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A team of biologists and engineers want to turn plants into chemical warfare detectors that can sniff out sarin gas or explosives. For now, though, they've succeeded in turning the flowering Arabidopsis thaliana into a pollutant detector using carbon nanotubes.

The MIT team of researchers has published the novel method in the journal Nature Materials, claiming it paves the way for an entirely new realm of scientific research it has called "plant nanobionics". "We could someday use these carbon nanotubes to make sensors that detect in real time, at the single-particle level, free radicals or signalling molecules that are at very low-concentration and difficult to detect," Juan Pablo Giraldo, a plant biologist and lead author on the paper, commented.


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The team began by first working out how to boost the plant's ability to convert light into energy, and thus ensure it would thrive and rebuild while working as a detector over long periods.

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This was done by manipulating chloroplasts -- organelles that manage photosynthesis and contain the chlorophyll -- and was tested outside of the plant where the molecules would usually die within hours.

To prevent loss or degeneration of the chloroplasts, the team introduced cerium oxide nanoparticles (an antioxidant). The substance was wrapped in polyacrylic acid to ensure it could pierce the membrane surrounding chloroplasts. Polyacrylic acid was then used to deliver carbon nanotubes that help the chloroplasts absorb different wavelengths of light. Measuring the electrons passing through the membranes, the team found these two techniques together enabled the chloroplasts to thrive for several additional hours even when removed from the plant.


When the technique was translated to a living plant, Arabidopsis thaliana, and the electron transport rate was compared alongside that of ordinary plants, the team found energy capture was boosted by 30 percent. Despite this, the team is still unsure how the additional electron flow relates to actual energy production, and trials for this are ongoing.

These steps will hopefully allow the chloroplasts to thrive as reliable sensors. The sensors themselves came in the form of carbon nanotubes that could detect nitric oxide. It was something Michael Strano, co-author on the paper, had already experimented with,

embedding them under human skin to see how levels behave over time.

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In plants, nitric oxide has a role in signalling but is notoriously hard to detect, and it is also a pollutant that contributes to acid rain. The carbon nanontubes, introduced through pores in the plant leaves, were wrapped in a polymer that made the nanotubes change appearance if nitric oxide bound to it.

The system can be adapted to detect different molecules, and so far Strano has already trialled hydrogen peroxide, TNT and nerve gas in other experiments unrelated to plants. For now though, the focus will be on adapting the nanotubes to help out with something a little closer to home. "Real-time sensing of nitric oxide in extracted chloroplasts and leaves could also be extended to detect a wide range of plant signalling molecules and exogenous compounds such as pesticides, herbicides and environmental pollutants," write the authors.

It can be adapted to pick up all different molecules, but for now sensing for nitric oxide will help the team learn more about the signalling processes plants use and hopefully shed light on how sugar production could be boosted by the increased electron flow. "Nanomaterials offer a promising way to engineer plant function, but the absorption, transport and distribution of nanoparticles within photosynthetic organisms remain poorly understood," comment the authors. This is why they are introducing "nanobionics" to the field, so that the processes can be delved into further and better understood. This means that one day we could potentially turn plants into an army of sensors for all types of global protection.