Combining DC and AC electric fields with deterministic lateral displacement for micro- and nano-particle separation

Abstract

This paper describes the behaviour of particles in a Deterministic Lateral Displacement (DLD) separation device with DC and AC electric fields applied orthogonal to the fluid flow. As a proof of principle, we demonstrate tunable microand nano-particle separation and fractionation depending on both particle size and zeta potential. DLD is a microfluidic technique that performs size-based binary separation of particles in a continuous flow. Here, we explore how the application of both DC and AC electric fields (separate or together) can be used to improve separation in a DLD device. We show that particles significantly smaller than the critical diameter of the device can be efficiently separated by applying orthogonal electric fields. Following the application of a DC voltage, Faradaic processes at the electrodes cause local changes in medium conductivity. This conductivity change creates an electric field gradient across the channel that results in a non-uniform electrophoretic velocity orthogonal to the primary flow direction. This phenomenon causes particles to focus into tight bands as they flow along the channel countering the effect of particle diffusion. It is shown that the final lateral displacement of particles depends on both particle size and zeta potential. Experiments with six different types of negatively charged particles and five different sizes (from 100 nm to 3 µm) and different zeta potential demonstrate how a DC electric field combined with AC electric fields (that causes negative-dielectrophoresis particle deviation) could be used for fractionation of particles on the nano-scale in micro-scale devices.

Charge-Based Separation of Micro- and Nanoparticles

“…Previous approaches have targeted one or more of these properties to separate particles in DLD based on, for example, shape [ 13 , 14 , 36 , 37 ], length [ 27 ], and deformability [ 6 , 36 , 38 ]. Surface charge has also been employed in the context of DLD [ 32 , 39 ], but in general in a different manner than in our current work. Zeming et al [ 32 ] modulated the effective size by tuning the electrostatic force between pillars and nanoparticles, which was achieved by adjusting the salt concentration of the running medium.…”

“…Hanasoge et al also used DC field to drive the flow and explore the effect of different array orientations on particle separation in eDLD [ 76 ]. The development of eDLD has been driven primarily by the Tegenfeldt group at Lund University, Sweden, [ 77 , 78 , 79 ] and Morgan group at University of Southampton, UK, [ 39 , 80 , 81 ], who have made use of AC fields in various modes and geometries. Among the benefits of using AC fields are the fact that the flow (carrying the particle through the device) is decoupled from the forces near to the posts (causing separation) and that much greater control can be achieved through the balancing of these forces.…”

“…Using this configuration, Calero et al demonstrated sorting of 500 nm from 1 and 3 µm polystyrene beads in a DLD array with a critical size of 6.3 µm using an AC voltage (50 Hz–10 kHz) [ 80 ]. In their subsequent work, by using an AC voltage with a DC bias, they were able to separate 100 nm from 500 nm and 1 µm polystyrene beads as well as sorting based on zeta potential for 3 µm microspheres [ 39 ]. Finally, in a very recent paper, Calero et al compared their experimental data at 50 kHz with DEP numerical simulation and found good agreement [ 81 ].…”

A review of dielectrophoretic separation and classification of non‐biological particles

“…This matches the predictions from the PNP equations that yield K CM -values much larger than 1 for particles with a thick double layer (Section 2.3). Calero et al [102] recently presented an electrokinetic-biased Deterministic Lateral Displacement channel (using isolating posts) that allowed the size separation of submicron particles (100, 500, and 1000 nm). The device operates using either ac, dc, or a combination of both in order to exploit size, polarizability, and ζ -potential differences between particles.…”

Continuous Particle Separation in Microfluidics: Deterministic Lateral Displacement Assisted by Electric Fields

“…Thus, the particle deviation can be externally controlled via an electrical signal. More recent work is based on the application of an electric field perpendicular to the flow direction [ 14 , 15 ]. This is accomplished by integrating electrodes on the sides of the microchannel, reducing the electrode gap and, consequently, the amplitude of the applied voltages.…”