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Silk inverse opals


Periodic nanostructures provide the facility to control and manipulate the flow of light through their lattices. Three-dimensional photonic crystals enable the controlled design of structural colour, which can be varied by infiltrating the structure with different (typically liquid) fillers. Here, we report three-dimensional photonic crystals composed entirely of a purified natural protein (silk fibroin). The biocompatibility of this protein, as well as its favourable material properties and ease of biological functionalization, present opportunities for otherwise unattainable device applications such as bioresorbable integration of structural colour within living tissue or lattice functionalization by means of organic and inorganic material doping. We present a silk inverse opal that demonstrates a pseudo-photonic bandgap in the visible spectrum and show its associated structural colour beneath biological tissue. We also leverage silk's facile dopability to manufacture a gold nanoparticle silk inverse opal and demonstrate patterned heating mediated by enhancement of nanoparticle absorption at the band-edge frequency of the photonic crystal.

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Figure 1: Fabrication steps for free-standing silk opal.
Figure 2: Optical response of SIO film.
Figure 3: Interface of SIO and biological material.
Figure 4: Absorption enhancements by the photonic band-edge.


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This material was based on work supported in part by the US Army Research Laboratory and the US Army Research Office (contract no. W911 NF-07-1-0618) and by DARPA-DSO (H.T., S.M.S., M.A.B., D.L.K., J.J.A. and F.G.O.) and the AFOSR. SEM images were obtained at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation (award no. ECS-0335765). CNS is part of the Faculty of Arts and Sciences at Harvard University.

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Authors and Affiliations



S.K. and F.G.O. conceived and performed SIO fabrication, optical measurements, computational work and data analysis. A.N.M. and J.D.S. contributed to the fabrication of water-insoluble opal and optical measurements. H.T. contributed to the laser-heating experiment. D.L.K and F.G.O. supervised the project. S.K. and F.G.O. wrote the paper. All authors commented on the results and the manuscript.

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Correspondence to Fiorenzo G. Omenetto.

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The authors declare no competing financial interests.

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Kim, S., Mitropoulos, A., Spitzberg, J. et al. Silk inverse opals. Nature Photon 6, 818–823 (2012).

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