Electrokinetic generation of temporally and spatially stable concentration gradients in microchannels

Generating stable microscale concentration gradients is key to numerous biological and chemical analyses, Microfluidic systems offer the ability to maintain laminar fluid diffusion interfaces ideal for the production of temporally stable concentration gradients. Previous efforts have focused on pressure driven flows and have relied on networks of branching channels to create streams of varying concentration which can subsequently be combined to form the desired gradients, In this Study, we numerically and experimentally demonstrate a novel electrokinetic technique which utilizes applied voltages and surface charge heterogeneity in simpler channel geometries to control and manipulate microscale concentration gradients without the need for parallel lamination, Flow rates ranged from 30 to 460 nl min(-1) for Peclet numbers between 70 and 1100. Spatial stability of 0.6 mm or greater was obtained for a wide range of gradient shape and magnitudes over lateral dimensions of 400-450 mu m. Sensitivity analysis determined that this technique is, largely independent of channel depth and species electrophoretic mobility, however channel width and the diffusion coefficient of the analyte are critical. It was concluded that by adjusting applied voltages and/or channel width, this approach to concentration gradient generation can be adapted to a wide range of applications. (c) 2005 Elsevier Inc. All rights reserved.