Drawing a line, with carbon nanotubes

Carbon nanotubes offer a powerful new way to detect harmful gases in the environment. However, the methods typically used to build carbon nanotube sensors are hazardous and not suited for large-scale production.

A new fabrication method created by MIT chemists - as simple as drawing a line on a sheet of paper - may overcome that obstacle. MIT postdoc Katherine Mirica has designed a new type of pencil lead in which graphite is replaced with a compressed powder of carbon nanotubes. The lead, which can be used with a regular mechanical pencil, can inscribe sensors on any paper surface.

The sensor, described in the journal Angewandte Chemie, detects minute amounts of ammonia gas, an industrial hazard. Timothy Swager, the John D. MacArthur Professor of Chemistry and leader of the research team, says the sensors could be adapted to detect nearly any type of gas.

''The beauty of this is we can start doing all sorts of chemically specific functionalised materials,'' Swager says. ''We think we can make sensors for almost anything that's volatile.''

Other authors of the paper are graduate student Jonathan Weis and postdocs Jan Schnorr and Birgit Esser.

Pencil it in
Carbon nanotubes are sheets of carbon atoms rolled into cylinders that allow electrons to flow without hindrance. Such materials have been shown to be effective sensors for many gases, which bind to the nanotubes and impede electron flow.