2.3. Fabrication of the Microfluidic Chips

Microfluidic devices were prepared by soft lithography using SU-8 molds on a Si wafer for casting the PDMS. Conventional photolithography was used to pattern first a SU-8 20 μm-thick layer and subsequently a 40 μm-thick layer on top in order to fabricate a microfluidic device with different structure heights. SU-8 molds were coated with trimethylsilyl chloride (TMCS) to prevent PDMS sticking during PDMS demolding. Then, a liquid PDMS mixture (10:1 base to crosslinker weight ratio) was degassed, poured on the SU-8 mold and cured at 80 °C for 2 h. After demolding and hole punching, the PDMS chip was air plasma activated, bonded onto a glass slide, and connected to external tubing.