Next time you find a strand of hair at a crime scene, pray the suspect doesn’t like the color of his or her natural hair.
Japanese researchers have developed a new method that can identify the difference between single hairs colored with different hair dye products. The method is based on the combination of surface-enhanced Raman spectroscopy (SERS) and X-ray fluorescence (XRF) analysis. In this case, the technologies are two pieces of a whole.
“SERS can easily detect the overall differences in composition between different types of hair dyes, such as permanent, semi-permanent, or natural dyes. However, it is not enough to distinguish between hair coloring products that contain or produce similar dyes,” explained study author Shinsuke Kunimura, a professor at Tokyo University of Science. “To do this, we relied on XRF analysis, which can detect the presence of metallic elements used in the ingredients of hair dye products."
The research team performed their experiment using five different permanent and semi-permanent hair dyes on white pig hair. The hair sample was first sandwiched between a quartz glass substrate and a silver evaporated film, as well as sandwiched between two quartz glass substrates.
One day post-dying, the researchers recorded strong Raman peaks for the samples sandwiched between the substate and film, but noticeable peaks were not detected when the sample was between the two glass substrates.
“This result shows that the intensities of Raman peaks originating from hair dye product can be enhanced by performing SERS,” the researchers wrote in their paper, published in Analytical Sciences.
Still, even with that boost, the SERS spectral pattern for hair dyes that contain similar types of dye did not produce presentative enough peaks. Thus, Kunimura and team turned to XRF analysis to see if it could detect characteristic metallic elements originating from the hair dye.
Indeed, XRF was able to detect iron, potassium, manganese and titanium from a single strand of dyed pig hair. In combination with the SERS data, researchers confirmed the method can positively identify the difference among hair dyed by different products. Additionally, both SERS and XRF are non-destructive methods, meaning further forensic analysis, such as DNA analysis, can be performed in the future, if need be.
Lastly, in their proof-of-concept experiment, the researchers purposely used portable Raman and XRF spectrometers to demonstrate easy on-site analysis, indicating the usefulness of the new technique at a crime scene.
“Therefore, the analysis of hair gathered at a crime scene using this combination can contribute to the rapid acquisition of information about the criminal and specifying the criminal,” the researchers conclude.