The potential of total excitation-emission fluorescence microscopy combined with multiway chemometric analysis was investigated for the nondestructive forensic analysis of textile fibers. The four pairs of visually indistinguishable fibers consisted of nylon 361 dyed with acid yellow 17 and acid yellow 23, acetate satin 105B dyed with disperse blue 3 and disperse blue 14, polyester 777 dyed with disperse red 1 and disperse red 19, and acrylic 864 dyed with basic green 1 and basic green 4. Excitation emission matrices were recorded with the aid of an inverted microscope and a commercial spectrofluorimeter. The full information content of excitation-emission matrices was processed with the aid of unsupervised parallel factor analysis (PARAFAC), PARAFAC supervised by linear discriminant analysis (LDA), and discriminant unfolded partial least-squares (DU-PLS). The ability of the latter algorithm to classify the four pairs of fibers demonstrates the advantage of using the multidimensionality of fluorescence data formats for the nondestructive analysis of forensic fiber evidence.
Discovering common origins of trace evidential textile fibers can be a challenging task when fiber structure or dye composition does not provide exclusive identifying information. Introduction of new chemical species after mass production and distribution of a textile may be exploited to trace its history and identify the origin of its fibers. In this article, fluorescence microscopy is used to examine the alteration in the fluorescence spectral fingerprint of single fibers resulting from exposure to commonly used detergents that contain fluorescent whitening agents. Dyed acrylic, cotton, and nylon fibers were laundered and the spectral contribution of the detergent on single fibers was quantified and shown to reach a maximum after five sequential washes; some detergents showed statistically meaningful differences to fiber spectra after only a single wash. Principal component cluster analysis was used to determine that the spectra of laundered fibers are distinct from the spectra of dyed, unwashed cotton or nylon, but not acrylic, fibers.
Trace fibers are an important form of trace evidence, and identification of exogenous substances on textile fibers provides valuable information about the origin of the fiber. Laundering textiles can provide a unique fluorescent spectral signature of the whitening agent in the detergent that adsorbs to the fiber. Using fluorescence microscopy, the spectral characteristics of seven detergents adsorbed to single fibers drawn from laundered textiles were investigated, and principal component analysis of clusters was used to characterize the type of detergent on the fiber. On dyed nylon fibers, spectra from eight different detergent pairs could be resolved and washed validation fibers correctly classified. On dyed acrylic fibers, five different detergent pairs could be resolved and identified. Identification of the detergent type may prove useful in matching a trace fiber to its bulk specimen of origin.
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