Deterministic Lateral Displacement (DLD) is a microfluidics-assisted technique that allows the size-based sorting of a suspension of mesoscopic objects entrained in a laminar flow through a periodic lattice of obstacles. Separation with unprecedented resolution has been obtained through DLD processes running under steady-state conditions for a variety of suspensions of biological interest, ranging from red blood cells down to the exosome scale. The separation mechanism hinges on the property that objects of different size migrate at different angles with respect to the average
direction of the carrier flow. Thus, a focused feeding stream entraining a population of suspended objects of different size separates into different currents, each characterized by assigned size ranges, which can be collected at different positions at device outlet. Alongside these experimental results, an effective transport model has been recently proposed by the proponent of this project, which predicts average particle velocity and dispersion features based on particle size and on the structure of the flow through the spatially periodic obstacle lattice. Two practically-relevant
aspects arise from the analysis of this model namely -(i) particle dispersion is enhanced over the bare particle diffusivity, with an enhancement factor that depends
sensitively on particle size -(ii) particle mobility is also strongly dependent on particle size and is typically anti-correlated with the dispersion enhancement factor. By exploiting this effect, a novel use of DLD devices is here proposed, where the separation process is operated in transient conditions, and the size-based sorting of suspended particles is performed over time and space. The scope of the research is to combine the effects of mobility and migration direction to overcome the resolution hindering effect of enhanced dispersion, thus allowing the separation
of a size-dispersed suspension in one and the same obstacle lattice.
As discussed above, the main goal of the research proposed is to suggest a novel and unexplored use of an existing microfluidic device to improve its separation performance. Alongside this main objective, a further aim of the project is to assess the potentialities of Brenner's macrotransport approach for interpreting recent experimental results [1,2] on a scaled-down realization of a DLD device to extend the domain of application of this technique from the size-based sorting of cell suspensions (order of few micrometers) down to the domain of macromolecular complexes such as exosomes, which typically fall in the range of tens of nanometers. Because in this scaled down version of DLD separators both lengthscales and characteristic velocities are considerably reduced, the resulting particle Peclet number falls in the range between 10 [1] Wunsch, Benjamin H., et al. "Nanoscale lateral displacement arrays for the separation of exosomes and colloids down to 20 nm." Nature nanotechnology 11.11 (2016): 936.
[2] Kim, Sung-Cheol, et al. "Broken flow symmetry explains the dynamics of small particles in deterministic lateral displacement arrays." Proceedings of the National Academy of Sciences 114.26 (2017): E5034-E5041.