Although a number of attempts have been made previously to augment plants’ function with electroactive materials, plants’ ‘circuitry’ has never been directly merged with electronics. Until now.
Researchers at Sweden’s Linköping University Laboratory for Organic Electronics have shown that analogue and digital electronic circuits can be created inside living flowers, bushes and trees using semi-conductive polymers.
And these ‘power plants’, futuristic hybrids of living tissue and inexpensive electronic circuitry, open up exciting new possibilities – from optimising growth using electronic signals received directly from plants’ internal workings, to creating colour-changing plants and developing photosynthesis-powered fuel cells.
A research team at the Laboratory for Organic Electronics led by Professor Magnus Berggren have built the key components of electronic circuits utilising the same channels that distribute water and nutrients in plants.
In an article published in Science Advances, the researchers detail how they’ve created living roses that produce both analogue and digital electronic circuits that, in the long term, could be used, say, to regulate the plant’s physiology.
“The roots, stems, leaves, and vascular circuitry of higher plants are responsible for conveying the chemical signals that regulate growth and functions,” say the researchers in ‘Electronic Plants’, the paper reporting their findings. “From a certain perspective, these features are analogous to the contacts, interconnections, devices, and wires of discrete and integrated electronic circuits.”
In traditional electronics, the signals sent and processed are electrical. In plants, a similar system transports and handles ions and growth hormones.
The emerging field of organic electronics, based on semi-conductive polymers, utilises both ions and electrons as signal carriers. With the help of bioelectronics, the Swedish research team found it was possible to combine electric signals with the plant’s own signalling system, in a sense ‘translating’ the plant’s signals into those of conventional electronics.
The team reported both analogue and digital organic electronic circuits and devices, manufactured in living plants. “The four key components of a circuit have been achieved using the xylem, leaves, veins, and signals of the plant as the template and integral part of the circuit elements and functions,” the paper states.
Once inexpensive organic electronics can be integrated into plants, a vast array of potential uses present themselves – from being able to ‘read’ and thus precisely regulate growth and other inner functions in plants, to utilising photosynthetic energy in fuel cells.
“Previously, we had no good tools for measuring the concentration of various molecules in living plants. Now we’ll be able to influence the concentration of the various substances in the plant that regulate growth and development. Here, I see great possibilities for learning more,” says Ove Nilsson, professor of plant reproduction biology at the Umeå Plant Science Center and co-author of the article.
How did it come about?
Since the early 1990s, Magnus Berggren – professor of Organic Electronics at Linköping University’s Norrköping campus – has been researching printed electronics on paper.
Now and then the idea of putting electronics into the tree itself cropped up, but research funders were indifferent – until the end of 2012, when independent research money came in from the Knut and Alice Wallenberg Foundation. The funds enabled Professor Berggren to hire three recent PhD graduates, Roger Gabrielsson, Eleni Stavrinidou and Eliot Gomez, to investigate – under senior scientific guidance – the feasibility of introducing electronics into living plants and, potentially, producing them in plant tissue.
By 2015, not much more than two years after they began their investigation, the group had managed to get living plants to produce both analogue and digital circuits.
Searching for a suitable PEDOT (aka poly 3,4-ethylenedioxythiophene, distinguished from many other polymers in that it is both a conductor and transparent), Gabrielsson found the polymer PEDOT-S, which turned out to be soluble in water. When it was absorbed into plant tissue – in a rose, for instance – the polymer was converted into a hydrogel, which formed a thin film along the channel through which the bloom absorbs water and nutrients.
Stavrinidou then got the test plants to produce 10-centimetre segments 50 centimetres thick, consisting of membranes – or ‘film’ – of the conductive PEDOT-S polymer. With an electrode at each end and a gate in the middle, the researchers had successfully created an analogue transistor in a plant.
“We’ve produced the perfect measurement values, which show that it really is a fully functional transistor,” claims Stavrinidou, who has measured the conductive ability of the polymer from 0.13 siemens [siemens being the SI unit for conductivity] per centimetre to as high as 1 siemens per centimetre.
Gomez used vacuum infiltration, a method common in plant biology, to send another PEDOT variant, along with nanocellulose fibres, into the foliage of the rose. When he did so the cellulose formed a 3-D structure with small cavities (like those you might find in a sponge) inside the leaf of the rose that filled with the conductive polymer.
Electrochemical cells were thus formed, with a number of pixels, partitioned by the veins. The electrolytes came from the fluid in the leaf, which suggests that the leaf functions in a similar way as does the printed character display on a roll manufactured at Acreo Swedish ICT in Norrköping.
“We can create electrochromatic plants in which the leaves change colour – it’s cool, but maybe not so useful,” Gomez says.
Potential uses for electronic plants
But the electronic plant has potential uses that are far less frivolous than disco-light leaves.
“With integrated and distributed electronics in plants, one can envisage a range of applications including precision recording and regulation of physiology, energy harvesting from photosynthesis, and alternatives to genetic modification for plant optimisation,” the researchers state in Science Advances.
For a start, what is usually a weakness of organic electronics – cold and wet environs – is avoided by encasing bioelectronics in a plant. As the tissue fully encapsulates the polymer, it is protected from wind and rain. “It seems as if the polymers we use had been created for their function,” notes Gabrielsson.
Professor Berggren sees an even bigger picture; an entirely new field of research opening up as a result of the new development.
“Now we can really start talking about ‘power plants’ – we can place sensors in plants and use the energy formed in the chlorophyll, produce green antennas or produce new materials,” he says. “Everything occurs naturally, and we use the plants’ own very advanced, unique systems.
“It [is] a new form of controlling and regulating electrochemistry in conductive polymers,” Professor Bergrren says. “As far as we know, there are no previously published research results regarding electronics produced in plants. No-one’s done this before.”
Read the article: ‘Electronic Plants’, by Eleni Stavrinidou, Roger Gabrielsson, Eliot Gomez, Xavier Crispin, Ove Nilsson, Daniel T Simon and Magnus Berggren, in Science Advances, DOI 10.1126/sciadv.1501136