This project demonstrates the first fully integrated, fieldable, gas chromatographic microanalytical system (µGC) for near-real-time determinations of trace-level vapor concentrations of marker compounds of explosives. This µGC, dubbed INTREPID, will be used for airport screening applications to protect workers and the public from terrorist threats. A top view of the current field prototype is shown above. It uses an adsorbent-packed, deep-reactive-ion-etched (DRIE) Si/glass microfocuser, a wall-coated DRIE-Si/glass microcolumn, and an integrated array of 4 chemiresistors coated with functionalized thiolate-monolayer-protected gold nanoparticle (MPN) interface layers. The four MPNs are: n-octanethiol (C8), 6-phenoxyhexane-1-thiol (OPH), 4-(phenylethynyl)-benzenethiol (DPA), methyl-6-mercaptohexanoate (HME), each of which yields a unique response to eluting vapors. A high-volume sampler is connected upstream to reduce analysis time and detection limits. Commercial valves and mini-pumps are used. All functions are set and automatically sequenced by a laptop computer, which runs routines written in-house in LabView. Laboratory testing of the INTREPID field prototype was performed with the following explosive markers: 2,4- dinitrotoluene (2,4- DNT) and 2,3-dimethyl-2,3-dinitrobutane (DMNB, an explosive taggant). Calculated limits of detection are 2.2 and 0.85 ng, corresponding to 0.31 and 0.11 ppb, for DMNB and 2,4-DNT, respectively (1-L sample). In the analysis of the mixture of the two markers and 19 other compounds, all targets were completely resolved from the interferences and a complete analysis required just 2 min as shown by the chromatogram above. This work is funded by the U. S. Department of Homeland Security, Science and Technology Directorate.