Fig. S1.

Effect of UV light on silk polymorphism. (A) ATR-FTIR microscopy spectra of amorphous and UV-cross-linked silk films. All silk films showed a dominant absorbance at 1,641 cm⁻¹, indicating the presence of the amorphous protein. The spectrum of the UV-exposed silk film had an additional absorbance peak at 1,607 cm⁻¹, consistent with the [2π + 2π] cycloaddition of stilbene. (B) Photoluminescence spectra of amorphous and UV–cross-linked silk films. As exposure time is increased, the intensity of fluorescence decreases, consistent with the trans-cis isomerization of stilbene. (C) Normalized photoluminescence spectra. Whereas the spectra showed an overall decrease in intensity, the peak at 415 nm (dityrosine) increased relatively.