Experimental Investigation on Spatiotemporal Concentration Profile of the Ion Concentration Polarization Layer*

Ion Concentration Polarization (ICP) is a fundamental electrokinetic phenomenon that occurs near a perm-selective membrane. With the balance of hydrodynamic drag force and electrophoretic force on the charged molecules, ICP can be applied to a preconcentrator for the detection of low abundant molecules. In this work, spatiotemporal concentration profile of diffusion-convection layer during ICP process had been measured with patterned microelectrode. Here, diffusion-convection layer was defined as the intermediate region between bulk region and ion depletion zone. Unlike the traditional diffusion-convection layer which had linear concentration profile, the measured data indicated near plateau concentration distribution over the diffusion-convection layer in a microfluidic environment. Also, even though the plateau concentration region had rather higher concentration compare to ion depletion zone, it acted as a virtual barrier against charged molecules as well. This anomalous concentration profile can provide a key information to the fundamental study on preconcentration dynamics of ICP.