Polyethylene imine capped copper nanoclusters- fluorescent and colorimetric onsite sensor for the trace level detection of TNT

Abstract

Rapid, reliable, onsite approaches for the trace level detection of trinitrotoluene (TNT) is a pressing necessity for both homeland security and environmental protection. Selective detection of TNT from other nitroaromatics is still challenging as it possess similar chemical structure and properties with its analogues. In the present work, the water soluble polyethylene imine protected copper nanoclusters (PEI CuNC) were developed as fluorescent and colorimetric probe which can detect TNT selectively and sensitively both in aqueous and vapour form. The PEI CuNC with size less than 3nm was prepared via a simple one pot microwave method and exhibited bright blue emission at 480nm. The fluorescence of PEI CuNC can be remarkably quenched by TNT through the formation of amine-TNT Meisenheimer complex. Quenching was further facilitated by fluorescence resonance energy transfer (FRET) and inner filter effect (IFE). A good linearity was observed for the PEI CuNC based fluorescence detection of TNT with limit of detection 14 pM. Meanwhile the formation of Meisenheimer complex resulted in a significant colour change of the solution from pale green to red, which enables visual detection of TNT with detection limit down to 0.05nM. The fluorescence as well as colorimetric method displayed excellent selectivity and sensitivity over other interfering compounds and ions. Fluorescent paper strip sensor was developed to detect TNT in vapour phase as well as solution form. PEI CuNC coated paper strips were able to detect TNT vapours with in one minute with a limit of detection 10nM, providing a valuable platform for sensing TNT in public safety and security.