(533c) A Self-Contained Solid-State Micro-Valve for Electrokinetic Separations in a Networked Microfluidic Chip

This paper reports a self-contained solid-state valve especially used to reduce dispersion and sample loss in electrokinetic flows when electrokinetic concentration zones pass by a T-junction in a networked microfluidic chip. The best way to control electrokinetic flow is to control current streamlines since the charged species are driven along the current streamlines. Computer simulations successfully demonstrated that such dispersion and sample can be reduced by applying an additional electric field within the junction channel to straight the current streamlines bended by the T-junction. A pair of platinum thin film microelectrodes integrated within the junction channel was used to control the current streamlines in the main channel. An electronic system has been successfully developed to detect the total current passing through the main channel every 30 milliseconds and automatically apply the corresponding currents onto the microelectrodes. Experiments showed that the dispersion was greatly reduced by this method when three adjacent protein concentration zones were isotachophoretically passing by the T-junction. The relationship between two key parameters, the electrode positions and the amount of current carried by the electrodes, was experimentally characterized in an effort to eliminate the dispersion and sample loss. With the electronic control system, two microelectrodes provides a simple and robust way to manipulate current streamlines, thus acting as an effective valve for charged species in electrokinetic separations.