Leveraging Preconcentration and Partial Separations with Silicon Nanowire Arrays to Improve the Detection of Low Volatility Trace Explosive Vapors

Abstract

Trace detection of explosive vapors in real world environments is hindered by strict sensitivity and selectivity requirements that need to be met in order for these techniques to be effective. The physical properties of most explosive molecules limit environmentally relevant vapor concentrations to the part per billion (ppbv) – part per trillion (pptv) range due to their saturated vapor pressures under real world conditions. Additionally, trace explosive vapor detectors must be able to discriminate against a number of potential chemical and biological interferents present in complex real world environments. In this work, we present silicon nanowire arrays (SiNW) as a novel tunable material aimed at providing trace explosive vapor detectors with the sensitivity and selectivity necessary for operational use.Dense, highly ordered silicon nanowires are fabricated through a nanosphere lithography process and topped with a porous gold electrode resulting in a high surface area adsorptive substrate intrinsically capable of rapid, precise temperature control via Joule heating. Explosive vapors are selectively preconcentrated onto the SiNW array by exploiting their affinities for the SiO2 surface of the nanowires. Chromatographic like partial separations of preconcentrated material on the array can be achieved through careful selection of desorption parameters. Using a multichannel detector such as an IMS or MS we demonstrate the preconcentration of a number of explosive vapors including 2,6-DNT, TNT, and RDX above and below their saturated vapor concentrations at room temperature, in addition to exploring the effects of desorption flow rates and temperatures on the partial separation of 2,6-DNT, 2,4-DNT, and TNT vapors. Figure 1