A small optical fiber sensor detects explosives in concentrations as low as 6.3 ppm, which could mean big things in the fight against terrorism. A team from the University of Adelaide, in collaboration with the Australian Defense Science and Technology Organization, has developed a fluorescent conjugated polymer that emits red light when illuminated by a green laser. The presence of explosives is detected by the reduction in the amount of red light emitted, with analysis time totaling only a few minutes. Inner walls of a suspended core fiber. The inset shows a wide-angle view of the same fiber. Courtesy of Sensors and Actuators B: Chemical. “Traditionally, explosives detection has involved looking for metals that encase them such as in land mines," said Dr. Georgios Tsiminis of the university's Institute for Photonics and Advanced Sensing, an Australian Research Council Super Science Fellow and a lead researcher in this study. “In today's world, however, homemade improvised explosive devices will often have no metal in them, so we need to be able to detect the explosive material itself.” In the study, the researchers created three small holes at the core of optical fibers coated with a thin layer of polymer. Explosives samples were then drawn through the fiber holes by capillary action, enabling the measurement of red light emitted. “This has high sensitivity and we can detect tiny quantities of an explosive in a small sample,” Tsiminis said. “And not only do we know if explosives are there, we can quantify the amount of explosive by looking at how the light emission changes over time.” A separate study by Brigham Young University researchers has similar military and security implications. Using data from Lawrence Livermore National Laboratory, that group developed a model that can distinguish nuclear weapons material in every pixel of an image taken with a LWIR camera. The Adelaide fiber sensor could be used in forensics investigations that involve potential explosives. “It requires very little explosives present so is very sensitive,” Tsiminis said. “So forensic investigators would be able to take swabs from various surfaces, place them in some organic solvent and within a few minutes, know if there have been explosives present.” The research is published in Sensors and Actuators B: Chemical (doi: 10.1016/j.snb.2014.03.031). For more information, visit: www.adelaide.edu.au.