A highly reflective biogenic photonic material from core–shell birefringent nanoparticles


Spectacular natural optical phenomena are produced by highly reflective assemblies of organic crystals. Here we show how the tapetum reflector in a shrimp eye is constructed from arrays of spherical isoxanthopterin nanoparticles and relate the particle properties to their optical function. The nanoparticles are composed of single-crystal isoxanthopterin nanoplates arranged in concentric lamellae around a hollow core. The spherulitic birefringence of the nanoparticles, which originates from the radial alignment of the plates, results in a significant enhancement of the back-scattering. This enables the organism to maximize the reflectivity of the ultrathin tapetum, which functions to increase the eye’s sensitivity and preserve visual acuity. The particle size, core/shell ratio and packing are also controlled to optimize the intensity and spectral properties of the tapetum back-scattering. This system offers inspiration for the design of photonic crystals constructed from spherically symmetric birefringent particles for use in ultrathin reflectors and as non-iridescent pigments.

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Fig. 1: Schematic of the eye and in situ images of isoxanthopterin nanoparticles.
Fig. 2: The structural properties of the nanoparticles.
Fig. 3: Close-packing of isoxanthopterin nanoparticles into compartments and their arrangement within the retina.
Fig. 4: The microstructure and optical properties of the tapetum.
Fig. 5: Scattering from isolated nanoparticles.
Fig. 6: Reflectivity from arrays of nanospheres.

Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.


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This work was supported by Israel Science Foundation Grants 354/18 and 583/17, the Crown Center of Photonics and the ICORE: The Israeli Center of Research Excellence ‘Circle of Light.’ L.A. is the incumbent of the Dorothy and Patrick Gorman Professorial Chair of Biological Ultrastructure. D.O. is the incumbent of the Harry Weinrebe Professorial Chair of laser physics. B.A.P. is the recipient of the 2019 Azrieli Faculty Fellowship.

Author information

B.A.P., S.W., L.A. and D.O. designed and directed the study. V.J.Y. carried out the scattering and reflectivity calculations and performed reflectivity measurements. N.S. and E.M.W. prepared the samples for cryo-SEM and TEM, and performed image analysis and optical microscopy measurements. B.A.P. performed cryo-SEM and optical microscopy measurements. N.E. performed the TEM measurements and TEM tomography analysis. A.S. and E.D.A. provided the specimens and knowledge of shrimp biology. B.A.P., V.J.Y., S.W., L.A. and D.O. wrote the manuscript with contributions from all the authors.

Correspondence to Benjamin A. Palmer or Dan Oron.

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One sentence summary: The birefringence of isoxanthopterin crystalline spherulites enhances the reflectivity of a biological photonic crystal.

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Supplementary Information

Supplementary Figs. 1–5, Materials and Methods and refs. 1–7.

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Palmer, B.A., Yallapragada, V.J., Schiffmann, N. et al. A highly reflective biogenic photonic material from core–shell birefringent nanoparticles. Nat. Nanotechnol. (2020) doi:10.1038/s41565-019-0609-5

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