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Researchers Inspired by How Plants, Bacteria Can Harvest Sunlight Energy

Posted November 14, 2019

Plants and bacteria use antennae and other physical structures to capture sunlight. But how is that sunlight energy transported to “reaction centers” for use by these organisms? What mechanisms allow this kind of energy transfer with such pinpoint accuracy — and how could scientists learn to master it and apply it to existing and new technologies?

Tobias Brixner leads a team of scientists at the Institute of Physical and Theoretical Chemistry at JMU Würzburg in Bavaria, Germany. They’re trying to answer precisely these questions and solve some tiny mysteries with huge scientific potential.

A green leaf. Image credit: Akshay Madan via Unsplash (Free Unsplash licence)

A green leaf. Image credit: Akshay Madan via Unsplash (Free Unsplash licence)

What Are the Implications of This Research?

Human technologies often imitate, and sometimes poorly, structures and features that Nature “thought of” first. SONAR, Velcro, submarines, suction cups and infrared cameras are all impressive, but not as impressive as their natural counterparts, like snakes’ eyes or a gecko’s feet. These and other inventions take advantage of biomimicry to provide functionality that would be difficult or impossible to achieve otherwise.

The group at JMU have published work with implications for biomimicry in the journal Nature, meaning their methods and findings are available to the public. Specifically, Brixner and the others describe two spectroscopic methods they’ve designed to observe how energy is transported at the “nanoscale.”

If scientists learn more about how plants and bacteria transfer and process energy, two fields could begin immediately putting their work to use: photovoltaics and optoelectronics. Of particular interest is the potential to build new and highly efficient light-harvesting antennae of our own.

What Did the Team Find?

The team used a method called exciton-exciton-interaction-two-dimensional spectroscopy, along with what they call a “microfluidic arrangement” to render this phenomenon visible. In the simplest terms, here’s how it works:

To mimic the antennae structure of photosynthetic bacteria, the team used double-walled nanotubes, fashioned from dye molecules, as a stand-in. As this nanotube arrangement is subjected to low-intensity light, energy “excitations” transfer from the outer wall to the inner wall of the tubes. Under higher-intensity light, the excitations travel on the outer wall only. When two excitations come into contact with one another, one of them is extinguished.

It may not sound like much, but scientists have long been unable to witness or measure this phenomenon properly. The team at JMU have solved that limitation. Of the achievement, Brixner said: “This effect, which has been known for some time, can be made directly visible with our method for the first time.”

In a second publishing, Brixner’s team also describes a method whereby they can measure energy flows in a fraction of the time allowed by previous methods. They refer to the method as a leap from two-dimensional to three-dimensional frequency analysis, meaning the team can measure more than a dozen 3D spectra in only minutes instead of taking several hours to measure just one.

The paper gets very technical very quickly, but here’s a way to understand why it’s important: in the same way that nuclear magnetic resonance grants us knowledge of the chemical structure of things, and flow reactors help control and observe the interactions between some of those chemicals, multidimensional spectroscopic analysis gives scientists insights in “vibrational and electronic structures and dynamics.” Three-dimensional spectroscopic analysis is a way to see into the unseen — and this team’s new methods can “see” more stuff, much faster, than any previous method.

Nature Continues to Inspire Innovation

The biomimicry examples mentioned earlier are just some of the ways nature has inspired scientific and technological process. Moreover, the team at JMU Würzburg aren’t the only ones interested in better understanding and learning to exploit the mechanisms used by nature to capture and put sunlight to use.

A team at MIT has their eyes fixed on the same “artificial photosynthesis” endgame. Of their research, Aurelia Chenu said: “Understanding the sensitive interplay between the self-assembled pigment superstructure [of plants and photosynthetic organisms] and its electronic, optical, and transport properties is highly desirable for the synthesis of new materials and … organic-based devices.”

Under consideration here are the many varieties of bacteria, algae and other plants that convert sunlight efficiently and convert it into usable energy along with starches, sugars and other necessary resources. Photosynthesis occurs at reaction centers where chlorophyll, carotenoids and other photosynthetic pigments absorb various colors of light and “put it to work.”

The photosynthetic pigments used by plants, bacteria, and even deep-sea organisms are the building blocks of light-harvesting antennae (or “complexes”) that are much more efficient at gathering energy from photons of sunlight than standard solar photovoltaic products.

Both of these teams see their work as important steps toward much more portable, efficient and ultimately more useful light-harvesting technologies.

Written by Kayla Matthews, Productivity Bytes.

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