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Controllable manipulation and effective mixing of fluids and colloids at the nanoscale is made exceptionally difficult by the dominance of surface and viscous forces. The use of megahertz (MHz)‐order vibration has dramatically expanded in microfluidics, enabling fluid manipulation, atomization, and microscale particle and cell separation. Even more powerful results are found at the nanoscale, with the key discovery of new regimes of acoustic wave interaction with 200 fL droplets of deionized water. It is shown that 40 MHz‐order surface acoustic waves can manipulate such droplets within fully transparent, high‐aspect ratio, 100 nm tall, 20–130 micron wide, 5‐mm long nanoslit channels. By forming traps as locally widened regions along such a channel, individual fluid droplets may be propelled from one trap to the next, split between them, mixed, and merged. A simple theory is provided to describe the mechanisms of droplet transport and splitting., Digital nanofluidics is enabled through rapid transport, splitting, combination, and mixing of 200 fL droplets using surface acoustic waves in a specially shaped, 130–150‐nm tall nanoslit channel with discretely entrapped droplets. ​

Furthering the promise of graphene‐based planar nanofluidic devices as flexible, robust, low cost, and facile large‐scale alternatives to conventional nanochannels for ion transport, we show how the nonlinear current–voltage (I–V) characteristics and ion current rectification in these platforms can be enhanced by increasing the system asymmetry. Asymmetric cuts made to the 2D multilayered graphene oxide film, for example, introduces further asymmetry to that natively inherent in the structurally symmetric system, which was recently shown to be responsible for its rectification behavior due to diffusion boundary layer fore–aft asymmetry. Supported by good agreement with theory, we attribute the enhancement to the decrease in the limiting current in the positive bias state in which counter‐ion trapping occurs within the negatively charged graphene oxide sheets due to increased film permselectivity as its cross‐section and surface charge distribution is altered on one end; these effects being shown to be sensitive to the electrolyte pH. Further, we show that an imbalance in the pH or concentration in the microreservoirs flanking the film can also increase asymmetry and hence rectification, in addition to displaying a host of other phenomena associated with the I–V characteristics of typical nanochannel electrokinetic systems.