Nano-PAD Fabrication Using Micro-Embossing

To begin, laser cut the 500-micrometer-thick polytetrafluoroethylene or PTFE films using the laser cutting machine to generate the microchannel mold. Disperse four grams of TEMPO-oxidized nanofibrillated cellulose gel in distilled water. Stir the suspension heavily at 120.8 G for 30 minutes until no cellulose flock is seen.

Vacuum filter the clear suspension to obtain a nanopaper gel. Next, place the PTFE mold on the surface of the nanopaper gel. Use a hot press to emboss the gel for 10 minutes under 750 kilopascals pressure at 50 degrees Celsius.

To release the mold, peel off an additional layer of filter nanopaper gel from the filter membrane. Attach the peeled layer on top of the embossed nanopaper gel and stack the two layers to create a hollow microchannel structure. Dry the stacked layers in a drying oven at 75 degrees Celsius for 30 minutes.

Next, prepare the Nano-PADs with straight and curved channels. Add red and blue droplets in the inlet zone simultaneously, allowing automatic channel flowthrough. Microchannel patterning at 200 micrometers was possible with micro-embossing.