New plant sensor to measure water use in crops

Scientists have developed a novel low-cost, graphene-based sensor that can be attached to plants to take real-time, direct measurements of water use in crops.
Using the sensor, researchers at Iowa State University in the US 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.
"With a tool like this, we can begin to breed plants that are more efficient in using water," said plant scientist Patrick Schnable from Iowa State University.
"That is exciting. We could not do this before. But, once we can measure something, we can begin to understand it," said Schnable.

The tool making these water measurements possible is a tiny graphene sensor dubbed "plant tattoo sensor" that can be taped to plants.
Graphene is a wonder material. It is a carbon honeycomb just an atom thick, it is great at conducting electricity and heat, and it is strong and stable.

"We are trying to make sensors that are cheaper and still high performing," said Liang Dong, associate professor at Iowa State, and lead author of the study published in the journal Advanced Materials Technologies.
The researchers have developed a process for fabricating intricate graphene patterns on tape.
Dong said the first step is creating indented patterns on the surface of a polymer block, either with a molding process or with 3D 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 five millionths of a metre wide - just a twentieth of the diameter of the average human hair.
Dong said making the patterns so small increases the sensitivity of the sensors.
In the case of plant studies, the sensors are made with graphene oxide, a material very sensitive to water vapour.

The presence of water vapour changes the conductivity of the material, and that can be quantified to accurately measure transpiration (the release of water vapour) from a leaf.
The plant sensors have been successfully tested in lab and pilot field experiments, Dong said.