Singapore: Scientists at the University of Texas at Arlington, US, have harnessed laser light's ability to gently push and pull microscopic particles, thus creating the fiber-optic equivalent of the world's smallest wrench in the process. The researchers call their new technique 'a fiber-optic spanner' (the British term for a wrench) and have published their study in Optical Society's (OSA) journal Optics Letters. This tool can precisely twist and turn the tiniest of particles, including living cells, DNA, and microscopic motors and dynamos used in biological and physical research.

Dr Samarendra Mohanty, assistant professor, physics, University of Texas at Arlington, and lead author of the study, and graduate student Mr Bryan Black used their new technique to rotate and shift human smooth muscle cells without damaging them. "This technique is already used to perform optical tweezing, which can move an object forward and backward along a straight line. Optical tweezing is useful for biomedical and microfluidic research, but it lacks the control and versatility of our fiber optic spanner, especially when it comes to working deep inside," said Dr Mohanty.

The innovation that distinguishes this technique from other optical tools is that it can, for the first time, spin or twist microscale objects in any direction and along any axis without moving any optical component. It's able to do this because it uses flexible optical fibers rather than stationary lasers to do the work. This has an added benefit that the optical fibers can be positioned inside the human body, where they can manipulate and help study specific cells or potentially guide neurons in the spinal cord.

Rather than an actual physical device that wraps around a cell or other microscopic particle to apply rotational force, or torque, the fiber-optic spanner is created when two beams of laser light, emitted by a pair of optical fibers, strike opposite sides of the microscopic object. Individual photons impart a virtually imperceptible bit of force when they strike an object, but an intense beam of laser light can create just enough power to gently rotate microscopic particles.

In the optical spanner, the optical fibers use laser beams to first trap an object and then hold it in place. By slightly offsetting the optical fibers, the beams are able to impart a small twisting force, which causes the object to rotate in place. Depending on the positioning of the fibers, it is possible to create rotation along any axis and in any direction. This greatly enhances researchers' ability to study and image cells and groups of cells for biological research and medical analysis.