Wearable Plant Sensors

Plant scientists are now able to measure the time it takes for corn plants to move water from their roots, to their lower leaves, and then to their upper leaves.

Patrick Schnable, Iowa State University plant scientist, says, this new, low-cost, easily produced, graphene-based, sensors-on-tape can be attached to plants and provide new kinds of data to researchers and farmers.

This type of tool will allow researchers to breed plants that are more efficient in water use. "We couldn't do this before," says Schable. "But once we can measure something, we can begin to understand it."

The tiny graphene sensor – a carbon honeycomb just an atom thick – capable of conducting electricity and heat, can be taped to plants. It's been dubbed the "plant tattoo sensor" by researchers and is the tool that makes water measurements possible. 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.

Researchers describe the various sensors and the "simple and versatile method for patterning and transferring graphene-based nanomaterials" to create the flexible sensors in a paper featured on the cover of the December 2017 issue of the journal Advanced Materials Technologies. The research has been primarily supported by the Faculty Scholars Program of Iowa State's Plant Sciences Institute.

"We're trying to make sensors that are cheaper and still high performing," says Liang Dong, an Iowa State associate professor of electrical and computer engineering, the lead author of the paper and developer of the technology.

They 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, says Dong.

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.

"This fabrication process is very simple," says Dong. "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 says.

A new three-year, $472,363 grant from the U.S. Department of Agriculture's Agriculture and Food Research Initiative will support more field testing of water transport in corn plants. Michael Castellano, an Iowa State associate professor of agronomy and William T. Frankenberger, professor in soil science, will lead the project. Coinvestigators include Dong and Schnable.

The Iowa State University Research Foundation has applied for a patent on the sensor technology.

"The concept of wearable electronic sensors for plants is brand-new," says Dong. "And the plant sensors are so tiny they can detect transpiration from plants, but they won't affect plant growth or crop production."

That's not all the sensors can do. The technology could open a new route for a wide variety of applications, the authors wrote in their paper, including sensors for biomedical diagnostics, for checking the structural integrity of buildings, for monitoring the environment and, after appropriate modifications, for testing crops for diseases or pesticides.