Nitroaromatic detection and infrared communication in wild-type plants via plant nanobionics.
After sensing dangerous chemicals, the carbon-nanotube-enhanced plants send an alert. Spinach is no longer just a superfood: By embedding leaves with CNTs, 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 Prof. Michael Strano, Chemical Engineering, MIT. In this case, the plants were designed to detect nitroaromatics,often used in landmines and other explosives. When one of these chemicals is present in the groundwater sampled by the plant, CNTs embedded in the plant leaves emit a fluorescent signal that can be read with an infrared camera. This 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. 2 years ago, Strano and former MIT postdoc Juan Pablo Giraldo used nanoparticles to enhance plants’ photosynthesis ability and to turn them into sensors for nitric oxide, a pollutant produced by combustion.
Strano’s lab has previously developed carbon nanotubes that can be used as sensors to detect a wide range of molecules, including H2O2, the 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, they embedded sensors for nitroaromatic compounds into the leaves of spinach plants. Using a technique called vascular infusion, where a solution of nanoparticles is applied to the underside of the leaf, they placed the sensors into 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. 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.
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.
http://news.mit.edu/2016/nanobionic-spinach-plants-detect-explosives-1031 http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4771.html
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