Abstract
Chlorine, commonly found in pools and tap water, presents an intriguing concern in forensic hair analysis due to its sources and composition. Current forensic analysis involves optical microscopy which is subjected to advanced training where even multiple experts can deliver opposing conclusions for the same hair sample. Despite challenges in traditional analysis methods, emerging techniques like surface-enhanced Raman spectroscopy (SERS) offer promising solutions, showcasing success even in harsh environments like prolonged sunlight or stagnant water immersion. This study employs partial least-squares discriminant analysis (PLS-DA) to evaluate SERS efficacy in identifying dyes on hair immersed in chlorinated and distilled moving water for up to eight weeks. Our results demonstrated that one semipermanent colorant overwhelmingly influenced Raman signals in dyed hair exposed to both chlorinated and nonchlorinated water over an eight-week period, masking other colorants' spectral signatures. Despite one colorant's dominance, PLS-DA identified underlying colorants and their exposure conditions, suggesting persistent, unique interactions between original colorants and the environment. This study demonstrates the high potential for PLS-DA-based identifications of dyes on hair using SERS.