Naked-Eye Detection of 3-Nitro-1,2,4-triazole-5-one at Sub-Femtomolar Levels with Melamine and Unlabeled Au Nanoparticles

Abstract

In this paper, a simple and rapid nanosensing assay was developed for 3-nitro-1,2,4-triazole-5-one (NTO) exploiting target-directed adsorption by unlabeled gold nanopartides (AuNPs) and competitive supramolecular association of NTO with melamine (MEL). While AuNPs aggregated in the presence of MEL with a color change from red to blue, AuNPs remained dispersed and retained their original plasmonic red color with the addition of NTO, owing to the hydrogen bonding affinity of the NTO triazole ring to MEL. The concentration of NTO leading to color change could be determined with the naked-eye even at the sub-femtomolar level. Analytical results showed that the absorption ratio (A(520nm)/A(630nm)) varied linearly with the logarithm of NTO concentration in the range of 3.08 x 10(-16) to 3.08 x 10(-12) mol L-1 with a correlation coefficient of 0.9994. The synthesized and resultant AuNPs (in the presence of NTO and/or MEL) were characterized using ultraviolet-visible spectrophotometry, scanning transmission electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and zeta-potential measurements. Possible interferences of various energetic substances in synthetic mixtures containing 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol, hexahydro-1,3,5-trinitro-1,3,5-triazine, and ammonium nitrate, of possible camouflage materials used in passenger belongings such as cationic surfactants (cetyltrimethylammonium bromide and cetylpyridinium chloride), D-(+)-glucose as a representative sugar, acetylsalicylic acid- and paracetamol-based painkiller drugs, and of commonly found soil ions (Cl-, NO3-, SO42-, Ca2+, Mg2+, Cu-II, Fe-II/III, and Ag-I) were also examined. In addition, recovery of NTO was successfully performed from NTO-based melt-cast formulations consisting of mixtures of TNT and NTO. The proposed method was statistically validated against a reference liquid chromatography-tandem mass spectrometry method applied to NTO standards, NTO-contaminated soil, and loam samples.