The silica shells of single-celled marine algae known as diatoms may have evolved to capture wavelengths of light found in the Sun’s spectrum. This finding, from researchers at McGill University in Canada, could have applications for solar energy because the shells, or frustules, are made from glass and are similar to materials already used in photonic chips and solar panels.
Diatoms evolved over millions of years to survive in any aquatic environment, including regions of the ocean that receive very little light. They owe this adaptability to the excellent optical response of their frustules, which are tens of nanometres thick and covered in pores separated by surprisingly regular distances. These pores respond to light differently depending on their size, spacing and configuration.
In the new work, a team led by David Plant and Mark Andrews sought to understand how the frustules function as a biophotonic device. To do this, they imaged different sections of the structures using four high-resolution microscopy techniques: scanning near-field optical microscopy; atomic force microscopy; scanning electron microscopy; and dark field microscopy. They then used these images to build a series of models to analyse each part of the frustule via three-dimensional simulations. These models showed how different wavelengths of light interact with the structures – including when it is captured and distributed; how long it is retained; and how it is likely absorbed by the cell, explains team member Yannick D’Mello.
Photosynthesis even in dim conditions
The results revealed that the wavelengths of light the frustules interacted with coincided with those absorbed during photosynthesis, suggesting that the structure could have evolved to capture sunlight in an optimum way. The results also showed that the frustules redistribute light so that it is absorbed across the plant cell. In addition, the team found that light circulates inside the frustule long enough for photosynthesis to occur even in dim conditions deeper underwater.
DNA origami produces silica ‘diatoms’
The new work could make it possible to cultivate diatom species that harvest light at different wavelengths for technological applications. The light absorption mechanisms the researchers discovered could also be used to improve the way solar panels absorb light – for example by allowing light to be collected at more angles, thereby avoiding the need for the panel to be directly oriented towards the Sun.
The study, which is detailed in Optical Materials Express, is part of D’Mello’s PhD thesis, which focuses on solar energy harvesting on a silicon photonic chip. He and his colleagues are now working on upgrading their model and applying it to other diatom species. “We will also investigate how frustules can be combined with silicon photonics and solar energy harvesting technologies to improve its efficiency, cost and scalability,” D’Mello tells Physics World.
