Wood-Cased Pencil Graphite as Voltammetric Sensor and Sampling by Drone for Field Detection of 2,4,6-Trinitrotoluene Explosive

This study introduces a novel approach for detecting 2,4,6-trinitrotoluene (TNT) explosives using a pencil-based sensor. The sensor utilizes the circular area of a 3 mm diameter pencil lead enclosed by a wooden shaft as the working electrode. Graphene and silver-silver chloride inks are printed onto transparent sticky tapes, as the counter and reference electrodes, respectively. These tapes are affixed to the pencil body, with copper wires as electrical conductors. Differential pulse adsorptive stripping voltammetry of standard TNT solutions (0.5-30 mg L^-1) in 0.5 mol L^-1 NaCl reveals two distinct peak signals at -0.46 and -0.64 V, along with a smaller peak at -0.75 V. The identification of TNT in a sample is confirmed by comparing the ratios of these three peak currents with those of standard TNT. The detection of TNT in the field is achieved by employing the pencil sensor in conjunction with drone sampling. The drone is equipped with four sampling devices, each housing a "gel-electrolyte adsorbent" attached to its landing gears. The gel effectively absorbs TNT residues upon landing on suspicious targets. In situ detection with the gel-medium yields a limit of detection (LOD) of 4.8 mg L^-1 TNT for standard solutions. Our method demonstrates the efficacy of the pencil sensor for on-site and rapid analysis (2.3 min). Following drone sampling, field detection yields a LOD of 0.026 ng cm^-2 TNT. This method proves suitable for remote security screenings in areas of terrorist activities and war zones.