Portable LIBS Paves the Way for More Effective Gunshot Residue Testing

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Forensics is a storied field, but one of the areas that lack reliable analysis techniques is the investigation of gunshot residue (GSR). The collection of GSR is often left to the discretion of the investigator, and with no routine screening methods available, turnaround times can reach up to two months.

Proccess of collecting possible gunshot residue from suspected man indoor | Image Credit: © Couperfield - stock.adobe.com

Proccess of collecting possible gunshot residue from suspected man indoor | Image Credit: © Couperfield - stock.adobe.com

In a new study, published in Spectrochimica Acta Part B: Atomic Spectroscopy, scientists present a Laser Induced Breakdown Spectroscopy (LIBS) instrument that is designed with enhanced magnification qualities for single particle targeting, argon gas flow, and a custom sample stage that is compatible with the standard aluminum stubs used by law enforcement and SEM-EDS detection(1). The portable LIBS system’s performance was compared to a laboratory LIBS instrument. Both instruments had more than 98.8% accuracy rates.

Gunshot residue contains inorganic and organic constituents, labeled as IGSR and OGSR, respectively, that land on nearby surface when a gun is fired. To identify IGSR, currently most scientists rely on Scanning Electron Microscopy-Energy Dispersive X-Ray Spectrometry (SEM-EDS). While this method can easily identify particles that are rarely found anywhere other than GSR, which stems from these particles’ spherical morphology and elemental compositions, it is a time-consuming process that can last hours to scan a single sample. Other methods of screening for IGSR have been proposed to reduce costs and analysis times, such as Raman spectroscopy and electrochemistry.

Portable LIBS systems, by comparison, can help speed up response times, enabling samples to be analyzed in minutes, compared to hours when using SEM-EDS. If properly incorporated into workflows, crime scene investigations can be improved, backlogs can be reduced, and case management will improve.

Previous studies have looked at LIBS as a method for analyzing GSR. However, these methods faced various issues, including being unable to work without direct contact, which risks damage to samples, a lack of argon flow that can increase analyte signals, and an inability to visualize the sample surface to establish sampling locations, which could lead to inaccurate analyses.

Reference

(1) Pyl, C. V.; Menking-Hoggatt, K.; Arroyo, L.; Gonzalez, J.; Liu, C.; Yoo, J.; Russo, R. E.; Trejos, T. Evolution of LIBS technology to mobile instrumentation for expediting firearm-related investigations at the laboratory and the crime scene. Spectrochim. Acta Part B At. Spectrosc. 2023, 207, 106741. DOI: https://doi.org/10.1016/j.sab.2023.106741