AMES, Iowa — Iowa State University plant scientist Patrick Schnable describes how he measured the time it takes for two kinds of corn plants to move water from their roots to their lower leaves and then to their upper leaves.
This was no technical, precise, poster talk. This was a researcher interested in working with new, low-cost, easily produced, graphene-based, sensors-on-tape that can be attached to plants and 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. “We couldn’t do this before. But, once we can measure something, we can begin to understand it.”
The tool making these water measurements possible is a tiny graphene sensor that can be taped to plants — researchers have dubbed it a “plant tattoo sensor.”
Graphene is 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.
“We’re trying to make sensors that are cheaper and still high performing,” said Liang Dong, an Iowa State associate professor of electrical and computer engineering.
The researchers have developed a process for fabricating intricate graphene patterns on tape. The first step is creating indented patterns on the surface of a polymer block, either with a molding process or with 3-D printing.
Engineers apply a liquid graphene solution to the block, filling the indented patterns. They use tape to remove the excess graphene. Then they take another strip of tape to pull away the graphene patterns, creating a sensor on the tape.
The process can produce precise patterns as small as 5 millionths of a meter wide — just a 20th of the diameter of the average human hair. Dong said making the patterns so small increases the sensitivity of the sensors.
“This fabrication process is very simple,” Dong said. “You just use tape to manufacture these sensors. The cost is just cents.”
In the case of plant studies, the sensors are made with graphene oxide, a material very sensitive to water vapor. The presence of water vapor changes the conductivity of the material, and that can be quantified to accurately measure transpiration (the release of water vapor) from a leaf.
The plant sensors have been successfully tested in lab and pilot field experiments, Dong said.
“The most exciting application of the tape-based sensors we’ve tested so far is the plant sensor,” Dong said. “The concept of wearable electronic sensors for plants is brand new. And the plant sensors are so tiny they can detect transpiration from plants, but they won’t affect plant growth or crop production.”
But that’s not all the sensors can do. The technology could “open a new route” for a wide variety of applications, including testing crops for diseases or pesticides.
A three-year, $472,363 grant from the USDA’s Agriculture and Food Research Initiative will support more field testing of water transport in corn plants.
The Iowa State University Research Foundation has applied for a patent on the sensor technology.