One-Step Instantaneous Detection of Multiple Military and Improvised Explosives Facilitated by Colorimetric Reagent Design

Although colorimetric detection based on reagents has been widely used in the fields of practical trace analysis, its versatility for detecting multitargets remains the most challenging problem. As a proof of concept, a general colorimetric reagent based on potassium isopropanol (C3H7KO) and dimethyl sulfoxide for one-step instantaneous detection and discrimination of typical military and improvised explosives was designed. Vivid colors from none to purple red, blue green, yellow green, and green were shown, respectively, when detecting 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), elemental sulfur (S), and potassium permanganate (KMnO4). The unique design including the specific nucleophilic addition reaction and the base-catalyzed oxidation-induced electron transfer ensures perfect selectivity even upon facing more than 20 interferents. It is further experimentally demonstrated that the confinement effect introduced by Tween-20 plays an essential role in enhancing the color signal on the surface and thus boosts the detection performance even with a mass as low as 1.45 ng. The applicability of this versatile colorimetric reagent was further verified by integrating the reagent onto paper strips for the in-field identification of TNT, DNT, S, and KMnO4 with the help of a portable smartphone-based microscope apparatus, and a practical detection mass of 10.3 ng could be realized. We expect the present colorimetric reagent design strategy would pave a way for one-step instantaneous visual detection toward trace multianalytes.