In order to properly manipulate liquids into microfluidic networks, an accurate sealing of the device is of paramount importance. Polydimethylsiloxane (PDMS) is ubiquitously used for fabricating microfluidic components, owing to its low cost, easy and fast fabrication, and optical transparency. However, PDMS is characterized by low surface energy, making its bonding to many substrates not trivial. Here is presented a versatile technique for PDMS microchannel bonding on untreated plastic and metal surfaces. First, the PDMS surface is functionalized with (3-aminopropyl) triethoxysilane (APTES) for further cross-linking with epoxy groups. Then, the PDMS-APTES surface is coated with Norland Optical Adhesive 74 (NOA74). Finally, the PDMS-APTES-NOA74 is put in contact with the target material and the glue is cured under a UV light. In order to characterize the bonding strength, a complete PDMS-on-gold microfluidic device is fabricated and tested with increasing injection pressures. Different liquids and a gas (nitrogen) are applied without leakage up to 2 bars, a value comparable to the one reported for the standard glass-PDMS bonding through plasma oxygen activation. The same technique is then successfully replicated with other nonmetallic substrates of interest for microfluidics, i.e., glass, poly(methyl methacrylate), polystyrene, polyethylene terephthalate, cyclic olefin copolymer, demonstrating its great versatility and potential for, but not limited to, microfluidic applications and LOC engineering.
Agostini, M., Greco, G., & Cecchini, M. (2019). Polydimethylsiloxane (PDMS) irreversible bonding to untreated plastics and metals for microfluidics applications. APL Materials, 7(8). https://doi.org/10.1063/1.5070136