Space-time resolution of size-dispersed suspensions in Deterministic Lateral Displacement microfluidic devices

Deterministic Lateral Displacement (DLD) is a relatively recent microfluidics-assisted technique which allows the size-based separation of a population of micrometric particles suspended in a buffer solution. The core of the device is a shallow channel with rectangular cross-section filled with an array of solid obstacles arranged in a spatially periodic lattice, whose directions are slanted with respect to the channel walls. In practical implementations of DLD, particles are continuously introduced at a localized position of the channel entrance and migrate along different average directions downstream the device according to their size. Thus, at steady state, size-sorted subpopulations can be collected at different positions of the channel outlet. Besides, theoretical predictions of recent models of particle transport in these devices suggest that not only the direction of the average particle velocity, but also its magnitude (i.e. the mobility) depends sensitively on particle size. By exploiting this dependence, a novel use of DLD devices is here proposed, where the size-driven separation is realized over time and space by running the process under transient conditions, thus mimicking a classical chromatographic separation. We show how this approach is particularly effective for particles of specific (critical) dimensions, which are known to impair the efficiency of the steady-state separation process. Numerical predictions based on a hard-wall repulsive potential for the particle-obstacle interaction suggest that unprecedented separation performance for near-critical particle size could be obtained in transient conditions within the same channel length used for the time-continuous separation. The case of cylindrical obstacles and spherically shaped particles is considered in detail as an illustrative example.