Plants have many valuable functions: They provide food and fuel, release
the oxygen that we breathe, and add beauty to our surroundings. Now, a
team of MIT researchers wants to make plants even more useful by
augmenting them with nanomaterials that could enhance their energy
production and give them completely new functions, such as monitoring
environmental pollutants.
In a new Nature Materials
paper, the researchers report boosting plants’ ability to capture light
energy by 30 percent by embedding carbon nanotubes in the chloroplast,
the plant organelle where photosynthesis takes place. Using another type
of carbon nanotube, they also modified plants to detect the gas nitric
oxide.
Together, these represent the first steps in launching a scientific field the researchers have dubbed “plant nanobionics.”
“Plants
are very attractive as a technology platform,” says Michael Strano, the
Carbon P. Dubbs Professor of Chemical Engineering and leader of the MIT
research team. “They repair themselves, they’re environmentally stable
outside, they survive in harsh environments, and they provide their own
power source and water distribution.”
Strano and the paper’s lead
author, postdoc and plant biologist Juan Pablo Giraldo, envision
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 potential is really
endless,” Strano says.
Supercharged photosynthesis
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 percent 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 percent 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 percent.
Yet to be discovered is how
that extra electron flow influences the plants’ sugar production. “This
is a question that we are still trying to answer in the lab: What is the
impact of nanoparticles on the production of chemical fuels like
glucose?” Giraldo says.
Lean green machines
The
researchers also showed that they could turn Arabidopsis thaliana
plants into chemical sensors by delivering carbon nanotubes that detect
the gas nitric oxide, an environmental pollutant produced by combustion.
Strano’s
lab has previously developed carbon nanotube sensors for many different
chemicals, including hydrogen peroxide, the explosive TNT, and the
nerve gas sarin. When the target molecule binds to a polymer wrapped
around the nanotube, it alters the tube’s fluorescence.
“We could
someday use these carbon nanotubes to make sensors that detect in real
time, at the single-particle level, free radicals or signaling molecules
that are at very low-concentration and difficult to detect,” Giraldo
says.
“This is a marvelous demonstration of how nanotechnology
can be coupled with synthetic biology to modify and enhance the function
of living organisms — in this case, plants,” says James Collins, a
professor of biomedical engineering at Boston University who was not
involved in the research. “The authors nicely show that self-assembling
nanoparticles can be used to enhance the photosynthetic capacity of
plants, as well as serve as plant-based biosensors and stress reducers.”
By
adapting the sensors to different targets, the researchers hope to
develop plants that could be used to monitor environmental pollution,
pesticides, fungal infections, or exposure to bacterial toxins. They are
also working on incorporating electronic nanomaterials, such as
graphene, into plants.
“Right now, almost no one is working in
this emerging field,” Giraldo says. “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 research was funded primarily by the U.S. Department of Energy.
source:MITNEWS
