Molecular sensors are important across many industries, including automotive, aerospace, fossil energy, and biomedical (e.g., wearables). Carbon nanotubes (CNTs) have been shown to be particularly promising as molecular sensors because of their high electrical conductivity, thermal and chemical stability, one dimensional form factor, high specific surface area and carbon lattice structure that makes them easy to functionalize. The ability to control and measure the flow of ionic material through CNTs would increase the utility of CNT technologies. This would allow assemblies of nanotubes or other nanostructures to be used as field-effect transistors (FET), electrical sensors, and other devices that rely on electrical current modulation from an externally applied field, or "gate".  To maximize sensitivity of a sensing device, it is common to apply a gating voltage to modulate the channel current and maximize the signal gain registered from a detection event. However, gating a thick film comprised of high-surface-area nanostructures or out-of-plane architectures is not possible with typical top-gate and bottom-gate configurations. The electric field may not extend sufficiently or uniformly through the entire ensemble of nanostructures, so their currents will not be modulated as desired.

Existing approaches for gating nanostructured films both non-contact techniques, which involve light probes, as well as contact methods, have limitations.  For thick films of nanostructures, light probes are not ideal due to the limits of optical penetration depth.  Existing contact methods are not effective for applications where the surface of the nanostructure must remain exposed for functionalization and sensing by direct contact with a medium.