Fabrication of a Microfluidic System for Capillary Electrophoresis Using a Two-Stage Embossing Technique and Solvent Welding on Poly(methyl methacrylate) with Water as a Sacrificial Layer

Abstract

Methods for fabricating poly(methyl methacrylate) microchips using a novel two-stage embossing technique and solvent welding to form microchannels in microfluidic devices are presented. The hot embossing method involves a two-stage process to create the final microchip design. In its simplest form, a mold made of aluminum is fabricated using CNC machining to create the desired microchannel design. In this work, two polymer substrates with different glass transition temperatures (Tg), polyetherimide (PEI) and poly(methyl methacrylate) (PMMA), were used to make the reusable secondary master and the final chip. First, the aluminum mold was used to emboss the PEI, a polymeric substrate with Tg approximately 216 degrees C. The embossed PEI was then used as a secondary mold for embossing PMMA, a polymeric substrate with a lower Tg ( approximately 105 degrees C). The resulting PMMA substrate possessed the same features as those of the aluminum mold. Successful feature transfer from the aluminum mold to the PMMA substrate was verified by profilometry. Bonding of the embossed layer and a blank PMMA layer to generate the microchip was achieved by solvent welding. The embossed piece was first filled with water that formed a solid sacrificial layer when frozen. The ice layer prevented channel deformation when the welding solvent (dichloroethane) was applied between the two chips during bonding. Electrophoretic separations of fluorescent dyes, rhodamine B (Rh B) and fluorescein (FL), were performed on PMMA microchips to demonstrate the feasibility of the fabrication process for microreplication of useful devices for separations. The PMMA micro-chip was tested under an electric field strength of 705 V cm-1. Separations of the test mixture of Rh B and FL generated 55 500 and 66 300 theoretical plates/meter, respectively.

Bonding of thermoplastic polymer microfluidics

“…Sacrificial phase change materials have also been explored as a highly robust solution for preventing channel collapse even after extended solvent exposure. In this approach, open microchannels filled with liquid wax or water (Koesdjojo et al 2008) are cooled to solidify the sacrificial material. When directly applying either acetonitrile or ethelyene dichloride (Koesdjojo et al 2008) to the chip surfaces, the sacrificial materials prevent solvation of the channels walls, and thus channel deformation can be virtually eliminated.…”

Microfluidics:A Boon for Biological Research

“…With the recent advances in microfluidic technology, protein targets have been characterized using microfluidic devices which can express, separate, label and quantify proteins to the level of single-cells. Researchers have developed microfluidic chips capable of separating the proteins through micellar electrokinetic chromatography (MEKC) 37 , capillary zone electrophoresis 37,38 and isoelectric focusing 39 in less than 20 min.…”

Solvent bonding of poly(methyl methacrylate) microfluidic chip using phase‐changing agar hydrogel as a sacrificial layer

“…A blank PMMA cover plate softened by chloroform was successfully bonded to a channel plate at low temperature. Recently, Woolley and Tennico employed wax and ice as sacrificial layers to protect the PMMA channels from the solvents that might dissolve the PMMA substrates [25,26]. When the wax sacrificial layer was used, the wax in the bonded channel needed to be removed with the aid of hot cyclohexane because the adsorbed wax on the channel might affect the EOF of the prepared microchips [25].…”

“…When the wax sacrificial layer was used, the wax in the bonded channel needed to be removed with the aid of hot cyclohexane because the adsorbed wax on the channel might affect the EOF of the prepared microchips [25]. To solve the problem, Tennico et al employed ice as a sacrificial layer that could be removed completely after solvent bonding [26]. However, the sacrificial ice layer in the channels had to be prepared by Zhibin Gan Luyan Zhang Gang Chen cooling the water-containing channel plates in a freezer at À201C for 2 h. In addition, solvent bonding had to be operated on a cooled block (À201C).…”