Although plants are living things, they are usually inanimate and incapable of communicating anything but their need for water. However, through the use of nanotechnology, researchers from the Massachusetts Institute of Technology have found a way to initiate communication between plants and humans. With this emerging technology, spinach, known for its high iron content, can now send emails to warn scientists about climate change.

Researchers injected the spinach leaves with single-walled carbon nanotubes (SWCNTs)—a strong yet very light allotrope of carbon. As their name suggests, SWCNTs are nanoparticles that are almost 50,000 times thinner than a human hair and formed by rolling thin sheets of graphene into cylinders. The carbon nanotubes in engineered spinach can then detect harmful compounds or pollutants in the soil. The technology was originally created to test for explosive compounds, known as nitroaromatics, and is one of the first developments in the emerging field of plant nanobionics.

David Juncker, professor and chair of the Department of Biomedical Engineering at McGill, studies how nanotechnology can be used to manipulate cells, proteins and tissues.

“Nanobionics refer to the integration of nanoscale artificial structures into living systems, [and] in this example, [into] single-walled carbon nanotubes into spinach plants,” Juncker wrote in an email to The McGill Tribune. “The general idea of bionics is to enhance biological function thanks to artificial structures, and in this case, they are materials at the nanoscale in plants.”

The carbon nanotubes in the engineered spinach are illuminated with infrared light, which is then emitted back, forming an image that acts as a reference for a nanotube not yet bound to any compounds. Chemicals present in the soil will make their way up to the leaves and bind to the carbon nanotubes, causing them to reemit the infrared radiation in a different manner, forming a different image. A small computer connected to the infrared camera then indicates the difference between the image formed and the reference. Once it does so, the computer automatically sends an email to the researchers signalling the presence of the target compound. 

This technique can be used to detect compounds and pollutants in the soil such as nitric oxide, which is formed as a result of combustion and contributes to climate change. Although only two plants—spinach and thale cress—were tested, the procedure could be applied to any other plant species. 

Nanobionics, however, come at a high cost.

“SWCNT[s] are expensive to make, and here are functionalized with a molecule that binds the chemical,” Juncker wrote. “They are likely very expensive [and] need to be externally introduced, which would not allow for broader use. But the concept could be replicated with biocompatible materials, and even with materials produced by the plant themselves thanks to genetic engineering.”

Plant nanobionics can also increase plant productivity. For instance, certain nanoparticles could be injected into plants to increase their absorbance of solar energy, leading to a faster rate of photosynthesis. Farmers can also detect specific compounds in the soil to help them determine the exact amount of fertilizers or pesticides they need to use. 

“This is an example where they take advantage of the material to create a visible change in response to chemicals found in explosives, which could help locate them,” Juncker wrote. “At large scale, this could be useful to detect explosives or other ground chemical[s] based on satellite imagery, similarly to how Roman ruins can be identified based on changes in the vegetation colour when they grow atop shallowly recovered structures.”

This is not the only technical application of spinach. In the past, scientists struggled to find a material that would replace platinum as a catalyst for fuel cell reactions. However, a study conducted by American University found that an engineered version of spinach is actually more efficient at sparking reactions than platinum. This discovery marks an eminent step towards clean energy dependency as fuel cells could replace the conventional internal combustion engine.