The present invention is directed to systems, devices and methods for identifying biopolymers, such as strands of DNA, as they pass through a constriction such as a carbon nanotube nanopore. More particularly, the invention is directed to such systems, devices and methods in which a newly translocated portion of the biopolymer forms a temporary electrical circuit between the nanotube nanopore and a second electrode, which may also be a nanotube. Further, the invention is directed to such systems, devices and methods in which the constriction is provided with a functionalized unit which, together with a newly translocated portion of the biopolymer, forms a temporary electrical circuit that can be used to characterize that portion of the biopolymer.