Engineers at the University of Connecticut (UConn) have developed a fluorescent nanofibrous film capable of detecting ultra-trace levels of explosive vapors from landmines and other buried explosive devices. In the presence of explosive molecules, the film’s fluorescence is suppressed when exposed to ultraviolet (UV) light. In this way, the lightweight film, which is similar to paper, could be rolled out over suspect areas to mark the location of explosive devices.

The ultra-thin film is cheaply and easily produced by electrospinning pyrene with polystyrene in the presence of an organic salt known as tetrabutylammonium hexafluorophosphate (TBAH). The team says the resulting nanofibrous membrane is highly porous and absorbs explosive vapors at ultra-trace levels quickly and reliably.

As well as detecting elements found in TNT and 2,4-DNT, which are the principle components in landmines, the film can also detect elements in harder to detect plastic explosives such as HMX, RDX, Tetryl, and PETN. It can detect elements from TNT at levels as low as 10 parts per billion, Tetryl at 74 parts per trillion (ppt), RDX at 5 ppt, PETN at 7 ppt, and HMX at 0.1 ppt, released from one billionth of a gram of explosive residue.

In the presence of explosive vapor, the recyclable film turns dark blue when exposed to UV light. The team says initial vapor detection takes place in seconds, with more than 90 percent fluorescent quenching efficiency occurring within six minutes.

While the system is still not as sensitive as a sniffer dog, which can detect explosives such as explosives at concentrations in the parts per quadrillion range, the researchers point out that dogs can get tired and also have difficulty differentiating between devices in dense minefields.

However, Erik Tollefsen, advisor for stockpile destruction, EOD and technology for the Geneva International Centre for Humanitarian Demining (GICHD), says chemical detection systems such as the nanofilm could be used in conjunction with sniffer dogs as a quality control tool.

"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."

Wang and Lei have also developed a new chemical test based on the fluorescent polymer for detecting TNT in water and other liquids at concentrations ranging from about 33 ppt (about one drop in 20 Olympic-sized swimming pools) to 225 parts per million. "The sensor can easily be incorporated into a paper test strip similar to those used for pregnancy tests, which means it can be produced and used at a very low cost," says Lei.

The engineers’ research appears in the May 11, 2012 online edition of Advanced Functional Materials.

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