Standard optical tweezers can grab bacteria at only one point, and cannot manipulate their orientation. But researchers at the University of Freiburg (Germany) have demonstrated the use of a fast-moving laser beam to exert an equally distributed force over an entire bacterium, even as it wriggles. At the same time, they recorded the movements of the trapped bacterium at high-speed and in three dimensions by measuring miniscule deflections of light.1
In their study, the scientists investigated spiroplasmas—spiral-shaped bacteria that are impossible to image sufficiently using a conventional optical microscope because of their small size (just 200 nm in diameter) and quick movements. With the new light-scanning optical trap, however, they were able to hold and orient the bacterium over its entire length.
Because interfering light particles can increase or decrease the brightness of lasers, light that hits the bacterium and is deflected from it superposes with the non-deflected light. It is thus amplified, enabling the generation of 3D images—with both high contrast and increased resolution—at up to 1,000 images/s.
The scientists hope that their plans to study the behavior and cellular mechanics of other bacteria that are difficult to treat with antibiotics will lead to a better understanding of bacterial infectious diseases.
1. M. Koch and A. Rohrbach, Nat. Photon., 6, 680–686, doi:10.1038/nphoton.2012.232 (2012).