Patterned fluoropolymer barriers for containment of organic solvents within paper-based microfluidic devices

In this study, we demonstrate for the first time the ability to pattern lipophobic fluoropolymer barriers for the incorporation of pure organic solvents as operating liquids within paper-based microfluidic devices. Our fabrication method involves replacing traditional wax barriers with fluoropolymer coatings by combining initiated chemical vapor deposition with inhibiting transition metal salt to pattern the polymer. Multiple techniques for patterning the transition metal salt are tested including painting, spray coating, and selective wetting through the use of a photoresist. The efficacy of the barrier coatings to contain organic solvents is found to be dependent on the conformality of the polymer deposited around the paper fibers. We demonstrate examples of the benefits provided by the containment of organic solvents in paper-based microfluidic applications including the ability to tune the separation of analytes by varying the operating solvent and by modifying the channel region of the devices with additional polymer coatings. The work exhibited in this paper has the potential to significantly expand the applications of paper-based microfluidics to include detection of water insoluble analytes. Additionally, the generality of the patterning process allows this technique to be extended to other applications that may require the use of patterned hydrophobic and lipophobic regions, such as biosensing, chemical detection, and optics.