What a difference a spray makes

A simple new spray‑on film developed by university chemists may one day allow airport security officials to confidently and quickly screen vehicles, people and their luggage for traces of nitrogen-based explosive residue.

A handprint contaminated by dynamite darkens the glow of an explosive-detecting gel.(UCSD photos/Jason Sanchez)

Airport screeners, for example, would apply an extremely thin spray of fluorescent polymer film on a suspect surface to reveal the presence of a dangerous chemical, such as nitroglycerin. Contaminated fingerprints leave dark shadows on the film, which glow blue under ultraviolet light. Incriminating traces are revealed as soon as the solution dries, usually within 30 seconds.

"No special instruments or training are needed to interpret the results, because the polymers fluoresce brightly when exposed to explosive residue," said William Trogler, a professor of chemistry and biochemistry at the University of California – San Diego. "It's a simple visual test for explosives that doesn't take a scientist to understand."

Trogler said only a minute amount of the spray is needed to provoke a chemical reaction. A single one-thousandth of a gram layer of the polymer is enough to detect as little as a few trillionths of a gram of residue on a surface the size of the palm of a hand. Any surface, including fingers, that has come in contact with nitrogen-based explosives will have 1,000 times that quantity or more stuck to it.
    

After a few seconds, the handprint glows green if the explosive is a nitrate ester such as nitroglycerin. (UCSD photos/Jason Sanchez)

One of the films can distinguish between different classes of explosive chemicals, a property that could provide
evidence to help solve a crime, or prevent one, Trogler said. The polymers were developed at UCSD by Trogler and graduate student Jason Sanchez.
         
Other explosive residue–sensing technologies exist, such as handheld electronic "sniffers" that sample the air, but Trogler said his technology is different because the UCSD films adhere directly to potentially contaminated surfaces. "This makes the films more sensitive than previous methods, which rely on capturing molecules that escape into the air."

Trogler told Homeland1 that the technology could possibly also be used to scan tickets or boarding passes to see whether a person had recently handled explosives.

Trogler's technology starred in a recent episode of the television series CSI: Miami, where it was used to connect fingerprints left on a video camera to a bomb used in a bank heist. In reality, the security systems company RedXDefense has licensed the technology and has developed a portable kit called XPAC based on the technology.