Nano-bionic spinach plants as sensor can now detect explosives

Researchers at the Massachusetts Institute of Technology (MIT) have embedded carbon nanotubes in spinach leaves, turning the plant into a sensor that can detect explosives and wirelessly transmit the information to a microcomputer.

This is one of the earliest demonstrations of “plant nanobionics”, an approach of engineering electronic systems into plants. According to Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT who is heading the research team, “The goal of plant nanobionics is to introduce nanoparticles into the plant to give it non-native functions.”

The research is presented in the October 31 issue of Nature Materials. Strano is the senior author of the paper along with lead authors Min Hao Wong and Juan Pablo Giraldo. Wong is an MIT graduate student who has also launched his own company Plantea to further develop the technology, while Giraldo, a former MIT post-doc, is an assistant professor at University of California, Riverside.

For the research, spinach plants were designed to detect nitroaromatics, the chemical usually found in landmines and other explosives. Using vascular infusion (the technique of applying solution of nanoparticles to a leaf’s underside), researchers embedded sensors into the leaves’ mesophyll layer where most photosynthesis occurs.

In case a nitroaromatic chemical is present in the groundwater naturally sampled by the plant, it takes 10 minutes for the plant to draw the explosive’s molecules up the leaves to the sensors embedded in the plant leaves which then emit a fluorescent signal. In addition, carbon nanotubes embedded in the leaves also emit a constant fluorescent signal to serve as reference. By comparing the two fluorescent signals, researchers are able to determine whether the sensors had detected any explosives.

To read the signal, researchers shine a laser onto the leaf. The nanotubes then emit near-infrared fluorescent light which can be detected by a small infrared camera connected to a Raspberry Pi, a $35 credit-card-sized computer similar to a smartphone. The information is ultimately communicated to the researchers via email.

The fluorescent signals can also be detected using smartphones by removing the infrared filter most camera phones have, researchers say. “This setup can be replaced by a cell phone and the right kind of camera,” Strano said, adding that the infrared filter prevented the use of cell phone cameras for the research.

Currently, the researchers are able to detect signals one meter away from the plant, and are working on increasing the distance. In addition, they have also engineered the spinach leaves to enable detection of dopamine (which influences plant root growth), and are working on additional sensors to track chemicals used by plants for conveying information within their own tissues.

“This is a novel demonstration of how we have overcome the plant-human communication barrier,” said Strano, who maintained that the plants could be used to warn of pollutants or detect environmental conditions such as drought.

“Plants are very environmentally responsive,” he claimed, adding that plants were able to sense a drought long before humans could and were able to detect minor variations in soil and water potential.
“If we tap into those chemical signaling pathways, there is a wealth of information to access,” Strano stated. He added that plants were ideal for monitoring the environment as they acquired a lot of information from the surroundings.

“Plants are very good analytical chemists,” he stated. “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.”

The sensors have a huge potential. Botanists could use these to research on the inner workings of plants, monitor plant health, and even maximize the yield of rare compounds produced by plants such as cancer-curing drugs from the Madagascar periwinkle.

According to Wong, the sensors relay real-time data from plants. “It is almost like having the plant talk to us about the environment they are in,” he said, adding, “In the case of precision agriculture, having such information can directly affect yield and margins.”

In 2014, for the first demonstration on plant nanobionics, Strano and Giraldo had used nanoparticles in the common laboratory plant Arabidopsis thaliana to enhance the plants’ photosynthesis ability and detect nitric oxide (a pollutant produced during combustion). However, to show the versatility of the technique, researchers had used the common spinach plant for the latest study. “You can apply these techniques with any living plant,” Strano said.

They had also developed carbon nanotubes to detect a range of molecules such as hydrogen peroxide, TNT and the nerve gas Sarin. The target molecules alter the tubes’ fluorescence when they bind to a polymer wrapped around the nanotubes.

University of Minnesota Associate Professor of Mechanical Engineering Michael Mc. Alpine believed the research held great potential not only for engineering sensors but also bionic plants that could receive radio signals or change color.

“When you have manmade materials infiltrated into a living organism, you can have plants do things that they don’t ordinarily do,” he said. He maintained that once living organisms are thought of as biomaterials, they could be combined with electronic materials to make this possible.

More information can be found at: MIT News.

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