Optical tractor beam traps bacteria

Up to now, if scientists wanted to study blood cells, algae, or bacteria under the microscope, they had to mount these cells on a substrate such as a glass slide. 

Physicists at Bielefeld and Frankfurt Universities have developed a method that traps biological cells with a laser beam enabling them to study them at very high resolutions. In science fiction books and films, the principle is known as the 'tractor beam'.

Using this procedure, the physicists have obtained superresolution images of the DNA in single bacteria. The physicist Robin Diekmann and his colleagues are publishing this new development in the latest issue of the research journal Nature Communications.

One of the problems facing researchers who want to examine biological cells microscopically is that any preparatory treatment will change the cells. Many bacteria prefer to be able to swim freely in solution. Blood cells are similar: They are continuously in rapid flow, and do not remain on surfaces. Indeed, if they adhere to a surface, this changes their structure and they die.

'Our new method enables us to take cells that cannot be anchored on surfaces and then use an optical trap to study them at a very high resolution. The cells are held in place by a kind of optical tractor beam.

The principle underlying this laser beam is similar to the concept to be found in the television series "Star Trek",' says Professor Dr. Thomas Huser. He is the head of the Biomolecular Photonics Research Group in the Faculty of Physics. 'What's special is that the samples are not only immobilized without a substrate but can also be turned and rotated. The laser beam functions as an extended hand for making microscopically small adjustments.'