Solute Focusing Techniques for Bioseparations

Evans, Lisa L.; Burns, Mark A.

doi:10.1038/nbt0195-46

Cited by 8 publications

(3 citation statements)

References 75 publications

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“…While label-based methods benefit from the high specificity with which markers can be applied and detected, separating cells based upon intrinsic properties, where applicable, circumvents the time and cost associated with the design of new assays. Combining intrinsic separation with equilibrium gradient methods, where a force field applied in a spatially nonuniform medium focuses particles to equilibrium positions, has revolutionized molecular separation over the past half century; − however, the relatively small niche in the context of cell sorting occupied by these methods reflects in part their limited variety (e.g., DGC, FFF) for effecting cell separation. , The utility of intrinsic equilibrium separations is directly related to the number of biophysical properties to which they can be applied. To extend their applicability to cell biology, we propose a new microfluidic equilibrium separation method, called isodielectric separation (IDS), that combines dielectrophoresis (DEP) with spatial gradients in electrical conductivity to sort electrically distinguishable cells and particles.…”

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confidence: 99%

An Equilibrium Method for Continuous-Flow Cell Sorting Using Dielectrophoresis

2008

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Separations represent a fundamental unit operation in biology and biotechnology. Commensurate with their importance is the diversity of methods that have been developed for performing them. One important class of separations are equilibrium gradient methods, wherein a medium with some type of spatial nonuniformity is combined with a force field to focus particles to equilibrium positions related to those particles' intrinsic properties. A second class of techniques that is nonequilibrium exploits labels to sort particles based upon their extrinsic properties. While equilibrium techniques such as iso-electric focusing (IEF) have become instrumental within analytical chemistry and proteomics, cell separations predominantly rely upon the second, label-based class of techniques, exemplified by fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS). To extend the equilibrium techniques available for separating cells, we demonstrate the first implementation of a new microfluidic equilibrium separation method, which we call isodielectric separation (IDS), for sorting cells based upon electrically distinguishable phenotypes. IDS is analogous to isoelectric focusing, except instead of separating amphoteric molecules in a pH gradient using electrophoresis, we separate cells and particles in an electrical conductivity gradient using dielectrophoresis. IDS leverages many of the advantages of microfluidics and equilibrium gradient separation methods to create a device that is continuous-flow, capable of parallel separations of multiple (>2) subpopulations from a heterogeneous background, and label-free. We demonstrate the separation of polystyrene beads based upon surface conductance as well as sorting nonviable from viable cells of the budding yeast Saccharomyces cerevisiae.

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An Equilibrium Method for Continuous-Flow Cell Sorting Using Dielectrophoresis

2008

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“…Attractors are called focusing points in a few separation techniques : isoelectric focusing, field gradient focusing, chromatographic focusing and others (see, for example, Evans & Burns 1995 ;Wang et al 2002). A technique called parametric pumping using two coherently oscillating fields (for example, an oscillating flow and oscillating temperature) was applied to separate particles without considering focusing points and repellers (Wilhelm et al 1968).…”

Section: Separation and Concentration Mechanismmentioning

confidence: 99%

Particle separation and concentration in natural systems

Atencio¹

2006

International Journal of Astrobiology

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A mechanism that permits the separation and concentration of particles in natural systems is proposed. According to the mechanism, the particles in an aquifer are moved by an alternating flow of ground water. The retardation factor oscillates in synchronism with the alternating water flow. The retardation factor or the flow depend on the position in the aquifer (the particle velocity is u=v/R, where v is the water velocity and R is the retardation factor). The alternating flow is induced by tides, geysers or periodic rains. The alternating water flow produces temperature and water composition oscillations in the aquifer. Moreover, the alternating flow is caused by pressure oscillations: therefore, the retardation factor (which depends on pressure, temperature and water composition) oscillates. The dependence of the retardation factor on position is due to the inhomogeneity of the aquifer medium or to the position dependence of temperature, composition or pressure. Different particles may be concentrated at different places in the aquifer or in different aquifers. The particle concentration and the time necessary for concentration are estimated. The particles may be atoms, molecules, colloids or microorganisms. Such a mechanism may have played a role in chemical evolution.

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“…Isoelectric focusing (IEF) is a fractionation technique that segregates amphoteric particles on the basis of isoelectric point and is commonly used for high-resolution analysis of biological samples, particularly for peptide and protein analysis. , In part because standard methods of IEF require high power and costly ampholyte solutions, the use of IEF for preparative applications is expensive compared to other options and therefore less commonly used . The microfluidic IEF device described in this report (see Figure ) addresses these concerns by generating a pH gradient between two closely spaced electrodes in a “natural” buffer system that requires low power and no synthetic ampholytes.…”

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Formation of Natural pH Gradients in a Microfluidic Device under Flow Conditions: Model and Experimental Validation

2000

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A new isoelectric focusing technique has been developed that incorporates natural pH gradient formation in microfluidic channels under flowing conditions. In conjunction, a one-dimensional finite difference model has been developed that solves a system of algebraic-ordinary differential equations that describe the phenomena occurring in the system, including hydrolysis at the electrodes, buffering effects of weak acids and bases, and mass transport due to both diffusion and electrophoresis. A quantitative, noninvasive, optically based method of monitoring pH gradient formation is presented, and the experimental data generated by this method are found to be in good agreement with model predictions. In addition, the model provides a theoretical explanation for initially unexpected experimental results. Model predictions are also shown to match well with experimental results of microfluidic isoelectric focusing of a single protein species. Accounting for the nonuniform velocity profile, characteristic of pressure-driven flow in microfluidic channels, is found to improve predictions of dynamic pH changes close to the electrodes and overall time required to reach steady state, but to reduce the accuracy of dynamic pH change predictions in other regions of the channel.

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Solute Focusing Techniques for Bioseparations

Cited by 8 publications

References 75 publications

An Equilibrium Method for Continuous-Flow Cell Sorting Using Dielectrophoresis

An Equilibrium Method for Continuous-Flow Cell Sorting Using Dielectrophoresis

Particle separation and concentration in natural systems

Formation of Natural pH Gradients in a Microfluidic Device under Flow Conditions: Model and Experimental Validation

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