Upconversion Nanoparticle Tagging of Explosives and Post-blast Residue Analysis by Single Particle ICP-MS

Automated teller machine (ATM) attacks involving improvised explosive devices (IEDs) pose a significant risk to public safety and property and have significantly increased in recent years. This study explores the use of upconverting nanoparticles (UCNPs) as novel forensic taggants and their decoding by single particle inductively coupled plasma-mass spectrometry (spICP-MS) analysis to enhance traceability for legal authorities and shed light on distribution networks of explosives that are used in ATM attacks. As a result, it can be used to identify individual vendors, manufacturers, or even production batches. Two types of UCNPs, NaYF₄:Yb,Er (Type A) and NaYbF₄:Tm (Type B), were incorporated into flash powder and a polymer-bonded explosive (PBX) based on pentaerythritol tetranitrate (PETN). Flash powder was used as the most common pyrotechnic mixture in ATM attacks, and PETN as one of the most common military high explosives. To assess postexplosion recovery test detonations, sampling was conducted with target plates made of copper, aluminum, and quartz glass, positioned at various distances from the blast site. Residue analysis using spICP-MS confirmed the successful and reproducible detection of UCNPs after detonation. Particle size distribution analysis showed minimal reduction within the standard deviation limits for the flash powder (Type A: 6.7% and Type B: 2.4%), while PETN explosions resulted in greater size reductions (Type A: 33.4% and Type B: 46.0%). No significant differences in recovery or size distribution were observed across the different target materials. These findings highlight the potential of UCNPs for forensic investigations, facilitating the identification and source attribution of postexplosive residues.