An anonymous reader shared this report from IEEE Spectrum:
Transistors inside modern computer chips are several nanometers across, and switch on and off at hundreds of gigahertz. Organic electrochemical transistors, made for biodegradable applications, are milimeters in size and switch at kilohertz rates. The world’s first wooden transistor, made by a collaboration of researchers through the Wallenberg Wood Science Center and reported this week in Publications of the National Academy of Sciences, is 3 centimeters across and switches at less than one Hertz. While it may not be powering any wood-based supercomputers anytime soon, it does hold out promise for specialized applications including biodegradable computing and implanting in into living plant material.
“It was very curiosity-driven,” says Isak Engquist, a professor at Linköping University who led the effort. “We thought: ‘Can we do it? Let’s do it, let’s put it out there to the scientific community and hope that someone else has something where they see these could actually be of use in reality…'”
Wood has great structural stability while being highly porous and efficiently transporting water and nutrients. The researchers leveraged these properties to create conducting channels inside the wood’s pores and electrochemically modulate their conductivity with the help of a penetrating electrolyte. Of the 60,000 species, the team chose balsa wood for its strength, even when one of the components of its structure — lignin — was largely removed to make more room for conducting materials. To remove much of the lignin, pieces of balsa wood were treated with heat and chemicals for five hours. Then, the remaining cellulose-based structure was coated with a conducting polymer…
Since the pores inside wood are made for transporting water, the PEDOT:PSS solution readily spread through the tubes. Electron microscopy and X-ray imaging of the result revealed that the polymer decorated the insides of the tube structures. The resulting wood chunks conducted electricity along their fibers.