‘World’s smallest wrench’ could help build solar sails

Taking advantage of laser light’s ability to gently push and pull microscopic particles, researchers have created what they’re calling the world’s smallest wrench.

It can precisely twist and turn the tiniest of particles, they say, from living cells and DNA to microscopic motors and dynamos used in biological and physical research.

It can be used to manipulate single cells for cancer research, twist and untwist individual strands of DNA, and perform many other functions where microscopic precision is essential.

What’s new about this technique 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, thanks to the use of flexible optical fibers rather than stationary lasers. It has the added benefit that the optical fibers can be positioned inside the human body.

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. An intense beam of laser light can create just enough power to gently rotate microscopic particles. Depending on the positioning of the fibers, it is possible to create rotation along any axis and in any direction.  

“When photons of light strike and then get reflected back from an object, they give it a small push from an effect called scattering forces,” says Samarendra Mohanty, assistant professor of physics at the University of Texas at Arlington.

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,” says Mohanty. “But it lacks the control and versatility of our fiber optic spanner, especially when it comes to working deep inside.”

One exciting application for the technique would be in the development of solar sails for spacecraft propulsion.

“I envision applications in the direct conversion of solar energy to mechanical energy, rotating large, macroscopic objects using this technique,” Mohanty says.

This would “simulate an environment in which photons radiated from the sun could propel the reflective motors in solar sails, a promising future technology for deep-space travel.”