A rapid and low-cost technique is presented for the fabrication of optical quality microfluidic devices in poly(methyl methacrylate) (PMMA) or cyclic olefin copolymer (COC). When polymer microfluidic devices are manufactured by rapid prototyping techniques, such as micromilling, the surface roughness is typically in the region of hundreds of nanometres reducing the overall optical efficiency of many microfluidic-based systems. Here we demonstrate a novel solvent vapour treatment that is used to irreversibly bond microfluidic chips while simultaneously reducing the channel surface roughness, yielding optical grade (less than 15 nm surface roughness) channel walls. We characterize this vapour bonding method and optimize the process parameters to avoid channel collapse, while achieving reflow of polymer and uniformity of bonding. The reflow of polymer is the key to enabling a fabrication process that takes less than a day and produces optical quality surfaces with low-cost rapid prototyping tools.

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 mM 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 present a reliable technique for irreversibly bonding chemically inert Viton® membranes to PMMA and COC substrates to produce microfluidic devices with integrated elastomeric structures. Viton® is widely used in commercially available valves and has several advantages when compared to other elastomeric membranes currently utilised in microfluidic valves (e.g. PDMS), such as high solvent resistance, low porosity and high temperature tolerance. The bond strength was sufficient to withstand a fluid pressure of 400 kPa (PMMA/Viton®) and 310 kPa (COC/Viton®) before leakage or burst failure, which is sufficient for most microfluidic applications. We demonstrate and characterise on-chip pneumatic Viton® microvalves on PMMA and COC substrates. We also provide a detailed method for bonding fluorinated Viton® elastomer, a highly chemically compatible material, to PMMA and COC polymers. This allows the production of microfluidic devices able to handle a wide range of chemically harsh fluids and broadens the scope of the microfluidic platform concept.

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