MIT engineers created sensors that can be printed onto plant leaves and reveal when the plants are experiencing a water shortage.

But gives farmers an early warning when their crops are in danger, says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of the new study.

“This appears to be the earliest indicator of drought that we have for agricultural applications,” Strano says. “It’s hard to get this information any other way. You can put sensors into the soil, or you can do satellite imaging and mapping. But you never really know what a particular plant is detecting as the water potential.”

Transpiration process

The new MIT sensor takes advantage of plants’ stomata small pores in the surface of a leaf that allow water to evaporate. As water evaporates from the leaf, water pressure in the plant falls. Allowing it to draw water up from the soil through a process called transpiration.

“People already knew that stomata respond to light, to carbon dioxide concentration, to drought, but now we have been able to monitor it continuously,” Koman says. “Previous methods were unable to produce this kind of information.”

Researchers used an ink made of carbon nanotubes and tiny hollow tubes of carbon to develop sensor that conduct electricity dissolved in an organic compound called sodium dodecyl sulfate, does not damage the stomata.

This ink printed across a pore to create an electronic circuit. When the pore is closed, the circuit is intact and the current measured by connecting the circuit to a device called a multimeter. When the pore opens, the circuit is broken and the current stops flowing, allowing the researchers to measure, very precisely, when a single pore is open or closed.

Seven minutes to open after light exposure and 53 minutes to close when darkness falls

By measuring this opening and closing over a few days. Under normal and dry conditions, the researchers found that they can detect, within two days. When a plant is experiencing water stress. They found that it takes stomata about seven minutes to open after light exposure and 53 minutes to close when darkness falls.

But these responses change during dry conditions. When the plants deprived of water, the researchers found that stomata take an average of 25 minutes to open. While the amount of time for the stomata to close falls to 45 minutes.

The researchers tested the sensors on a plant called the peace lily. They chose in part because it has large stomata. To apply the ink to the leaves, the researchers created a printing mold with a microfluidic channel. When the mold placed on leaf, ink flowing through the channel deposited onto the leaf surface.

The MIT team is now working on a new way to apply the electronic circuits. By simply placing a sticker on the leaf surface. In addition to large-scale agricultural producers, gardeners and urban farmers interested in such device, the researchers propose.