Much like the Jedis in Star Wars use “the force” to control objects from a distance, scientists can use light or “optical force” to move very small particles. The inventors of this ground-breaking laser technology, known as “optical tweezers,” were awarded the 2018 Nobel Prize in Physics. Optical tweezers are used in biology, medicine, and materials science to assemble and manipulate nanoparticles such as gold atoms. However, the technology relies on a difference in the refractive properties of the trapped particle and the surrounding environment. Now scientists have discovered a new technique that allows them to manipulate particles that have the same refractive properties as the background environment, overcoming a fundamental technical challenge. The study “Optical Tweezers Beyond Refractive Index Mismatch Using Highly Doped Upconversion Nanoparticles” was published online on February 18, 2021 in Nature Nanotechnology (https://www.nature.com/articles/s41565-021-00852-0). "This breakthrough has huge potential, particularly in fields such as medicine," says leading co-author Dr. Fan Wang from the University of Technology Sydney (UTS). "The ability to push, pull, and measure the forces of microscopic objects inside cells, such as strands of DNA or intracellular enzymes, could lead to advances in understanding and treating many different diseases such as diabetes or cancer. Traditional mechanical micro-probes used to manipulate cells are invasive, and the positioning resolution is low. They can only measure things like the stiffness of a cell membrane, not the force of molecular motor proteins inside a cell," he says. The research team developed a unique method to control the refractive properties and luminescence of nanoparticles by doping nanocrystals with rare-earth metal ions.
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