Advanced forensic detection of gunshot residues using luminescent lanthanide metal-organic framework

The global rise in firearms-related crimes underscores the urgent need for rapid, sensitive, and field-deployable analytical tools to detect gunshot residues (GSR). Unlike earlier studies that utilized Lanthanide Metal-Organic Frameworks (Ln-MOFs) primarily as optical taggants incorporated in non-toxic ammunition, this work introduces a direct analytical interface between a separate luminescent Ln-MOF pellet and Organic analytes of GSR (OGSR) generated by firing of an optical taggant-free conventional ammunition, bridging molecular spectroscopy with forensic microanalysis. Nine luminescent Ln-MOFs were synthesized via the solvothermal method using various lanthanide metal precursors to explore their potential in OGSR identification. Among them, the gadolinium-based framework [Gd(NDC)] exhibited significant fluorescence quenching upon the addition of GSR, achieving a detection limit as low as ∼1 ppm. To enhance field applicability, a low-cost polystyrene-[Gd(NDC)] composite pellet was developed, enabling rapid, portable, and post-incident OGSR detection with minimal sample preparation. Comprehensive photophysical, microstructural, and surface analyses of Gd(NDC), including FTIR, XRD, BET, TGA, and DLS, revealed a clear correlation between the framework's structural parameters and its luminescent sensing performance.