Igor K. Lednev* and Shelby R. Khandasammy | University at Albany – State University of New York Abstract: Gunshot residue (GSR) is an important type of trace evidence, which is often associated with a violent crime. Traditionally, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, also known as SEM-EDS or SEM-EDX, is used for detection and identification of GSR particles. The application of this two-step method is limited to inorganic GSR (IGSR) because it relies solely on the detection of heavy metals (i.e., lead, barium, and antimony). This is problematic because environmental concerns have led to the increased popularity of heavy metal- free or “green” ammunition. It has been found that accurate identification of GSR samples using current elemental analysis techniques is severely hindered in the absence of heavy metals. Additionally, the probability of environmental and manufacturing particles being incorrectly assigned as GSR has increased with the onset of “green” ammunition. Recently, organic GSR (OGSR) has been the focus of many forensic researchers for several reasons. First, the total amount of OGSR generated because of the discharge of a firearm is much larger than the amount of IGSR. Second, OGSR particles are typically much larger than IGSR particles. In addition, the chemical composition of OGSR is quite complex and includes partially burned and unburned smokeless powder, stabilizers, and plasticizers. As a result, it is easier to detect and identify OGSR particles, although new methods are required. The research team’s laboratory has developed a new two-step approach for fast detection of OGSR particles using fluorescence spectroscopy followed by a confirmatory identification by Raman microspectroscopy. The method uses a single instrument combining a confocal scanning Raman microscope and a fluorescence microscope working in reflection mode. In the first proof-of-concept study, the research team used adhesive tape to collect OGSR particles. Most recently, they significantly expanded this emerging methodology by demonstrating the possibility of detecting and identifying IGSR particles. In addition, they explored the ability of the method to detect GSR particles on original common substrates (e.g., cotton fabric), eliminating the initial GSR particle transfer stage. This presentation will demonstrate and discuss the results of these recent studies and the challenges and future steps for the proposed two-step method development for the detection and confirmatory identification of both OGSR and IGSR particles. In addition, results from the most recent proof-of-concept study involving the direct detection of GSR particles on a fabric substrate (without using an adhesive tape) will be reported.