Spotting H₂O₂

IN AN EFFORT TO SNIFF OUT peroxide-based explosives, such as those used in the 2005 bombing of the London transit system, scientists have developed a simple, inexpensive sensor that selectively detects hydrogen peroxide vapor (J. Am. Chem. Soc., DOI: 10.1021/ja710324f). In addition to its application in counterterrorism, the device could be used to detect H₂O₂ in industrial settings, where exposure to the chemical is an important health issue.

The recipe for peroxide-based explosives calls for H₂O₂ as a precursor, so peroxide bombs usually contain traces of the chemical. The matchbook-sized sensor, invented by a team from the University of California, San Diego, led by William C. Trogler, Andrew C. Kummel, and Ivan K. Schuller, can detect H₂O₂ vapor in the parts-per-billion range. According to the researchers, the cheap, compact device improves upon standard methods of H₂O₂ detection, which rely on complex, expensive instruments to do the job.

The device employs thin films of metal phthalocyanines as its key sensing components. These films are chemiresistors—their conductivity varies depending on their exposure to different chemicals. "For metal phthalocyanines, oxidants normally introduce an increase in current," whereas reducing agents have the opposite effect, Trogler explains.

In the presence of the oxidant H₂O₂, however, metal phthalocyanines behave differently. Cobalt phthalocyanine shows a decrease in current, but other phthalocyanines with metals, such as copper or nickel, show an increase in current. A sensor array with both cobalt phthalocyanine and copper phthalocyanine therefore displays a unique signature for H₂O₂.

Joseph Wang, a chemical engineering professor at Arizona State University, calls the work "a very elegant and effective approach for detecting hydrogen peroxide vapor." He adds that the "ability to tailor the response via a judicious choice of the specific metal center of the phthalocyanine holds great promise for a wide range of monitoring applications."