The potential for and challenges of detecting chemical hazards with temperature-programmed microsensors

Several recent demonstrations of the abilities of micro-electromechanical systems (MEMS)-based microsensor technology to detect hazardous compounds and their simulants in a variety of background conditions are presented. In each case, two pairs of conductometric metal oxide sensors (TiO2 and SnO2) produced via chemical vapor deposition are operated using temperature-programmed sensing (TPS). NIST microdevices can utilize this operating mode to sample a wide operating temperature range (50 °C–480 °C) in a very short time (<15 s). The voluminous databases generated by this method can be analyzed using signal processing techniques, such as artificial neural networks (ANNs), to provide actionable outputs.Several examples are presented: cyclohexyl methyl methylphosphonate (CMMP), a simulant for cyclosarin (GF), is detected at concentrations ranging from 700 pmol/mol to 90 nmol/mol in air backgrounds ranging from 0% relative humidity (RH) to 70% RH. The chemical warfare agents (CWAs) tabun (GA), sarin (GB), and sulfur mustard (HD) are detected at 25 nmol/mol in dry air, humidified air (40% RH), and diesel fume-laden air (3.5% saturation). Finally, a selection of five toxic industrial chemicals (TICs) and one chemical warfare simulant (CWS) are measured at immediate danger to life and health (IDLH) and permissible exposure limit (PEL) levels in an array of backgrounds, including seven different interferences, each at three concentration levels (from 0.1% to 2.0% saturation), with humidity ranging from 50% RH to 90% RH, and ambient temperature spanning 0 °C–40 °C. Technical developments that have enabled the illustrated performances, as well as future directions for conductometric microsensor research aimed at meeting the various stringent demands faced in the hazardous chemical detection application sector, are described.