High-Resolution Size-Discrimination of Single Non-Ionic Synthetic Polymers with a Highly Charged Biological Nanopore

Electrophysiological studies of the interaction of polymers with pores formed by bacterial toxins (1) provide a window on single molecule interaction with proteins in real time, (2) report on the behavior of macromolecules in confinement and (3) enable label-free single molecule sensing. Using pores formed by the staphylococcal toxin alpha-hemolysin (aHL), a particularly pertinent observation was that under high salt conditions (3-4 M KCl) the current through the pore is blocked for periods of hundreds of microseconds to milliseconds by poly(ethyleneglycol) (PEG) oligomers (degree of polymerization approx. 10-60). Notably, this block showed monomeric sensitivity on the degree of polymerization of individual oligomers, allowing the construction of size or mass spectra from the residual current values. Here, we show that the current through the pore formed by aerolysin (AeL) from Aeromonas hydrophila is also blocked by PEG but with drastic differences in the voltage-dependence of the interaction. In contrast to aHL, AeL strongly binds PEG at high transmembrane voltages. This fact, which is likely related to AeL's highly charged pore wall, allows discrimination of polymer sizes with particularly high resolution. Multiple applications are now conceivable with this pore to screen various non-ionic or charged polymers.