Reaction and diffusion dynamics in a microfluidic format
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Reaction and diffusion dynamics in a microfluidic format Dietrich Kohlheyer, Rob G. H. Lammertink, Stefan Schlautmann, Geert A. J. Besselink, Paul Vulto and Richard B. M. Schasfoort MESA+ Research Institute, Biochip Group, University of Twente P.O. Box 217 7500 AE Enschede The Netherlands
Abstract A novel microfluidic structure based on the electroosmotic guiding of reagent streams is presented that can be used as a fully adjustable diffusion based microreactor. The position and the width of two aqueous reactant streams entering a laminar-flow chamber can be controlled individually by changing the flow ratio of three parallel guiding streams containing buffer only. To control the intensity of product formation, the overlapping area between the diffusion regions of the two different reagent streams can be adjusted. This article describes the fabrication and experimental characterization of the device. 1. Introduction In the last decade the research and development of microfluidic systems has grown rapidly, allowing the fabrication of “micro total analysis systems” (µ-TAS) and “lab-on-a-chip” devices using technologies from the microelectronics industry [1, 2]. These microfluidic systems draw their advantages from efficient mass transport and high surface to volume ratios, allowing fast and efficient analysis procedures. One important factor is the energy and sample consumption, which is due to the small dimensions of microfluidic structures much lower than in traditional reactors. Flow in microfluidic channels is always laminar because of low Reynolds numbers [3]. This makes it possible to have parallel flowstreams without turbulent mixing [4]. In such systems mass transport is based on diffusion only. Micro total analysis systems include several passive and active microfluidic components. Mixers and reactors that can be integrated in such systems have been developed in different shapes and ways of working [2, 4, 6, 8]. All these reactors can be controlled by changing the flow velocity inside the reacting areas or the reactant concentrations. In some cases it is interesting to control the reaction intensity without changing the flow velocity or concentration. The microreactor presented in this article fulfills these requirements. Electro osmotic flow (EOF) is a simple technique that can be used for pumping aqueous solutions through micro channels. The major advantage of using EOF is that no external pumps or other moving parts are needed. Here, we report on the design and evaluation of a microfluidic reactor driven by EOF.
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1.1 Address-flow principle The original idea of address-flow [5] is to control the position and the width of a central fluid stream (containing sample or reagent) entering a wider microfluidic chamber by applying parallel guiding streams. By adjusting the flow ratio of the two guiding streams the position of the sandwiched sample stream can be changed in a controllable way. Address-flow is only possible in micro systems where fluids behave laminar, and turbulent mixing is absent.
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