Optical properties of chitin: surface-enhanced Raman scattering substrates based on antireflection structures on cicada wings

The transparent wings of some cicada species present ordered arrays of papillary structures with a spacing of approximately 200 nm. These structures serve an antireflection function, with optical transmission peaking at a value of approximately 98% and rising above 90% over a broad band from 450 to 2500 nm. The dimensions of the papillae are comparable to the roughness scale of surface-enhanced Raman scattering (SERS) substrates. SERS measurements performed on silver- and -old-coated wings display enhancement factors of approximately 106 with no apparent background contribution from the wing.