A novel highly flexible, simple, rapid and low-cost fabrication tool for paper-based microfluidic devices (μPADs) using technical drawing pens and in-house formulated aqueous inks

Paper-based microfluidic devices (μPADs) are capable of achieving rapid quantitative measurements of a variety of analytes inexpensively. μPADs rely on patterning hydrophilic-hydrophobic regions on a sheet of paper in order to create capillary channels within impermeable fluidic brakes on the paper. Here, we present a novel, highly flexible and low-cost fabrication method using a desktop digital craft plotter/cutter and technical drawing pens with tip size of 0.5 mm. The pens were used with either commercial black permanent ink for drawing fluidic brakes, or with specialty in-house formulated aqueous inks. With the permanent marker ink it was possible to create barriers on paper rapidly and in a variety of designs in a highly flexible manner. For instance, a design featuring eight reservoirs can be produced within 10 s for each μPAD with a consistent line width of brakes (%RSD < 1.5). Further, we investigated the optimal viscosity range of in-house formulated inks controlled with additions of poly(ethylene glycol). The viscosity was measured by capillary electrophoresis and the optimal viscosity was in the range of ∼3-6 mPa s. A functional test of these μPADs was conducted by the screening of antioxidant activity. Colorimetric measurements of flavonoid, phenolic compounds and DPPH free radical scavenging activity were carried out on μPADs. The results can be detected by the naked eye and simply quantified by using a camera phone and image analysis software. The fabrication method using technical drawing pens provides flexibility in the use of in-house formulated inks, short fabrication time, simplicity and low cost.