Density dependent speed-up of particle transport in channels

Collective transport through channels has surprising properties due to one-dimensional confinement: particles in a single-file exhibit sub-diffusive behaviour, while liquid confinement causes distance-independent correlations between the particles. Interactions in channels are well-studied for passive Brownian motion but driven transport remains largely unexplored. Here, we demonstrate a speed-up effect for actively driven particle transport through microfluidic channels. We prove that particle velocity increases with particle density in the channel due to hydrodynamic interactions. The magnitude depends on the driving force, where we measure and compare systems driven by electrophoretic and gravitational forces. We employ numerical models to demonstrate that the observed speed-up of transport originates from a hydrodynamic piston-like effect. Our discovery is fundamentally important for understanding protein channels, transport through porous materials, and for designing novel molecular sensors.