Sensors made with carbon nanotubes — ultra-small sheets of carbon atoms rolled into cylinders — are great for detecting harmful gases in the atmosphere. The problem, though, is that making such sensors requires using a solvent like dichlorobenzene, in a process that can be both hazardous and unreliable.
Chemists at the Massachusetts Institute of Technology (MIT) believe they’ve found a better solution: using a special “pencil lead” of compressed carbon nanotube powder to draw sensors onto paper.
Here’s how it works: with their special pencil lead, researchers can draw lines of carbon nanotubes onto paper that’s imprinted with small electrodes of gold. Upon applying an electrical current to the paper, they can then measure the current as it flows through the resistor of carbon nanotubes. If the currrent is altered as it passes through, that’s evidence of a gas that has bound itself to the carbon nanotubes.
A variety of gases have the habit of binding themselves to carbon nanotubes, which then impedes electron flow. As a result, drawn-on sensors can be adapted to detect nearly any type of gas.
“The beauty of this is we can start doing all sorts of chemically specific functionalized materials,” said Timothy Swager, leader of the MIT research team. “We think we can make sensors for almost anything that’s volatile.”
Pencil-drawn sensors, for example, could be used to detect ethylene to monitor the ripeness of fruit as it’s shipped and stored. They could also detect sulfur compounds, making them a promising way to identify natural gas leaks.