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Researchers from MIT have demonstrated a technique that allows them to draw a line of carbon nanotubes – with a mechanical pencil.

Their aim is to develop a production technique for nanotube-based sensors for detecting hazardous chemicals in the environment. Nanotubes are good at this, but expensive and difficult to produce.

Colour me carbon: MIT's nanotube pencil. Source: MIT

So why not just draw them on paper? That’s just what the MIT boffins have achieved: the graphite in the pencil is replaced with a rod made of a compressed powder of nanotubes. In a normal mechanical pencil, this can draw sensors onto any surface.

The particular sensor the MIT researchers demonstrated detects minute traces of ammonia gas in the air, but team leader Timothy Swager says the sensors can be modified to detect “nearly any” type of gas: “we can start doing all sorts of chemically specific functionalized materials … we think we can make sensors for almost anything that’s volatile”.

Getting the carbon to act as a sensor is surprisingly easy: gold electrodes are imprinted into the paper, allowing a current to pass through the carbon. If a gas binds to the nanotubes, the resistance – and therefore the current – changes.

Swager says that as well as being cheap, the nanotube pencil is very stable, and he says it’s delivering highly reproducible results. By altering the carbon – for example, adding metal atoms to the nanotubes – they can be made sensitive to different materials. A material that senses ethylene could monitor fruit ripening in transit, while sulphur compounds indicate gas links.

The MIT’s release, complete with video, is here. ®

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