Fluorescence and Piezoresistive Cantilever Sensing of Trinitrotoluene by an Upper-Rim Tetrabenzimidazole Conjugate of Calix[4]arene and Delineation of the Features of the Complex by Molecular Dynamics

A new benzimidazole-functionalized calix[4]­arene receptor (<b>R</b>) was synthesized and characterized. The receptor <b>R</b> shows better selectivity toward trinitrotoluene (TNT) compared to the other nitro explosives in solution, which also retains its effectiveness for solid-phase detection. The chemical interactions of the molecule with different nitro explosive analytes were studied by fluorescence spectroscopy and by a molecular dynamics approach. The molecular dynamics studies show a 1:3 complex between <b>R</b> and TNT, and hence high sensitivity was imparted by fluorescence studies. The detection of explosive vapors in ambient conditions was tested by using a sensitive coating layer of <b>R</b> on an SU-8/CB-based piezoresistive cantilever surface. The developed device showed large sensitivity toward TNT compared to cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) in the solid state at their respective vapor pressures at room temperature. The detection sensitivity of the device was estimated to be 35 mV for TNT at ambient conditions. Moreover, the sensor does not show a response when exposed to humidity. These results demonstrate that <b>R</b> can be used as one of the coating materials for a cantilever for the detection of TNT using piezoresistivity measurement. <b>R</b> can also detect the explosives in solution with high sensitivity and selectivity by fluorescence spectroscopy