Signal detection limit of a portable Raman spectrometer for the SERS detection of gunshot residue
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Research Letter
Signal detection limit of a portable Raman spectrometer for the SERS detection of gunshot residue Evan Thayer, Wilson Turner, Stephen Blama, Mary Sajini Devadas, and Ellen M. Hondrogiannis, Department of Chemistry, Towson University, 8000 York Road, Towson, MD 21252, USA Address all correspondence to Ellen M. Hondrogiannis at [email protected]; Mary Sajini Devadas at [email protected] (Received 17 June 2019; accepted 22 July 2019)
Abstract Signal detection limit (SDL), limit of detection (LOD), and limit of quantitation of a portable Raman spectrometer were measured for smokeless gunpowder stabilizers, diphenylamine (DPA) and ethyl centralite (EC), in acetone, acetonitrile, ethanol, and methanol. Acetone yielded the lowest LOD for three of four DPA peaks, and acetonitrile yielded the lowest LOD for two of three EC peaks and the remaining DPA peak. When gold nanoparticles were added to the DPA solutions in acetone and acetonitrile, statistically significant changes were observed (DPA peak position, full width at half maximum, and/or total area) and SDL was improved for the majority of all peaks in both solvents.
Introduction Gunshot residue (GSR) evidence is used forensically to determine if a firearm was discharged. The most common gunpowder is smokeless powder which consists of organic and inorganic components that make up the energetics, stabilizers, plasticizers, flash suppressants, deterrents, opacifiers, and dyes.[1] According to ASTM 1588-10,[2] GSR is exclusively identified by its morphology and the presence of lead, barium, and antimony measured by scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM-EDX). Recently, manufacturers have started producing lead-free ammunition, so analysis has shifted to the SEM-EDX detection of gadolinium, titanium, zinc, gallium, copper, tin, titanium, and strontium found in the GSR. A combination of the above, or just one of these elements, is considered consistent with GSR identification.[3] The issue with this approach is that some of these elements can also be found in the environment, in fireworks, and in some paints, thus creating the increased potential for false positives.[4] Recently, Raman spectroscopy has been used for the identification of GSR due to its ability to detect both the organic and inorganic components. Advances in Raman analysis of GSR are summarized by Doty and Lednev[5] as well as Suzuki and Buzzini,[6] in addition to the recent reviews by Maitre et al.[3] and Brozek-Mucha[7]. One drawback with Raman spectroscopy is its low sensitivity. Surface-enhanced Raman spectroscopy (SERS) overcomes this by using metal nanoparticles, typically gold, silver, or copper, to enhance the analyte’s signal via chemical or electromagnetic enhancement.[8] SERS applications to GSR have also been summarized by Suzuki and Buzzini.[6] The most recent work involving GSR SERS uses a gold substrate to identify organic components of low explosives. These
investigators used a Raman microscope and a 633-nm helium– neon laser to analyze
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