From wearables for leaves to rose cyborgs, researchers are trying to weave electronics into greenery

There’s a human phenomenon known as “plant blindness.” Used to describe the human perception of plants as mere background noise, plant blindness was a useful evolutionary trait that kept the brain from being overwhelmed by the sheer volume of green surrounding us. But an evolutionary disregard for plants will need to be overcome as we turn to the natural world for solutions to our modern problems.

Anna-Maria Pappa is a researcher at Khalifa University. She says measures to enhance plant productivity and nutrient content are urgently needed — as is a fundamental understanding of plant development and how plants acclimate to environmental stresses:

Plants are increasingly becoming victims of human-caused climate changes, she says. But the classic kind of research in plant sciences that might offer answers can be invasive and may disturb the way plant cells communicate with each other.

Her potential solution? “Real-time, non-invasive plant sensing can be achieved by placing sensors either on the surface of the plant or inserted inside them. Amalgamating plants and electronic materials makes it possible to combine electric signals with the chemical processes of the plant.”

Pappa calls this futuristic technological concept “e-Plants.” Her research uses conjugated polymers — a kind of organic semiconductor — to create electronic devices for bridging the gap between the biotic and the abiotic. Recent research has seen organic electronic materials used in biologically relevant ion sensing, ion pumps and neural activity transducers in humans.

They more seamlessly integrate with complex biological systems and offer more effective signal transduction of biological events. For e-Plants, they can be either “wearable,” where they are placed on the surface of leaves or stems, for example, or implantable.

Conjugated polymers are mixed conductors. The electronics surrounding us in our daily lives use electrons as the dominant charge carrier; biological systems use ions.
Conjugated polymers can use both, which makes them perfect for direct coupling with biological systems.

Plus, they’re flexible and light. The ease and versatility of integrating flexible polymers instead of hard metals into delicate biological structures is an obvious advantage on top of their other inherent advantages over conventional electronics, Pappa says.

“As in conventional bioelectronics devices, plant-integrated bioelectronics enable bidirectional communication through sensors that can translate plant biosignals to electronic readouts and actuators that can modulate their biological functions,” Pappa explains.

“The combination of ionic and electronic carriers aids signal transduction not only for sensing, but also for converting electronic signals into the specific delivery of chemicals. This could be a key measure for enhancing sustainable farming, which is the main pillar of the fast-growing agricultural revolution we are now facing.”

FLOWER POWER

Pappa’s research focuses on developing hydrogel materials from those polymers that can augment plant seeding and growth in environments that are not that favorable, but that’s not the only avenue for e-Plant technology.

A team of researchers from Sweden’s Linkoping University went down the implantable route, developing a molecule that can be absorbed and polymerized inside the plant, creating long threads throughout that conduct electricity.

Similar to dyeing a flower by feeding it a solution with food coloring, the researchers dissolved a molecule called ETE-S into a solution that was transported through the vascular system of a rose. The ETE-S polymerized throughout this network, turning it electronic.

During photosynthesis, plants use sunlight to split water atoms into hydrogen and oxygen.

The electrons released are used to combine with carbon to produce sugars, but researchers at the University of Georgia have developed a way to interrupt this pathway, capturing the electrons before they can be squirreled away into sugar molecules.

Ramaraja Ramasamy led the team in manipulating the proteins contained in thylakoids, the structures in plants responsible for capturing and storing energy from sunlight. The modified thylakoids were then immobilized on carbon nanotubes, which act as electrical conductors, funneling the electrons from plant cells and out along wires.

A team of researchers at the University of Cambridge discovered something similar. Using ultrafast transient absorption spectroscopy (lasers at speed), the team observed electrons moving through the photosynthetic process.

They identified what they described as a “leaky pathway”: The cell in which photosynthesis starts was leaking electrons. Gathering these electrons could be a way to generate renewable energy from a self-generating, carbon-sequestering source — a truly green energy.

While the photosynthesis process has been honed over millions of years of plant evolution, it could always be better.

Michael Strano is a self-described “plant hacker” at MIT. In 2014, his team managed to insert nano-machines into a plant’s chloroplasts. Before this (literal) breakthrough, there wasn’t a way to penetrate the cell wall of the structures used by plants for photosynthesis. Strano’s team coated their nano-machines with electrically charged molecules, which were absorbed by the chloroplasts.

They weren’t doing this just to see if they could. Chloroplasts use chlorophyll, a pigment that absorbs blue and red light and reflects green — hence, greenery. If a chloroplast can be “re-wired” to absorb a wider range of light wavelength, theoretically, it should see a boost in productivity. Strano’s nanobionic plants produced 30 percent more energy from sunlight than their control counterparts.

Combine this plant hacking with the techniques to harvest electrons and we could have veritable power plants at our disposal for all our energy needs.

FEED THE WORLD

The interplay between nanobionic approaches and electroactive plants, what Pappa calls “biohybrids,” could have large implications for agriculture, making plants a technically advanced system to tackle and adapt environmental stresses beyond their natural capacity, as well as to better complement modern urban ecosystems.

“Current research in this area is only the tip of the iceberg,” Pappa says. “This is despite the significant advances in the fields of bioelectronics and materials sciences, mainly for human applications.” Pappa’s own previous research has been focused on developing bioelectronics for in vitro applications in drug design and so-called “membrane-on-chip” devices that use conducting polymer electrodes and transistors to interface with human cell membranes.

“Considering the advancements in bioelectronics, material sciences, synthetic biology and artificial intelligence, a few plants could be used as model indictors to understand the fundamentals for optimizing and correlating productivity on a larger scale,” she says.

“Although they might appear as science fiction, plant-integrated technologies could be the future of not only agriculture, but also modern urban ecosystems, as light-emitting, energy-generating or -storing, -sensing and -communicating biohybrid plants,” Pappa says. “We need to harness the potential of plants if we want to realize the goal of zero hunger by 2030.”

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