Drawing Carbon Nanotube-Based Sensors on Paper

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 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 detects minute amounts of ammonia gas, an industrial hazard, and could be adapted to detect nearly any type of gas.

Transcript

00:00:00 [MUSIC PLAYING] My name is Katherine Mirica and my research focuses on making gas sensors from carbon nanotubes. These sensors might ultimately find applications in the food industry, health care, and homeland security. A carbon nanotube is a tube-shaped molecule made up of carbon atoms. It is one to 10 nanometers in diameter, which is 50,000 times thinner than a human hair

00:00:31 and about a billion times thinner than this model of a carbon nanotube. Carbon nanotubes are chemically related to the main component in the lead of a pencil, which is graphite. Graphite is composed of flat sheets of carbon atoms. If you take one of these flat sheets and roll it up into a cylinder you get the structure of a carbon nanotube. You can view the nanotube as a very conductive, hollow

00:01:02 molecular wire. Because all the atoms of the nanotube are on its surface, when something else, like a molecule, interacts with that surface it can have a very large effect on the flow of current through the nanotube. And this type of sensitivity is very useful for making sensors. Are approach for overcoming the challenges of working with carbon nanotubes relies on a solvent-free method that is essentially similar to drawing with pencil on paper.

00:01:34 Instead of using a graphite-based lead, like a regular pencil, we make our own lead that's composed of carbon nanotubes. To make our pencil lead we take a commercial powder of carbon nanotubes and compress it into the shape of a lead using a press. To make the sensors we take a piece of standard copy paper and deposit gold electrodes onto its surface. These electrodes help us measure the electrical current running

00:02:01 through the carbon nanotubes. We then take our pencil lead and draw our carbon nanotubes-based sensor between the electrodes. And that's it. We've just made a sensor that's capable of sensing ammonia gas at low part per million concentrations. Sensing ammonia is important because it's a toxic gas that's sometimes used in refrigeration and food processing applications.