Elucidation of the effect of heat exposure on hair colored by permanent and semipermanent colorants using surface-enhanced Raman spectroscopy

• NCJ Number: 308047
• Journal: Journal of Forensic Sciences Volume: 68 Issue: 3 Dated: 2023 Pages: 807-814
• Author(s): Mackenzi Steczkowski; Dmitry Kurouski
• Date Published: 2023
• Length: 8 pages
• Grant Number(s): 15PNIJ-21-GG-04169-RESS
• Agencies: NIJ-Sponsored
• Publication Type: Research (Applied/Empirical)

Annotation

This paper on the use of surface-enhanced Raman spectroscopy (SERS) to analyze hair colorants found that short and especially long-term heat exposure at 220°C could alter chemical structure, and consequently SERS spectra, of permanent and semipermanent colorants.

Abstract

A growing body of evidence shows that surface-enhanced Raman spectroscopy (SERS) could be a confirmatory, minimally destructive, and fully noninvasive analysis of hair colorants. In this work, the authors determine the effect of a short- and long-term heat exposure on SERS-based analysis of hair colored with blue and red permanent and semipermanent dyes. The study found that short and especially long-term heat exposure at 220°C could alter chemical structure, and consequently SERS spectra, of permanent and semipermanent colorants. This thermal degradation of permanent dyes complicates their direct identification using SERS. The authors also found that partial least squares discriminant analysis can be used to overcome this issue allowing for highly accurate identification of both permanent and semipermanent dyes on colored hair that was exposed to 220°C for 6–12 min. These results show that heat exposure of colored hair should be strongly considered upon their SERS-based examination to avoid both false positive and false negative identification of chemical dyes. Confirmatory identification of hair colorants can be used to establish a connection between a suspect and the crime science or demonstrate the absence of such connections. In SERS, a signal that provide the information about the chemical structure of both permanent and semipermanent dyes present on hair is enhanced by a million-fold using noble metal nanostructures. However, it is unclear whether the information of hair colorants can be revealed if hair was contaminated or exposed to harsh environments such as sunlight and heat. (Published Abstract Provided)