The main objective of developing µTAS was to create new means for chemical sensing since sensors at the time could not provide the best results in terms of selectivity and lifetime. Miniaturization was initially intended to enhance analytical performance rather than to reduce its size. It was soon realized that the small size presented the advantage of a smaller consumptions of carrier, reagent, and mobile phase. Additionally, it could provide the integration of sample handling, analysis (i.e. chromatography, electrophoresis), and detection. The concept of a microfluidic chip has been cost effective in terms of reduced reagent consumptions and faster analysis time. In this work, we developed a series of fabrication techniques capable of producing polymer-based microfluidic devices.
A two-stage embossing process was developed to fabricate polymer-based microchips. The microchannel in the master mold was produced by CNC machining or by SU-8 photolithography. In two-stage embossing, two polymer substrates with different glass transition temperatures (Tg) were employed. In the first step, a polymer with a higher Tg was embossed with the master mold to produce a secondary mold. Then the secondary mold can be used to emboss polymers with lower Tg. We have showed that successful feature transfer from the aluminum mold to the final substrates can be achieved reproducibly employing this method. This fabrication approach offers several advantages. The expensive process of producing the primary master only needs to be performed once. Additionally, the life of the primary master can be preserved via the two-stage embossing approach since the replication process can be repeated many times using the secondary mold.
Sealing techniques to form the microchannel are also developed by using different sacrificial layer in solvent bonding. Our bonded PMMA microchips could withstand an internal pressure of > 2000 psi, more than 17 times stronger than the thermally bonded chips. In our current work, we developed a new bonding technique that readily produces complete microfluidic chips, without the need of a sacrificial layer to form complete multilayer microfluidic devices. The advantages of this technique is that it provides a more direct method to generate hard polymer microfluidic chips than classical techniques and therefore is highly amenable to rapid prototyping, which can easily be translated into a production approach. In addition, the technique can readily be applied to many polymers, facilitating device production for a variety of applications, even permitting hybrid polymer chips, and provides a rapid, cost effective, simple, and versatile approach to the production of polymer-based microdevices.