A cell is like a house with many doors. Some doors open only for certain guests, others let anyone through. To understand how these doors work, scientists build models of them. The new model is a glass slide with 52 miniature wells. Each well is covered with an ultrathin lipid film, like a jar with a lid. A protein that forms a channel through the film was inserted into it. Through this channel, some substances enter, and others leave.
Inside each well, a green fluorescent dye was placed in advance. Outside, a solution with potassium ions was added. The pores in the film let small potassium ions in and release larger dye molecules out. Both flows are visible simultaneously: an electrical sensor under the well detects the arrival of ions, while a camera records the dye's fluorescence fading. Potassium ions are small and quick, so they slip through fast. Dye molecules are larger and move more slowly. The instrument clearly separates these two events in time.
This assembly of 52 wells is just the beginning. It can be scaled up to hundreds or thousands. Then scientists could test many different pore-forming proteins at once and see how they work in conditions close to those in a living cell.
The pore formed by the protein alpha-hemolysin is only 2.6 nanometers in diameter. That is 30,000 times thinner than a human hair.
Science fiction often shows nanorobots repairing cells from within. Devices like the one in this work are a first step toward seeing and controlling molecular doors in real time.