Super-sensitive spray-on explosive detector

Published 27 May 2008

A new explosive detection system: A spray detects the presence of just a billionth of a gram of explosive, and shows the difference between nitrate esters, such as trinitroglycerin, and nitroaromatic explosives, such as TNT

American scientists have designed a new spray-on explosive detector sensitive enough to detect just a billionth of a gram of explosive. After treatment the explosive glows blue under UV light, making it perfect for use in the field. William Trogler and his team at the University of California, San Diego, made a silafluorene-fluorene copolymer to identify nitrogen-containing explosives. It is the first of its kind to act as a switchable sensor with picogram (10-15g) detection limits, and has been reported in the Royal Society of Chemistry’s Journal of Materials Chemistry. Trogler’s polymer can detect explosives at much lower levels than existing systems because it detects particles instead of explosive vapours. In the team’s new method, a user can simply spray the polymer solution over the test area, let it dry, and shine UV light on it. Spots of explosive quench the fluorescent polymer and turn blue.

The polymer is able to show the difference between nitrate esters, such as trinitroglycerin, and nitroaromatic explosives, such as TNT. Initially, polymer-treated spots of both compounds appear blue under UV light, but after further exposure the trinitroglycerin spot fluoresces green-yellow whilst the TNT spot remains blue. This colour change is thought to be due to photooxidation of the fluorenyl groups of the polymer. Trogler was surprised to find that adding a spirofluorene co-monomer gave the polymer a 100 per cent efficient conversion of UV light into fluorescence, describing this increase as dramatic. The technology is now being commercially produced by Rockville, Maryland-based security company RedXDefense.

The team is currently working on a similar system to detect peroxide-based explosives and say they hope to be able to investigate perchlorates and organic nitrates too.