Solar energy harvesting mechanisms of the frustules of Nitzschia filiformis diatoms

Abstract

Diatoms are major contributors to the global oxygen and carbon cycles. Their ability to thrive on photosynthesis, even in low and intermittent lighting conditions, is attributed to the optical response of the frustule, among other factors. However, how the frustule functions as a biophotonic feature is unknown. Using a toolkit consisting of numerical models and four microscopy techniques, we evaluated the optical response of frustules belonging to the species Nitzschia filiformis. Localized regions of the frustule exhibited functionalities including diffraction, lensing, waveguiding, circulation, filtering, resonances, and dispersion control. We show that these functionalities are complementary to each other in contributing to the solar energy harvesting mechanisms of capture, redistribution, and retention. In this context, frustule performance is evidently enhanced by perturbations to its sub-wavelength structure. We therefore modeled the frustule as a photonic circuit from which we estimated a contribution of approximately 9.83% to photosynthetic activity. To our knowledge, this represents the first model of the entire frustule, including its inherent disorder and the complementary behavior of localized optical functionalities. This provides quantitative support to the hypothesis that the frustule enhances photosynthesis in the cell. It supports the case for cultivating diatoms as sustainably mass-manufacturable devices with applications in solar energy, carbon sequestration, sensing, medicine, and metamaterials.