Phase-Changing Sacrificial Materials for Solvent Bonding of High-Performance Polymeric Capillary Electrophoresis Microchips

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Abstract
A new method for solvent bonding polymeric substrates to form microfluidic systems has been demonstrated. Prior to device sealing, channels in an embossed poly(methyl methacrylate) (PMMA) piece are filled with a heated liquid (paraffin wax) that forms a solid sacrificial layer at room temperature. The sacrificial material prevents the bonding solvent (acetonitrile) and softened PMMA from filling the channels. Once the sealing step is complete, the sacrificial layer is melted and removed, leaving enclosed microfluidic channels. We found that PMMA substrates welded together using this method could withstand internal pressures of >2250 psi, more than 1 order of magnitude higher than their thermally bonded counterparts. To demonstrate the usefulness of this method, microchip capillary electrophoresis (CE) devices in PMMA were created and tested. Amino acid and peptide mixtures were separated in 40 000 theoretical plates in a 2.5-cm separation distance. Electric fields as high as 1.5 kV/cm were applied in these microchips, and >300 CE runs were performed on a single device with no degradation of separation performance. The simplicity of the methods presented here and the improved robustness of the resulting devices should facilitate the broader implementation of polymer microchips in microfluidic analyses.