Tunable Hydrodynamic Chromatography of Microparticles Localized in Short Microchannels

Abstract

This paper describes a new way to perform hydrodynamic chromatography (HDC) for the size separation of particles based on a unique recirculating flow pattern. Pressure-driven (PF) and electro-osmotic flows (EOF) are opposed in narrow glass microchannels that expand at both ends. The resulting bidirectional flow turns into recirculating flow because of nonuniform microchannel dimensions. This hydrodynamic effect, combined with the electrokinetic migration of the particles themselves, results in a trapping phenomenon, which we have termed flow-induced electrokinetic trapping (FIET). In this paper, we exploit recirculating flow and FIET to perform a size-based separation of samples of microparticles trapped in a short separation channel using a HDC approach. Because these particles have the same charge (same zeta potential), they exhibit the same electrophoretic mobility, but they can be separated according to size in the recirculating flow. While trapped, particles have a net drift velocity toward the low-pressure end of the channel. When, because of a change in the externally applied PF or electric field, the sign of the net drift velocity reverses, particles can escape the separation channel in the direction of EOF. Larger particles exhibit a larger net drift velocity opposing EOF, so that the smaller particles escape the separation channel first. In the example presented here, a sample plug containing 2.33 and 2.82 microm polymer particles was introduced from the inlet into a 3-mm-long separation channel and trapped. Through tuning of the electric field with respect to the applied PF, the particles could be separated, with the advantage that larger particles remained trapped. The separation of particles with less than 500 nm differences in diameter was performed with an analytical resolution comparable to that of baseline separation in chromatography. When the sample was not trapped in the separation channel but located further downstream, separations could be carried out continuously rather than in batch. Smaller particles could successfully pass through the separation channel, and particles were separated by size. One of the main advantages of exploiting FIET for HDC is that this method can be applied in quite short (a few millimeters) channel geometries. This is in great contrast to examples published to date for the separation of nanoparticles in much longer micro- and nanochannels.

Hydrodynamic chromatography separations in micro‐ and nanopillar arrays produced using deep‐UV lithography

“…Plot of the channel aspect ratio (λ) as a function of the hydrodynamic retention factor (τ). Experimental points (♦) obtained in the different pillar array columns are compared to recent obtained () experimental data by U liyanchenko et al in packed‐bed columns filled with sub‐2‐μm particles . The hydrodynamic retention model has also been added for three different a ‐values; (····) a = 1, (‐‐‐) a = 1.5, (– –) a = 2.…”

“…As a consequence, they will experience a higher average velocity as compared to the smaller molecules that are not excluded from these low‐velocity regions, and will elute hence earlier. Recent applications and extensions of the HDC concept have among others been proposed by Uliyanchenko et al, Thompson et al, Jellema et al, and Brewer and Striegel .…”

Using electrophoretic exclusion to manipulate small molecules and particles on a microdevice

“…Some of the initial applications of this technique were performed by the Tsuda Laboratory [27] and the Jorgenson group [28]. Electrophoretic separations that take advantage of counterflow to increase separation efficiency include flow-induced electrokinetic trapping [29,30], gradient techniques including temperature gradient focusing [31][32][33][34][35][36][37], electric field gradient focusing [38][39][40][41][42][43], dynamic field gradient focusing [44][45][46][47][48], and the use of an electro-fluid-dynamic device [49,50]. Additional techniques that use counterflow to perform electrophoretic separations are gradient elution moving boundary electrophoresis (GEMBE) [6,[51][52][53][54][55][56][57][58] and gradient elution ITP (GEITP) [59,60].…”

Electrokinetic flow in connected channels: a comparison of two circuit models

“…∆ p t < 0 and ∆ φ t > 0). Such opposing flows have been used to generate recirculation in contraction-expansion devices for particle separation ('flow-induced electrokinetic trapping' (Jellema et al 2009(Jellema et al , 2010) and preconcentration (Lettieri et al 2003).…”