A Tunable Reflector Enabling Crustaceans to See but not be Seen

Keshet Shavit ¹ Avital Wagner ^1,2,3 Lukas Schertel ⁴ Viviana Farstey ^4,5 Derya Akkaynak Gan Zhang ^1,6 Alexander Upcher ^7,8 Amir Sagi ⁹ Venkata Jayasurya Yallapragada ² Johannes Haatja Benjamin Palmer ¹

¹Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, 8410501, Israel
²Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, U.K.
³Department of Physics, University of Fribourg, Chemin du Musée 3, 1700 Fribourg, Switzerland.
⁴The Interuniversity Institute for Marine Sciences, Eilat, 8810302, Israel
⁵Hatter Department of Marine Technologies, University of Haifa, Haifa, 3498838, Israel
⁶Ilse Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Be’er Sheba, 8410501, Israel
⁷Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, 8410501, Israel
⁸The National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, 8410501, Israel
⁹Department of Physics, Indian Institute of Technology, Kanpur, Uttar Pradesh, 208016, India

Many oceanic prey animals use transparent bodies to avoid detection. However, conspicuous eye pigments, required for vision, compromise the organisms’ ability to remain unseen. We report the discovery of a reflector overlying the eye pigments in larval decapod crustaceans and show how it is tuned to render the organisms inconspicuous against the background. The ultra-compact reflector is constructed from a photonic glass of crystalline isoxanthopterin nanospheres. The nanospheres size and ordering are modulated to tune the reflectance from deep blue to yellow, enabling concealment in different habitats. The reflector may also function to enhance the acuity or sensitivity of the minute eyes by acting as an optical screen between photoreceptors. This multifunctional reflector offers inspiration for constructing tunable artificial photonic materials from bio-compatible organic molecules.