Quantifying the performances of SU-8 microfluidic devices: high liquid water tightness, long-term stability, and vacuum compatibility

Despite several decades of development, microfluidics lacks a sealing material that can be readily fabricated, leak-tight under high liquid water pressure, stable over a long time, and vacuum compatible. In this paper, we report the performances of a micro-scale processable sealing material for nanofluidic/microfluidics chip fabrication, which enables us to achieve all these requirements. We observed that micrometric walls made of SU-8 photoresist, whose thickness range from 35 to 135 µm, are at least leak-tight to 1.5 bars and up to 5.5 bars, exhibit no water porosity even after 2 months of aging, and are able to sustain under 10^-5 mbar vacuum. This sealing material is therefore reliable and versatile for building microchips, part of which must be isolated from liquid water under pressure or vacuum. Moreover, the fabrication process we propose does not require the use of either aggressive chemicals or high-temperature or high-energy plasma treatment. It thus opens a new perspective to seal microchips with sensitive surfaces containing nanomaterials.