When tobacco cells meet carbon nanotubes

For more than half a century, biologists have known that living plants respond sensitively to changes in temperature through changes in their electrical conductivity. But that sensitivity disappears when they die. By growing tobacco cell cultures in the presence of carbon nanotubes, Raffaele Di Giacomo and his colleagues at ETH Zürich and the University of Salerno in Italy have now permanently stabilized the temperature response. The nanotubes penetrate the cell walls and form an intracellular network, which confers structural integrity and electrical conductivity to the resulting composite. Even if dead and dehydrated, as shown here, the material, which the researchers dub cyberwood, can be fashioned into an electrical circuit. After affixing gold contacts to a sample and applying a voltage across them, the researchers found that the sample’s electrical resistance decreases by almost three orders of magnitude over a range of 40 °C. That corresponds to an effective temperature coefficient of resistance (TCR) of −1730% K⁻¹. By comparison, vanadium oxide, the sensor of choice in today’s thermal cameras, has a TCR of about −6% K⁻¹ in the same temperature range. Through a series of tests, the researchers determined that the extremely high sensitivity arises from the temperature-dependent release of calcium ions from pectin, the polysaccharide molecule that confers strength and expansibility to cell walls. (R. Di Giacomo, C. Daraio, B. Maresca, Proc. Natl. Acad. Sci. 112, 4541, 2015 .)