  The field of nanofluidics has shown considerable progress over the past
decade thanks to key instrumental advances, leading to the discovery of a
number of exotic transport phenomena for fluids and ions under extreme
confinement. Recently, van der Waals assembly of 2D materials allowed
fabrication of artificial channels with angstr\"om-scale precision. This
ultimate confinement to the true molecular scale revealed unforeseen behaviour
for both mass and ionic transport. In this work, we explore pressure-driven
streaming in such molecular-size slits and report a new electro-hydrodynamic
effect under coupled pressure and electric force. It takes the form of a
transistor-like response of the pressure induced ionic streaming: an applied
bias of a fraction of a volt results in an enhancement of the streaming
mobility by up to 20 times. The gating effect is observed with both graphite
and boron nitride channels but exhibits marked material-dependent features. Our
observations are rationalized by a theoretical framework for the flow dynamics,
including the frictional interaction of water, ions and the confining surfaces
as a key ingredient. The material dependence of the voltage modulation can be
traced back to a contrasting molecular friction on graphene and boron nitride.
The highly nonlinear transport under molecular-scale confinement offers new
routes to actively control molecular and ion transport and design elementary
building blocks for artificial ionic machinery, such as ion pumps. Furthermore,
it provides a versatile platform to explore electro-mechanical couplings
potentially at play in recently discovered mechanosensitive ionic channels.
