Detection of nitroaromatic explosives using π-electron rich luminescent polymeric nanocomposites

Sensitive detection of trace amounts of explosives is significantly imperative in the present scientific world due to security concerns and environmental pollution problems. In this endeavour, carbon and silver nanoparticle impregnated graft polymers of poly(vinylalcohol) and polythiophene are synthesized via a single step free radical polymerization reaction for sensing nitroaromatic compounds via fluorescence measurements. The key role of the conducting nanoparticles is to enhance the pi-electron density of the luminescent polymer. These electron rich nanocomposites are successfully utilized for highly selective and ultrasensitive detection of electron deficient nitroaromatic explosives based on a fluorescence quenching method. Quenching efficiencies of the carbon and silver nanocomposites for highly electron deficient picric acid (PA) and 2,4,6-trinitrotoluene (TNT) are found to be 99% and 95% respectively. Mechanistic studies have been further explored in detail and it is observed that in most of the analytes including picric acid, a combination of excited state Forster Resonance Energy Transfer (FRET) and Photoinduced Electron Transfer (PET) leads to quenching of fluorescence. On the other hand, in analytes such as 2,4,6-trinitrotoluene, 1,4-dinitrobenzene and nitrobenzene excited state PET is the only reason behind fluorescence quenching. The detection limits of the carbon and silver nanocomposites are found to be in the nM level. Easy synthesis and scalable production of these materials in bulk quantities ensures their widespread future application in defence and industrial sectors for real time explosive detection.