Tape one atom thick measures plant growth

A clear strip of graphene tape, just one atom thick and housing hundreds of microscopic sensors, tells plant breeders which strains best use water and nutrients and therefore grow faster.

In corn breeding experiments at Iowa State University, the sensors allow researchers to measure the time it takes for two kinds of corn plants to move water from their roots up to their lower leaves and then to their upper leaves. The new, low-cost graphene-based tapes are easily produced. Sensors on the tape can provide new kinds of data to researchers and farmers.

“With a tool like this, we can begin to breed plants that are more efficient in using water,” he said.

“That’s exciting. We couldn’t do this before. But once we can measure something, we can begin to understand it,” says Iowa State plant scientist Patrick Schnable.

According to the university, graphene has been dubbed a wonder material. It’s a carbon honeycomb just an atom thick. It’s great at conducting electricity and heat, and it’s strong and stable. The graphene-on-tape technology in this study has also been used to produce wearable strain and pressure sensors, including sensors built into a “smart glove” that measures hand movements.

Lead researcher on the project is Liang Dong, associate professor of electrical and computer engineering, who said they are trying to make the sensors cheaper without sacrificing performance. They have developed a process for fabricating intricate graphene patterns on tape.

“This fabrication process is very simple. You just use tape to manufacture these sensors. The cost is just cents,” Dong said.

“The process can produce precise patterns as small as five millionths of a metre wide. That’s just a twentieth of the diameter of the average human hair. Making the patterns so small increases the sensitivity of the sensors.”

Researchers first create indented patterns on the surface of a polymer block, using a molding or 3-D printing process. Then they apply a liquid graphene solution to the block, filling the indented patterns. Tape is used to remove the excess graphene. Then they take another strip of tape to pull away the graphene patterns, creating a sensor on the tape.

In the plant science department, the sensors are made with graphene oxide, which is very sensitive to water vapour. The presence of water vapour changes the conductivity of the material. The amount of vapour is quantified to accurately measure transpiration, or the release of water vapour from a leaf. Dong said the plant sensors have been successfully tested in lab and field experiments.

However, that’s not all the sensors can do. The technology could open a new route for sensors for biomedical diagnostics, checking the structural integrity of buildings, for monitoring the environment for testing crops for diseases or pesticides.

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