On‐chip pressure generation using a gel membrane fabricated outside of the microfluidic network

Abstract

On-chip generation of pressure gradients via electrokinetic means can offer several advantages to microfluidic assay design and operation in a variety of applications. In this article, we describe a simple approach to realizing this capability by employing a polyacrylamide-based gel structure fabricated within a fluid reservoir located at the terminating end of a microchannel. Application of an electric field across this membrane has been shown to block a majority of the electroosmotic flow generated within the open duct yielding a high pressure at the channel–membrane junction. Experiments show the realization of higher pressure-driven velocities in an electric field-free separation channel integrated to the micropump with this design compared to other similar micropumps described in the literature. In addition, the noted velocity was found to be less sensitive to the extent of Debye layer overlap in the channel network, and therefore more impressive when working with background electrolytes having higher ionic strengths. With the current system, pressure-driven velocities up to 3.6 mm/s were realized in a 300-nm-deep separation channel applying a maximum voltage of 3 kV at a channel terminal. To demonstrate the separative performance of our device, a nanofluidic pressure-driven ion-chromatographic analysis was subsequently implemented that relied on the slower migration of cationic analytes relative to the neutral and anionic ones in the separation channel likely due to their strong electrostatic interaction with the channel surface charges. A mixture of amino acids was thus separated with resolutions greater than those reported by our group for a similar analysis previously.

A microchip device to enhance free flow electrophoresis using controllable pinched sample injections

“…Separation is a critical process for both posttreatment of synthesis and sample pretreatment of instrumental analysis . While shrinking separation columns to micro‐ or nano‐scale, separation speeds and efficiencies can be increased significantly along with less sample and buffer consumption . However, throughput mismatch with regular size sample preparation and/or downstream analysis procedures limits further application of microfluidic separation technique.…”

An integrated plastic microchip for enhancing electrophoretic separation using tunable pressure‐driven backflows

“…Moreover, for a given operating voltage at $${\varphi _p} = {\varphi _s}$$, the $${u_{net}}$$ can be reduced to nearly one‐third by fabricating a gel membrane in the bottom of reservoir 4 using a 10% v/v gel precursor solution, indicating the sufficient pressure generation capability of the gel membrane pumping unit. According to literature reports [32], pore size in gel structure due to precursor concentration can significantly influence the pumping performance of gel membrane involved micropump. Therefore, the effect of gel precursor concentration on $${u_{net}}$$ was carefully evaluated and the results are shown in Figure 2B.…”

A review of the zone broadening contributions in free‐flow electrophoresis

“…Moreover, nonuniformities in the electric field combined with those in the channel surface charge and/or liquid properties like viscosity can prevent local conservation of electroosmotic flow (EOF). Unwanted pressure-gradients, including those across the channel width (𝑥-coordinate), arise in these situations to balance the overall liquid flow further convoluting analyte transport [27][28][29]. Similarly, gas bubbles generated at the electrodes can also significantly alter liquid flow and electric field in an FFE system.…”