Photonic adaptations of plants for light harvesting

This interdisciplinary project will investigate two biological photonic systems with the aims of characterising the impact of the photonics on photosynthetic processes, and determining if these systems could provide inspiration for enhancing artificial light capture.
The ability of photosynthetic organisms such as plants and algae to harvest energy from light through photosynthesis is not only one of the fundamental processes of life, but can act as a source of inspiration for artificial energy harvesting. This is because unlike animal cells, plant cells are designed to interact with light to harvest energy. One of the more unexpected mechanisms by which plants interact with light, that may have implications for energy harvesting, is the presence of structures that lead to plants becoming iridescent (a form of structural colour that changes hue depending on the viewing angle).
The iridescence is produced by materials that are micro-structured at a scale comparable to the wavelength of light similar to man-made “photonic crystals”. While iridescence produced by animals such as peacocks and butterflies has been widely studied, iridescence in plants has largely been ignored because plant cells contain significantly more absorbing, scattering and fluorescent structures. Yet, these biological microstructures have properties not seen in “photonic crystals”. In particular, the low refractive index contrast combined with disorder appears to control light over a wider spectral range – which could enhance the harvesting of required light wavelengths for photosynthesis while minimising exposure to less useful or damaging wavelengths. To gain insights for enhancing energy harvesting through optical structures we propose to investigate two established model systems:
1. The brown alga Cystoseira tamariscifolia (which grows in rock pools along the Cornish coast) appears to produce its iridescence through the production of ‘iridescent bodies’. The position of this iridescent body in the algal cell may hint at its function and TEM analysis has found that the iridescent body is usually surrounded by chloroplasts (where photosynthesis occurs).
2. Many of the highly diverse genus Begonia also produce iridescence, but through a uniquely modified cell structure (similar to a choroplast) called an iridoplast. These iridoplasts move in response to both light levels and specific wavelengths.
The student will use a range of methods to determine the structure and function of cell components including a range of microscopy techniques. These measurements will be used to provide the necessary input to model the effect of local microstructure on photosynthesis using FDTD modelling. Through the combination of measurement and modelling the project will use the most promising aspects of either/both systems to design bio-inspired photonic structures optimised to enhance light capture.