# Scanning Electron Microscopy Techniques in the Analysis of Gunshot Residues: A Literature Review
## 3 Results
### Gunshot Residue Analysis: Detection, Persistence, and Emerging Forensic Solutions  
Gunshot residue (GSR) analysis represents a crucial component of forensic investigations, allowing the reconstruction of shooting events and the establishment of a possible link between suspects, victims, and firearms. GSR particles, composed of both inorganic (iGSRs) and organic components (OGSRs), are traditionally analyzed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS) to detect characteristic elements such as lead (Pb), barium (Ba), and antimony (Sb), which form during the rapid cooling of the molten metals expelled from the firearm discharge. Recent studies have expanded our understanding of the distribution, persistence, and secondary transfer dynamics of these residues, highlighting the complexity of their forensic interpretation. For example, a study conducted on police vehicles in Zagreb County revealed a significant prevalence of iGSR contamination on multiple vehicle surfaces, notably on the driver and back seats. The research demonstrated that 63.1% of the sampled vehicles contained characteristic GSR particles, with logistic regression identifying the transport of individuals involved in shooting incidents as a statistically significant risk factor for GSR contamination within police vehicles [36]. This finding underscores the necessity of implementing contamination control protocols during forensic evidence collection to preserve its integrity. In addition to contamination risks, the dynamics of GSR secondary transfer were comprehensively evaluated through experimental studies involving various common surfaces, including ceramic, glass, metal, paper, and plastic. The results revealed that paper retained the highest quantity of transferred particles, followed by plastic and ceramic, while washing hands with water and soap significantly reduced particle persistence. This highlights the importance of accounting for surface material and post-discharge activities when interpreting secondary transfer evidence [37]. Moreover, research on the persistence and spatial distribution of GSRs on different regions of the human body emphasized the variability in residue retention based on sampling location. While the highest concentrations of both OGSRs and iGSRs were found on the hands, alternative collection sites, such as the forearms and face, were identified as reliable sampling options when hand-washing occurred. Interestingly, sampling from the nostrils showed minimal residue retention, making it less suitable as an alternative site [38]. The ear, however, emerged as an innovative sampling site due to its relative protection from environmental exposure and cleaning. Sampling the concha and external auditory canal proved effective in capturing GSRs following shotgun discharge, particularly the right ear, which was most affected due to body posture during firing [39]. Technological advancements have greatly enhanced the precision and efficiency of GSR analysis in recent years. Portable SEM devices have revolutionized on-site forensic investigations by enabling the real-time detection of GSR particles directly at crime scenes, significantly reducing the delay between evidence collection and analysis while maintaining a high level of accuracy [40]. Furthermore, combined analytical approaches integrating SEM/EDS with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) now allow the simultaneous detection of both inorganic and organic GSRs from a single sample. This methodological innovation increases the probative value of GSR evidence by offering a more comprehensive chemical profile. The sequential analysis protocol using SEM/EDS for iGSR detection followed by UHPLC-MS/MS for OGSRs demonstrated excellent recovery rates for both types of residues without significant particle loss, making it a valuable tool for complex forensic investigations [41].