This article presents several methods for the chemical modification of poly(methyl methacrylate) (PMMA) surfaces for the application of wall coating polymers to suppress EOF and to reduce analyte-wall interactions.
The development and optimization of surface-coating strategies is of critical importance for reliable, repeatable, and high-efficiency electrophoretic DNA separations. Organic substrates such as glass and silica have commonly been used for the fabrication of microfluidic devices, and numerous silane-based chemistries originally developed to passivate fused-silica capillary surfaces were relatively simple to transfer to silica-based microfluidic devices; however, the devices made from glass and silica substrates are not as economical as polyumeric microfluidic devices for mass production. In addition, the low cost of mass manufactured polymeric microfluidic devices could make the production of microfluidic devices feasible for applications in which cross-contamination produces unacceptable results. The development of robust and simple surface-modification techniques for polymeric substrates is challenging due to the wide variety of polymeric materials available for microfluidic device fabrication. The current study compared a few methods for the application of wall coating polymers to PMMA microchannels. The results identify several important parameters of the coating polymer protocols needed to improve the aggregate separation performance. The hydrophilicity of the PMMA surface was altered by UV irradiation and HNO3 treatment in air at atmospheric pressure and at room temperature. Contact angle measurements were conducted to determine the change in wettability of the surface. Electrophoretic separations of ssDNA were successfully performed in microchips prepared using these methods. The researchers determined that 10 min UV irradiated surfaces coated with hydroxypropyl-methyl-cellulose (HPMC) produced better separation performance than surfaces irradiated with UV for 15 min and coated with HPMC. UV/ozone-treated surfaces coated with poly(vinyl alcohol) and HNO3-treated surfaces coated with HPMC resulted in the highest separation performance. 7 figures and 32 references