Acoustic Nanofluidics via Room-Temperature Lithium Niobate Bonding: A Platform for Actuation and Manipulation of Nanoconfined Fluids and Particles

Controlled nanoscale manipulation of fluids and colloids is made exceptionally difficult by the dominance of surface and viscous forces. Acoustic waves have recently been found to overcome similar problems in microfluidics, but their ability to do so at the nanoscale remains curiously unexplored. Here, it is shown that 20 MHz surface acoustic waves (SAW) can manipulate fluids, fluid droplets, and particles, and drive irregular and chaotic fluid flow within fully transparent, high-aspect ratio 50–250 nm tall nanoslits fabricated via a new direct, room temperature bonding method for lithium niobate (LN). Applied in the same direction, SAW increases the capillary filling rate of the hydrophilic LN nanoslit by 2–5 times. Applied in opposition, the SAW switches the flow direction and drains the channel against 1 MPa capillary pressure, and can be used to controllably manipulate ≈10 fL droplets. Finally, entire 10 μL droplets can be sieved via SAW through the nanoslit to pass only particles smaller than its height, providing pumpless size exclusion separation.