Influence of Different Capillary Geometries on the Plug Distortion in Hybrid Micro Channels
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1004-P03-21
Influence of Different Capillary Geometries on the Plug Distortion in Hybrid Micro Channels Lars Storsberg1, Lars Schˆler1, Konstantin Seibel1, Heiko Sch‰fer1, Marcus Walder1, RenÈ Johannes P¸schl2, Bernd Wenclawiak2, and Markus Bˆhm1 1 Institute for Microsystem Technologies, University of Siegen, Hˆlderlinstr. 3, Siegen, Germany 2 Analytical Chemistry, University of Siegen, Adolf Reichwein Str. 2-4, Siegen, Germany
ABSTRACT The plug distortion for on-chip capillary zone electrophoresis systems with rectangular separation channels, manufactured in a hybrid layer system with different material properties of the vertical and the horizontal walls has been examined. Experimental data and simulation results indicate that plug widening caused by different values of the ζ-potential of the walls in contact with the fluid depends strongly on the aspect ratio of the channel cross section. If the height to width ratio is much greater or much smaller than 1, as is often the case for commonly used labchip architectures, plug widening may be negligible. The difference of the ζ-potentials between the vertical and the horizontal side walls has been determined from the shape of the plug edges. For an architecture using glass for the top and bottom walls, but SU-8 for the side walls, the difference of the ζ-potentials was measured to be on the order of only 2.4 mV for a pH of 9.2, suggesting that such device architectures may be used for on-chip electrophoresis analysis without uniform coating of the channel inside for less demanding applications. INTRODUCTION Lab-on-Chip systems provide a powerful platform for chemical and biochemical applications. Microfluidic devices on the chip allow for pumping, mixing, separation, and detection of very small amounts of reagents. If an Application Specific Integrated Circuit (ASIC) is combined with on-chip microfluidics the system becomes even more powerful since it enables the integration of control and detection circuitry. Based on this concept application specific labchips can be fabricated with a wide variety of on-chip functional components like e.g. mixers [1,2], pumps [3,4], flow-focusing devices [5], integrated optical or electrical sensors [6-8], and integrated reactors [9]. Most of these systems use glass or silicon as substrates for device fabrication and a variety of different materials (e.g. PMMA, PDMS, SU-8) as fluidic layers because they are chemical inert and easy to fabricate. In Capillary Zone Electrophoresis (CZE) systems the Electroosmotic Flow (EOF) depends on the ζ-potential at the walls of the separation capillary. In circular glass capillaries the well-known stamp like EOF profile is observed. This profile ensures that the injected sample plug is not distorted by streaming effects, and high separation efficiency is obtained. If, however, different materials are used at the side walls and at the top and bottom of a rectangular capillary, which is the case for certain advanced labchip architectures, the different ζ-potentials at the capillary walls lead to par
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