Surface-enhanced Raman spectroscopy enables highly accurate identification of different brands, types and colors of hair dyes.

Hair is present at nearly all crime scenes. Forensic analysis of hair can be used to establish a connection between a suspect and a crime scene or demonstrate the absence of such connection. Almost half of people around the world color their hair. However, there is no robust and reliable forensic approach that can be used for a confirmatory analysis of artificial colorants present on hair. A growing body of evidence suggests that surface-enhanced Raman spectroscopy (SERS), a modern analytical technique, can be used to detect and identify colorants present on hair. In the current work, we examined the potential of SERS in identification of more than 30 different colorants. We found that the accuracy of detection and identification of individual hair colorants is 97%, on average. We also investigated the extent to which SERS can be used to differentiate between different brands and types of colorants, as well as to identify hair color regardless of the type and brand of the colorant used to dye hair. Our results showed that individual colorants could be identified with on average 97% accuracy, whereas different brands can be predicted with nearly 100% accuracy. We also found that SERS offered nearly 100% accurate identification of the type of the colorant and on average 97.95% accurate prediction of the hair color. These results demonstrate that SERS can facilitate the forensic analysis of hair providing highly important information about the artificial colorants present on the analyzed specimens.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.