DetectionDetecting explosives, not toothpaste
Researchers want airports, border checkpoints, and others to detect homemade explosives made with hydrogen peroxide without nabbing people whose toothpaste happens to contain peroxide. This is part of the challenge faced in developing a portable sensor to detect a common homemade explosive called a FOx (fuel/oxidizer) mixture, made by mixing hydrogen peroxide with fuels.
Sandia National Laboratories researchers want airports, border checkpoints, and others to detect homemade explosives made with hydrogen peroxide without nabbing people whose toothpaste happens to contain peroxide.
This is part of the challenge faced in developing a portable sensor to detect a common homemade explosive called a FOx (fuel/oxidizer) mixture, made by mixing hydrogen peroxide with fuels, said Chris Brotherton, principal investigator for a Sandia research project on chemiresponsive sensors. The detector must be able to spot hydrogen peroxide in concentrations that don’t also raise suspicions about common peroxide-containing products.
“Hydrogen peroxide explosives are a challenge because they are dangerous, but there are so many personal hygiene products that have hydrogen peroxide in them that the false positive rate is very high,” Brotherton said.
A Sandia Lab release reports that hydrogen peroxide is found in everyday products ranging from soap, toothpaste, and hair color to laundry bleach, carpet cleaners and stain removers.
Brotherton’s Early Career Laboratory Directed Research and Development (LDRD) project proved a sensor could identify relatively high concentrations of hydrogen peroxide and differentiate that from a common interfering substance such as water, he said. The next step, Brotherton said, would be to work with an industrial partner to design an overall system that works faster and can be mass produced.
His work is built on field-structured chemiresistor technology developed at Sandia more than a decade ago by researchers James Martin and Doug Read. Chemiresistors are resistance-based sensors for volatile organic compounds, and the material developed by Martin and Read, who published several papers on their work, allows users to tailor the sensors’ response range and sensitivity.
Finding the right polymer
A major challenge was distinguishing between hydrogen peroxide and water, which exhibit similar behavior in chemiresistors. The key was choosing certain molecules in a polymer matrix, suggested by Brotherton’s Sandia technical mentor, polymer chemistry expert David Wheeler. When exposed to peroxide, those molecules react in a different way than when exposed to water.
The idea is to engineer the polymer to be as similar to the target material as possible, relying on the undergraduate rule that like dissolves like. For example, Wheeler said, if the target is a substance that’s not very polar, you would choose a polymer with nonpolar groups. If the target has a lot of polarity, like water does, you’d develop polymers that could hydrogen-bond with water.
The tiny sensor incorporates the polymer and chains of miniscule conductive metal beads. The polymer reacts
