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Spinach Enhanced to Detect Chemicals, Send Signals

Spinach plant

(U.S. Department of Agriculture)

1 November 2016. A chemical engineering group showed the feasibility of embedding sensors in common spinach plants that can detect and signal the presence of explosive chemicals in the soil. A team from the Massachusetts Institute of Technology lab of chemical engineering professor Michael Strano published its findings in the 31 October issue of the journal Nature Materials (paid subscription required).

In addition, the lead author of the journal article, graduate student Min Hao Wong, is co-founder of Plantea, a start-up company in Boston further developing and commercializing the technology. The company plans to offer systems that allow growers to monitor crops for pesticide levels and other key chemical indicators.

“Plants are very good analytical chemists,” says Strano in a university statement. “They have an extensive root network in the soil, are constantly sampling ground water, and have a way to self-power the transport of that water up into the leaves.” He and colleagues built on recent discoveries showing how plants can be enhanced with nanoscale materials to enhance their photosynthesis and detect environmental pollutants, such as nitrogen oxide, a pollutant from the burning of fossil fuels.

Other work by Strano’s group embedded  hollow nanoscale carbon tubes into plants, and with polymer plastics containing reagents on the tubes, turning the plants into sensors, detecting molecules such as hydrogen peroxide and the nerve gas sarin. The tubes were also wrapped with polymer plastics allowing the plants to fluoresce, or light up, when encountering the target gas or substance.

The earlier work, however, used model Arabidopsis plants, well-researched plant species designed to grow in the lab. In the new study, the MIT researchers extend these capabilities to spinach, a common crop plant, to detect chemicals known as nitroaromatics, nitrogen-based compounds used in industry, but also in land mines. The single-walled carbon nanotubes were contained in a solution applied to the underside of the spinach leaves, for infusion into the leaves’ photosynthesis layer.

The nanotubes in this case contained chemicals that gave off continuous fluorescent signals, which at designated levels, serve as a baseline measure. Meanwhile, the embedded nanotubes contained bombolitin-2, a peptide found in bumblebees that detects nitroaromatic chemicals. When the peptide-laden nanotubes detect a presence or change in the nitroaromatic compounds in ground water, the fluorescent signals change, thus acting as an alert. The team says it takes about 10 minutes for the spinach plants to take in the ground water, test for nitroaromatics, and send a new fluorescent signal.

The researchers also built a detection device around an inexpensive open-source hand-held Raspberry Pi computer, similar to a smartphone processor, connected to an infrared camera. The camera shines an infrared beam on the spinach leaves that detects their fluorescent signals. The authors say a smartphone could work as well, if modified to remove the built-in infrared filter. Proof-of-concept tests show the device could read fluorescent signals from the plants as far as 1 meter way.

The team is extending the reading distance of the device and expanding the compounds detected with this technology, including those that address day-to-day needs of growers. “Plants are very environmentally responsive,” Strano adds. “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.”

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