Plant Bling - Tape Tattoos and Graphene Sensors

Engineers at Iowa State University, in Ames Iowa, have been working on some exciting new technologies for agriculture - graphene-based sensors that go on tape. These low-cost, easy to produce sensors can be attached to plants and can provide new kinds of data to researchers and farmers.

Growing up on a farm, in Iowa nonetheless, I learned at an early age, the importance of not only rain, but the right amount of it. I also learned rather quickly, that there’s nothing you can do about the rain, other than hope for it. The right amount of rain, at the right times throughout the growing season, coupled with a myriad of other uncontrollable variables that would hopefully go your way that year, would normally result in the highest yield possible for your crops.

Since early on in human history, as far as crops are concerned, humans would select the best individual performing plants to breed to create seeds with the highest possible yield. In more recent history, improvements in this process have allowed companies to improve their seed by breeding specific plants in an effort to make them more drought resistant, disease resistance, stress tolerant, etc.

While there is still no magic technology that can control the rain, thanks to researchers at Iowa State University, there are now tools to help breed plants that produce seed that can optimize the rain it does receive over a growing season.

"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.", explained Iowa State University plant scientist Patrick Schnable.

This technology has allowed Schnable to measure 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. Plant “tattoos” made of tiny graphene sensors that can be taped to plants, have made this possible. The graphene is a carbon honeycomb that is just an atom thick and in addition to being very strong and stable, it’s very good at conducting electricity and heat.

The process for fabricating intricate graphene patterns on tape starts with creating indented patterns on the surface of a polymer block, either with a molding process or with 3-D printing. Engineers then apply a liquid graphene solution to the block, filling the indented patterns. Next they use tape to remove the excess graphene. Finally they take another strip of tape to pull away the graphene patterns, creating a sensor on the tape. This process can produce patterns as small as 5 millionths of a meter wide. To help visualize that, it’s just a twentieth of the diameter of the average human hair. Researches explained that making the patterns so small increases the sensitivity of the sensors. This same graphene-on-tape technology has even been used to produce wearable strain and pressure sensors, including sensors built into a "smart glove" that measures hand movements

Liang Dong, an Iowa State associate professor of electrical and computer engineering, is the lead author of the paper and developer of the technology. He explains, "This fabrication process is very simple, you just use tape to manufacture these sensors. The cost is just cents."

For use in studying plants, the sensors are made with graphene oxide, a water vapor sensitive material. 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.

These plant sensors have already been successfully tested in both lab and pilot field experiments, and a new three-year, $472,363 grant from the U.S. Department of Agriculture's Agriculture and Food Research Initiative will support additional 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. Co-investigators include Dong and Schnable.

In addition to testing water transport in plants, this technology could lead to additional 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.