Initial vapour detection took place within seconds with more than 90 percent fluorescent quenching efficiency within six minutes.
While explosive material can be concealed within landmines and IEDs, the seal is often not airtight and small amounts of vapours escape allowing detection.
The film developed by Wang and Lei is very lightweight, similar to paper, and can be rolled out over a suspect area like a sheet. The electrospinning process makes it both easy and affordable to produce.
Wang and Lei have also developed a novel chemical test for detecting TNT in water and other liquids. The application could be used to detect potential terrorist threats in airports as well as groundwater contamination in areas where explosives were used in construction. Wang and Lei have applied for patents for both chemical sensing systems.
The images used here are courtesy of Ying Wang/UConn and Advanced Functional Materials, Wiley-VCH Verlag GmbH & Co. KGaA