Electrokinetic concentration enrichment within a microfluidic device using a hydrogel microplug

A simple and efficient approach for concentration of charged molecules in microfluidic devices is described. The functional component of the system is a hydrogel microplug photopolymerized within the main channel of a microfluidic device. When an appropriately biased voltage is applied across the hydrogel, charged analyte molecules move from the source well toward the hydrogel. Transport of the analyte through the hydrogel is slow compared to its velocity in the microfluidic channel, however, and therefore it concentrates at the hydrogel/solution interface. For an uncharged hydrogel, a bias of 100 V leads to a ∼500-fold enrichment of the DNA concentration within 150 s, while the same conditions result in an enrichment of only 50-fold for fluorescein. Somewhat lower enrichment factors are observed when a negatively charged hydrogel is used. A qualitative model is proposed to account for the observed behavior.