Charge-based particle separation in microfluidic devices using combined hydrodynamic and electrokinetic effects

Abstract

A new microfluidic approach for charge-based particle separation using combined hydrodynamic and electrokinetic effects is presented. A recirculating flow pattern is employed, generated through application of bi-directional flow in a narrow glass microchannel incorporating diverging or converging segments at both ends. The bi-directional flow in turn is a result of opposing pressure-driven flow and electro-osmotic flow in the device. Trapping and preconcentration of charged particles is observed in the recirculating flow, under conditions where the average net velocity of the particles themselves approaches zero. This phenomenon is termed flow-induced electrokinetic trapping (FIET). Importantly, the electrophoretic mobility (zeta potential) of the particles determines the flow conditions required for trapping. In this paper, we exploit FIET for the first time to perform particle separations. Using a non-uniform channel, one type of particle can be trapped according to its zeta-potential, while particles with higher or lower zeta-potentials are flushed away with the pressure-driven or electro-osmotic components, respectively, of the flow. This was demonstrated using simple mixtures of two polystyrene bead types having approximately the same size (3 microm) but different zeta potentials (differences were in the order of 25 to 40 mV). To gain more insight into the separation mechanism, particle separations in straight, 3 cm-long microchannels with uniform cross-section were also studied under conditions of bi-directional flow without trapping. A thorough theoretical analysis confirmed that trapping occurs when electrokinetic and pressure-driven particle velocities are equal and opposite throughout the diverging segment. This makes it possible to predict the pressure and electric field conditions required to separate particles having defined zeta potentials.

Effects of non-Newtonian power law rheology on mass transport of a neutral solute for electro-osmotic flow in a porous microtube

“…1 Applications of microfluidic devices in bio-analysis, 2,3 microelectronics, 4 development of biosensors, 5 controlled drug delivery 6 and drug discovery, 7 micro-separation systems separating biomolecules, 8 ions, 9 neutral solutes, 10 etc., are very promising owing to their high surface to volume ratio and complex fluid flow associated with electrokinetic effects. 11,12 Microfluidic flows occur due to the effect of pressure gradient or electroosmotic effect or combination of both. Heat and Mass transfer analysis in microfluidic flows is significant for operation of all the microfluidic devices and separation systems.…”

Recent developments in electrophoretic separations on microfluidic devices

“…Borofloat glass microfluidic chips were used to separate and trap particles of interest in two different types of channels [8]. One study used straight channels with a uniform diameter to better understand the behavior of the particles, followed by the use of elements with converging and diverging dimensions.…”

“…Various processes, such as FFE, are well known on the preparative-scale, whereas others, such as IEF, have been well characterized for analytical-scale separations. There have been many innovative areas of development on the smaller scale, including taking advantage of hydrodynamic counterflow [6,7], different channel designs [8], and applying electric fields perpendicular to the flow of the sample [9][10][11][12][13].…”

Size-dependent microparticles separation through standing surface acoustic waves

“…The complicated processes associated with these methods also entail high-costs. In physical methods, by contrast, the target particles are separated by their natural physical properties, such as the size, density, or permittivity under force fields that are centrifugal (Pamme 2007;Seo et al 2007), hydrodynamic (McCloskey et al 2003;Qu et al 2008), or electrokinetic/dielectrophoretic (Baret et al 2009;Jellema et al 2009). These methods are simple and fast, but have lower resolution and sample selectivity than immunological methods (Yang et al 1999;Guillong et al 2003;Kang and Park 2005;Yamada et al 2004).…”