Engineers recently demonstrated a surprising application of spinach plants: by embedding carbon nanotubes into the leaves, the engineers transformed the spinach plants into a sensor capable of detecting explosive compounds. The research provides one of the first demonstrations of an approach called plant nanobionics, which integrates electronic systems within plants.

(Image courtesy of Christine Daniloff/MIT.)

Spinach Sensors

The spinach plants (Spinacia oleracea) were designed to detect nitroaromatics, a type of chemical compound found in landmines and other explosives. The idea is straightforward: when nitroaromatics are present in the groundwater sampled by the plant, they’ll be drawn up into the leaves. Embedded in the leaves are single-walled carbon nanotubes (SWCNTs).

By shining a laser onto the spinach leaves, the SWCNTs are stimulated to emit a near-infrared fluorescent light. The engineers designed two different types of SWCNTs: one which changes in response to nitroaromatic binding (B-SWCNTs), altering its emitted signal, and one that doesn’t (P-SWCNTs), which serves as a reference. By comparing the signal intensities of the two emitters, you can determine whether or not nitroaromatics are present in the groundwater.

Left: nitroaromatics in the groundwater are taken up into the spinach leaves. Right: the two different types of SWCNTs serve to indicate the presence of the nitroaromatics. See full paper for details. (Image courtesy of Nature Materials.)

To detect the infrared signals, the researchers used an infrared camera hooked up to a Raspberry Pi. This type of setup can send alerts to your smartphone if it detects explosives. Alternatively, the researchers say that phone cameras without their infrared filters could also be used to detect the signals.

Putting Plants to Work

This research opens the door to using plants for a variety of environmental sensing applications. As researcher Michael Strano explains, they’re already well suited for the job. “Plants are very good analytical chemists,” he said. “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.”

Further developing plant nanobiotic techniques could see plants move far beyond sensors. We may someday see bionic plants that can change color or receive radio waves.

“When you have manmade materials infiltrated into a living organism, you can have plants do things that plants don’t ordinarily do,” said engineer Michael 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.”

For more news about carbon nanotubes, read Water Exhibits Surprising Behavior Inside Carbon Nanotubes.