Fabrication and characterization of a fritless microfabricated electroosmotic pump with reduced pH dependence.
ABSTRACT A fritless electroosmotic pump with reduced pH dependence has been fabricated on a glass microchip and its performance characterized. The chip design consists of two 500-microm channels, one packed with anion exchange beads and the other packed with cation exchange beads, which produce convergent electroosmotic flow streams. The electroosmotically pumped solution flows away from the intersection of the two pumping channels through a field-free channel. This simple design allows for the production of a fritless electroosmotic pump and easy replacement of the ion exchange beads whose charged surfaces generate the flow. The pump was found to produce volumetric flow rates of up to 2 microL/min for an applied voltage of 3 kV at a pH of 6.8. Moreover, the electroosmotic pump can generate high flow rates over an extended pH range of at least 2-12, a significant advantage over previously fabricated electroosmotic pumps, which typically have a more limited range in which they can achieve high flow rates.
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ABSTRACT: A micropump provides flow and pressure for a lab-on-chip device, just as a battery supplies current and voltage for an electronic system. Numerous micropumps have been developed, but none is as versatile as a battery. One cannot easily insert a micropump into a nonterminal position of a fluidic line without affecting the rest of the fluidic system, and one cannot simply connect several micropumps in series to enhance the pressure output, etc. In this work we develop a flow battery (or pressure power supply) to address this issue. A flow battery consists of a +EOP (in which the liquid flows in the same direction as the field gradient) and a -EOP (in which the liquid flows opposite to the electric field gradient), and the outlet of the +EOP is directly connected to the inlet of the -EOP. An external high voltage is applied to this outlet-inlet joint via a short gel-filled capillary that allows ions but not bulk liquid flow, while the +EOP's inlet and the -EOP's outlet (the flow battery's inlet and outlet) are grounded. This flow battery can be deployed anywhere in a fluidic network without electrically affecting the rest of the system. Several flow batteries can be connected in series to enhance the pressure output to drive HPLC separations. In a fluidic system powered by flow batteries, a hydraulic equivalent of Ohm's law can be applied to analyze system pressures and flow rates.Analytical Chemistry 03/2011; 83(7):2430-3. · 5.70 Impact Factor
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ABSTRACT: Microchannels in microfluidic devices are frequently chemically modified to introduce specific functional elements or operational modalities. In this work, we describe a miniaturized hydraulic pump created by coating selective channels in a glass microfluidic manifold with a polyelectrolyte multilayer (PEM) that alters the surface charge of the substrate. Pressure-driven flow is generated due to a mismatch in the electroosmotic flow (EOF) rates induced upon the application of an electric field to a tee channel junction that has one arm coated with a positively charged PEM and the other arm left uncoated in its native state. In this design, the channels that generate the hydraulic pressure are interconnected via the third arm of the tee to a field-free analysis channel for performing pressure-driven separations. We have also shown that modifications in the cross-sectional area of the channels in the pumping unit can enhance the hydrodynamic flow through the separation section of the manifold. The integrated device has been demonstrated by separating Coumarin dyes in the field-free analysis channel using open-channel liquid chromatography under pressure-driven flow conditions.Lab on a Chip 07/2011; 11(18):3081-8. · 5.70 Impact Factor
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ABSTRACT: A glass microfluidic device is presented in which a microchannel is split into two regions with different electric fields by a nanochannel intermediate electrode junction formed by dielectric breakdown. The objective is to sink current through the nanochannel junction without sample loss or broadening of the band as it passes the junction. This type of performance is desired in many microfluidic applications, including the coupling of microchannel/CE with ESI-MS, electrochemical detection, and electric field gradient focusing. The voltage offsets in this study are suitable for microchannel/CE-ESI-MS. Imaging of the transport of model anions and cations through the junction indicates that the junction exhibits nanofluidic behavior and the mean depth of the nanochannel is estimated to be approximately 105 nm. The ion permselectivity of the nanochannel induces concentration polarization and enriched and depleted concentration polarization zones form on opposite sides of the nanochannel, altering the current and electric field distributions along the main microchannel. Anion transport efficiency past the junction was high, 96.0%, and varied little over the pH range of 4.0-8.0. In contrast, cation transport is much lower, and decreases from 72 to 11% from pH 4.0 to 8.0. Band broadening increases with increasing pH less than 70% over the pH range of 4.0-8.0. It is anticipated that this characterization will aid in the understanding and optimization of such junctions made from permselective membranes and porous glass.Electrophoresis 08/2010; 31(15):2686-94. · 3.26 Impact Factor