Direct detection and speciation of trace explosives using a nanoporous multifunctional microcantilever

We have developed a highly selective and sensitive nanomechanical infrared (IR) calorimetric spectrometer for use in the direct detection of ultralow concentrations of explosive vapors using a nanoporous TiO₂ cantilever. These cantilevers were fabricated using a two-step anodization and photolithography process. By patterning nanoscale wells onto a cantilever, its surface area is increased by 2 orders of magnitude and the surface is converted into a preconcentrator. Resonant excitation of adsorbed molecules using IR radiation causes the cantilever to bend due to temperature changes originating from the nonradiative decay process. The porous structure of the cantilever increases its thermomechanical sensitivity as well as the number of adsorbed molecules. The system performance was demonstrated by detecting binary explosive mixtures under ambient conditions. The TiO₂ sensor surface also allows regeneration through the photocatalytic decomposition of adsorbates under UV irradiation.