Electronic plants: New transistors made of wood could help in agriculture and forest management

The wooden transistors can be used as sensors in trees and other plants.
Sejal Sharma
The wooden transistor
The wooden transistor

Van Chinh Tran 

Wood, although an insulator, has been previously modified with conductive materials for use in batteries, supercapacitors, and other electrical systems. Though its varied usage indicates that wood has huge potential for energy and electronic technology, there is evidently no record of an electrical transistor made out of wood.

Now, a team of researchers in Sweden has made an electrochemical transistor carved out of balsa wood. This opens up the possibility of installing sensors and other electronic gadgets in plants and living trees, which could help in agriculture and forest management.

Isak Engquist, a co-author of the study, told New Scientist: “There is an emerging research field called electronic plants, where scientists look at different ways to send signals inside plants or to incorporate functionality such as sensors in plants, even in living plants.”

The researchers used balsa wood modified with conducting polymers, which are electrically conductive materials composed of organic polymers. The team then removed lignin, which transports water and provides mechanical support and resistance to stresses from the wood. With the removal of lignin, there is higher porosity in the cell walls of wood. As a result of which, when the wood was soaked in a liquid solution containing a conductive polymer, the wood was able to absorb it better. The diffusion saw a higher electrical conductivity in the wood.

The team then ran several switching tests to check the transistor’s operations and concluded that their transistor exhibited similar switching properties to that of organic electrochemical transistors. In a preliminary test, the team also tested birch and ash along with balsa but observed that balsa performed better in preparing high–CW electrodes.

Taking their research on the wood-based device to the next level, the team will work on incorporating and growing conductive wood with the polymer already inside, Engquist told New Scientist. “It seems most probable that each piece of wood, or each plant, would incorporate only a few wood electrochemical transistors, and that these would be on the millimetre-size scale.”

Study abstract:

The nature of mass transport in plants has recently inspired the development of low-cost and sustainable wood-based electronics. Herein, we report a wood electrochemical transistor (WECT) where all three electrodes are fully made of conductive wood (CW). The CW is prepared using a two-step strategy of wood delignification followed by wood amalgamation with a mixed electron-ion conducting polymer, poly(3,4-ethylenedioxythiophene)–polystyrene sulfonate (PEDOT:PSS). The modified wood has an electrical conductivity of up to 69 Sm−1 induced by the formation of PEDOT:PSS microstructures inside the wood 3D scaffold. CW is then used to fabricate the WECT, which is capable of modulating an electrical current in a porous and thick transistor channel (1 mm) with an on/off ratio of 50. The device shows a good response to gate voltage modulation and exhibits dynamic switching properties similar to those of an organic electrochemical transistor. This wood-based device and the proposed working principle demonstrate the possibility to incorporate active electronic functionality into the wood, suggesting different types of bio-based electronic devices.

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