Hm, is that a minefield? Let me just throw my magic bomb-sniffing spinach over there

The humble spinach plant has been elevated into a bomb-sniffing sensor by embedding carbon nanotubes into its leaves.

A group of researchers from Massachusetts Institute of Technology (MIT) found that spinach can be turned in a chemical sensor for nitroaromatic compounds – a chemical rarely found in nature, but often found in landmines and explosives.

Working on the boundaries of biology and electrical engineering, the researchers label their work under ‘plant nanobiotics’ and is published in Nature Materials [paywalled].

First, the spinach leaves are injected with a solution containing 10 nanometre particles. The idea is that nitroaromatic compounds, such as picric acid, can enter groundwater systems and is sucked up by the roots of the bionic spinach plants, or escape as vapor that the leaves can detect.

A chemical reaction between the plant’s peptides and its nanoparticles begin when picric acid molecules bind to the nanoparticles. It causes the nanoparticles to fluoresce in the near-infrared region when a laser is shone onto the leaves.

The researchers took an extra step to allow an explosive detected alert signal to be sent to a user’s mobile phone. An infrared camera connected to a Raspberry Pi, senses the light and sends an email alert.

In experiments, it only took ten minutes for the contaminated groundwater to reach the leaves. Although spinach was used in the lab, the bomb-sniffing sensors can be embedded into any living plant.

"Plants are very good analytical chemists," Michael Strano, professor of chemical engineering at MIT and the leader of the research team, 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."

There are drawbacks to using plants as chemical sensors, however. Since every spinach plant slightly varies, the sensitivity to nitroaromatic compounds varies.

Strano’s team specialises in developing carbon nanotubes as sensors that can detect other chemicals from hydrogen peroxide, another type of explosive TNT, to the nerve gas sarin.

In the lab experiments, the researchers can pick up a signal from the plant about a metre away, and they are now trying to increase the distance for potential applications. ®