Plants that use nanoparticles to pick up the presence of pollution, or even explosives, have been engineered by scientists in the US.
Monitoring an environment for the presence of toxins, pollutants or other hazards can be costly. Sensors need to be checked and maintained, batteries require regular replacement, and designing a device that can reliably sniff air or taste groundwater for substances of interest is an engineering challenge.
So why not use plants, MIT researcher Michael Strano and his colleagues wondered?
Powered by the sun, plants soak up a constant stream of water from the soil and ship it to their leaves, and the leaves draw in air for growth. This, as the MIT team put it in their paper inNature Materials, is the recipe for the perfect "microfluidic, self-powered autosampler."
To realise the detection potential of plants the team designed a suite of molecular sensors.
Based on carbon nanotubes, which are cylindrical cages of carbon atoms, the sensors selectively bind to certain chemical structures, like the constituents of an explosive or the nerve gas Sarin.
When this happens it changes the way the nanotube behaves whenever certain wavelengths or colours of light hit it, shifting the amount of infrared light that it gives off by a detectable amount.
To make use of this property, Strano and his team made a solution of these nanotubes and applied them to the leaves of spinach plants.
The leaves take up the particles, which sit harmlessly within the leaf tissue. Watering the plants with low-concentrations of the chemical picric acid, which is used to make explosives, produced measurable changes within just 10 minutes when the leaves were viewed using a budget infrared camera hooked up to a Raspberry Pi computer.
The technique also worked when small amounts of picric acid was sprayed onto the leaves and allowed to soak in, proving that the plants could also be used to monitor air quality as well as soil water.
Previously scientists have used genetic engineering techniques to grow plants capable of reacting to environmental contamination and threats like landmines.
These approaches mean that it's easy to mass-produce detector plants, which is one drawback on the present study, but there is the risk of the escape into the environment of the modified plant or the associated genetic changes.
The reaction times of these GM plants has also tended to be on much longer timescales, unlike these bionic plants that monitor both air and water in real time and indicate within minutes.
"Our paper outlines how one could engineer plants like this to detect virtually anything," says Strano.
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