Sorting Particles by Deterministic Lateral Displacement : Effects of Shape and Size from Single Particles to Clusters

This thesis investigates particle sorting in deterministic lateral displacement (DLD) microfluidic devices, with a focus on how particle size and shape influence sorting behavior. A broad range of synthetic and biological particles were studied, including polystyrene particles, fabricated silicon-based structures, and bacterial samples with diverse physical properties.While DLD has traditionally been applied to particles with well-defined and discrete size and shape, this work addresses complex samples with continuous size and shape distributions, which remain challenging for conventional DLD-based separation. Group A Streptococcus (GAS) bacteria were used as a model biological sample due to their tendency to form clusters of varying size and shape, spanning a wide size range from approximately 0.8 to 100µm. By employing a DLD array with high periodicity, effective size-based separation of these bacterial clusters was achieved. This enabled subsequent biological investigations, in which sorted clusters of different sizes were exposed to human immune cells, revealing that bacterial clustering can influences pathogenic activity.The role of particle shape in DLD sorting was further examined using samples with well-defined geometries. Non-spherical polystyrene particles were first studied to quantify how shape affects particle–post interactions and sorting outcomes. This analysis was extended to biological samples, including small bacterial chains and clusters, demonstrating that particle shape induces distinct rotational dynamics during transport in laminar flow and interaction with DLD posts. Particle symmetry was found to play a key factor in determining sorting behavior.Motivated by these findings, a systematic investigation of shape-dependent sorting was conducted using custom-fabricated particles with continuously varying shapes. Together, these results provide a basis for the tailored design of DLD devices capable of separating bioparticles with complex morphologies and physical properties, such as cell clusters and diverse bacterial forms.