“Plants provide us with food and fuel, and even the oxygen we breathe, but they have been little used in technology applications until now,” says team member Juan Pablo Giraldo. “We are talking about a new field at the interface between nanotechnology and plant biology, which we have called plant nanobionics.”

The researchers, led by Michael Strano, have shown that nanobionic plants with semiconducting carbon nanotubes in their leaves can better convert energy from sunlight into electrical current. The researchers obtained their result using two techniques to measure electron flow in plant leaves and chloroplasts in the lab. The first relied on measuring the changes in colour of a dye that intercepts electrons between the photosystems in chloroplasts extracted from plants. The second is based on monitoring changes in chlorophyll fluorescence in extracted chloroplasts and leaves. Chloroplasts are organelles inside a plant cell that use chlorophyll to capture and store the energy from solar radiation.

30% more photocurrent than non-treated plants

According to the MIT team, the nanotubes appear to enhance the amount of light absorbed by chlorophyll at wavelengths that are normally only weakly captured by plants, such as the green, ultraviolet and near-infrared parts of the electromagnetic spectrum. The result is that the nanoparticle-treated plant leaves can produce as much as 30% more photocurrent than non-treated plants.

The researchers also found that nanotubes combined with polymer nanoparticles containing ceria (a rare-earth metal oxide) act as “antioxidants” and dramatically reduce the number of damaging oxygen radicals in extracted chloroplasts, something that could help increase photosynthetic activity too.

Self-repairing artificial plant-like systems

“Being able to enhance chloroplast photosynthesis with nanoparticles could allow us to develop artificial plant-like systems that would be powered by solar energy and be able to repair themselves like real plants,” says Giraldo. “Both these and the nanoparticle-augmented ordinary plants, might, for example, be used as biochemical detectors for monitoring pollutants, such as nitric oxide, in the environment. They might even be able to detect dangerous chemicals and gases depending on the type of nanoparticle incorporated.”

The team says that it would now like to better understand how carbon nanotubes capture and transfer light energy to the photosynthetic machinery in plant chloroplasts. “The ultimate goal is to find out whether assembling chloroplasts with nanoparticles such as carbon nanotubes can help increase the amount of chemical fuels (such as glucose) that plants produce,” Giraldo told nanotechweb.org. “Such studies will take our technology to a new level of applications, such as increasing crop yields or algae biofuel production.

“Ideally, we need remote detection instruments that allow us to image in real time the near-infrared fluorescence changes of carbon nanotubes in plants under real-life conditions,” he added.

The research is detailed in Nature Materials.

Further reading

'Self-repairing' photovoltaics rival conventional solar cells (Sep 2010)
Enter the 'thermopower wave' (Mar 2010)
Nanotube sensors detect live biomarkers (Nov 2013)