TitleFabrication and application of polymer based microfluidic devices
Publication TypeThesis
Year of Publication2009
AuthorsKoesdjojo, MT
UniversityOregon State University
CityCorvallis, Or.

The concept of reducing laboratory operations in scale such that they fit on a microfluidic chip has been met with great enthusiasm. Lab-on-a-chip devices promise to be cost effective to operate due to reduced reagent consumption, have the potential to offer shorter analysis times due to their short path lengths, and may be useful in biological applications in that they are inherently compact and inexpensive to build, thus they may be disposable. In this work, a series of fabrication techniques for the production of polymer-based microfluidic devices are explored. In the first component of this research effort an aluminum mold was fabricated using CNC machining to create the desired microchannel design, followed by a two-stage embossing process, involving two polymer substrates with different glass transition temperatures (Tg), polyetherimide (PEI; Tg{\textasciitilde}216oC) and poly(methyl methacrylate) (PMMA; Tg{\textasciitilde}105oC). Successful feature transfer from aluminum mold to PMMA substrates was achieved reproducibly employing this method. With this approach, the expensive process of producing the aluminum master need be performed only once. Electrophoretic separations of fluorescent dyes, rhodamine B and fluorescein were performed on the PMMA microchips, with peak efficiencies of 55500 and 66300 theoretical plates/meter, respectively. The next stage of work explored a new bonding method by solvent welding using ice as sacrificial layer to prevent channel deformation. Water is one of the most compatible sacrificial media; it is readily available, non toxic, has a low evaporation rate, a high freezing point relative to the bonding solvent, and a low melting point which makes it easier to flush out after sealing, as compared to using other sacrificial media (paraffin wax or low-melting temperature alloys). The bonded PMMA microchips could withstand an internal pressure of> 2000 psi, more than 17 times stronger than the thermally bonded chips. In the final stage of work a new bonding technique was developed that readily produces complete microfluidic chips, without the need of a sacrificial layer to form complete multilayer microfluidic devices. Also developed was the use of an SU-8 master in the two-stage embossing process to create microchannels. This approach is faster, simpler and less costly than CNC machining. The fabrication technique was utilized to build a microfluidic liquid chromatography (LC) system that was shown to generate high separation efficiencies of 10,000- 45,000 plates/m. In addition, a passive micromixer containing high-density microfeatures was fabricated to perform a glycine assay using O-phthaldialdehyde. With glycine concentrations ranging from 0.0 to 2.6 [mu]M, a linear calibration plot (R2 = 0.9982) was obtained with a detection limit of 0.032 [mu]M.