Microspectroscopic soft X-ray analysis of keratin based biofibers

• STXM and TEM were employed for nanoscopic imaging of mammalian hair morphology.
• Resonant imaging achieves ultimate contrast for structural components of hair.
• NEXAFS gives insight into chemistry of various hair components and species.
• A quantitative study of X-ray induced processes within hair is presented.

Scanning soft X-ray transmission microspectroscopy (STXM) and transmission electron microscopy (TEM) have been employed for a high-resolution morphological and chemical analysis of hair fibers from human, sheep and alpaca. STXM allows optimum contrast imaging of the main hair building blocks due to tuneable photon energy. Chemical similarities and deviations for the human hair building blocks as well as for the three investigated species are discussed on the basis of the local near-edge X-ray absorption fine structure (NEXAFS). The spectra of melanosomes corroborate the state-of-the-art model for the chemical structure of eumelanin. Complementary TEM micrographs reveal the occurrence of cortex sectioning in alpaca hair to some extent. A spectroscopic analysis for human hair cortex indicates low mass loss upon soft X-ray irradiation, but transformation of chemical species with decreasing amount of peptide bonds and increasing NEXAFS signal for unsaturated carbon–carbon bonds.