MASSACHUSETTS INSTITUTE OF TECHNOLOGY, MASSACHUSETTS, USA. A carbon nanotube “lead” that can be used with a typical mechanical pencil can actually inscribe sensors on any type of paper surface. Detecting harmful gases in the environment can be detected with the use of carbon nanotubes. However, the large-scale production of building carbon nanotube sensors have adverse effects especially to a person’s health. This new method of fabrication can certainly avoid these life-threatening concerns.

A team of MIT Chemists developed a pencil that replaced graphite with compressed powder of carbon nanotubes. It can inscribe sensors that detect minute amounts of a hazardous industrial material like ammonia gas. The sensors can be adapted to sense almost any type of gas. This can be the start of creating sensors for anything that is volatile.

Sheets of carbon atoms that are rolled into cylinders are known as carbon nanotubes. They allow electrons to flow without any form of interference. They are effective sensors for many gases but they require hazardous solvents like dichlorobenzene to dissolve nanotubes.

A solvent-free fabrication method that is based on a paper is an effective solution. The carbon nanotubes (single-walled carbon nanotubes) are compressed into a graphite-like material that worked as a substitute for pencil lead. In creating the sensors using their pencil, the researchers draw a line of carbon nanotubes on a sheet of paper imprinted with minute electrodes made of gold.

An electrical current was applied and measured the current that flowed through the carbon nanotube strip that acted as a resistor. Once the current is altered, that means that the gas has bound to the carbon nanotubes. The device was tested on several types of paper and they found out that smoother papers produce the best results. Also, the sensors produced consistent results even when the marks were not uniform.

This new technique is inexpensive and the pencil lead is immensely stable. The new sensor can be used for a number of applications. Currently, the sensors are being customized to detect a wide range of gases.