Surface-Enhanced Raman Spectroscopic Characterization of Chitosan Extracted from Black Soldier Fly Pupa Shells

Chitosan is widely used as a matrix in metal nanoparticle-based surface-enhanced Raman scattering (SERS) substrates; however, its intrinsic spectral features may interfere with analyte identification. Conventional Raman spectroscopy of chitosan is further limited by strong fluorescence, resulting in scarce, reliable spectral data. In this study, chitosan extracted from Black Soldier Fly (BSF) (Hermetia illucens) pupa shells was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and silver nanoparticle-enhanced SERS. SERS measurements enabled the acquisition of well-resolved vibrational spectra of chitosan despite the strong fluorescence observed in conventional Raman measurements. Comparison with commercial chitosan and literature data allowed identification of characteristic spectral features associated with the chitosan molecular structure. The synthesized chitosan exhibited distinct structural and spectroscopic characteristics compared with the commercial material, including differences in relative crystallinity and characteristic FTIR and SERS spectral features. The results demonstrate that SERS is a suitable complementary spectroscopic approach for the characterization of chitosan and provides spectral information for the interpretation of chitosan-associated signals in SERS measurements.