Such sensors could be useful for not only monitoring household plants and gardens, say the researchers, but agricultural crops as well, where it may also help researchers find new ways to engineer drought-resistant plants. According to the researchers, this approach appears to offer the earliest indicator of drought for agricultural applications.
“It’s hard to get this information any other way," says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the senior author of a paper on the research. "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."
The sensors work by detecting the opening and closing of plant stomata - tiny openings or pores in plant leaves that are used for gas exchange and allow water to evaporate. While it is known that stomata open when exposed to light and close in darkness, this process has not been extensively studied due to difficulties in measuring it in real time.
"People already knew that stomata respond to light, to carbon dioxide concentration, to drought - but now we have been able to monitor it continuously," says Volodymyr Koman, an MIT postdoc and lead author of the paper. "Previous methods were unable to produce this kind of information."
The sensors the researchers created use an ink comprised of carbon nanotubes dissolved in an organic compound that does not damage the stomata. The ink can then be printed across a pore to create an electronic circuit whose current flow remains intact as long as the pore is closed, but is broken when the pore opens.
Using this approach, the researchers found that they were able to detect - within two days - when a plant is experiencing water stress. According to their findings, stomata normally take about about seven minutes to open after light exposure and 53