Gold nanoparticle coated U-bend fibre optic probe for localized surface plasmon resonance based detection of explosive vapours

In this study, we report a chemical sensor utilizing localized surface plasmon resonance (LSPR) of gold nanoparticles (GNP) for vapour phase detection of explosives like 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX). The GNP were immobilized on a U-bend fibre optic sensor probe of 200 μm core diameter and bend diameter of 1.5 mm for evanescent field based excitation of localized surface plasmons of the GNP. The immobilized GNP were functionalized with receptor molecules viz. 4-mercaptobenzoic acid (4-MBA), l-cysteine and cysteamine to provide the binding sites for the nitro-based explosive molecules. Binding of the explosive analytes to the surface moieties of the GNP was found to elicit refractive index changes in the environment surrounding the nanoparticles. This led to changes in the absorbance characteristics of the GNP-LSPR spectrum. Furthermore, the GNP coated probes modified with l-cysteine and cysteamine exhibited a high degree of selectivity towards TNT. The detection limit of the LSPR fibre optic probe for TNT vapours was found to be in the lower parts per billion (ppb) with further scope for improvement.