Eat Your Spinach; It Can Detect Explosives

Spinach is best known for its health benefits, but in the future the plant could play a very different role: detecting explosive material in soil.

Chemical engineers at MIT have integrated nanotechnology into spinach plants, transforming them into sensors that can detect explosives and then wirelessly relay that information to a handheld device.

Specifically, researchers embedded the leaves of spinach plants with carbon nanotubes in one of the earliest demonstrations of what’s called “plant nanobionics,” in which electronic systems are engineered into plants to allow them to interact in an intelligent way with their environment and transmit useful information to observers.

Plants are, quite literally, a natural fit for this type of task, as they already communicate extensively with the world around them, said Min Hao Wong, a graduate student at MIT and lead author on a paper about the work published in the journal Nature Materials.

“When we think of plants, we tend to think of them as being essentially static,” he told Design News. “The fact is that plants are enormous sources of information. They interact constantly with the environment that we live in, absorbing and accumulating various particulates and compounds, and responding to changes in temperature or humidity. Our goal in this work is to show that humans can readily access this valuable information, and that actually plants can even signal this information to us.”

Designers & Innovators. Learn more about some of the latest designers and innovators and what they're up to at ESC Silicon Valley , Dec. 6-8, 2016 in San Jose, Calif. Register here for the event, hosted by Design News ’ parent company, UBM. 

Wong’s team—led by Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT—designed the plants to detect chemical compounds known as nitroaromatics, which are typically used in landmines and other explosives.

After engineering by the team, the plant, in its usual process of drawing water from the ground, can detect if one of these chemicals was present in the ground water. If that’s the case, the plant leaves emit a fluorescent signal that can be read with an infrared camera. The camera can be attached to a device similar to a smartphone, which then sends an email to the user to alert them that the chemical is present.

To give the plant its detection and information-transmission properties, the team used two types of single-walled carbon nanotubes, Wong said.

“For one type, we wrapped the carbon nanotube in a polymer that rendered it insensitive to any chemical near it, and used this as an infrared reference signal,” Winn explained. “The other was wrapped in a different polymer such that an explosive molecule changes the fluorescence if it binds.”

READ MORE ARTICLES ON NANOTECHNOLOGY:

The two infrared signals can be picked up on a smart phone to indicate the presence and the amount of explosives, he said. “The nanoparticles enter the plant by pressurizing a solution onto the leaf surface using a needle-less syringe,” Wong said. “The fluid enters pores in the surface of the leaf and fills a space called the mesophyll. The explosive flows from the ground into the leaf, triggering the detection.”

Using spinach plants as sensors in this way and other ways could be useful for precision agriculture, or to warn agriculturalists and others of soil pollutants or impending environmental conditions such as drought, he said.

“In this role, plants serve as environmentally friendly, and net-zero-carbon sensors of the environment that we live in,” Wong said.

The researchers also have also engineered spinach plants that can detect dopamine—which influences plant root growth—and are now working on additional sensors, including some that track the chemicals plants use to convey information within their own tissues.

The team also will continue its research to use the sensors to learn more about the plants themselves, Wong said.

“We would like to turn the sensors ‘inward,’ meaning that we would like to employ these sensors to understand a bit more about cellular signaling and biochemical pathways within the plant,” he said. “Having such information is immensely valuable for bioprocess engineering and other areas.” 

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal