1. A polynucleotide sequencing system comprising (a) a structure comprising an ion-permeable passage connecting a first pool of a medium and a second pool of a medium, wherein a polynucleotide to be sequenced and a blocking oligomer are present in the first pool; (b) an enzyme having binding affinity for said polynucleotide; (c) an electronic power source for creating a potential difference between the two pools; and (d) a detection system operative to detect a property of the polynucleotide, wherein the blocking oligomer inhibits an interaction between the enzyme and the polynucleotide.