A droplet-based lab-on-a-chip for colorimetric detection of nitroaromatic explosives

Portable and automated field screening equipment would be very effective in detecting and quantifying explosives at various sites. A droplet-based microfluidic lab-on-a-chip utilizing electrowetting is presented for the colorimetric detection of TNT (trinitrotoluene). The method uses the reaction between nitroaromatics and a strong base which forms the highly colored Jackson-Meisenheimer complex. Microliter-sized droplets of TNT are programmed to transport, mix, and react with potassium hydroxide (KOH) on the microfluidic chip. Colorimetric reactions of TNT are characterized both on a spectrophotometer and on the microfluidic chip. The detection of TNT on the chip is linear in the range of 4-20 μg/mL with a time-to-result of 2.5 minutes. It is also observed that the absorbance peaks of DNT (dinitrotoluene) and TNT are mutually independent and that the presence of DNT does not affect the detection of TNT. Electrowetting also does not seem to influence the colorimetric complex as observed from a comparison of results between a spectrophotometer and on-chip.