Switchable ion channels in membranes—which can change conductivity in response to external stimuli—are common in nature and useful components in nanotechnology. Yugang Wang, Lei Jiang and co-workers1 have created an artificial nanopore using DNA inspired by biotechnology. The ion conductivity of the pores changes in response to variations in pH and the structures should be more robust for applications. A DNA conformational change provides the basis for the stimuli response.

The researchers started with a polymer membrane, in which they create conical nanopores that were several hundred nanometres at one side, but tapered to just 5 to 44 nm on the other side. Next, they chemically planted a layer of DNA strands on the inner walls of the pores.

Fig. 1: How the nanopores switch ‘on’ and ‘off’.

The DNA strands used, changed their conformation in solutions of different pH. At a low pH of 4.5, the strands were densely packed together in what is known as an ‘i-motif’ (Fig.1). This happens because at low pH, some cytosine base pairs are protonated, and an attraction occurs between unprotonated cytosine and protonated cytosine on the strands. This densely packed layer on the inside of the pore effectively reduces the pore diameter, thereby reducing the conductivity. This is called the ‘off’ state.

When the pH was raised to 8.5, the protons were lost from the cytosine base pairs, so the attraction ceased and the tightly packed i-motif was no longer held together. The DNA strands changed to a loosely packed, extended conformation, which was unable to efficiently reduce the internal diameter of the pores. This resulted in a higher ion conductivity, so the pores were now said to be in an ‘on’ state.

Wang says that their nanopores have advantages over other artificial channels that are fabricated in fragile lipid membranes. “Our nanopore–DNA system is embedded in a polymer film, which could work well in different environments, and it is easily made with mass production techniques,” he says.

One of the next steps is to hybridize the pores to extend functionality. “Grafting a series of bio-molecules or polymers onto the inner wall of the solid nanopore should expand the bio-function of this system,” says Wang.