Scientists Create 'Sun Sponges' to Capture Sunlight

There may be a new way to capture sunlight. Scientists have created a ring of protein and pigments, half synthetic and half natural, that can be used to quickly prototype light-harvesting antennas that absorb more sunlight than natural ones.

In all, the researchers created two prototype antennas that they built on a testbed, a platform for rapid prototyping of light-harvesting antennas that take the first step in converting sunlight into usable energy. The antennas themselves are made up of protein scaffolding that holds pigment molecules in ideal positions to capture and transfer the sun's energy. The number and variety of the pigment molecules determines how much of the sun's energy that the antennas can grab and dump into an energy trap.

It's the dye that really makes the difference between these two antennas. Nature has evolved many different systems to capture the sun's energy, but all rely on pigments. Most plants, for example, use chlorophyll, which makes them appear to be green. Yet plants miss the middle part of the visible spectrum in their light collection and also miss light at wavelengths longer than we can see.

"Since plant pigments actually reject a lot of the light that falls on them, potentially there's a lot of light you could gather that plants don't both with," said Neil Hunter of the University of Sheffield in a news release.

In this case, one of the antennas incorporated synthetic dyes called Oregon Green and Rodamine Red. The other antenna combined Oregon Green and a synthetic version of the bacterial pigment bacteriochlorophyll that absorbs light in the near-infrared region of the spectrum. With the use of these pigments, both of these designed soaked up more of the sun's spectrum than native antennas in purple bacteria that provided the inspiration and some components for the testbed.

"This is an example of what the field would refer to as semi-synthesis," said Jonathan Lindsey, one of the researchers, in a news release. "We take naturally occurring materials and combine them with synthetic ones to make something that doesn't exist in nature. By taking lots of material from nature we can make molecules that are architecturally more complex than those we can make from scratch."

In the future, these antennas could potentially be used in a two-part system consisting of an antenna and a second unit called a reaction center. This system could serve as a miniature power outlet into which photochemical modules could be plugged. The sun's energy could them be used directly to split water or generate electricity.

The findings are published in the journal Chemical Science.