ABSTRACT
Following the trend in miniaturization of integrated circuits for electronic devices, integrated micro¤uidic circuits are currently developed and are expected to have great impact on (bio) chemical synthesis and analysis. Such labs-on-a-chip are glass or plastic plates, typically a few centimeters on a side, with interconnected microreservoirs and micropathways on its surface. Minute amounts of liquids and suspended solids are moved around the channels from one reservoir to another. A crucial aspect in the performance of such microreactors is the precise manipulation of ¤uid ¤ow. Electrokinetic actuation is eminently suited to control the motion of ¤uids and reagents on the chip. This is effected by strategically placed electrodes creating electrokinetic forces that drive the ¤uids and reagents through selected pathways. More specically, because of its planar velocity prole, electroosmotic ¤ow allows for efcient and controlled material transport. Furthermore, electrophoresis provides a powerful separation technique of reactants and products. Thus, lab-on-a-chip technology, making tools smaller and more integrated and, therefore, less expensive and faster, has great potential use in various elds of the life sciences, such as genomics, proteomics, clinical diagnostics, and basic biomolecular research. (Figure courtesy of Mesaplus, University of Twente, Twente, the Netherlands.)
Electrokinetic phenomena involve the migration of a charged (colloidal) particle or a charged macroscopic surface, relative to the surrounding liquid medium, which is an electrolyte solution. They are the result of motion and electric interactions in the electrical double layer. Electrokinetic phenomena may be classied based on the driving force and the ensuing motion. The driving force is either an externally applied electric potential gradient (electric eld) or a “mechanical” potential gradient (pressure difference, or a gravitational or centrifugal eld). With respect to the motion, distinction is made between a mobile phase and a stationary phase. Table 10.1 summarizes the different groups of electrokinetic phenomena.
