Electrokinetic flow focusing and valveless switching integrated with electrokinetic instability for mixing enhancement

Abstract

This study performs an experimental investigation into electrokinetically-driven flow phenomena in microfluidic chips. The study commences by investigating the electrokinetic focusing/valveless switching of multiple sample flows in an M × N microfluidic chip, where M is the number of sample streams and N is the number of outlet channels. The experimental results show that the sample flows can be electrokinetically pre-focused into narrow streams via sheath flows and then guided to the desired outlet ports by applying a simple voltage control model which specifies the intensity of the external electrical field to be applied to the inlet channels and the required potential conditions of the individual outlet channels, i.e. grounded or isolated. The study then investigates the electrokinetic instability phenomenon induced at the interfaces between the sample flows and the sheath flows by the application of an external electrical field of sufficient intensity. It is shown that inducing this instability phenomenon yields a significant improvement in the mixing performance within the microchannel. Finally, it is demonstrated that by applying a high electrical potential to the inlet channel and specifying appropriate potential conditions for the individual outlet channels, two sample streams can be directed to any one of the N outlet channels in order to carry out mixing via electrokinetic instability effects.