Reduction of surface roughness for optical quality microfluidic devices in PMMA and COC

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.