Structural Analysis of the Outermost Hair Surface Using TOF-SIMS with Gas Cluster Ion Beam Sputtering

In the study, researchers used time-of-flight secondary ion mass spectrometry (TOF-SIMS) with argon gas cluster ion beam (Ar-GCIB) sputtering to analyze the structure of the hair cuticle's outermost surface, known as the epicuticle. They previously confirmed the presence of lipids and a cysteine-rich layer on the epicuticle using a different technique. In this analysis, they focused on the shallow depth profile of the cuticle surface with an Ar-GCIB impact energy of 5 keV. The findings showed that the decay of the 18-methyleicosanic acid (18-MEA) thiolate peak was the fastest among other amino acid peaks, suggesting that 18-MEA is abundant on the hair's outermost surface. The results support the hypothesis that the outermost surfaces of hair cuticles have a multilayer structure composed of lipid and protein layers.