Thermal bonding of polymeric capillary electrophoresis microdevices in water

A new method for thermally bonding poly(methyl methacrylate) (PMMA) substrates to form microfluidic systems has been demonstrated. A PMMA substrate is first imprinted with a Si template using applied pressure and elevated temperature to form microchannel structures. This embossing method has been used to successfully pattern over 65 PMMA pieces using a single Si template. Thermal bonding for channel enclosure is accomplished by clamping together an imprinted and a blank substrate and placing the assembly in boiling water for 1 h. The functionality of these water-bonded microfluidic substrates was demonstrated by performing high-resolution electrophoretic separations of fluorescently labeled amino acids. Testing of bond strength in four microdevices showed an average failure pressure of 130 kPa, which was comparable to the bond strength for devices sealed in air. Subsequent profilometry of separated substrates revealed that the dimensions of the channels were well preserved during the bonding process. This new methodology for generation of microfluidic constructs should facilitate the permanent incorporation of hydrated, molecular size-selective membranes in microdevices, thus circumventing problems associated with membrane swelling in microfluidic systems upon exposure to water.