Cell Sorting in Pillar Arrays based on Electrokinetics and Morphology

Abstract: Deterministic Lateral Displacement (DLD) is a method capable of sorting cells based on size where mechanicalinteractions between a sufficiently large particle and obstacles in a microfludic pillar array force the particle tofollow a different trajectory than their smaller counterparts, resulting in continuous lateral separation. To extendthe capability of DLD, electrical interaction between particles and pillars can be employed to complement themechanical interaction, making electrical/dielectric properties additional parameters for sorting. Another idea isto exploit the morphologies of cells and as a concequence, their dynamical properties, to sort them in DLD. Thedevelopment of DLD cell sorting methods based on those two ideas has brought forth five papers appended to thisthesis: paper I, III, and V (combination of electrokinetics and DLD), and paper II and IV (exploiting morphologyin sorting by DLD).In the first topic, differences in electric properties or dielectric properties of particles and cells are employed toextend the capability of DLD. In Paper I, an AC electric field was applied across DLD devices having insulatingpillars to sort similar-sized polystyrene particles having different surface charge, viable from non-viable yeast cells,and viable from non-viable E. coli bacteria. In Paper III, the same method was utilised on open channel DLDdevices, showing unaltered effectiveness but offering the ability to flexibly change the distance between the electrodes.Also in the topic of combining electrokinetics and DLD, Paper V introduced a new type of DLD devicewhere the electrodes were defined locally on every pillar, making it easier to generate a high electric field strength.Besides electrical properties, morphology is another useful accompaniment to DLD. In Paper II, pathogenicStreptococcus pneumoniae bacteria were fractionated in DLD devices according to the difference in their morphology,viz. their chain length. It was also demonstrated, in paper IV, that an AC field can be used to rotatenon-spherical red blood cells and in turn, change their trajectory in a DLD device. This implies an opportunity tosort red blood cells from cells having different morphology, either spherical cells or parasites like trypanosomes.