three-dimensional photonic crystals with different lattice constants
and a structure in the form of an inverse opal entirely composed
of silk fibroin (a silk inverse opal, SIO). Theoretical calculations
are paired with experimental characterization of the spectral
responses of the device and reveal the existence of a pseudo-photonic
bandgap (pPBG) in the visible spectral range. Tuning of the colorimetric
response is shown by immersing the SIOs in a liquid, and
their potential use as a chemical-free contrast agent is demonstrated
by embedding the SIO within scattering biological tissue in vitro. In
addition, by mixing gold nanoparticles into the silk solution, we
show the simple fabrication of functionalized SIOs and demonstrate
photonic crystal-enhanced absorption and associated patterned
laser heating.