  This paper presents experimental results about transport of dilute
suspensions of nano-objects in silicon-glass micrometric and sub-micrometric
channels. Two kinds of objects are used: solid, rigid latex beads and spherical
capsule-shaped, soft polymersomes. They are tracked using fluorescence
microscopy. Three parameters are studied: confinement (ratio between particle
diameter and channel depth), Brownian diffusion and particle nature. The aim of
this work is to understand how these different parameters affect the transport
of suspensions in narrow channels and to understand the different mechanisms at
play. Concerning the solid beads we observe the appearance of two regimes, one
where the experimental mean velocity is close to the expected one and another
where this velocity is lower. This is directly related to a competition between
confinement, Brownian diffusion and advection. These two regimes are shown to
be linked to the homogeneity of particles distribution in the channel depth,
which we experimentally deduce from velocity distributions. This inhomogeneity
appears during the entrance process into the sub-micrometric channels, as for
hydrodynamic separation or deterministic lateral displacement. Concerning the
nature of the particles we observed a shift of transition towards the second
regime likely due to the relationships between shear stress and polymersomes
mechanical properties which could reduce the inhomogeneity imposed by the
geometry of our device.
