William Trogler, a chemistry professor at the University of California, San Diego, who developed the technology behind the device developed a sprayable polymer that fluoresces blue-green under ultraviolet (UV) light, unless in the presence of explosive molecules, including PETN and TNT. When the polymer is sprayed on a surface and examined under UV light, explosives appear as black spots. The polymer is described in a recent issue of the Journal of Materials Chemistry.

This new detection kit, called the XPak, consists of a plastic viewing box and a removable baton. First, the soldier or police officer using the device rolls the paper-covered baton over the surface to be tested or has the subject grip the roller as it is placed inside the viewing box, where it is then sprayed with the luminescent polymer. The user then looks through the viewfinder using UV light. If there are no explosives present, the baton will look entirely blue. However, if there are traces of explosives, even as small as a few picograms, black spots will appear visible to the naked eye, allowing for intuitive, on the spot analysis without the overhead of image-analysis software or spectrometry.

While the chemistry behind the XPak is not new, it has been commercialized by ICx Technologies of Arlington, Virginia in a slightly more sensitive detector aimed at the detection of buried land mines. But such sensitivity is not always necessary. If you're directly detecting solid explosives, as in the case of the XPak, you don't have to detect such small amounts.

TFOT recently covered variable speed bullets as well as a spray which enables “dusting” for explosives and the TRON – high tech identification system. In 2006 TFOT covered a new technology developed in Israel, aimed at identifying TATP, one of the most elusive explosives used in many deadly terrorist acts of the last few decades, using a simple and cost-effective pen-like device.