A Continuous Microfluidic Sieve for the Size-based Fractionation of Particle Suspensions and Colloids

We report of a novel microfluidic device concept for the continuous fractionation of a size-dispersed suspension of micrometric/nanometric particles. The device geometry consists of parallel channels communicating through a narrow slit of assigned width, which act as a cutoff length for the size-based separation of the particles. The suspension is fed to one of the channels, and particles of size below the cutoff length spread throughout the device cross-section as they flow downstream, whereas larger particles remain confined to the injection channel. Two regimes are investigated, namely (i): a Brownian-sieving regime, where particle transport across the channels relies entirely on transversal diffusion, and (ii): a convective-sieving regime, where pressure between the channels is made different, and small particles are (primarily) driven by convection from
one channel to the other(s). This latter regime is ideally suited for scaling up the device to micrometer-sized suspensions, in that the diminished particle diffusivity has negligible impact on the separation performance. Potentialities and limitations of the method proposed are compared and contrasted to those of other emerging microfluidics-assisted techniques, such as Field-FlowFractionation (FFF) and Deterministic Lateral Displacement (DLD).