Schiffmann Nathan, Wormser Eyal Merary, Brumfeld Vlad, Addadi Yoseph, Pinkas Iddo, Yallapragada Venkata Jayasurya, Aflalo Eliahu D, Sagi Amir, Palmer Benjamin A, Weiner Steve, Addadi Lia
Department of Structural Biology, Weizmann Institute of Science, Rehovot, 7610001, Israel.
Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 8410501, Israel.
Faraday Discuss. 2020 Oct 23;223(0):278-294. doi: 10.1039/d0fd00044b.
Reflective assemblies of high refractive index organic crystals are used to produce striking optical phenomena in organisms based on light reflection and scattering. In aquatic animals, organic crystal-based reflectors are used both for image-formation and to increase photon capture. Here we report the characterization of a poorly-documented reflector in the eye of the shrimp L. vannamei lying 150 μm below the retina, which we term the proximal reflective layer (PR-layer). The PR-layer is made from a dense but disordered array of polycrystalline isoxanthopterin nanoparticles, similar to those recently reported in the tapetum of the same animal. Each spherical nanoparticle is composed of numerous isoxanthopterin single crystal plates arranged in concentric lamellae around an aqueous core. The highly reflective plate faces of the crystals are all aligned tangentially to the particle surface with the optical axes projecting radially outwards, forming a birefringent spherulite which efficiently scatters light. The nanoparticle assemblies form a broadband reflective sheath around the screening pigments of the eye, resulting in pronounced eye-shine when the animal is viewed from a dorsal-posterior direction, rendering the eye pigments inconspicuous. We assess possible functions of the PR-layer and conclude that it likely functions as a camouflage device to conceal the dark eye pigments in an otherwise largely transparent animal.
高折射率有机晶体的反射组件用于基于光反射和散射在生物体中产生引人注目的光学现象。在水生动物中，基于有机晶体的反射器既用于成像，也用于增加光子捕获。在这里，我们报告了对凡纳滨对虾眼睛中一个记录较少的反射器的表征，该反射器位于视网膜下方150μm处，我们将其称为近端反射层（PR层）。PR层由密集但无序排列的多晶异黄蝶呤纳米颗粒组成，类似于最近在同一动物的反光层中报道的那些颗粒。每个球形纳米颗粒由许多异黄蝶呤单晶片组成，这些晶片围绕着一个水核以同心薄片的形式排列。晶体的高反射板面都与颗粒表面相切排列，光轴径向向外突出，形成一个双折射球晶，有效地散射光。纳米颗粒组件在眼睛的屏蔽色素周围形成一个宽带反射鞘，当从背侧后方观察动物时会产生明显的眼耀，使眼色素不明显。我们评估了PR层的可能功能，并得出结论，它可能起到伪装装置的作用，以隐藏原本大部分透明的动物体内深色的眼色素。
