I recently read an article in the scholarly journal AIP Advances that really brought back memories, as I was working on a similar project several years ago. The simple fact is that there are approximately 110,000,000 landmines currently deployed in the world, spread across 70 countries. Every twenty minutes, someone is involved in a landmine incident, whether it’s a maiming or a death. I have no doubt that landmines can be effective in a war situation; the problem starts when the war ends, and civilians move back into the ex-war zone. We’ve all seen pictures of American soldiers who are missing limbs due to explosive bombs. Now, picture the same thing happening in a country where medical care is abysmal, and finish with the thought that the population group most likely to be running aimlessly through the woods / underbrush are children, out having fun. The very same woods where the 110 million landmines are buried, ready to detonate.
Something has to be done. Metal detectors are useless; most landmines are made of plastic. That’s why I was glad to read this particular article in AIP Advances. Researchers in Scotland have developed a material that can reliably sense explosive vapor through several feet of earth. As landmines grow old, their explosive contents begin to break down, and molecular fragments break off from the main chunk and volatilize into the air. It’s this (extremely) faint “scent” of landmines that the Scottish apparatus is designed to detect.
The chemistry behind the sensor is pretty clever. The researchers used a conjugated polymer, a group of materials I’ve studied extensively and have written about before. In a conjugated polymer, electrons have more freedom than they normally do in a plastic material. They can reside in a variety of energy states – high, low, etc. The normal process is that most electrons are in the lower state to begin with – the “ground state” – and then, upon absorption of light, the electrons soak up that light energy and go into a higher energy level – the “excited state”. After a few moments there, they fall back down to the ground state and shed the excess energy they temporarily possessed by emitting a flash of light.
This new Scottish invention uses a thin film of this type of polymer, along with the appropriate beams of light to “excite” the polymer as well as detectors to measure any light being reemitted by the film. The trick is that many common landmine decomposition vapors (dinitrotoluene, for example) can soak into the film and if the vapor molecules collide with an “excited” polymer strand, the excess energy temporarily held by the conjugated molecule will just be harmlessly dissipated as heat and will never be reemitted as light. The polymer returns to the ground state without so much as a tiny twinkle. When this happens, the researchers know that there is explosive vapor nearby.
Combine all of this into a sort of metal detector apparatus, with lamps and detectors for the light, and you can easily see how this invention might be used. The fluorescence is quenched when the detector senses a landmine “rotting” in the ground. Personally, if this type of thing saves even one life, I’m all for it. Remember – every twenty minutes, someone is hurt by a landmine. Thank goodness for these Scottish scientists and their clever innovation.
The source of this article can be found at: Wang, et al. “Ultra-portable explosives sensor based on a CMOS fluorescence lifetime analysis micro-system”. AIP Advances, 2011, 1, 3.