Graphite is one of the most well-known forms of carbon because of its use in pencils, but it is no longer the only carbon-based pencil lead. Researchers at MIT have created carbon-nanotube pencil lead for creating devices, such as gas sensors. As this method of placing nanotubes on a device is free of solvents, it is both safer and cheaper than some other methods.
Typically carbon nanotubes are added to a device while in a solution with a potentially hazardous solvent. Inspired by graphite pencil lead, the researchers compressed a powder of nanotubes into the shape of pencil lead for a mechanical pencil. With a mechanical pencil, they then started drawing connections on pieces of paper with gold electrodes, and found the lines they drew worked. Even when the lines were irregularly shaped, the nanotubes' ability to detect gases was not compromised.
The researchers are now testing to see if they can expand this method's selectivity. Pure carbon nanotubes, like those they used, are great for detecting even minute amounts of ammonia, but to detect other gases other materials have to be added, such as metal atoms or polymers. If those doped nanotubes can also be made into pencil lead, we could see a myriad of low cost gas sensors with carbon nanotubes at their heart.