Nanofilm diodes Ion-Current Diode with Aqueous Gel/SiO2 Nanofilm Interfaces**

Non-linear ion transport through nanoscale structures can be used in new types of microcircuit, inspired by biological processes such as adenosine triphosphate synthesis and neural transmission. The non-linear current resulting from preferential direction of ion flow can be used for signal transmission as well as signal processing, for example, ionic current rectification and amplification as in electronic circuits. Electronic signal-processing systems using ionic current conduction are capable of operation in aqueous phase, which makes them suitable for biomedical and chemical applications such as molecular delivery and sensing. Recent advances in nanofabrication have enabled control of selective ionic transport by designing various nanostructures of controlled surface charge, such as aligned nanochannels, nanopippettes, and cone-shaped nanotubes. Ionic flows can be selectively gated by electrostatic field at the charged channel walls. Furthermore, asymmetric distribution of charges on two surfaces of the nanofluidic channel walls creates an ionic junction in the channels and engenders onedirectional ionic flows. On a larger scale, the so-called ‘‘electrolyte diodes’’ provide an example of device-like structures operating on ionic conductance. Aqueous electrolyte junctions between acidic (e.g., HCl) and basic (e.g., KOH) solutions exhibit rectifying properties analogous to the junction of nand p-type semiconductors. Our group reported earlier a practical ionic rectifier – hydrogel-based polyelectrolyte diode constructed by bringing into contact two gels doped with polyelectrolytes of opposite charges. The junction formed at the interface between the gel layers rectifies