4. Diatoms: Glass Ornaments of the Earth’s Waters

The Earth’s waters contain hundreds of thousands of different species of beautiful, microscopic glass crystals called diatoms. Among every single one of its many species, diatoms exhibit exquisite architecture of their shells, and their applications in engineering are growing ever more known in the scientific community. Diatoms are one of the most common microaquatic single celled algae. They are eukaryotic and photosynthetic and have an estimated 200,000 species and 250 living genera (Gordon et al., Trends Biotechnol 27(2):116–127, 2008). Diatoms exist in any body of water that has enough nutrients—oceans, lakes, rivers, ponds, and even in household aquariums. They exist in various forms: planktonic or free-floating, colonial or solitary, or attached to objects such as sea ice, rocks, or other algae (Leventer, Diatoms. In: Gornitz V (ed) Encyclopedia of paleoclimatology and ancient environments. Springer, Netherlands, pp 279–280, 2009). To the naked eye, diatoms take on the appearance of scum at the top of the ocean, lake, or even the back of a whale. The slimy brown patches present on rocks in rivers are actually layers of diatoms. While they look like muck, the cells are actually surrounded by beautiful glass silica shells called frustules, and these frustules have a hierarchical structure (Dimas and Buehler, Hierarchical mechanics of diatom algae: from atoms to organism and weakness to strength, http://​imechanica.​org/​node/​11366, 2011). In addition to the astonishing beauty of diatom shells that has captivated artists, scientists, and researchers, diatoms have a wide variety of current uses including DNA purification, liquid absorbents, and matting agents. Researchers are also looking at using diatoms in the development of nano-scale biosensors (Marshall et al., PLoS One 7(3):e33771, 2012), drug delivery vehicles (Gordon et al., Trends Biotechnol 27(2):116–127, 2008), and solar panels with optimal absorption of solar energy (Norwegian University of Science and Technology, A bright future—with algae: diatoms as templates for tomorrow’s solar cells, http://​www.​sciencedaily.​com/​releases/​2012/​07/​120717100117.​htm, 2012).