Simple route to hydrophilic microfluidic chip fabrication using an Ultraviolet (UV)-cured polymer

Herein, we introduce a simple route to fabricating hydrophilic microfluidic chips with an alternative material, a UV-cured poly-urethane-related polymer, known as Norland Optical Adhesive (NOA 63). Conventionally, polydimethylsiloxane (PDMS) is widely used to fabricate microfluidic chips as an alternative to glass or SiO₂ because PDMS is easily molded and relatively cheap. However, despite these advantages, the hydrophobicity of PDMS entails critical problems when it is used in microfluidic chips because microchannels inside the microfluidic chips, which have extremely low surface tension, are difficult to fill with aqueous solution without an extra pumping system. To overcome these problems, significant efforts have been focused on developing procedures to change the PDMS surface to be hydrophilic. However, the resulting hydrophilicity is generally short-lived and the modification procedures require cumbersome multi-steps. In the present study, we demonstrate that microchannel-molding and microfluidic chip construction are easier using NOA 63 than when using PDMS and that the hydrophilicity of the NOA surface, which is induced by treatment with O₂ plasma, lasts longer, for at least one month. Due to the longer lasting hydrophilicity, microchannels in NOA 63 microfluidic chips are spontaneously filled with solution by capillary reaction without any extra pumping over the period. The feasibility of NOA 63-based microfabrication is verified by demonstrating NOA 63 microfluidic platforms with antibody-immobilized beads for immunoassays.