Swift and sensitive TNT detection

Selective detection of explosive material at concentrations as low as 6 μM in the field


Optical image of a cotton swab with AIS QDs (top cotton swab) and after exposure to 1 millimolar TNT (bottom cotton swab). The scale bar is 10 mm. (Navy photo)

Trinitrotoluene (TNT) has various applications in industrial settings and is also used as energetic material in military ordnance.

The U.S. government is concerned about TNT’s unlawful use as a weapon. But also its lawful use’s impact on the environmental, such as at military installations. Trace amounts of TNT can be found in water streams and soils near military installations, presenting a possible public health hazard.

TNT had been identified at more than 30 sites on the EPA’s National Priorities List. Inhalation of dust and ingestion and dermal absorption of TNT particulates can cause disease, including liver necrosis and aplastic anemia.

Accurately detecting TNT through inductively coupled plasma mass spectrometry (ICP-MS) in a laboratory is expensive. And field expedient methods are not sufficiently sensitive and too slow, making them impractical.

Tasked with developing alternative analytical methods and devices for identifying the presence of TNT at very low levels in a field setting, Navy scientists have developed a simple approach utilizing non-toxic, environmentally stable, quantum dots (QDs).

The QDs are functionalized by the attachment of a ligand which, when in contact with TNT, fluoresces for an instant visual test. A primary function of a suitable ligand is that it binds to the target compound and triggers a charge transfer between the target molecule and the nanoparticle. Preferred ligands include hetero-straight chain, heterocyclic, or hetero-aromatic compounds such as dodecylamine, dodecanethiol, phenanthroline, bipyridine, and thiocyanate.

While many chemical structures of the QDs are listed in the patent, the preferred composition is Silver, Indium, and Sulphur (AIS) QDs, synthesized by a thermal decomposition reaction. The AIS QDs show strong fluorescent properties that can be tuned to detect TNT molecules at concentrations as low as 6 μM in solution. The AIS QD nanomaterials can be patterned on low-cost paper (test strips) for portable TNT field detection by the eye under UV light.

Collectively, the ease of the synthesis of the less toxic AIS QDs, and the ability to visually detect TNT molecules will enable highly sensitive and portable substrates for environmental monitoring, chemical weapons detection, and other useful applications.

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