Who would have thought that your living-room ficus might someday be part of the Internet of Things? A team of researchers led by Professor Magnus Berggren at Linköping University in Sweden have found a method of convincing cut roses to tolerate having a conductive-but-hydrated polymer related to polystyrene, called PEDOT, present in their stems. (Rumor has it wine and a nice dinner were part of the requirements.)
Since the polymer is compatible with dissolution in water, the rose drew the polymer into its stem along with the water in which it was dissolved, and when it cured, it created a length of delicate wires threading along the anatomical pathways traced out by the xylem. This produced a living plant with a network of conductive fibers traveling through intact anatomical pathways: a first in the study of organic electronics.
Individual researchers on the project have gone on to make different advances from the same basic discovery. Dr. Eleni Stavrinidou used a PEDOT variant to grow long (10cm, 4-inch) wires in the xylem lines of a rose, and then used their interaction with the electrolytic environment of the xylem to successfully demonstrate an electrochemical logic circuit: a transistor-like logic gate that can convert ionic flux into digital signals.
To say nothing of the obvious implications for organic semiconductors, this is a process not unlike signal transduction in the human nervous system. When a nerve fires, an action potential travels down the axon much, much faster than the speed at which chemical signals can be transmitted through sessile plant tissues and rigid plant cell walls. And action potentials represent a digital aspect of the human nervous system: Either a nerve fires or it doesn’t, all or nothing, one or zero. Biological computation may be much closer than we think, and much easier to understand by modeling low-level physiological computational architecture in plants without dissecting the human brain.
What’s more, during the same project, Dr. Eliot Gomez used a vacuum to perfuse another PEDOT variant into the leaves of a live cut rose, forming “pixels” separated by the veins — when voltage was applied to the leaves, the pixels actually changed color due to ionic interactions, changing the color of the leaf something like a cross between an active-matrix OLED/FOLED and an LCD. The leaves changed color in response to differential voltage without actually emitting light, which is more like an LCD (and, sadly, not as much like James Cameron’s Avatar as I had hoped). But the architecture achieved by Dr. Gomez is organized without a central driver controlling each individual pixel: each cell could be controlled by an associated discrete electrode, like an OLED.
In other words, someday your potted plants could change color to match what’s playing on your TV or stereo. Imagine shrubs that had color programs you could change for the holidays, instead of putting up lights.
But why on earth do we want to put wires in plants in the first place? Aren’t plants doing fine on their own? To address the practical impact of this organic-electronics project, the study’s lead author punned on “power plants,” pointing out that such plants could be externally controlled according to environmental cues, like an untimely freeze or dry spell, or even used as antennas for sophisticated communication between fields or groves.
Perhaps just as interesting to the world of medical pharmacology, these fibers may provide an incredibly sophisticated way of measuring the flow of molecules within and between cells in plants — opening up avenues for isolating the pharmacodynamics of plant-based medicines. Such remedies occupy crucial, if underpublicized, positions in medicine: paclitaxel, for example, is an anticancer drug originally isolated from the yew tree, and atropine from deadly nightshade is used as an antidote to organophosphate poisoning. Medical, technological and aesthetic opportunities abound.
While biological semiconductors are still an emergent field in the throes of primary research, this study demonstrates clear proof of concept. Given that Linköping University has an entire department called the Laboratory of Organic Electronics, we expect more developments along this vein in the not-too-distant future.
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