A Novel Two-Step Method for the Detection of Organic Gunshot Residue for Forensic Purposes: Fast Fluorescence Imaging Followed by Raman Microspectroscopic Identification.

Gunshot residue (GSR) is potentially key evidence during a criminal investigation of a shooting accident. Current standardized forensic science methods target the detection of inorganic GSR (IGSR). In this proof-of-concept study, a new two-step method for the detection and identification of organic GSR (OGSR) is proposed. This method utilizes highly sensitive fluorescence hyperspectral imaging of a sample area to detect potential GSR particles, followed by confirmatory identification of the detected particles using Raman microspectroscopy. In this study, two different GSR samples on adhesive tape substrates were created. One sample was made by manually placing a known amount of OGSR particles onto an adhesive tape substrate. The second sample mimicked a real crime scene situation and had an unknown number of GSR particles mounted onto an adhesive tape substrate using a most common tape-lifting procedure for the recovery of GSR from the skin of a suspect and other surfaces. These two samples were subjected to the developed two-step analysis method. It was found that this method was accurately able to detect and identify all OGSR particles. Representative spectra of OGSR particles showed characteristic Raman peaks at 850 cm-1, 1287 cm-1, and 2970 cm-1. This methodology offers a promising means to meet current needs within the framework of GSR analysis by providing a way to accurately detect and identify OGSR.