Described are devices and methods for forming one or more nanomembranes including electroactive nanomembranes within a nanowell or nanotube, or combinations thereof, in a support material. Nanopores/nanochannels can be formed by the electroactive nanomembrane within corresponding nanowells. The electroactive nanomembrane is capable of controllably altering a dimensionality, a composition, and/or a variety of properties in response to electrical stimuli. Various embodiments also include devices/systems and methods for using the nanomembrane-containing devices for molecular separation, purification, and sensing.