The graphene-based ‘tattoo’ sensors are easily produced, and can be taped to plants. The technology was developed by researchers at Iowa State University, building on previous work with graphene that had been used to create wearables for humans.
In the case of plants, the sensors use graphene oxide – a material which changes conductivity in the presence of water vapour, and can therefore be used to accurately measure when it is released from a leaf.
“With a tool like this, we can begin to breed plants that are more efficient in using water,” said plant scientist Patrick Schnable. “That’s exciting. We couldn’t do this before. But, once we can measure something, we can begin to understand it.”
To fabricate the intricate graphene patterns on the tape, the engineers first created indents on the surface of a polymer block, using either moulding or 3D-printing, explained lead author Liang Dong. They then filled those indents with a liquid graphene solution, and used tape to remove the excess graphene.
Finally, another piece of tape is used to pull away the patterns – creating a sensor on the tape, with patterns that can be twenty times smaller than the width of a human hair, thus increasing the sensitivity of the sensor. “This fabrication process is very simple," Dong said. "You just use tape to manufacture these sensors. The cost is just cents.”
The sensors have been successfully tested in both laboratory and field settings, and will now be further developed with a grant from the US Department of Agriculture. “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.”
Similar technology could also be used for a number of other applications, according to the authors, including biomedical sensors, structural sensors for buildings, or testing crops for diseases.
Graphene was first discovered in 2004 by scientists at the University of Manchester, but it took until 2015 for the first commercial applications to hit the market. Progress is now accelerating for this so-called ‘wonder material,’ with running shoes and wearables being developed.
However, there remain problems with mass-producing the thin sheets of carbon. “Current strategies to produce graphene use and waste copious amounts of harsh chemicals and also waste high-purity deionised water,” University of Illinois researcher Michael Cai Wang told PE last month.
Clive Backer, a director at agricultural technology firm Precision Decisions, told PE that he is "a big believer in using the plant as a sensor". "While we can monitor and measure the physical environment, we still don't understand all the factors that can influence plant growth or stress."
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.