  Collective transport through channels shows surprising properties under
one-dimensional confinement: particles in a single file exhibit sub-diffusive
behavior, while liquid confinement causes distance-independent correlations
between the particles. Such interactions in channels are well studied for
passive Brownian motion, but driven transport remains largely unexplored. Here,
we demonstrate gating of transport due to 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 under electrophoretic and gravitational forces. Numerical models
demonstrate that the observed speed-up of transport originates from a
hydrodynamic piston-like effect. Our discovery is fundamentally important for
understanding protein channels and transport through porous materials and for
designing novel sensors and filters.
