How to Improve Optical Tweezers

A particle in Brownian motion that explores a random landscape created by a pattern of light known as a speckle pattern. (Source: Univ. Gothenburg)

This year’s Nobel Prize in Physics, awarded for discoveries in laser physics, recognizes optical tweezers. Now researchers from the Univer­sity of Gothen­burg have developed a method that greatly simplifies and improves the use of optical tweezers. “The idea came to me during a visit to the National Auto­nomous University of Mexico last year. It turned out that the lab there already had all the data needed to prove that this new method worked,” says Giovanni Volpe, a senior lecturer at the Department of Physics, Unive­rsity of Gothen­burg.

Optical tweezers were discovered in the late 1980s. They can be described as light beam fingers that can take hold of particles, atoms, molecules and even bacteria and other living cells. The technique consists of an optical laser with the ability to hold onto a single cell, for example, without damaging it. This makes it possible to make very precise measure­ments. The challenge in using optical tweezers has been the need to cali­brate the optical laser exactly. Researchers using optical tweezers need to know exactly what they want to look at, and in what way, to make the precise settings required before the measure­ments begin.

With the new disco­very, the technique will now be consi­derably easier to use. “We have managed to develop a method of measure­ment that is more accurate, but that uses 10 times less data and is 100 times faster than the methods currently available,” says Giovanni Volpe. “The method is completely automated and does not require any pre-set parameters to work.” With this method, optical tweezers can now be moved out of the physics laboratory and be used in pharma­ceutical research.

“Perso­nally, what I find most exciting about the new method is the possibility of studying systems that are not in equi­librium, systems that are in flux,” says Volpe. “We will be able to measure pheno­mena we knew about before but have not been able to see.” According to the researchers, optical tweezers can now be used in bio­logical appli­cations to measure extremely small forces. The method also makes it possible to analyse what are known as extended force fields.

The tool was invented by Arthur Ashkin and represents a reali­sation of his science fiction dream – to use the force field of light to move physical objects. When Arthur Ashkin success­fully used laser light to push small particles towards the midpoint of the beam and keep them there, optical tweezers were born. A major break­through came in 1987, when Ashkin captured live bacteria with the tweezers without damaging them. He imme­diately began using the tweezers to study bio­logical systems. Today optical tweezers are widely used within the research commu­nity. (Source: U Gothenburg)

Reference: L.P. Garcia et al.: High-performance reconstruction of microscopic force fields from Brownian trajectories, Nat. Commun. 9, 5166 (2018); DOI: 10.1038/s41467-018-07437-x

Link: Soft Matter Lab, Dept. of Physics, University of Gothenburg, Gothenburg, Sweden


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