Tinkering with wood turned an insulator into a tree transistor

But don’t expect to see lumber-based transistors in your next iPhone.
Green forest with sun shining through trees
Wood is a natural insulator, but can be turned into a solid conductive material. Deposit Photos

It’s often one of the earliest science facts learned in grade school: Wood is a natural insulator. For those who need a refresher, that simply means the material generally isn’t a great conductor for electricity. But as elementary as that information may be, a team of researchers have added an asterisk to the rule of thumb: It turns out some wood, once tweaked, can conduct electricity. What’s more, they can be converted into natural transistors.

According to a paper recently published in Proceedings of the National Academy of Sciences, engineers at Sweden’s Linköping University successfully altered balsa wood by first leeching it of lignin—a natural binding substance found in wood and other plantlife. Once the lignin is removed, what remains is a network of tubing that transports water throughout the balsa known as lumina. The remaining hollowed balsa can be submerged in a liquid solution containing an electrically conductive polymer. What results is a material that can transport electrolyte-containing water through its lumina, and a new, natural transistor.

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Before balsa, the team attempted to engineer conductive wood with other samples, including birch and ash. These alternatives, however, didn’t not possess the same levels of structural integrity after being submerged in the polymer solution, nor did they properly absorb the polymer. The team also noted that, unlike its other test options, balsa displays a compositional ubiquity throughout the year’s seasons.

But don’t expect to see wood transistors in your next iPhone. Compared to modern silicon transistors, the team’s wood variation is much larger and slower. As New Scientist explains, a single fingernail-sized computer chip today frequently contains billions of transistors, each of which can switch on and off billions of times a second. A single balsa transistor, by comparison, is roughly three centimeters long. On top of that, it takes one second to switch off, and around five seconds to switch back on.

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Still, wood transistors show immense promise in other areas, such as forestry and agricultural monitoring. Wood conductors are also more sustainable than existing alternatives, and could even be used to monitor flora resistance to climate change and other environmental issues. Going forward, researchers told New Scientist they hope to one day grow wood samples with conductive polymers already inside them via using different versions that enter the wood without needing to remove lignin.