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Design and evolution of explosives monitoring and detection platforms to address the challenges of trace level chemical identification have led investigations into the use of intricately designed microfluidic devices. Microfluidic devices are unique tools that possess distinct characteristics that, when designed properly and configured with optical and fluidic components, can produce detection platforms with unmatched performance levels. Herein, we report the design, fabrication and integration of a bifurcated high aspect ratio microfluidic device containing 128 microchannels (40 mm × 40 μm × 250 μm; L × W × H) for explosives detection at trace levels. Aspect ratios measuring >6:1 support improved receptor-target molecule interactions, higher throughput and extremely low limits of detection (LOD). In addition to superior assay sensitivity, the bifurcated microfluidic device provides greater durability and versatility for substrate modification. Using the explosive 2,4,6-trinitrotoluene (TNT) as the model compound in a fluorescence-based displacement immunoassay, we report LODs for TNT at 10 parts-per-trillion (pptr) using a neutravidin-coated biotinylated anti-TNT microfluidic device. Solution to wall interactions were also simulated in COMSOL Multiphysics to understand fluid flow characteristics. Reynolds numbers were calculated to be 0.27⁻2.45 with a maximum pressure of 1.2 × 10 -2 psi., Competing Interests: The authors declare no conflicts of interests. The views expressed here represent those of the author and do not reflect those of NRL, the Navy and the Department of Defense (DOD).

A field demonstration and longevity assessment for long-term monitoring of the explosive 2,4,6-trinitrotoluene (TNT) in a marine environment using an anti-TNT microfluidic immunosensor is described. The TNT immunosensor is comprised of a microfluidic device with 39 parallel microchannels (2.5 cm × 250 µm × 500 µm, L × W × D) fabricated in poly(methylmethacrylate) (PMMA), then chemically functionalized with antibodies possessing a high affinity for TNT. Synthesized fluorescence reporter complexes used in a displacement-based assay format were used for TNT identification. For field deployment the TNT immunosensor was configured onto a submersible moored steel frame along with frame controller, pumps and TNT plume generator and deployed pier side for intermittent plume sampling of TNT (1h increments). Under varying current and tidal conditions trace levels of TNT in natural seawater were detected over an extended period (>18 h). Overnight operation and data recording was monitored via a web interface.

Fluorescence immunoassays employing monoclonal antibodies directed against the explosive 2,4,6-trinitrotoluene (TNT) were conducted in a multi-channel microimmunosensor. The multi-channel microimmunosensor was prepared in poly (methyl methacrylate) (PMMA) via hot embossing from a brass molding tool. The multi-channeled microfluidic device was sol-gel coated to generate a siloxane surface that provided a scaffold for antibody immobilization. AlexaFluor-cadaverine-trinitrobenzene (AlexaFluor-Cad-TNB) was used as the reporter molecule in a displacement immunoassay. The limit of detection was 1-10 ng/mL (ppb) with a linear dynamic range that covered three orders of magnitude. In addition, antibody crossreactivity was investigated using hexahydro-1,3,5-triazine (RDX), HMX, 2,4-dinitrotoluene (DNT), 4-nitrotoluene (4-NT) and 2-amino-4,6-DNT.