Abstract
This paper presents an investigation into two crucial aspects of microfluidic applications, namely electrokinetic focusing and switching. This study commences by modeling the electrokinetic focusing phenomenon theoretically using the potential flow theory. A new theoretical model is derived and applied to predict the width of the focused stream. The results predicted by the theoretical model are shown to be in good agreement with the experimental data. The paper then proceeds to study the electrokinetic switching functions systematically using both experimental and theoretical approaches. A new control model for 'one-to-multiple' electrokinetically pre-focused micro flow switches is proposed. Using this new model, the sample flow can be pre-focused electrokinetically into a narrow stream and then injected directly into the desired outlet port. The results of this study provide a useful methodology for the analysis of flow control in microfluidic devices. Finally, an electrokinetically driven micro flow cytometer utilizing electrokinetic focusing and switching effects is demonstrated. Experimental data show that the developed methods could successfully focus microparticles and direct them into any desired outlet port. © 2005 IOP Publishing Ltd.