Forensic Identification of Red Dyes on Fabric Fibers Using Raman Microscopy and Surface-Enhanced Raman Scattering via Microwave Assisted Microextraction

Abstract

Improving the reliability of methods for fiber analysis is crucial toward the ability of forensic examiners to establish the association of the perpetrator with a crime scene or a victim. This interest has led to the development of analytical methods including various forms of mass spectrometry, infrared microscopy, UV-vis microspectrophotometry, thin-layer chromatography (TLC) and Raman microscopy. The imaging capability of Raman microscopy and the analytical sensitivity of surface-enhanced Raman scattering (SERS) coupled with its ability to overcome fluorescence have been demonstrated for the identification of textile fibers through its polymeric composition and dyes. In this study, Raman microscopy has been evaluated in forensic examination of fibers with different polymer composition and visually similar red dyes. The experimental conditions of laser power, excitation wavelength, and spectral processing techniques were investigated for their influence on the discriminating power of the Raman technique. Furthermore, a novel approach based on the use of colloidal silver solution for microwave-assisted microextraction of dyes has been used to discriminate similar dyes extracted from single strands of sub-milligram fiber samples followed by SERS analysis. This new method allows identification of fluorescent and non-fluorescent dyes on fiber. Special efforts are devoted to the acquisition of distinctive spectra for each unique combination of dye and the polymer substrate. The development of a customized Raman spectral database and evaluation of criteria relevant to spectral search algorithm are explored for facilitating the identification and classification of dyes on fiber.