A rose by any other name would… conduct electricity? The worlds of botany and consumer electronics don’t typically overlap. But a new device has merged electronics with biology, taking a step towards a world in which plants and computers are more intertwined.
The breakthrough came earlier this year in a lab in southern Sweden. Magnus Berggren, a professor of organic electronics at Linköping University, led a team that built a working electronic circuit from an ordinary garden rose by filling its veins with conductive polymer.
The experiment opens the door for electronics that can plug into plants. Living tissues are known to be conductive – with living slime moulds already finding their way into gadgets – and plants are no exception. Propositions dreamed up by scientists include photosynthesis-powered fuel cells and crops that keep tabs on their own physiological properties.
But first, the Linköping team had to figure out whether it was even possible to weave electronics into the flesh of a plant – and they struggled to find a suitable conductive material. It had to be water-soluble, with decent electrical conductivity, and be able to travel through a plant’s vascular system and form wires. Many materials that the researchers tried turned out to be toxic for the rose, clogging up at the opening of the stem or failing to stick to the inner surface of the plant’s veins – the xylem.
Finally, they found one that worked. PEDOT, or poly(3,4-ethylenedioxythiophene), is a classical conducting polymer used in traditional electronics. The researchers soaked a garden rose, with its roots and leaves removed, in a solution of PEDOT. Over the course of a couple of days, the polymer was taken up by the plant’s network of xylem and then solidified inside it as a gel. When they peeled away the outer bark and tissue at the bottom of the stem, the researchers could see slender dark wires winding through the rose.
Eleni Stavrinidou, a postdoctoral researcher who did much of the work, went to show Berggren. “When Eleni showed me these beautiful microscope pictures, we understood immediately: we could make circuits out of this,” Berggren says. “The performance, the shape of the wires, were just outstanding, unbelievable.”
The team used the xylem wires to make a transistor – a basic building block of computing and electronics. They tacked gold electrodes and probes along the length of the plant, then connected it to an external resistor and ran a current through it.
In a second experiment, they flushed PEDOT into the rose’s leaves, forcing the polymer into its pores using a basic pressure chamber. When they ran a current across the leaf, they saw its colours changing faintly in response to the voltage.
The Linköping group aren’t the first to try plugging into plant life. In 2012, a team at Disney Research led by Ivan Poupyrev linked orchids with a sensing technology that could measure how electricity moved through the plant. Their project, nicknamed Botanicus Interacticus, allowed the scientists to track and visualise the movements of a human hand along the plant’s body. At Massachusetts Institute of Technology, chemical engineer Michael Strano has created “Iron Man” plants with photosynthesis-boosting nanomachines buried deep inside their chloroplasts.
Although the research on the electronic rose takes several important first steps towards transforming plants into electronics, Strano cautions that this isn’t a perfect example of a living circuit. The stem and leaves were severed for the experiment: “both systems,” he says, “are quite dead.”
But he does see promise in these new bioelectronics. Existing devices are made from petroleum-derived plastics and use rare earth metals. Devices like the one from the Linköping lab don’t have these problems. “That is a step in the right direction for sustainable technology,” Strano says.
Berggren and his colleagues are interested in building botanical circuits that let them sense and record changing hormone levels in plants. They imagine future systems that might be able to nudge a plant’s physiological properties in the desired direction, serving as an alternative to genetic modification.
They also think that their biological circuitry could be useful for the paper industry, allowing them to exert more control over growing trees. It was the lab’s interest in trees that led them to experiment on garden roses, with the flower’s bark and root system making it a useful miniature model.
The electronic rose is “yet another wonderful development in the field of living technologies – hybrids of wetware and hardware”, says Andrew Adamatzky, a professor of unconventional computing at the Bristol Robotics Laboratory in the UK, who has experimented in the past with applying voltage to lettuce seedlings.
Adamatzky says this work opens the door to a weird new world: “In the very distant future – neither ourselves nor our kids will see this – we can grow vegetable computers in our gardens.”
Journal reference: Science Advances, DOI: http://advances.sciencemag.org/content/1/10/e1501136
(Image credits: Top: Magda Turzanska/Science Photo Library; Second image: Eliot Gomez/Linköping University)
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