the structure. This can be achieved either by doping the silk or by
filling the structure. Spectral responses were measured using an
optical set-up under white-light illumination by collecting visible–
near-infrared reflectance spectra. By decreasing the refractive
index contrast, the wavelengths corresponding to the peak reflected
light are redshifted. To illustrate this concept simply, we exposed the
SIO to acetone, which has a low enough surface tension to infiltrate
the nanostructured lattice and is volatile enough not to cause any
swelling in the protein matrix