Transport Rectification in Nanopores with Outer Membranes Modified with Surface Charges and Polyelectrolytes

MARIO TAGLIAZUCCHI; RABIN, YITZHAK; IGAL SZLEIFER

ACS NANO

AMER CHEMICAL SOC

Lugar: Washington; Año: 2013 vol. 7 p. 9085 - 9097

1936-0851

This work reports a comprehensive theoretical studyof the transport-rectification properties of cylindrical nanopores with neutral inner walls and  chemically modified outer membrane. The chemical species on the two outer sides of the membrane have charges of opposite sign and can be either surface-confined species (i.e.surface charges) or polyelectrolyte brushes. The advantage of this design over other types of rectifying nanopores is that it requires controlling the composition of the outer walls of the pore (which are easy to access) rather than the inner walls, thus simplifying the fabrication process. Ion-current rectification in nanopores with charged outer walls is ascribed to applied-potential-induced changes in the ionic concentration within the pore. The rectification efficiency is studied as a function of pore length, radius, surface charge and bulk electrolyte concentration. An analytical model is derived for the case of surface-confined charges that predicts the current-potential curves in very good agreement with the numerical calculations. Neutral nanopores with  polyelectrolyte-modified outer walls have two distinct advantages compared to surface-chargedsystems: i) they exhibit higher rectification factors due to the large charge density immobilizedby the polyelectrolyte brushes, ii) the applied potential deforms the polyelectrolyte chains towards the oppositely charged electrode. This deformation brings the polyelectrolyte brushes intothe pore in the low conductivity state and expels them from the pore in the high conductivity  regime. Calculations of the potentials of mean-force suggest that the applied-field-induced conformational changes can be used to control the translocation of cargoes larger than ions, suchas proteins and nanoparticles.