MIT uses pencil to draw carbon nanotube circuits

ExtremeTech : A team of MIT chemists led by Katherine Mirica produced a special pencil lead by compressing single-walled carbon nanotubes. Drawing on paper with the resulting substance deposits a thin layer of whole nanotubes. If the paper has been imprinted with gold electrodes, the carbon nanotubes act as resistors between the electrodes. Because nanotubes’ conductivity changes in the presence of certain molecules, Mirica’s team was able to use the circuits as simple sensors for the presence of ammonia gas. Previous nanotube circuit sensors required the use of potentially dangerous solvents. And other methods for producing nanotubes often produce less stable molecules and are more expensive. The new sensor was sensitive enough to detect concentrations as low as 0.5 parts per million. The team hopes to create similar sensors to detect molecules such as ethylene and sulfur.