Electroosmosis

Microchips for analytical purposes have attracted great attention over the last 20 years. In the present review, we focus on the most recent development of microchips for electrophoretic separation of proteins. This review starts with a short recalling about the microchips covering the basic microchip layout for CE and the commercial chips and microchip platforms. A short paragraph is dedicated to the surface treatment of microchips, which is of paramount importance in protein analysis. One section is dedicated to on-line sample pretreatment in microchips and summarizes different strategies to pre-concentrate or to purify proteins from complex matrixes. Most of the common modes used for CE of proteins have already been adapted to the chip format, while multidimensional approaches are still in progress. The different routes to achieve detection in microchip are also presented with a special attention to derivatization or labeling of proteins. Finally, several recent applications are mentioned. They highlight the great potential of electrophoretic separations of proteins in numerous fields such as biological, pharmaceutical or agricultural and food analysis. A bibliography with 151 references is provided covering papers published from 2000 to the early 2007.

The growing interest of researchers in the phenomenon of electrokinetic can be seen as a direct and natural response to the importance and significance of its applications in our life. Transporting of fluids under the influence of electroosmosis or electrophoresis has significance implication nowadays in the fabrication of microfluidic devices and thus in biomedicine and micro-electromechanical systems. Obvious examples are separation and lap-on-a-chip devices. The overall aim of the present paper is to investigate how electroosmotic flow could effectively contribute to the intracellular biomolecules flow. The significance of the current study arises from being one of the early attempts to study electroosmosis in Iraq. Utilizing the numerical analysis, two mathematical models have been built in order to shapes the electroosmosis-based microflow of the negatively charged messenger proteins to the negatively charged nucleus. To shed more light on the electroosmotic flow behavior through microchannels with contraction, the well-known computer software COSMOL has been used to develop the simulations. The potential impacts of several design parameters on temperature distribution and velocity profiles for a variety of contraction shapes have been analyzed and presented. Such design parameters include wall zeta potential, external electric field, and channel wall material.

Pumping of fluids with precise control is one of the key components in a microfluidic device. The electric field has been used as one of the most popular and efficient nonmechanical pumping mechanism to transport fluids in microchannels from the very early stage of microfluidic technology development. This review presents fundamental physics and theories of the different microscale phenomena that arise due to the application of an electric field in fluids, which can be applied for pumping of fluids in microdevices. Specific mechanisms considered in this report are electroosmosis, AC electroosmosis, AC electrothermal, induced charge electroosmosis, traveling wave dielectrophoresis, and liquid dielectrophoresis. Each phenomenon is discussed systematically with theoretical rigor and role of relevant key parameters are identified for pumping in microdevices. We specifically discussed the electric field driven body force term for each phenomenon using generalized Maxwell stress tensor as...

Electrokinetic micropumps received extra attention due to its applications in pumping of biological and chemical fluids, such as blood, DNA, and saline PBSs. In this paper the electroosmotic flow in microchannel has been numerically investigated by developing a model from the basic governing equations (continuity, momentum, energy, and Laplace and Poison-Boltzmann equations) through a square channel with contraction of different geometries. Utilizing the numerical analysis, a mathematical model has been built in order to study the electroosmosis-based microflow of the negatively charged messenger proteins to the negatively charged nucleus to shed more light on the electroosmotic flow behavior through microchannels with contraction. The results obtained show a considerable effect of the zeta potential on the velocity and many parameters studied such as shapes, depth and number of contractions and channel wall material. Adding materials with different thermal conductivity to channel wall, affect the heat distribution throughout channel length. In particular, five wall materials typically used in Microelectromechanical systems (MEMS). It shows that a material with low thermal conductivity works as isolation against dissipating the heat generated from Joule heating effect.

The objective of this study was to investigate the influences of electroosmosis (EO) and electrophoresis (EP) on the permeate flux in submerged membrane bioreactors. When a polymeric membrane is placed in between an anode and a cathode, both EO and EP occur simultaneously,
causing enhancement in flux. Results showed that after 150 min of filtration, the permeate fluxes were 60, 115, 175 and 260 L/m2/h at 0, 30, 40 and 50 V, respectively. It was shown that the EO was linearly changing with increasing voltage, reaching up to 54 L/m2/h at 50 V. EP was found to be a
significant process in removing soluble microbial products from the membrane surface, resulting in an increase in permeate flux as the filtration progressed. About 20-fold of smaller protein and carbohydrate concentrations were found in the cake layer when the electrical field (EF) was applied. However, the EF application promoted pore fouling, because of the calcium and magnesium scaling.

Lab-on-a-chip electrophoresis is becoming increasingly useful for protein analysis, thanks to recent developments in this field. This review is an update of the review we published at the start of 2008 [Peng, Y., Pallandre, A., Tran, N. T., Taverna, M., Electrophoresis 2008, 29, 156–177]. The superiority of polymers for the manufacture of analytical microchips has been confirmed. This trend implies several modifications to the processes previously used with glass/silicon chips and requires a better understanding of the interfacial phenomena of these materials. Significant progress in chip-based techniques for protein analysis has been made in the last 2 years. In addition to advances in traditional electrokinetic modes, counter-flow gradient focusing techniques have emerged as useful methods not only for separation, but also for the online preconcentration of samples. This review, with more than 175 references, presents recent advances and novel strategies for EOF measurement, surface treatment, sample pretreatment, detection and innovations relating to the different modes of separation.

