Imagine human-designed ‘bionic’ plants with enhanced energy production that can perform valuable functions such environmental pollutant monitoring. Sort of like plant-based substitutes for conventional machines. Sounds a bit far-fetched? Well, apparently it’s not — in fact, it’s already a reality.
Researchers from MIT have succeeded in substantially boosting the light-capturing abilities of various plants via the implantation of nano-materials, as well as giving the plants completely new functions — such as the monitoring of environmental pollutants.
The gains made with regard to the plants’ ability to capture light energy — an increase of 30% — were achieved through the use of embedded carbon nanotubes in the chloroplast — the plant organelle where photosynthesis takes place. The plants were also then modified with carbon nanotubes in order to be able to detect the gas nitric oxide.
This research represents some of the first in the emerging field of “plant nanobionics.”
Michael Strano, the Carbon P Dubbs Professor of Chemical Engineering, and also the lead researcher behind the new work, explains the appeal of the approach: “Plants are very attractive as a technology platform. They repair themselves, they’re environmentally stable outside, they survive in harsh environments, and they provide their own power source and water distribution.”
In addition to the functions represented in the new work, the researchers see a great many other possibilities, including “turning plants into self-powered, photonic devices such as detectors for explosives or chemical weapons. The researchers are also working on incorporating electronic devices into plants.”
The press release from MIT provides the specifics on how the research was performed:
The idea for nanobionic plants grew out of a project in Strano’s lab to build self-repairing solar cells modeled on plant cells. As a next step, the researchers wanted to try enhancing the photosynthetic function of chloroplasts isolated from plants, for possible use in solar cells.
Chloroplasts host all of the machinery needed for photosynthesis, which occurs in two stages. During the first stage, pigments such as chlorophyll absorb light, which excites electrons that flow through the thylakoid membranes of the chloroplast. The plant captures this electrical energy and uses it to power the second stage of photosynthesis — building sugars.
Chloroplasts can still perform these reactions when removed from plants, but after a few hours, they start to break down because light and oxygen damage the photosynthetic proteins. Usually plants can completely repair this kind of damage, but extracted chloroplasts can’t do it on their own.
To prolong the chloroplasts’ productivity, the researchers embedded them with cerium oxide nanoparticles, also known as nanoceria. These particles are very strong antioxidants that scavenge oxygen radicals and other highly reactive molecules produced by light and oxygen, protecting the chloroplasts from damage.
The researchers delivered nanoceria into the chloroplasts using a new technique they developed called lipid exchange envelope penetration, or LEEP. Wrapping the particles in polyacrylic acid, a highly charged molecule, allows the particles to penetrate the fatty, hydrophobic membranes that surrounds chloroplasts. In these chloroplasts, levels of damaging molecules dropped dramatically.
Using the same delivery technique, the researchers also embedded semiconducting carbon nanotubes, coated in negatively charged DNA, into the chloroplasts. Plants typically make use of only about 10% of the sunlight available to them, but carbon nanotubes could act as artificial antennae that allow chloroplasts to capture wavelengths of light not in their normal range, such as ultraviolet, green, and near-infrared.
With carbon nanotubes appearing to act as a “prosthetic photoabsorber,” photosynthetic activity — measured by the rate of electron flow through the thylakoid membranes — was 49% greater than that in isolated chloroplasts without embedded nanotubes. When nanoceria and carbon nanotubes were delivered together, the chloroplasts remained active for a few extra hours.
The researchers then turned to living plants and used a technique called vascular infusion to deliver nanoparticles into Arabidopsis thaliana, a small flowering plant. Using this method, the researchers applied a solution of nanoparticles to the underside of the leaf, where it penetrated tiny pores known as stomata, which normally allow carbon dioxide to flow in and oxygen to flow out. In these plants, the nanotubes moved into the chloroplast and boosted photosynthetic electron flow by about 30%.
With regard to the sensors which rely on this increased electron flow rate, the researchers are next looking to develop plants that can function as monitors for environmental pollution, pesticides, fungal infections, or exposure to bacterial toxins.
“Right now, almost no one is working in this emerging field,” Giraldo states. “It’s an opportunity for people from plant biology and the chemical engineering nanotechnology community to work together in an area that has a large potential.”
The new research was detailed in a paper published in the journal Nature Materials.
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