Invisible barcodes based on the unique thermal properties of nanoparticles may be a promising approach to tracking, authenticating and tracing the origins of various items. The technique, described in Scientific Reports, could be used to tag explosives, drugs and ink.

Visible barcodes that are widely used to label objects can be altered or duplicated, and face challenges from product counterfeiting and unlawful use. Covert (invisible) tags represent a promising alternative, although existing techniques are not suitable for large-scale labelling due to various problems, such as being easily degraded or having limited coding capacity. A new covert barcode system based on nanoparticles that can be identified by their unique melting points, reported by Ming Su and colleagues, may overcome these issues.

The researchers show that nanoparticle barcodes can be added to solid and liquid drugs, where they remain stable and seem to have no appreciable toxic effects. Thus, these covert barcodes may be used for drug authentication. Su’s team demonstrate that this technique could be used forensically to trace the origins of explosives by tagging dinitrotoluene, a precursor to the trinitrotoluene (TNT), then detecting the thermal signatures in the debris after detonation. They also suggest that adding selected nanoparticles to ink and polymers used in printing could be used for anti-counterfeiting purposes.

The authors conclude that their method could label a large number of objects thanks to the small sizes of nanoparticles, sharp melting peaks and large temperature range of thermal analysis, and could enhance forensic investigations.