Microfluidic colourimetric chemical analysis system: Application to nitrite detection

The design, fabrication, analysis and characterisation of a continuous flow, microfluidic absorption cell and detection system is described. A low cost optical illumination and detection method is integrated with a simple microfluidic system. Nitrite is detected at nM concentration using the Griess reaction. The device is based on a novel optical absorption scheme with microfluidic channels made from tinted PMMA. An absorbance path length of 25 mm enables nitrite to be detected from 50 nM to 10 μM with a limit of detection of 14 nM. The system was used to characterise the reaction kinetics and maximum sample resolution. In this report the system is used to detect nitrite, but it could equally be used to assay a range of different chemistries using colourimetric methods. The system provides a cost-effective, simple system that could be deployed in a range of scenarios for environmental monitoring. We have demonstrated a novel and generic low-cost, high performance colourimetric detector based on a tinted PMMA absorbance cell.