Developing self-generated calibration curves using a capillary-driven wax-polyester lab on a chip device and thermal gates

Here we describe the development of a capillary-driven wax-polyester lab on a chip device and the concept of thermal gates to create self-generated calibration curves. The devices were fabricated by printing a wax pattern on a polyester film, and laminating two mirrored layers together. Victoria Blue R and a diluent of methanol/water (1:1) were placed in separate wells, and capillary forces drove the reagents through three additional mixing wells, resulting in respective dilutions of 50%, 25% and 12.5% of the original dye concentration (100%). A photo was taken after the capillary action ceased, and the color brightness of the four different concentrations was used for the creation of a calibration curve, resulting in a coefficient of determination of 0.99. The chip was readily adapted to include an additional channel to perform chemical reactions with KOH to increase the available detection options. The chip designs required up to three reagents to be simultaneously added, with any discrepancies in the synchronization of reagent addition leading to irreproducible results. To overcome these synchronization discrepancies, thermal gates were added by printing 0.15 mm wax barriers across the channel inlets to prevent liquid movement. These gates were simultaneously opened to allow the solutions to flow by applying heat, controlled by an Arduino-based instrument controller, through bent copper filaments positioned adjacent to the barriers for 380 milliseconds.