Light transmission of the marine diatom Coscinodiscus wailesii Shih-Hsin Hsu* a , Camille Paoletti a , Moacir Torres b , Raymond J. Ritchie b , Anthony W. D. Larkum b , and Christian Grillet a a Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS), Institute of Photonics and Optical Science (IPOS), School of Physics, University of Sydney, NSW 2006, Australia; b School of Biological Sciences, University of Sydney, NSW 2006, Australia ABSTRACT The results of a detailed investigation of light transmission behavior of a centric marine diatom species Coscinodiscus wailesii are reported. We measured 3-dimentional intensity distributions of both broadband and monochromatic light transmitted through individual valves of the diatom in air and water. Cross-sectional intensity profiles of transmitted light indicates valves of C. wailesii can concentrate light into certain regions. At a distance from the valve shorter than its diameter, light intensities close to the optical axis are relatively higher than those in the surrounds; at a longer distance, transmitted light intensities display ring-shaped profiles. The distance showing this light concentration characteristic becomes shorter as the wavelength of incoming light goes up. These results may offer insight into the understanding of biological functions of diatom frustules’ intricate structures and inspire new optical biomimetic applications. Keywords: Biomaterials, diatom, microscopy, transmission 1. INTRODUCTION Diatoms (Bacillariophyceae), which are unicellular microalgae and found in aquatic environments, have attracted a great deal of research interests 1-5 . They are renowned for their peculiar, species-specific silica cell walls (frustules), which consist of two valves and possess regular arrays of micro- to nanometer pores. There are more than 100,000 species with very diverse morphologies 2, 6-7 . Due to their abundance and major contribution to photosynthesis (about 40% in oceans and up to 25% in the world) 8-10 , in-depth studies of the optical properties of frustules are of great value. In the past few years, a few studies have reported that the silica frustule can manipulate the passage of light and the interaction of light and matter 11-18 . Studies on their optical properties suggest they might be considered as photonic crystals 11-13 . Higher transmittance for longer wavelengths than shorter wavelengths in the visible region has been pointed out 12, 15 , and visible photoluminescence of silica frustules excited by ultraviolet lasers has also been observed 17-18 . Moreover, it has been demonstrated that valves of centric marine diatoms Coscinodiscus wailesii can focus incoming light into a spot of several micrometers 14, 16 . However, the underlying mechanisms of these interesting optical properties are not fully understood. In this report, we present the results of a detailed investigation of light transmission behavior of a centric diatom species C. wailesii by optical microscopy. The three-dimensional (3-D) intensity distributions of both broadband and monochromatic light transmitted through individual valves of the diatom in air as well as in water were measured by acquiring transmission images at varying objective-sample distances. By constructing cross-sectional intensity profiles of transmitted light, we can easily visualize and compare the transmission property of valves. In order to quantify the light transmission characteristic, an approach based on analyzing mean intensities of specified regions of interest (ROIs) was also conducted. *shsu@physics.usyd.edu.au; phone 61 2 93517697; fax 61 2 93517726 Bioinspiration, Biomimetics, and Bioreplication 2012, edited by Akhlesh Lakhtakia, Raúl J. Martín-Palma, Proc. of SPIE Vol. 8339, 83390F · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.915044 Proc. of SPIE Vol. 8339 83390F-1