Ultrasensitive optical detection of trinitrotoluene by ethylenediamine-capped gold nanoparticles

This study found that 1,2-ethylenediamine (EDA) as a primary amine could be modified onto the surface of citrate-stabilized gold nanoparticles (Au NPs), and the EDA-capped Au NPs were successfully used as an ultrasensitive optical probe for TNT detection. The strong donor–acceptor (D–A) interactions between EDA and trinitrotoluene (TNT) at the Au NP/solution interface induced significant aggregation of the EDA-capped Au NPs, and enabled to easily realize the direct colorimetric detection of ultratrace TNT. The results showed that such a color change was readily seen by the naked eye, and the colorimetric detection could be down to 400 pM level of TNT with excellent discrimination against other nitro compounds. UV–vis absorption spectroscopy was used to examine the TNT-induced changes in local surface plasmon resonance (LSPR) of EDA-capped Au NPs, and a new LSPR band at ca. 630 nm arose along with the addition of TNT, which produced a detection limit of TNT down to ca. 40 pM. Furthermore, dynamic light scattering measurements evidenced the ultratrace TNT-induced small changes in the size of the EDA-capped Au NPs, and realized the quick and accurate detection of TNT in 0.4 pM level. These results demonstrated the ultrahigh sensitivity of this optical probe for TNT detection. Moreover, this optical probe is sample, stable, low-cost, and these excellent properties make it quite promising for infield and rapid detection of TNT.

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► EDA can interact with the citrate-stabilized Au NPs through electrostatic attraction.
► EDA-capped Au NPs can be used as an ultrasensitive optical probe for TNT detection.
► Direct colorimetric assays for TNT have a detection limit of 400 pM.
► DLS assays evidenced the aggregation of the probe induced by TNT in 0.4 pM level.
► The probe has an excellent discrimination against other nitro compounds.