Harnessing laser light’s ability to gently push and pull microscopic particles, researchers have created the fiber-optic equivalent of the world’s smallest wrench. This virtual tool can precisely twist and turn the tiniest of particles, from living cells and DNA, to microscopic motors and dynamos used in biological and physical research.

This new twist on controlling the incredibly small, developed by physicists at The University of Texas at Arlington, will give scientists the ability to skillfully manipulate single cells for cancer research, twist and untwist individual strands of DNA, and perform many other functions where microscopic precision is essential.

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 the 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. This technique is already used to perform optical “tweezing,” which can move an object forward and backward along a straight line.

In the team's new 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.

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