Electrokinetically driven deterministic lateral displacement for particle separation in microfluidic devices

migrating in different directions with respect to the array, thus causing the two-dimensional and continuous fractionation of the mixture (Huang et al. 2004; Inglis et al. 2006). Microfluidic DLD devices have been successfully applied to the fractionation of different mixtures, and in particular for cell sorting and the separation of biological material (Xuan and Lee 2013; Davis et al. 2006; Li et al. 2007; Huang et al. 2008; Morton et al. 2008a, b; Green et al. 2009; Holm et al. 2011; Inglis et al. 2011; Joensson et al. 2011; Zhang et al. 2012). In addition, different modifications of the original DLD design have been proposed for specific applications, such as the separation of deformable and nonspherical bioparticles (Al-Fandi et al. 2011; Zeming et al. 2013) or to improve performance (Loutherback et al. 2010; Beech and Tegenfeldt 2008; Beech et al. 2009). In recent work, we demonstrated a unique operating mode for high-purity DLD separation based on a uniform force driving the suspended particles, in particular gravity (g-DLD) (Devendra and Drazer 2012, 2014; Bowman et al. 2012). In terms of external fields, a variety of powerful separation methods take advantage of electric fields to drive the suspended mixture through a stationary phase to affect the separation, both in traditional and in microfluidic systems. In fact, arrays of insulating posts analogous to those found in DLD systems have been used in combination with DC electric fields for the continuous separation of particles by means of insulator-based dielectrophoresis (Cummings and Singh 2003; Cummings 2003). Moreover, the integration of insulator-based dielectrophoretic forces into DLD systems by adding AC electric fields has been shown to provide external control to the separation of different mixtures (Beech et al. 2009). Interestingly, virtual post arrays entirely based on negative DEP forces generated by patterned electrodes were successfully used to continuously separate particles by a method similar to DLD (Chang and Abstract An electrokinetically driven deterministic lateral displacement device is proposed for the continuous, two-dimensional fractionation of suspensions in microfluidic platforms. The suspended species are driven through an array of regularly spaced cylindrical posts by applying an electric field across the device. We explore the entire range of orientations of the driving field with respect to the array of obstacles and show that, at specific forcing angles, particles of different size migrate in different directions, thus enabling continuous, two-dimensional separation. We discuss a number of features observed in the motion of the particles, including directional locking and sharp transitions between migration angles upon variations in the direction of the force, that are advantageous for high-resolution two-dimensional separation. A simple model based on individual particle–obstacle interactions accurately describes the migration angle of the particles depending on the orientation of the driving field and can be used to reconfigure the electric field depending on the composition of the samples.