The cell membrane isn't just a wall; it's a turnstile gate. Embedded within it are protein channels that let ions in and out, creating an electric charge, like a battery that powers nerves and muscles. Engineers have long tried to make such channels artificially, but they couldn't replicate one tricky detail: the dipole potential. This is a tiny electric field at the channel's mouth, just a few angstroms thick (one angstrom is ten billionths of a meter, or one ten-thousandth the thickness of a human hair).
A research team took a one-atom-thick material called molybdenum sulfide selenide (MoSSe). It already has a built-in electric field, like two halves of a coin with opposite charges. They punched a nanometer-sized pore in this sheet. Then things got strange. Usually, the more salt in water, the better it conducts electricity: more ions mean more current. But here, the current didn't change even when salt concentration was increased a millionfold. The pore acted as a limiter: no matter how many ions crowded at the entrance, the same number passed through per second.
Computer simulations showed that the key lies in the water inside the pore. In such a narrow space, water molecules arrange into a special order and stop behaving like ordinary liquid. The material's built-in field alters the properties of this water, causing it to pass ions at a constant rate, like a conveyor belt with a fixed speed. This discovery offers a new way to control ion transport — without changing pore size, just by choosing the right material.
One angstrom is ten billionths of a meter. If you scaled an atom up to the size of a soccer ball, an angstrom would become the length of a soccer field.
In the TV series 'The Expanse', ion drives on ships use electric fields to accelerate ions. Controlling ion flow through nanopores is a step toward such technology in reality.