Simple and sensitive colorimetric detection of a trace amount of 2,4,6-trinitrotoluene (TNT) with QD multilayer-modified microchannel assays

Rapid and selective detection of trace levels of nitroaromatic explosives, in particular, 2,4,6-trinitrotoluene (TNT), is a key challenge for both public security and environmental monitoring. In the present study, we fabricated two colored quantum dot (QD) multilayer-decorated microchannel assays via a layer-by-layer assembly technique. Due to the energy transfer between red QDs and green QDs, the fluorescence intensity of the red QDs significantly enhanced. When the assays were exposed to TNT aqueous solution, the formation of Meisenheimer complexes between the electron-poor aromatic groups of TNT and electron-rich amines on the surface of the red QDs caused fluorescence quenching of the red QDs and partial recovery of the green QDs, thus resulting in multicolor changes of the multilayers from red to yellow to green and then to colorless. The assay has a broad linear range of 10 ppt to 10⁷ ppt and low detection limit (5.24 ppt) for TNT. The specificity of this assay for the detection of TNT is demonstrated against several TNT analogs. Additionally, this technique was successfully applied to detect TNT concentration in different water samples. Due to its simplicity, short detection time, high sensitivity and low cost, the assay is well suited for the detection of ultratrace levels of TNT.