Electrochemical tape-and-paper-based sensors for the detection of inorganic explosives

Chemicals with dual-use nature, such as potassium chlorate, that can be used as weed killers or fireworks, and precursors for improvised explosives devices (IEDs) are a problem for homeland security. As IEDs represent a global threat due to their destructive potential, easy access to raw materials, and online manufacturing instructions. Potassium chlorate, since its discovery, has been used as the principal constituent of chlorate-based explosives due to its strong oxidizing properties. The standard methods to detect chlorate are mainly designed for laboratory testing or rely on techniques that generate more complex data to interpret, such as Raman spectrometry and capillary electrophoresis, and thus do not easily meet the requirements for in-field detection. To address the need for in-field detection of chlorate, we developed an electrochemical tape-and-paper-based device that integrates electroanalytical assays with flexible substrates allowing for user-friendly, inexpensive, portable, and disposable analytical devices. The sensing element of our device is an electrodeposited molybdate layer, as chlorate was reported to have a catalytic effect on the molybdate reduction. The sensing concept to detect chlorate relies on monitoring the change in redox activity of the molybdate sensing layer using cyclic voltammetry (CV). We have effectively demonstrated the detection and quantification of chlorate in solution with a limit of detection of 0.14 mg/mL. Additionally, we have performed interferent studies with sugar, commonly used as fuel in IEDs, and other common white household powders. We also evaluated the selectivity of the sensor by testing other oxidizers such as perchlorate, nitrate, and bromate. To prepare for the end application by the user, we designed encased prototypes to allow for an in-field presumptive test, storage, and transport for in-laboratory confirmatory tests. We evaluated different sample collection and handling methods, such as swiping solids. Finally, we successfully analyzed chlorate in combusted and post-blast samples.