Compared to most animals, plants use much subtler forms of communication, emitting faint electrical signals in response to environmental changes. For years, scientists have been trying to pick up and decode this elusive plant ‘language’—signals that could hold clues to improving agricultural practices and protecting vulnerable species.
However, devices used to capture these signals often cannot do so without damaging delicate leaves and stems. So far, non-invasive measurement technologies have fallen flat as their electrodes cannot conform to the intricate structures and surface features of plants, being too rigid or adhering too weakly to take reliable measurements.
The fine, hair-like structures that cover the stems of most plants are among the most challenging topographies to tackle, said Xian Jun Loh, Executive Director at A*STAR’s Institute of Materials Research and Engineering (IMRE). In collaboration with Nanyang Technological University, Singapore’s Xiaodong Chen, Loh sought to develop technologies for measuring electrical signals from a wide array of plants, even those with complex surface structures.
The researchers developed a novel material that simultaneously conforms and sticks to plants while connecting the plant to the attached electrodes. This thermogel was created using a specialized polymer developed in Loh’s lab that transforms from a liquid to a solid substance when heated. Applied cold, the thermogel molds perfectly to irregular hairy surfaces before gradually solidifying on stems and leaves as it warms to room temperature.
This chemical reaction, known as a sol-gel transition, sets the new adhesive material apart from others on the market. “The unique sol-gel behavior allows the gel to form good adhesive links to the plant surface, unlike other types of hydrogel,” Loh said.
Loh and the team showed that the thermogel remained attached even when stretched 20 times from its original thickness in a strength test. This powerful adhesive strength translated to more sensitive signals; when applied to hairy sunflower stems, the morphable electrode recorded signal amplitudes about 2.4 times greater than those measured by a solid hydrogel.
According to the authors, the beauty of the team’s new thermogel is that while it sticks on firmly, it can also be easily removed without damaging delicate plant structures. Simply cooling the gel causes it to revert to its fluid state, which allows the electrode to be gently removed.
“Our morphable electrode provides not only a useful toolkit for fundamental plant studies but also an effective solution for plant-electronic hybridization, offering inspiration for soft material-incorporated bioelectronics,” Loh concluded.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).