This figure illustrates a protein nanopore-based sensor for the detection of proteins in a complex biological fluid at single-molecule precision. On the left side, the sensor, which is an engineered transmembrane protein, adopts a conformation with a 'bobber' moving at the tip of the pore. On the right side, the capture of the prey protein pulls the bobber away from the nanopore opening. The compartment on the top of the membrane contains blood serum. In addition, a voltage is applied between both sides of the membrane in order to generate an electrical current, creating a signal that scientists can monitor and see when a protein enters the nanopore.