Thousandfold signal increase using field‐amplified sample stacking for on‐chip electrophoresis

Field‐amplified sample stacking (FASS) leverages conductivity gradients between a volume of injected sample and the background buffer to increase sample concentration. A major challenge in applying FASS to on‐chip assays is the initial setup of high‐conductivity gradient boundaries in the region of the injected sample volume. We have designed, fabricated, and characterized a novel FASS‐capillary electrophoresis (CE) chip design that uses a photoinitiated porous polymer structure to facilitate sample injection and flow control for high‐gradient FASS. This polymer structure provides a region of high flow resistance that allows the electromigration of sample ions. We have demonstrated an electropherogram signal increase by a factor of 1100 in electrophoretic separations of fluorescein and Bodipy with, respectively, 2 μ M and 1 μ M initial concentrations.