Sensor sniffs out shoe bombs

U. ILLINOIS (US) — A hard-to-detect chemical explosive used by convicted “shoe bomber” Richard Reid may now be easier to identify.

A newly developed colorimetric sensor can detect very low levels of vapor from the powerful explosive triacetone triperoxide (TATP), which was used in Reid’s attempted detonation of a shoe bomb on an American Airlines flight in 2001 and is suspected of being used in some of the bombs detonated on London subway trains in 2005.

The explosive is easy to make using commonly found ingredients but difficult to detect, and current detection methods require expensive instrumentation and time-consuming lab work.

The University of Illinois team who developed the new sensor has built a prototype of a handheld device that incorporates the technology as a way to provide the kind of portable, quick, and low-cost solution required for screening passenger and luggage at airports.

In a paper published in the Journal of the American Chemical Society, developers Kenneth Suslick and Hengwei Lin discuss the challenges of detecting TATP and how their sensor overcomes them.

They write that TATP “has emerged as an explosive of choice for terrorists in recent years” and that it is extremely difficult to detect due to its lack of ultraviolet absorbance, fluorescence, or facile ionization.

“Techniques that are able to detect generally require expensive instrumentation, need extensive sample preparation, or cannot detect TATP in the gas phase,” they continue.

In contrast, their simple, disposable, colorimetric sensor is “capable of sensitive and semiquantitative detection of the vapor phase of the primary explosive TATP with limits of detection below 0.02 percent of its saturation vapor pressure. The printed array is highly selective for TATP, is unaffected by changes in humidity or by the presence of many common potential interferents, and can differentiate TATP from other chemical oxidants.”

The printed array is smaller than a postage stamp and, the researchers add, the shelf life, stability, and reproducibility of the sensor technology make it ideal for practical applications. The handheld prototype incorporating the sensor also uses inexpensive white LED illumination and a small digital camera.

“The handheld device makes the whole process portable, sensitive, fast and inexpensive,” Suslick says.

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