Fluoro explosives sensor made
The newly developed chemosensor will, in theory, stop glowing when in the presence of explosives.
Image: ytwong/iStockphoto

A promising fluorescent chemosensor for explosives detection has been developed by researchers at The Hong Kong University of Science and Technology.
Commonly used at airports and country borders, explosive detection is a non-destructive inspection process to determine whether a luggage bag or container contains explosive material.

Several techniques have been developed to detect trace signatures of various explosive materials, and ion mobility spectrometry (IMS) is the most commonly used technology in U.S. airports. Here, the time an ion takes to move a specified distance in an electric field indicates its identity.

Another technique, chemiluminescence, was used frequently in the 1990s, but is less common than the more ubiquitous IMS. Using amplifying fluorescent polymers (AFP) that recognize the molecular patterns of explosive materials, the presence of minute amounts of these explosives can then “turn off” or quench the fluorescence of a polymer.

In this study, the team led by Prof. Ben Zhong Tang, Professor of Chemistry at The Hong Kong University of Science and Technology, made hyperbranched polymers by the polycyclotrimerisation of tetraphenylethenes.

The polymers are completely soluble in common organic solvents such as chloroform, toluene, and THF. They are also thermally stable with high degradation temperatures of up to 443 and 446 °C, respectively, in nitrogen and air.

Whereas their solutions are almost non-emissive or weakly fluorescent, their aggregates in poor solvents and solid powders are brightly fluorescent with quantum yields of up to 81 percent, demonstrating a novel phenomenon of aggregation-induced or enhanced emission.

In these poor solvents and aggregated states, the light emission of the polymer can be quenched efficiently by picric acid – an effect similar to the explosives TNT and DNT, making the polymer a promising fluorescent chemosensor for detecting explosives.

The article can be found at: Hu R et al. Polymer Chemistry (2012) Hyperbranched conjugated poly(tetraphenylethene): synthesis, aggregation-induced emission, fluorescent photopatterning, optical limiting and explosive detection.

Editor's Note: Original news release can be found here.