Investigation of dyed human hair fibres using apertureless near‐field scanning optical microscopy

The study investigated dyed human hair fibers using apertureless near-field scanning optical microscopy. Researchers examined 5-µm-thick cross-sections of hair that were bleached and then dyed with two different molecular probes. These probes either diffused deep inside the fiber or spread mainly at its periphery. The study achieved an optical resolution of about 50 nm, which is below the diffraction limit. The images showed varying optical contrasts in the cuticle region, depending on the dye used. The findings suggested that dye confined to the hair periphery was primarily located at the surface and in the endocuticle.