Tunable deterministic lateral displacement of particles flowing through thermo-responsive hydrogel micropillar arrays

Deterministic lateral displacement (DLD) is a promising technology that allows for the continuous and the size-based separation of suspended particles at a high resolution through periodically arrayed micropillars. In conventional DLD, the critical diameter (D_c), which determines the migration mode of a particle of a particular size, is fixed by the device geometry. Here, we propose a novel DLD that uses the pillars of a thermo-responsive hydrogel, poly(N-isopropylacrylamide) (PNIPAM) to flexibly tune the D_c value. Upon heating and cooling, the PNIPAM pillars in the aqueous solution shrink and swell because of their hydrophobic-hydrophilic phase transitions as the temperature varies. Using the PNIPAM pillars confined in a poly(dimethylsiloxane) microchannel, we demonstrate continuous switching of particle (7-μm beads) trajectories (displacement or zigzag mode) by adjusting the D_c through temperature control of the device on a Peltier element. Further, we perform on/off operation of the particle separation (7-μm and 2-μm beads) by adjusting the D_c values.