Abstract
The ability to control liquid flux across porous membranes is important in separation, purification, and sensing. Here we describe a way to open and close a nanoscale pore by a voltage and pH. We produce track-etched pores in polyethylene terephthalate (PET) and chemically etch them into a conical shape. This is followed by a pore modification where we attach 30 mer single-stranded DNA to the pore walls. This process is applied to pores that have a narrow opening diameter between 3nm and 20nm. The DNA modification is restricted to the region next to the small opening of a pore. We find that the attached DNA occludes sub-10 nm in diameter nanopores with an extent that depends on the ionic strength of the electrolyte medium. The result can be explained by the ionic strength dependent DNA conformation. At low KCl concentrations (e.g. 10 mM KCl) the DNA is expected to be fully extended and rigid, which is observed as a large reduction in current compared to the current values before DNA attachment. In addition, for pores with diameters below 5 nm, the deflection of the DNA strands in the electric field reverses the direction of ion current rectification compared to the as prepared pores. These pores feature therefore a voltage-dependent opening diameter. The effect of pH of the background KCl solution will also be discussed. This system has possible applications in drug delivery and separations.
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