Fabrication of NOA microfluidic devices based on sequential replica molding

Polydimethylsiloxane (PDMS) microfluidic devices, though they are commonly utilized in microfluidic applications, have several limitations, such as short-term modified surface condition, swelling in the presence of organic solvents, and deformation under high pressure or when built with low aspect ratios. To resolve the restrictions, Norland Optical Adhesive (NOA) has been introduced as an excellent alternative for PDMS. Here, we present a practical protocol for the fabrication of NOA microfluidic devices via a step-wise molding process. Through the indirect molding of NOA on wafers, the damage to the wafers can be significantly reduced. Furthermore, because we use positivepatterned wafers, which are commonly used to fabricate PDMS devices, no additional fabrication of the wafer is required. This simple strategy thus avoids damage to the wafers and simultaneously allows for the mass production of NOA devices without deformation. We also test the performance of NOA devices in oil-in-water droplet production and in a microfluidic process using organic solvents.