Translocation Dynamics of Poly(styrenesulfonic acid) through an α-Hemolysin Protein Nanopore

Abstract

The transport of linear anionic poly(styrenesulfonic acid) (PSS) chains through an α-hemolysin protein channel, embedded in a lipid bilayer which is suspended on a glass nanopore membrane, is reported as a function of applied voltage and chain length. By investigating individual event details, we observed mainly four types of events with distinct bilevel current blockades. The majority of the translocation events have a shallow block level with current decrease of ∼60%, followed by a deep block level with current decrease of ∼85%. A mechanism for PSS translocation is proposed and compared with that for ssDNA translocation through the ion channel. Although similar bilevel blockades are observed for both PSS and ssDNA, differences in the chain rigidity between PSS and ssDNA result in distinct populations for each type of event and quite different characteristic translocation times. At a voltage of 160 mV, the PSS chains are more likely to thread the narrowest constriction and translocate through the pore than to escape from the vestibule against the applied voltage gradient. Increasing the applied voltage decreases the duration time of chain translocation through the pore, while increasing the characteristic time of the PSS within the vestibule. We further find that the translocation event rate is exponentially dependent on the applied potential while the most likely duration time also decreases exponentially with the voltage. These results demonstrate how the nature of the polyelectrolyte chain influences translocation process through protein ion channels.