Carbon nanotube pencil allows designers to draw sensors on paper
Graphite lead in mechanical pencil, replaced with carbon nanotubes, allows sensors to be drawn
Oh you need a sensor? Here, let me sketch you one real fast.
This may soon be the conversation that manufacturers everywhere will be having with clients, thanks to a group of ambitious chemists at MIT.
MIT researchers have created a carbon nanotube-based pencil.
MIT postdoc Katherine Mirica, along with Timothy Swager, the John D. MacArthur Professor of Chemistry and leader of the research team, have designed a new type of pencil in which the graphite lead portion of the instrument is replaced with a compressed powder of carbon nanotubes.
This, in turn, allows the sensor manufacturer / designer to draw a fully functioning carbon nanotube sensor onto a sheet of paper.
A report on this new technology was first described in the journal Angewandte Chemie (link below).
Some background on carbon nanotubes
Carbon nanotubes are sheets of carbon atoms rolled into cylinders which allow electrons to flow through them without any sort of hindrance. They make for good sensors because when exposed to gases, the vapors bind to the nanotubes, thereby impeding the flow of electrons.
The reason why carbon nanotube sensors haven’t really taken off is because their actual production can be a bit hazardous. You see, the sensors require dissolving nanotubes in a solvent like dichlorobenzene, a material that is not only dangerous, but also unreliable. As a result, carbon nanotube sensors cannot be produced on the large-scale level yet.
Taking a different approach
Swager and Mirica decided to try to create a solvent-free fabrication method for carbon nanotube sensors. They were inspired by pencils on Mirica’s desk, which led to the idea of compressing carbon nanotubes into a graphite-like material that could be used to substitute pencil lead and allow for the actual sensors themselves to be produced on sheets of paper instead.
The whole process is pretty simple: The designer uses the pencil to draw a line on a piece of paper imprinted with small electrodes made of gold. After that, an electrical current is applied and measured as it flows through the carbon nanotubes strip (with the strip acting like a resistor).
If the current is at all altered, it means gas has bonded to the nanotubes.
Mirica explains the process in the video below:
Results
The team tested the carbon nanotube-filled mechanical pencil on many different types of paper and found that the best response came when sensors were drawn on smooth sheets. Also, they reported that more consistent results were given when the marks weren’t uniform.
Now, besides the obvious time-saving and safety conveniences of being able to actually draw a carbon nanotube sensor, this new technology has two other major advantages: it’s inexpensive, and since the molecules are all immobilized, the “pencil lead” is considered very stable.
Outlook
Research is still in the very early stages — the group has only focused on using pure carbon nanotubes so far. The next step is to create nanotubes capable of detecting a wide range of gases (selectivity can be altered by adding metal atoms to the nanotube walls, or by wrapping polymers or other materials around the tubes).
The group will first focus on creating a carbon nanotube powder capable of detecting the gas ethylene, as it could be useful for monitoring the ripeness of fruit as it’s shipped and stored. After that, they plan to pursue sensors for sulfur compounds, which would be useful for detecting natural gas leaks.
Read the full report in Angewandte Chemie ■
Story via: MIT.edu
Advertisement
Learn more about Electronic Products Magazine
