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Hand held sensor sniffs out shoe bombs
Article Type: Mini features From: Sensor Review, Volume 31, Issue 4
A team at the University of Illinois has developed a technology that is being applied to a hand held device (Figure 1) to sniff out Triacetone Triperoxide (TATP), the explosive of choice by many aircraft bombers. Previously, TATP, especially the vapor, was very difficult to detect and what methods were available were not suitable for rapid airport screening. The easy to prepare high-powered explosive was the choice of many such as the shoe bomber. TATP was hard to detect by the more standard chemical sensing methods as it did not fluoresce, absorb ultraviolet light or readily ionize.
The TATP project is part of a larger project at the University of Illinois to develop a colorimetric method to detect a number of toxic or dangerous industrial gases below permissible exposure levels. The approach has been to employ chemically sensitive responsive dyes that change in color when exposed to the subject toxic gas in even very low levels.
The dyes contain metal ions that respond to Lewis basicity, pH indicators that respond to Bronsted acidity/basicity, vapochrometric/solvatochromic dyes that respond to local polarity and metal slat redox indicators. The techniques have been improved by employing nanoporous pigments (Feng et al., 2010).
Professor Ken Suslick has led a team that has developed a colorimetric sensor array that can detect very low levels of TATP vapor down to 2 parts per billion. The heart of the approach is a printed array of 16 tiny colored dots, each a different pigment on an inert plastic film. An acid catalyst breaks down the TATP vapor into detectable components that will cause the pigments to change color.
The color pigment array is photographed by a digital camera or scanned before and after exposure to the to the TATP. The hand held unit draws in vapor passes over the catalyst then over the pigment array. The image of before exposure is compared with the after image and any change in the colors of the sensor dots indicates the concentration level of any TATP vapor present.
The researchers have found that the color change patterns are unique fingerprints of different concentration levels. They have also found that the array is not affected by many other chemicals that might be found in traveler’s baggage or on clothing such as personal hygiene products or laundry detergents.
In the airport security application, a new array would be placed in the hand held unit each time it is used. The arrays have a very long shelf life. The postage stamp size array is very low cost and easily stored near the airport security checkpoint. A digital camera such as in a cell phone could be used for the before and after imaging.
The technology is now in the process of being incorporated into a commercial product by iSense, a sensor manufacturer with operations in Palo Alto, CA and West Palm Beach, Florida. For more information on the technology e-mail: firstname.lastname@example.org. For more information on iSense, Inc. please visit: www.isensesystems.com