Potential attacks on aircraft could be more easily detected thanks to a new test for hydrogen peroxide, one of the liquids that have sparked dramatic security clampdowns at airports around the world. Researchers at the University of California, Berkeley, US, say that a test they developed to help diagnose diseases in the human body could be adapted to detect the chemical precursors of homemade explosives.
UK authorities recently uncovered an alleged plot to blow up aircraft using homemade explosives produced on board using chemicals such as hydrogen peroxide. Similar homemade explosives were used in the London subway bombings last year, which killed over 50 people. The explosives triacetone triperoxide (TATP) and hexamethylene triperoxide diamine, (HMTD) can be made using hydrogen peroxide and other chemicals. But airport screening devices are not able to detect hydrogen peroxide directly. In the wake of arrests associated with the recent plot, airport security guards have prevented liquids and gels from being taken on board flights and many airlines have continued the ban.
White powder
The new test uses a class of chemical compounds called "Peroxysensors" which were designed to detect hydrogen peroxide, which is generated in cells that are undergoing oxidative stress from ageing and ageing-related diseases. Christopher Chang, a chemist at UC Berkeley, says his group developed the compounds for basic research into oxidative stress. "When we saw a lot of these terrorist explosive mixtures contain peroxides and other molecules that are similar, we made the link and saw that this technique could be applicable," Chang says.
The new sensors are based on fluorescein, a dye that glows under ultraviolet light. But the fluorescein has been modified by having boronates attached to the molecule. This changes it from a fluorescent dye into a white powder that does not fluoresce. However, when it reacts with hydrogen peroxide the boronates are stripped off and the molecule becomes fluorescent again. It can be made to glow yellow or red. Chang says that paper test strips coated with Peroxysensors could be dipped in suspicious liquids. They could also be made to detect more than one kind of peroxide, so that innocent liquids that might have trace amounts of household hydrogen peroxide could be distinguished from other liquids.
Blue to yellow
Another test using a different chemical was recently developed at by Allen Apblett and other chemists at Oklahoma State University in Stillwater, US. In this case, the test is a spin-off from a method they developed to neutralise explosives made with hydrogen peroxide. The researchers made a material called "molybdenum blue" by mixing molybdic oxide with n-butanol and hydrochloric acid. When mixed with a peroxide-based explosive, molybdenum blue breaks it down into its harmless chemical constituents. In the process, molybdenum blue also changes from dark blue to pale yellow.
Apblett says he and his colleagues have developed a test strip using the molybdenum blue that will change colour when dipped in a solution with the high level of peroxides that would be needed for bomb-making.But Ivan Oelrich, head of the Strategic Security Project at the Federation of American Scientists in Washington DC, says that the new techniques will only work once security personnel have found a suspicious substance.
"With any of these schemes, you have to think through how you are going to use them. Airport screeners are not going to be using droppers to put liquids into test tubes. It has to be fast, almost 100% automated, and have a very small false alarm rate," he says.
