October 19, 2021

Forensic identification of a lock of dyed hair is now possible

A single strand of hair at a crime scene contains many clues that can help identify an abuser. In a recent study, scientists at Tokyo University of Science, Japan, combined two modern techniques, called Surface Enhanced Raman Spectroscopy (SERS) and X-ray Fluorescence (XRF), to distinguish the different colors of strands of individual hairs. Both of these techniques are almost non-destructive and can be used with portable devices, making them a promising way to obtain supporting evidence in forensic investigations.

In crime scene investigations, a single strand of hair can make a huge difference in the progress of a case or trial. In most cases, forensic scientists have to search for clues hidden in tiny amounts of substances or materials found at crime scenes. If a fallen strand of hair with attached root cells is found, a DNA test can reveal the identity of a criminal; unfortunately, this rarely happens. Although other types of DNA analysis can be performed using ‘mitochondrial DNA’ embedded in the hair shaft itself, such tests are not sufficient to reliably identify a person and generally require additional evidence. .

But what if a little fashion awareness could inspire a new forensic technique? In a recent study published in Analytical sciences, scientists at Tokyo University of Science have developed a strategy to identify criminals from a single strand of hair, taking advantage of the fact that hair dyeing is increasingly common. Their approach is to find out if two strands of hair belong to the same person based on the makeup of the hair dye products they contain. To do this, they used the two well-known analytical methods: SERS and XRF analysis.


Related article: From Muscles to Maggots: How a Variety of Samples Help Forensic Toxicologists Decipher the Past


An overview of the analytical techniques used in this study, which together distinguish two single strands of colored hair.

Tokyo University of Science Shinsuke Kunimura

Raman spectroscopy is an analytical technique based on the physical phenomenon of Raman scattering, which models certain energetic interactions that occur when photons collide with matter. SERS is a special type of Raman spectroscopy that provides a “structural fingerprint” of a material even when very few molecules are present in the target sample. On the other hand, XRF analysis involves irradiating a material with X-rays and examining the energies of the re-emitted photons when the electrons in the sample leave the excited states. XRF analysis is particularly useful for determining which metallic elements are present in a material.

Scientists performed SERS and XRF analyzes using portable devices to see if they could distinguish between single strands of pig hair dyed with different products. Associate Professor Shinsuke Kunimura, who led the study, explains why the two analytical methods had to be used in combination, “SERS can easily detect the overall differences in composition between different types of hair dyes, such as permanent dyes, semi-permanent or natural. However, it is not enough to distinguish hair dye products that contain or produce similar dyes. To do this, we also relied on XRF analysis, which can detect the presence of metallic elements used in the ingredients of hair coloring products. Using the two techniques, the scientists were able to easily distinguish five different dyes applied to individual strands of pig hair.

Since the two analytical methods used are almost non-destructive, the strategy proposed in this study could be used to quickly analyze hair found at on-site crime scenes before it is sent for DNA analysis. “Our approach provides useful information to more reliably identify hair found at a crime scene,” notes lead author Momona Horiguchi. “It could help us clarify whether someone is a criminal, which means that our methodology could greatly assist in forensic investigations.”

Overall, this study shows how analytical tools normally used in chemistry and materials science can be creatively adapted to very different fields, such as forensic investigations. Hopefully in the future this will prevent criminals from escaping by a hair’s breadth!

This press release was originally posted on the Tokyo University of Science Media Relations website. It was edited for style


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