Plants are important buffers in the climate system through their carbon dioxide absorption. Now researchers may have found a new way to increase CO2 absorption and growth in plants – through nanoparticles. The experiment showed that if you put tiny nanoparticle chains made of a conductive polymer into the soil with the water, the plants absorb them with their roots and transport the nanoparticles to their leaves. There, the synthetic particles act like light antennas and increase the plant’s photosynthetic activity. As a result, the biohybrid plant absorbs eleven percent more CO2 than normal and grows stronger. Such biohybrid plants could increase the binding of CO₂ from the atmosphere, but also advance the production of bioenergy, as the team reports.
Advances in electronics and nanotechnology, particularly in conductive organic materials, are opening up new opportunities to combine nature and technology. For example, by supplementing or strengthening plants with engineered components, one can exploit their natural electrophysiology, for example to turn them into biohybrid sensors for environmental stimuli, to monitor their internal state or to influence their metabolic processes and photosynthesis. “If one could create biohybrid plants for energy production, this would help to overcome some of the hurdles of conventional approaches such as photovoltaics,” explain Manuela Ciocca from the Free University of Bozen-Bolzano and her colleagues. So far, such use of biohybrid organisms to convert sunlight into usable energy has only been implemented in simple model systems such as bacteria and microalgae. So far there have only been isolated tests on higher plants.
Conductive nanoparticle chains in plant tissue
Ciocca’s team is now presenting a method with which plants can be relatively easily converted into biohybrid systems. As a biological element, the researchers used thale cress (Arabidopsis thaliana), a species that has been well studied in plant research and is often used for experiments. To make this plant a biohybrid, they added the organic polymer P3HT (poly(3-hexylthiophene)) to the irrigation water. This material is electrically conductive and is already being researched for the development of flexible solar cells and for so-called green electronics applications. In order for this polymer to get into the plant tissues, Ciocca and her team used chain-shaped nanoparticles made of this polymer that are only around 150 nanometers in size. They consist of many small, repeating molecular units whose structure is comparable to a string of pearls.
Previous studies had already shown that this material absorbs light in the wavelength range of 450 to 650 nanometers. “This corresponds to the spectral range in which the chlorophyll of plants has only minimal light absorption,” explain the researchers. “These spectral properties suggest that P3HT nanoparticles have the theoretical potential to complement and enhance plant light absorption.” The experiments showed that the polymer nanoparticles were absorbed by the plant via the roots and distributed throughout its tissues, as hoped. The P3HT nanoparticles were also detectable in the leaves. The thale cress plants had integrated the synthetic component into their tissues. “This study represents the first example of a biohybrid plant that was created by introducing P3HT nanoparticles directly into the plant itself,” says Ciocca. “In previous work, only one part of the plant – such as a leaf or the roots – was connected to artificial components.”
Increased growth and increased CO2 uptake
The test plants absorbed the biocompatible nanoparticles without this affecting their growth. Instead, as hoped, there was even a positive effect: As soon as the P3HT nanoparticles reached the leaves, they acted like tiny antennas that expanded the natural light-collecting abilities of chlorophyll. Analyzes showed that the biohybrid plants absorbed more light in the green region of the spectrum, while at the same time an electron transfer from the nanoparticles to the photosynthetic apparatus of the plants took place, as Ciocca and her colleagues found. This was an advantage for the plants: the additional energy increased their photosynthesis, which, on the one hand, led to a higher absorption of CO₂ from the atmosphere and, on the other hand, to stronger plant growth. The biohybrid plants developed roots that were 45 percent longer and their biomass increased by 17 percent compared to control plants. At the same time, CO2 absorption and binding increased by eleven percent, as the team reports.
According to Ciocca and her colleagues, such biohybrid plants could pave the way for numerous applications – from capturing CO2 from the atmosphere to producing bioenergy. “This technology opens up numerous possible applications because it allows the properties of plant organisms to be changed without modifying their DNA,” says Ciocca. “The fields of application are very diverse – from sustainable agriculture to renewable energies: these plants can bind more CO₂, produce more oxygen and contribute to the green energy systems of the future.”
Source: Manuela Ciocca (Free University of Bozen) et al., Materials Horizons, doi: 10.1039/D5MH00341E