Capture dynamics of colloidal particles in microfluidic model membrane channels

Studies of transport across membranes often focus on particle dynamics in confining channels. Yet flux can be critically limited by the rate of entry to the pore. This process is governed by a complex interplay of factors including the entropic barrier to pore entry, particle-particle/particle-pore interactions, and the external driving force. Here, we use video microscopy to study the capture dynamics of colloidal particles driven through microfluidic devices. By obtaining full trajectories for particles as they move from the bulk into confining channels, we map the spatial velocity and concentration fields for the system in detail. We consider behaviour in conservative and non-conservative flow fields, for different flow velocities, and at different packing fractions. Furthermore, by comparing to COMSOL models of fluid flow we assess the effect of many-body interactions on the capture process and how these modify stochastic fluctuations in the capture rate. Our results provide new insights into the concept of a 'capture radius' – the distance at which a particle is irrevocably drawn into the pore – which plays a key role in transport models for biological channels and nanopore sensors.