Near-infrared excitation Raman analysis of Underlying colorants on redyed fabric

Forensic analysis of fabric is often critically important to establish a relationship between a suspect and a crime scene or demonstrate the absence of such connections. Most of commercially available fabric is colored with primarily organic colorants. These dye substances are highly fluorescent, which limits the use to conventional Raman spectroscopy for the analysis of the colorant content of fabric. At the same time, elucidation of the chemical composition of dyes in fabrics can be used to advance the importance of this physical piece of evidence for forensic research. Our recent findings showed that near-infrared excitation Raman spectroscopy (NIeRS) could be used to overcome this limitation. However, it remains unclear to what extent NIeRS could be used to identify the presence of several different colorants on fabric, as well as utilize for the analysis of dyes on fabric contaminated with paints. In this study, we utilized a hand-held NIeRS instrument to ex-amine re-colored cotton fabric and cotton fabric with household paints applied on it. Our results indicate that NIeRS coupled with chemometrics highly accurately identify the presence of several colorants on cotton. We also found that the presence of paint fully obscures the ability of NIeRS to extract the information about the dye content of the fabric. These results expand our understanding of the use of NIeRS in the forensic analysis of colored fabric. Forensic analysis of fabric is often critically important to establish a relationship between a suspect and a crime scene or demonstrate the absence of such connections.