PhD defence S. Fernandez Poza

Microfluidic particle trapping and separation using combined hydrodynamic and electrokinetic effects

The thesis of Sergio Fernandez Poza describes a new methodology for particle trapping and fractionationusing flow-induced electrokinetic trapping (FIET). FIET is a particle-trappingmechanism that relies on bidirectional, recirculating flow profiles generated byopposition of pressure-driven (PF) and electroosmotic (EOF) flows in straightchannels that expand at both ends. Micrometer-sized particles are captured inthe closed recirculating streamlines and fractionated according to differences insurface charge (zeta potential) and size.First, the behavior of trapped particles inside the straight, narrow channel wascharacterized under conditions of constant pressure and varying applied voltage.For this, we propose a Gaussian model that accurately describes the spatialdistribution of particles along the trapping channel length as a function of theapplied voltage. This model provides valuable information about the trappingprocess, such as the range of applied voltage within which particles of a particularsize and charge are caught inside the channel and the specific voltage at which amaximum number of particles experience trapping. FIET enrichment of polymerparticle suspensions is also evaluated using the optimal trapping parametersdetermined experimentally.Second, we evaluate the implementation of this distribution model forquantitative fractionation of binary mixtures of polymer microparticles in FIETmicrofluidic channels. For this, particle distributions of beads having differentsize or charge were registered as a function of applied voltage. A comparison ofthe fractionation capacity for each mixture was subsequently conducted atdifferent applied pressures based on the acquired distribution curves. Particleshaving different sizes exhibited better separation rates (clearer collected fractionsfor both particle types) at lower applied pressures, whilst particles havingdifferent zeta potentials could be fractionated at higher pressures. This factevidenced a clear distinction between two well-defined mechanisms(hydrodynamic and electrokinetic) co-existing in the FIET process.Lastly, the applicability of this model is further extended to the fractionation ofternary mixtures of particles having different size and zeta potential. Thesynergistic exploitation of the hydrodynamic and electrokinetic mechanismsdescribed above was accomplished by a stepwise increasing voltage programapplied at two different pressures. Two separation dimensions were clearlyrevealed, with one based on size, and the other based on charge. Thesimultaneous occurrence of these two mechanisms in the same FIET microfluidicdevice leads to a unique orthogonality, described here for the first time in therealm of microfluidic particle separations.

Promotores: Prof.dr. E.M.J. Verpoorte and Prof.dr. T.I.F.H. Cremers