.
Nevertheless, advancing our fundamental understanding of fluid
transport on the smallest scales requires mass and ion dynamics to
be ultimately characterized across an individual channel to avoid
averaging over many pores. A major challenge for nanofluidics
thus lies in building distinct and well-controlled nanochannels,
amenable to the systematic exploration of their properties. Here
we describe the fabrication and use of a hierarchical nanofluidic
device made of a boron nitride nanotube that pierces an ultrathin
membrane and connects two fluid reservoirs. Such a transmembrane
geometry allows the detailed study of fluidic transport
through a single nanotube under diverse forces, including electric
fields, pressure drops and chemical gradients. Using this device, we
discover very large, osmotically induced electric currents generated
by salinity gradients, exceeding by two orders of magnitude their
pressure-driven counterpart. We show that this result originates
in the anomalously high surface charge carried by the nanotube’s
internal surface in water at large pH, which we independently
quantify in conductance measurements. The nano-assembly route
using nanostructures as building blocks opens the way to studying
fluid, ionic and molecule transport on the nanoscale, and may lead
to biomimetic functionalities. Our results furthermore suggest
that boron nitride nanotubes could be used as membranes
