Some natural structures show three-dimensional morphologies on the micro- and nano- scale, characterized by levels of symmetry and complexity well far beyond those fabricated by best technologies available. This is the case of diatoms, unicellular microalgae, whose protoplasm is enclosed in a nanoporous microshell, made of hydrogenated amorphous silica, called frustule. We have studied the optical properties of Arachnoidiscus sp. single valves both in visible and ultraviolet range. We found photonic effects due to diffraction by ordered pattern of pores and slits, accordingly to an elaborated theoretical model. For the first time, we experimentally revealed spatial separation of focused light in different spots, which could be the basis of a micro-bio-spectrometer. Characterization of such intricate structures can be of great inspiration for photonic devices of next generation.

The characterization of partially coherent light transmission by micrometer sized valves of marine diatoms is an interesting optical challenge and, from the biological point of view, is of outmost relevance in order to understand evolution mechanisms of such organisms. In the present work, we have studied the transmission of light coming from a monochromator through single valves of Coscinodiscus wailesii diatoms. Incoming light is confined by the regular pore pattern of the diatom surface into a spot of few microns, its dimensions depending on wavelength. The effect is ascribed to the superposition of wavefronts diffracted by the pores’ edges. Numerical simulations help to demonstrate how this effect is not present in the ultraviolet region of the light spectrum, showing one of the possible evolutionary advantages represented by the regular pores patterns of the valves.

Diatoms are ubiquitous monocellular microalgae, responsible for about 20–25% of the global oxygen produced by photosynthesis. Living in environments where sunlight is not so easily accessible, evolution shaped diatoms in order to exploit light with high efficiency. In particular, diatoms are provided with an external, micro- and nanopatterned silica shell, the frustule, surprisingly similar to artificial photonic crystals and able to manipulate light in many different ways. The present paper reviews the most relevant studies on optical and photonic properties of diatoms that have been performed throughout the last years making use of SEM characterizations, transmittance measurements at different wavelengths, holographic microscopy, Raman spectroscopy and imaging, photoluminescence spectroscopy, and the predictive support of different numerical simulation algorithms.