Washington, June 4 : A new aerosol spray that glows blue under UV light would help CSI (Crime Scene Investigation) officers to hunt for common explosives.
According to a report in New Scientist, William Trogler and Jason Sanchez at the University of California at San Diego in the US have developed the aerosol.
Spraying an object with the aerosol and illuminating it with an ultraviolet torch makes the object glow blue.
But any colourless patches betray traces of explosive as faint as a trillionth of a gram per square centimetre.
Some explosives can already be looked for using portable devices that detect vapours released in even trace amounts. But most modern explosives must be detected by directing a puff of air at a surface and collecting samples to be tested in a lab.
The new spray can instead detect those substances at the scene and even distinguish between different explosives.
The aerosol contains a polymer that normally dries to form a film that fluoresces blue under UV light. However, if it is exposed to any of a range of explosives, including nitroglycerin and TNT, it reacts with nitrogen groups in the explosives to become colourless.
"The polymer emits at the blue wavelength most visible to the eye," said Trogler. "The visible detection is very intuitive - it doesn't require a scientist to operate," he added.
The polymer can change colour to reveal different classes of explosives after continued exposure to UV light. The light catalyses a reaction between explosives in the class that includes nitroglycerin and PETN.
"It yields a green luminescence," said Trogler.
That feature of the spray could help investigators gather evidence at a crime scene usually only known after a trip back to the lab.
According to Michael Knapp at the University of Massachusetts, Amherst, US, sensors able to directly reveal what they have found to investigators can lead to more sensitive results.