In a nanofluidic system, the electroosmotic flow (EOF) is a complex fluid transport mechanism, where the formation of an electrical double layer (EDL) occurs ubiquitously at the dissimilar atomic interface. Several studies have suggested various interface boundaries to calculate the EDL thickness. However, the physical origin of the interface boundary and its effects on the flow properties is not yet clearly understood. Combining the theoretical framework and molecular dynamics (MD) simulations, we show the effects of different interfacial boundaries on the EDL thickness and EOF characteristics. Implemented interface boundaries exhibit the EDL thickness–boundary relation, i.e., the EDL thickness from MD simulations shows the tendency of converging toward the continuum approximation. Furthermore, inserting these values of EDL thicknesses into the continuum equation shows the convergence of flow transition of the molecular state to a neutral from an electrical violation phase, which takes a parabolic to plug-like shape in the velocity profile. Different interface boundaries also affect the hydrodynamic properties (viscosity and electroviscosity) of EOF, which varies from the bulk to interface region, as well as the fluid flow. Therefore, we can infer that, at the molecular level, the dissimilar atomic boundary and hydrodynamic properties dominate the electrokinetic flow. Our simulation results and theoretical model provide fundamental insightful information and guidelines for the EOF study based on the atomic interface and dynamic structure-based hydrodynamic property.

The use of UV/ozone surface treatments for achieving low temperature bonds between PMMA and COC microfluidic substrates is evaluated. Low temperature bond strengths, approaching those of native polymer substrates bonded above their glass transition temperatures, are demonstrated for both thermoplastics. To evaluate the effects of the UV/O3 surface treatment on the operation of bonded microfluidic devices, the relationship between UV/O3

Electro-osmotically driven displacement between two solutions having a conductivity mismatch is theoretically examined. Internal pressures induced by the conductivity mismatch can affect the propagation of the solution interface and the behavior of the transient current. Combining Ohm’s law and fluid mass conservation, we derive a coupled set of length-averaged equations accounting for how the electric current and the traveling distance of the solution interface vary with time, electric field, and the solution conductivities. Extension to successive displacements involving multiple solution zones is made to reveal non-monotonic and stagewise changes in transient currents. For the first time, critical roles of surface conductance on displacements in highly charged channels are unraveled. We show that if the lower conductivity solution has a greater valence than the higher one, the effective conductivity of the former can exceed that of the latter when the channel height is below some critical value. The resulting transient current behavior can turn opposite to that usually observed in the large-channel case, offering a new paradigm for gauging the importance of surface conductance in submicron charged channels. Possible impacts of diffusion smearing and hydrodynamic dispersion are also discussed by including the additional mixing zone into the analysis. Having shown good agreement with the existing experimental data, our analysis not only captures the natures of solution displacement by electro-osmotic flow (EOF), but also extends the applicability of the current monitoring method for measuring surface zeta potentials of microchannels.

Heat-transfer characteristics of mixed electro-osmotic and pressure-driven flows are obtained in a two-dimensional straight microchannel by a solving steady-state energy equation. Both thermally developing and fully developed regions are considered for hydraulically fully developed mixed flows under isoflux channel wall conditions. The steady temperature distribution is obtained from the superposition of homogeneous solution and particular function. The particular solution is derived based on the constant heat-flux condition in the fully developed region, while the homogeneous solution is presented in terms of infinite series containing Kummer confluent hypergeometric functions due to the existence of non-self-adjoint eigenvalues. The coefficients of the homogeneous solution are found by utilizing the Gram-Schmidt orthogonalization procedure, and the Secant method is utilized to obtain the corresponding eigenvalues. Our analytical techniques are verified by obtaining an excellent agreement with existing literature for slug, pressure-driven, and pure electroosmotic flow cases. In the fully developed region, the Nusselt number of mixed flow is independent of the thermal Peclet number for a particular Joule heating and imposed surface heat flux. The entry length of mixed flow significantly depends on the applied/induced pressure gradient to the electro-osmotic flow

Heavy metals as well as other pollutants are widespread and create deleterious impact to the environment and human health. There are different in situ and ex situ technologies of immobilization and removal of contaminants; electrokinetic remediation is one of such technologies. It can be applied for treatment of wide areas, e.g., former industrial and military firing-grounds. Technology is applicable to water soluble contaminants at sites with homogeneous soils that are fine-grained and exhibit both, high permeability and high moisture contents. The aim of the study was to test the efficiency of electrokinetic remediation for copper contaminated clayey soil in laboratory conditions. Pilot scale experiments were applied to test the efficiency of electrokinetic removal of contaminants from soil by application of low voltage direct current (DC). Experimental results show that the use of DC power can be selected for treatment of heavy metal contaminated soils. Batch scale experiments we...

In this paper, the surface modification of silk fiber using anhydrides to graft the polysaccharide chitosan and dyeing ability of the grafted silk were studied. Silk fiber was degummed and acylated with two anhydrides, succinic anhydride (SA) and phthalic anhydride (PA), in different ...