Transport of Ions, DNA Polymers, and Microtubules in the Nanofluidic Regime
Nanofluidic devices provide an arena for interesting science and new technological applications. We review experimental work that illustrates qualitative differences in the behavior of ions, polymers, and molecular motors at the nanoscale as compared with their behavior at macroscopic scales. Ionic transport is governed by the surface charge density inside a nanofluidic device and the overlap of Debye screening layers becomes significant. Furthermore, pressure-driven fluid flows entrain significant ionic streaming currents, and this electrokinetic effect has been used to probe the phenomenon of surface charge inversion and to harness mechanical work and convert it into electrical power. Polymers like DNA must pay an entropic penalty under nanofluidic confinement, which governs its configurational statistics, and in turn influences DNA's transport characteristics in pressure-driven fluid flows and in more complex electrokinetic flows driven by electric fields. Finally, the molecular motor kinesin has been incorporated into fluidic devices in order to drive the motion of microtubules. Within a network of fluidic channels, electric fields can be applied to steer and sort kinesin-driven microtubules, and to probe the mechanical bending of single microtubules.