Unambiguous detection of nitrated explosive vapours by fluorescence quenching of dendrimer films.

Yan Geng,Mohammad A. Ali,Andrew J. Clulow,Paul E. Shaw,Paul Meredith,Paul L. Burn,Ian R. Gentle,Shengqiang Fan

doi:10.1038/ncomms9240

Abstract

Unambiguous and selective standoff (non-contact) infield detection of nitro-containing explosives and taggants is an important goal but difficult to achieve with standard analytical techniques. Oxidative fluorescence quenching is emerging as a high sensitivity method for detecting such materials but is prone to false positives—everyday items such as perfumes elicit similar responses. Here we report thin films of light-emitting dendrimers that detect vapours of explosives and taggants selectively—fluorescence quenching is not observed for a range of common interferents. Using a combination of neutron reflectometry, quartz crystal microbalance and photophysical measurements we show that the origin of the selectivity is primarily electronic and not the diffusion kinetics of the analyte or its distribution in the film. The results are a major advance in the development of sensing materials for the standoff detection of nitro-based explosive vapours, and deliver significant insights into the physical processes that govern the sensing efficacy.

Highlights

Unambiguous and selective standoff infield detection of nitro-containing explosives and taggants is an important goal but difficult to achieve with standard analytical techniques
Dendrimer 3 has a PL quantum yield (PLQY) of 67±7% in solution and 47±5% in the solid-state indicating that the first generation dendrons are sufficient to reduce the intermolecular interactions of the chromophores that would otherwise lead to the quenching of the luminescence in a film
Naphthalene was chosen as the interferent as it is the active component in widely used mothballs, is a solid so is simple to handle yet has a high vapour pressure, is an aromatic molecule with no nitro-groups, and is readily available in the perdeuterated form required for the neutron reflectometry (NR) experiments

Summary

Introduction

Unambiguous and selective standoff (non-contact) infield detection of nitro-containing explosives and taggants is an important goal but difficult to achieve with standard analytical techniques. An emerging concept in this space has been the utilization of oxidative fluorescence quenching for the detection of nitro-group containing explosive materials This has driven the development of fluorescent conjugated polymers[3,4,5,6], supramolecular structures[7,8,9], micelles[10] and dendrimers[11,12] capable of detecting vapours of nitroaromatic compounds such as 2,4,6-trinitrotoluene (TNT), which is the primary explosive in landmines and is part of numerous explosive compositions. The design criteria for sensing materials for the detection of nitro-containing explosives are ‘well established’[4,15] These criteria include the energetics of the system, which must be appropriate to ensure the target analyte molecule can accept an excited electron from the sensing material (see Fig. 1a for the general mechanism). Dendrimer and not just polymer sensing materials can show ‘amplified quenching’ where a single analyte can quench more than one chromophore[18]

Methods

Results

Conclusion