Durable carbon nanotube sensors can be etched with mechanical pencils

October 9, 2012 by Anne Trafton
MIT chemists designed a new type of pencil lead consisting of carbon nanotubes, allowing them to draw carbon nanotube sensors onto sheets of paper. Credit: Jan Schnorr

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 created by MIT chemists—as simple as drawing a line on a sheet of paper—may overcome that obstacle. MIT postdoc Katherine Mirica has designed a new type of pencil lead in which 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, described in the journal Angewandte Chemie, detects minute amounts of , an industrial hazard. Timothy Swager, the John D. MacArthur Professor of Chemistry and leader of the research team, says the sensors could 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," Swager says. "We think we can make sensors for almost anything that's volatile."

Other authors of the paper are graduate student Jonathan Weis and postdocs Jan Schnorr and Birgit Esser.

Pencil it in

Carbon nanotubes are sheets of rolled into cylinders that allow to flow without hindrance. Such materials have been shown to be effective sensors for many gases, which bind to the nanotubes and impede . However, creating these sensors requires dissolving nanotubes in a solvent such as dichlorobenzene, using a process that can be hazardous and unreliable.

Swager and Mirica set out to create a solvent-free fabrication method based on paper. Inspired by pencils on her desk, Mirica had the idea to compress carbon nanotubes into a graphite-like material that could substitute for pencil lead.

To create sensors using their pencil, the researchers draw a line of carbon nanotubes on a sheet of paper imprinted with small made of gold. They then apply an electrical current and measure the current as it flows through the carbon nanotube strip, which acts as a resistor. If the current is altered, it means gas has bound to the carbon nanotubes.

This video is not supported by your browser at this time.

The researchers tested their device on several different types of paper, and found that the best response came with sensors drawn on smoother papers. They also found that the sensors give consistent results even when the marks aren't uniform.

Two major advantages of the technique are that it is inexpensive and the "pencil lead" is extremely stable, Swager says. "You can't imagine a more stable formulation. The molecules are immobilized," he says.

The new sensor could prove useful for a variety of applications, says Zhenan Bao, an associate professor of chemical engineering at Stanford University. "I can already think of many ways this technique can be extended to build devices," says Bao, who was not part of the research team. "Compared to other typical techniques, such as spin coating, dip coating or inkjet printing, I am impressed with the good reproducibility of sensing response they were able to get."

Sensors for any gas

In this study, the researchers focused on pure carbon nanotubes, but they are now working on tailoring the sensors to detect 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.

One gas the researchers are particularly interested in is ethylene, which would be useful for monitoring the ripeness of fruit as it is shipped and stored. The team is also pursuing for sulfur compounds, which might prove helpful for detecting natural gas leaks.

Explore further: Super Sensitive Gas Detector Goes Down the Nanotubes

Related Stories

Super Sensitive Gas Detector Goes Down the Nanotubes

January 13, 2009

When cells are under stress, they blow off steam by releasing minute amounts of nitrogen oxides and other toxic gases. In a recent paper,* researchers at the National Institute of Standards and Technology described a new ...

Nanotubes Sniff Out Cancer Agents in Living Cells

January 16, 2009

(PhysOrg.com) -- A multidisciplinary team at the Massachusetts Institute of Technology (MIT) has developed carbon nanotubes that can be used as sensors for cancer drugs and other DNA-damaging agents inside living cells. The ...

New biosensor benefits from melding of carbon nanotubes, DNA

November 15, 2011

Purdue University scientists have developed a method for stacking synthetic DNA and carbon nanotubes onto a biosensor electrode, a development that may lead to more accurate measurements for research related to diabetes and ...

Researchers devise new means for creating elastic conductors

January 24, 2012

Researchers from North Carolina State University have developed a new method for creating elastic conductors made of carbon nanotubes, which will contribute to large-scale production of the material for use in a new generation ...

Comparing apples and oranges

April 30, 2012

Every year, U.S. supermarkets lose roughly 10 percent of their fruits and vegetables to spoilage, according to the Department of Agriculture. To help combat those losses, MIT chemistry professor Timothy Swager and his students ...

Recommended for you

Physicists develop new technique to fathom 'smart' materials

November 26, 2015

Physicists from the FOM Foundation and Leiden University have found a way to better understand the properties of manmade 'smart' materials. Their method reveals how stacked layers in such a material work together to bring ...

Mathematicians identify limits to heat flow at the nanoscale

November 24, 2015

How much heat can two bodies exchange without touching? For over a century, scientists have been able to answer this question for virtually any pair of objects in the macroscopic world, from the rate at which a campfire can ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Oct 10, 2012
Let's suppose that this sensor doesn't stolen by the MIT quasi-researchers as some other nanosensors- http://www.usw.co...activity

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.