By embedding spinach leaves with carbon nanotubes, engineers
transformed spinach plants into sensors that can detect explosives and
wirelessly relay that information to a handheld device similar to a
smartphone.
Spinach is no longer just a superfood: By embedding leaves with
carbon nanotubes, MIT engineers have transformed spinach plants into
sensors that can detect explosives and wirelessly relay that information
to a handheld device similar to a smartphone.
This is one of the first demonstrations of engineering electronic
systems into plants, an approach that the researchers call “plant
nanobionics.”
“The goal of plant nanobionics is to introduce nanoparticles into the
plant to give it non-native functions,” says Michael Strano, the Carbon
P. Dubbs Professor of Chemical Engineering at MIT and the leader of the
research team.
In this case, the plants were designed to detect chemical compounds
known as nitroaromatics, which are often used in landmines and other
explosives. When one of these chemicals is present in the groundwater
sampled naturally by the plant, carbon nanotubes embedded in the plant
leaves emit a fluorescent signal that can be read with an infrared
camera. The camera can be attached to a small computer similar to a
smartphone, which then sends an email to the user.
“This is a novel demonstration of how we have overcome the
plant/human communication barrier,” says Strano, who believes plant
power could also be harnessed to warn of pollutants and environmental
conditions such as drought.
Strano is the senior author of a paper describing the nanobionic plants in the October 31 issue of Nature Materials.
The paper’s lead authors are Min Hao Wong, an MIT graduate student who
has started a company called Plantea to further develop this technology,
and Juan Pablo Giraldo, a former MIT postdoc who is now an assistant
professor at the University of California at Riverside.
Environmental monitoring
Two years ago, in the first demonstration of plant nanobionics,
Strano and Giraldo used nanoparticles to enhance plants’ photosynthesis
ability and to turn them into sensors for nitric oxide, a pollutant
produced by combustion.
Plants are ideally suited for monitoring the environment because they
already take in a lot of information from their surroundings, Strano
says.
“Plants are very good analytical chemists,” he says. “They have an
extensive root network in the soil, are constantly sampling groundwater,
and have a way to self-power the transport of that water up into the
leaves.”
Strano’s lab has previously developed carbon nanotubes that can be
used as sensors to detect a wide range of molecules, 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.
In the new study, the researchers embedded sensors for nitroaromatic
compounds into the leaves of spinach plants. Using a technique called
vascular infusion, which involves applying a solution of nanoparticles
to the underside of the leaf, they placed the sensors into a leaf layer
known as the mesophyll, which is where most photosynthesis takes place.
They also embedded carbon nanotubes that emit a constant fluorescent
signal that serves as a reference. This allows the researchers to
compare the two fluorescent signals, making it easier to determine if
the explosive sensor has detected anything. If there are any explosive
molecules in the groundwater, it takes about 10 minutes for the plant to
draw them up into the leaves, where they encounter the detector.
To read the signal, the researchers shine a laser onto the leaf,
prompting the nanotubes in the leaf to emit near-infrared fluorescent
light. This can be detected with a small infrared camera connected to a
Raspberry Pi, a $35 credit-card-sized computer similar to the computer
inside a smartphone. The signal could also be detected with a smartphone
by removing the infrared filter that most camera phones have, the
researchers say.
“This setup could be replaced by a cell phone and the right kind of
camera,” Strano says. “It’s just the infrared filter that would stop you
from using your cell phone.”
Using this setup, the researchers can pick up a signal from about 1
meter away from the plant, and they are now working on increasing that
distance.
Michael McAlpine, an associate professor of mechanical engineering at
the University of Minnesota, says this approach holds great potential
for engineering not only sensors but many other kinds of bionic plants
that might receive radio signals or change color.
“When you have manmade materials infiltrated into a living organism,
you can have plants do things that plants don’t ordinarily do,” says
McAlpine, who was not involved in the research. “Once you start to think
of living organisms like plants as biomaterials that can be combined
with electronic materials, this is all possible.”
“A wealth of information”
In the 2014 plant nanobionics study, Strano’s lab worked with a common laboratory plant known as Arabidopsis thaliana. However,
the researchers wanted to use common spinach plants for the latest
study, to demonstrate the versatility of this technique. “You can apply
these techniques with any living plant,” Strano says.
So far, the researchers have also engineered spinach plants that can
detect dopamine, which influences plant root growth, and they are now
working on additional sensors, including some that track the chemicals
plants use to convey information within their own tissues.
“Plants are very environmentally responsive,” Strano says. “They know
that there is going to be a drought long before we do. They can detect
small changes in the properties of soil and water potential. If we tap
into those chemical signaling pathways, there is a wealth of information
to access.”
These sensors could also help botanists learn more about the inner
workings of plants, monitor plant health, and maximize the yield of rare
compounds synthesized by plants such as the Madagascar periwinkle,
which produces drugs used to treat cancer.
“These sensors give real-time information from the plant. It is
almost like having the plant talk to us about the environment they are
in,” Wong says. “In the case of precision agriculture, having such
information can directly affect yield and margins.”
Publication: Min Hao Wong, et al.,”Nitroaromatic detection and
infrared communication from wild-type plants using plant nanobionics,”
Nature Materials (2016) doi:10.1038/nmat4771
Source: Anne Trafton, MIT News
From: SciTech Daily
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