Circumventing substrate interference in the Raman spectroscopic identification of blood stains  Gregory McLaughlin, Vitali Sikirzhytski, Igor K. Lednev  Forensic Science International  Volume 231, Issue 1, Pages 157-166 (September 2013) DOI: 10.1016/j.forsciint.2013.04.033 Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 1 Photograph of blood stains on various substrates (cotton, glass, tile denim and recovered blood). Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 2 Raman spectra of pure blood acquired using 406.7 (A), 457.9 (B), 488 (C), 514.5 (D), 647.1 (E) and 785 (F) nm excitations. Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 3 Raman spectrum of a blood stain on glass acquired using 406.7 (A), 457.9 (B), 488 (C), 514.5 (D), 647.1 (E) and 785 (F) nm excitations. For comparison, the black traces are the normalized spectra for the substrate reference. In F, the green trace is the normalized result of manual substrate contribution subtraction. (For interpretation of the references to color in the artwork, the reader is referred to the web version of the article.) Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 4 Raman spectrum of a blood stain on tile acquired using 406.7 (A), 457.9 (B), 488 (C), 514.5 (D), 647.1 (E) and 785 (F) nm excitations. For comparison, the cyan traces are the normalized spectra for the substrate reference. In F, the green trace is the normalized result of manual substrate contribution subtraction. (For interpretation of the references to color in the artwork, the reader is referred to the web version of the article.) Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 5 Raman spectrum of a blood stain on cotton acquired using 406.7 (A), 457.9 (B), 488 (C), 514.5 (D), 647.1 (E) and 785 (F) nm excitations. For comparison, the blue traces are the normalized spectra for the substrate reference. Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 6 Normalized stack plot Raman spectra for selected dilute blood and blood recovery experiments. The left panel is the raw spectrum, and the right panel is the result after subtraction of a reference spectrum for cotton. A–A′ is 2:1, B–B′ is 40:1, C–C′ is 60:1 (water:blood), and D–D′ is blood recovered from a blood stain on glass. (D and D′ spectra were manually baselined for representation). Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 7 Normalized stack plot of Raman spectra of a blood stain on denim. (A) Raw blood stain on denim, (B) Blank denim spectrum (C) Blank cotton spectrum (D) Pure blood reference (E) Baselined blood stain spectrum (F) Subtraction result after eliminating the denim contribution. Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions

Fig. 8 The Raman spectra of blood on different substrates with the fitted spectroscopic signature of blood (green lines). For comparison the same fitting procedure was performed for the Raman spectrum for pure cotton. (For interpretation of the references to color in the artwork, the reader is referred to the web version of the article.) Forensic Science International 2013 231, 157-166DOI: (10.1016/j.forsciint.2013.04.033) Copyright © 2013 Elsevier Ireland Ltd Terms and Conditions