On Light and Diatoms: A Photonics and Photobiology Review

Diatoms are microscopic unicellular algae with shells (frustules) made of amorphous hydrated silica with various architectures. Their repetitive, multiscale features ranging from 0.3 nm to 5 cm, i.e., 8 orders of magnitude, result in a number of interesting optical properties, including potential light piping and/or optical communication in colonial diatoms. This wide dynamic range of length scales occurring in a single, nearly chemically pure structure, the diatom frustule, makes diatoms truly unique. This leads for certain species' frustules to photonic crystal features, as suggested by recent studies, which may lead to their ability to focus light of specific wavelengths, and their selective transmittance and reflectance of other wavelengths, besides their common photoluminescence properties. Such optical properties might help diatoms in their photoregulation, as well as other photobiological phenomena found in diatoms such as phototaxis and karyostrophy (i.e., the movement of chloroplasts along cytoplasmic strands toward the nucleus). Therefore, there are a number of lessons that we can learn from how diatoms manipulate electromagnetic fields, especially visible light. As a cheap and readily available material, diatom frustules could lead to more efficient solar energy harvesters, with diatom solar panels proposed for the production of both electricity and biofuel. Diatom based sensors and photocatalysts can be fabricated efficiently. The power of diatoms to work with light is both fascinating in itself and can be regarded as a powerful source for the development of new nanotechnologies.