Free Surface MicroFluidics for Explosives Detection

Summary A novel microfluidic, chemical detection platform has been developed for real-time sensing of airborne agents. The key enabling technology is a newly developed concept termed Free-Surface Fluidics (FSF), where one or more fluidic surfaces of a microchannel flow are confined by surface tension and exposed to the surrounding atmosphere. The result is a unique open channel flow environment that is driven by pressure through surface tension, and not subject to body forces, such as gravity. Evaporation and flow rates are controlled by microchannel geometry, surface chemistry and precisely-controlled temperature profiles. The free-surface fluidic architecture is combined with Surface-Enhanced Raman Spectroscopy (SERS) to allow for realtime profiling of atmospheric species and detection of airborne agents. The results indicate that airborne explosive agents such as DNT, TNT, RDX, TATP can be readily detected. Free Surface MicroFluidics (FSF) During the past fifteen years, there has been significant development in using micro/nanofluidic-based platforms for detection of chemical and biological agents i . These platforms show high sensitivity, reduced sample size and reagent volume. In addition, microfluidic devices have the potential to be field-portable detection platforms. However, all the ‘lab on a chip’ platforms reported in the literature can process samples only after the sample is injected into the microchannel. No integrated device currently exists for capturing airborne agents directly into a microchannel. This is a longstanding technological/scientific barrier that can ultimately limit the viability of ‘lab on a chip’ platforms for monitoring of airborne species. We are not aware of any previous demonstration of a feasible microfluidic platform for monitoring airborne molecules. We have developed an integrated micro/nanofluidic platform that can monitor airborne molecules in real time. Free-surface fluidics allows airborne molecules, such as those of common explosives to be captured. Once absorbed into the microchannel, the analytes can be detected using Surface Enhanced Raman Spectroscopy (SERS). Figure 1 shows the integrated free-surface microfluidic platform combined with SERS for molecular-specific detection. The free-surface flow utilizes surface tension to create pressure-driven flow. Once absorbed through the surface, the airborne molecules or particles adsorb on the silver nanoparticles which causes them to aggregate and leads to the greatly-enhanced SERS effect (up to 14 orders of magnitude increase in signal over Raman). As the particles advect downstream, colloidal particles continue to aggregate, where monomers form dimers, and dimers form trimers, etc. The maximum SERS signal (per ad-molecule) is obtained from nanoparticle dimers, and decreases significantly with trimers.