A theory of cross-coupled flow equations in unsaturated soils is necessary to predict (1) electroosmotic flow with application to electroremediation and agriculture, (2) the electroseismic and the seismoelectric effects to develop new geophysical methods to characterize the vadose zone, and (3) the streaming current, which can be used to investigate remotely ground water flow in unsaturated con...

Analytical results for the velocity distribution, mass flow rate, pressure gradient, wall shear stress, and vorticity in mixed electroosmotic/pressure driven flows are presented for two-dimensional straight channel geometry. We particularly analyze the electric double-layer (EDL) region near the walls and define three new concepts based on the electroosmotic potential distribution. These are th...

The predictability and constancy over time of the electroosmotic flow in microchannels is an important consideration in microfluidic devices. A common cause for alteration of the flow is the adsorption of analytes to channel walls, for example, during capillary electrophoresis of proteins. It is shown that certain experimental data, published by Towns and Regnier (Towns, J. K; Regnier, F. E. An...

The flux of solvent water coupled to the transit of ions through protein pores is considerable. The effect of this electroosmotic solvent flow on the binding of a neutral molecule [beta-cyclodextrin (betaCD)] to sites within the staphylococcal alpha-hemolysin pore was investigated. Mutant alpha-hemolysin pores were used to which betaCD can bind from either entrance and through which the directi...

A microchannel device is presented which separates and focuses charged proteins based on electric field gradient focusing. Separation is achieved by setting a constant electroosmotic flow velocity against step changes in electrophoretic velocity. Where these two velocities are balanced for a given analyte, the analyte focuses at that point because it is driven to it from all points within the c...

Optical tweezers enable one to trap a single particle without any mechanical contact and to measure its position and the forces acting on it with high resolution (+/-4 nm, +/-160 fN). Taking advantage of a specially designed microfluidic cell the electrophoretic response of the colloid under study and the electroosmotic effect on the surrounding medium are determined using the identical colloid...

Microfluidic field-effect flow control (FEFC) modifies the zeta potential of electroosmotic flow using a transverse electric field applied through the microchannel wall. Previously demonstrated in silicon-based and glass microsystems, FEFC is presented here as an elegant method for flow control in polymer-based microfluidics with a simple and low-cost fabrication process. In addition to direct ...

Control of surface properties in microfluidic systems is an indispensable prerequisite for successful bioanalytical applications. Poly(dimethylsiloxane) (PDMS) microfluidic devices are hampered from unwanted adsorption of biomolecules and lack of methods to control electroosmotic flow (EOF). In this paper, we propose different strategies to coat PDMS surfaces with poly(oxyethylene) (POE) molecu...

The scope of this work was to investigate the migration behavior of the currently used protease inhibitors for antiretroviral therapy of people infected with the human immunodeficiency virus and to develop a method for their capillary electrophoretic separation and determination. All of the protease inhibitors (indinavir, saquinavir, nelfinavir, amprenavir, and ritonavir) contain at least one b...

Isoelectric focusing of proteins in a silica nanofluidic channel filled with citric acid and disodium phosphate buffers is investigated via numerical simulation. Ions in the channel migrate in response to (i) the electric field acting on their charge and (ii) the bulk electroosmotic flow (which is directed toward the cathode). Proteins are focused near the low pH (anode) end when the electromig...