Koch, M. & Rohrbach, A. Nat. Photonics 6, 680–686 (2012).

Optical trapping is a powerful tool for manipulating molecules, cells and beads. Attempts to trap and hold onto objects with changing shapes, however, have faced major technical challenges. Koch and Rohrbach now report an optical trapping approach to trap and image the rapidly shape-shifting helical bacterium Spiroplasma, which is of biomedical interest (it lacks a cell wall and is resistant to antibiotics). The researchers adapted the shape of the optical trapping potential to the body of the bacterium by time-sharing the laser focus. Once caught, the bacterium could be imaged with nanometer precision at up to a kilohertz rate, allowing the researchers to generate three-dimensional movies of its rapid and complex shape-shifting movements.