Voltage-driven polyelectrolyte complexation inside a nanopore*

We have investigated how a pair of oppositely charged macromolecules can be driven by an electric field to form a polyelectrolyte complex inside a nanopore. To observe and isolate an individual complex pair, we employ a model protein nanopore embedded in artificial phospholipid membrane, allowing compartmentalization (cis/trans). A polyanion in the cis and a polycation in the trans compartments are subjected to electrophoretic capture by the pore. We find that the measured ionic current across the pore has the distinguishable signature of complex formation, which is different from the passage of the individual molecules through the pore. Analysis of the complexation events support a four step-mechanism: (i) The polyanion is captured by the pore, (ii) the polyanion starts threading through the pore. (iii) The polycation is captured, a complex pair is formed in the pore, and the polyanion slides along the polycation. (iv) Depending on strength of the applied voltage, the complex pair can be pulled through the pore into the trans compartment or dissociate.