Confocal Raman Spectroscopy of Whole Hairs

Abstract

This paper describes the application of Raman spectroscopy to whole hair fibers. Previously this has proved difficult because the hairs are relatively opaque, and spatial resolution diminishes with depth because of the change in refractive index. A solution is to couple confocal Raman with multivariate curve resolution (MCR) data analysis, which separates spectral differences with depth despite this reduction in resolution. Initially, it is shown that the cuticle can be separated from the cortex, showing the differences in the proteins, which can then be plotted as a function of depth, with the cuticle factor being seen only at the surface as expected. Hairs that had been treated in different ways, e.g., by bleaching, treatment with the active molecule resorcinol followed by rinsing and treatment with a full hair care product, were also examined. In all cases, changes to the hair are identified and are associated with specific parts of the fiber. Since the hair fiber is kept intact, it can be repeatedly treated and measured, hence multistep treatment processes can be followed. This method expands the potential use of Raman spectroscopy in hair research.

What can Raman spectroscopy do for criminalistics?

“…Pudney et al also analyzed bleached hairs from yaks and humans, and showed similar results to Kuzuhara . They demonstrated that for a depth study using both dry and immersion microscope objectives the cuticle region could be distinguished from the cortex, after applying multivariate curve resolution analysis.…”

A Raman spectroscopic investigation of the mechanism of the reduction in hair with thioglycerol and the accompanying disulphide conformational changes

“…The band frequency and FWHM of the six components in the S-S band region are shown in Table I. According to Schlucker et al's method [28], the band frequency of the six components was selected. Here, the band frequency and FWHM of the six components of all hair samples were fixed, as the band intensity of all hair samples was changed.…”

“…As the work of Frushour and Koenig [8], which provided assignments for the side and main chain vibrations in wool keratin, Raman spectroscopy has been used in structural studies of keratin fibres related to wool finishing [9][10][11][12][13][14][15][16] and hair science [5][6][7][17][18][19][20][21][22][23][24][25][26][27][28].…”

“…on a slide glass, to investigate the internal structure in the fibres. Cross-sectional samples were produced using white human hair, and sections (spot diameter of laser beam: 1 lm) of the hair at varying depths(1,2,3,4,5,10,15,20,25,28 and 30 lm) from the surface were measured with a Raman microscope.…”

Nanoscale Molecular Characterisation of Hair Cuticles using Integrated AFM-IR

“…Previous work using vibrational spectroscopy to study hair structure, such as ATR-FTIR and Raman spectroscopies, provided bulk spectra with some depth profiling of the fibre. 22,23 Chemical microscopies e.g confocal Raman, have been applied to determine chemical variation through the hair fibre using microtome cross-sections. 24 These methods yield relatively poor spatial resolution however, owing to the diffraction limit of light, and thus cannot reveal many crucial sub-micron features of the fibre.…”