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Light-driven tiny ‘motors’ is straight out of sci-fi

Washington: Taking a leaf out of sci-fi movies, a team of researchers has added another exciting thing to the list of fanciful devices that allow light to interact forcefully with matter.

The Massachusetts Institute of Technology team created in simulations the first system in which particles ranging from roughly molecule to bacteria-sized can be manipulated by a beam of ordinary light rather than the expensive specialized light sources required by other systems.,

Most research that attempts to manipulate matter with light, whether by pushing away individual atoms or small particles, attracting them, or spinning them around, involves the use of sophisticated laser beams or other specialized equipment that severely limits the kinds of uses of such systems can be applied to. “Our approach is to look at whether we can get all these interesting mechanical effects, but with very simple light,” Ognjen Ilic noted.

The team decided to work on engineering the particles themselves, rather than the light beams, to get them to respond to ordinary light in particular ways. As their initial test, the researchers created simulated asymmetrical particles, called Janus (two-faced) particles, just a micrometer in diameter, one-hundredth the width of a human hair. These tiny spheres were composed of a silica core coated on side with a thin layer of gold.

When exposed to a beam of light, the two-sided configuration of these particles causes an interaction that shifts their axes of symmetry relative to the orientation of the beam, the researchers found. At the same time, this interaction creates forces that set the particles spinning uniformly. Multiple particles can all be affected at once by the same beam. And the rate of spin can be changed by just changing the colour of the light.

The same kind of system, the researchers, said, could be applied to producing different kinds of manipulations, such as moving the positions of the particles. Ultimately, this new principle might be applied to moving particles around inside a body, using light to control their position and activity, for new medical treatments. It might also find uses in optically based nanomachinery.

About the growing number of approaches to controlling interactions between light and material objects, Ido Kaminer said, “I think about this as a new tool in the arsenal, and a very significant one.”

Ilic noted that the study “enables dynamics that may not be achieved by the conventional approach of shaping the beam of light,” and could make possible a wide range of applications that are hard to foresee at this point. For example, in many potential applications, such as biological uses, nanoparticles may be moving in an incredibly complex, changing environment that would distort and scatter the beams needed for other kinds of particle manipulation. But these conditions would not matter to the simple light beams needed to activate the team’s asymmetric particles.

“Because our approach does not require shaping of the light field, a single beam of light can simultaneously actuate a large number of particles,” Ilic continued. “Achieving this type of behaviour would be of considerable interest to the community of scientists studying optical manipulation of nanoparticles and molecular machines.” Kaminer added, “There’s an advantage in controlling large numbers of particles at once. It’s a unique opportunity we have here.”

The findings are reported in the journal Science Advances. (ANI)