Trained dogs are incredible chemical sensors, far better at detecting explosives, narcotics and other substances than even the most advanced technological device. But one challenge is that dogs have to be trained, and training them with real hazardous substances can be inconvenient and dangerous.
NIST scientists have been working to solve this problem using a jello-like material called polydimethylsiloxane, or PDMS for short. PDMS absorbs odors and releases them slowly over time. Enclose it in a container with an explosive or narcotic for a few weeks until it absorbs the odors, and you can then use it to safely train dogs to detect the real thing.
But a few weeks is a long time, and now, NIST researchers have developed a faster way to infuse PDMS with vapors. In the journal Forensic Chemistry, they describe warming compounds found in explosives, causing them to release vapors more quickly, then capturing those vapors with PDMS that is maintained at a cooler temperature, which allows it to absorb vapors more readily. This two-temperature method cut the time it took to “charge” PDMS training aids from a few weeks to a few days.
“That time savings can be critical,” said NIST research chemist Bill MacCrehan. “If terrorists are using a new type of explosive, you don’t want to wait a month for the training aids to be ready.”
For this experiment, MacCrehan infused PDMS with vapors from dinitrotoluene (DNT), which is a low-level contaminant present in TNT explosives but the main odorant that dogs respond to when detecting TNT. He also infused PDMS with vapors from a small quantity of TNT. Co-authors at the Auburn University College of Veterinary Medicine then demonstrated that trained detection dogs responded to the DNT-infused PDMS training aids as if they were real TNT.
While this study focused on DNT as a proof of concept, MacCrehan says he believes the two-temperature method will also work with other explosives and with narcotics such as fentanyl. Some forms of fentanyl are so potent that inhaling a small amount can be harmful or fatal to humans and dogs. But by controlling how much vapor the PDMS absorbs, MacCrehan says, it should be possible to create safe training aids for fentanyl.
Other safe training aids already exist. Some are prepared by dissolving explosives and applying the solution to glass beads, for example. “But most have not been widely accepted in the canine detection community because their effectiveness has not been proven,” said Paul Waggoner, a co-author and co-director of Auburn’s Canine Performance Sciences Program. “If you put an explosive in a solvent, the dogs might actually be detecting the solvent, not the explosive.”
To test the two-temperature method, MacCrehan devised a PDMS “charging station” with a hot plate on one side and a cooling plate on the other (so the “hot stays hot and the cool stays cool,” as a 1980s commercial jingle put it). He prepared various samples