Polymeric materials have seen increasing use as microfluidic device substrates due to their low cost and the simplicity of templated fabrication procedures. I showed that poly(methyl methacrylate) (PMMA) microdevices could be enclosed in a boiling water bath, which allowed the seal to form more quickly than in conventional approaches, and enabled microchannels to remain hydrated throughout the bonding process. Microchip capillary electrophoresis (µ-CE) devices were fabricated using water-based enclosure, and a mixture of fluorescently labeled amino acids was separated in 30 s in these microchips. To create more robust capillary electrophoresis (CE) microdevices with improved separation performance, phase-changing sacrificial materials were developed for solvent bonding of polymer microchips. Devices were fabricated by filling channels in embossed PMMA with a heated liquid that formed a solid sacrificial layer at room temperature. The sacrificial material prevented the bonding solvent and softened PMMA from filling the channels. Once the sealing step was finished, the sacrificial layer was melted and removed, leaving enclosed microchannels. These solvent-welded devices withstood internal pressures >2,200 psi, and 300 CE runs were performed on a single microchip without any loss of separation performance. Furthermore, CE separations of peptides and amino acids were completed in ~10 s, with peak efficiencies of 43,000 theoretical plates. Electric field gradient focusing (EFGF), which uses a combination of pressure-driven flow and an electric field gradient to separate charged species according to their electrophoretic mobilities, was explored for protein analysis. Capillary-based EFGF devices were characterized; mixtures of four proteins were resolved, band focusing dynamics were studied, and analytes were enriched 10,000-fold. EFGF was miniaturized further to a microfluidic platform. Phase-changing sacrificial layers were employed to interface an electric field gradient enabling semi-permeable copolymer with microchannels. Because of decreased channel dimensions, EFGF microchips produced narrower bands and yielded threefold higher resolution compared with capillary-based devices. Beyond providing improved performance for polymer-based µ-CE and EFGF, the advances in microchip fabrication technology presented here should be applicable broadly in interfacing microfluidics with hydrogel structures, for example in sample pretreatment.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



Date Submitted


Document Type





EFGF, microfluidics, microdevice, PMMA, electrophoresis, peptides, proteins, amino acids