Interdisciplinary Applied Mathematics

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is transported from the ends of the cross-shaped segments to the reservoir marked as the “Final Species.” Most microfluidic chips transport the fluid electrokinetically (see Chapter 7) and/or by pressure. Electrokinetic transport and control of fluids has the advantage that it eliminates the need for mechanically moving parts, such as valves and pumps, which have thus far been difficult to construct and interface to microchip systems (Weigl et al., 2003).


An important element of the p,-TAS is the reaction chamber. As shown in Figure 18.1, chemical/biological species are transported to the reaction chambers, where chemical reactions take place leading to the formation of a product. The rate of formation of the product is dependent on the flux of the reactant, the proportion of the various reactants in the solution, the order of the reaction, and the reaction kinetics. The solution from the reaction chamber is sometimes tapped for detection. The detection of the product is typically easier than the detection of the reacting species. In such a case, the presence of the product and the concentration of the product can give quantitative information about the reacting species. Thus, often reaction and detection schemes are intrinsically linked together, and both of these form an integral part of the p,-TAS.


Another important functionality in p,-TAS is the separation of biomolecules and biochemical species. Electrophoresis and isoelectric focusing (see Chapter 7 for details) are the most commonly employed methods of separation. In Figure 18.1, for example, the separation is based on electrophoresis. Higher field intensity is generally tolerable for electrophoretic separation in microchannels (Ehrfeld, 2003). Smaller characteristic dimensions in combination with higher field intensities lead to a shorter time scale of separation, which is a fundamental advantage in p,-TAS compared to macroscopic devices.

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