New Technique for Optical Tweezers

A team of researchers from the Univer­sities of Glasgow, Bristol and Exeter, have created a new method of moving microscopic objects around using micro-robotics. Currently, optical tweezers – which are used to study proteins, biological molecular motors, DNA and the inner life of cells – use light to hold objects as small as a single nano­particle in one place. They use the unusual optical forces created by tightly focused laser beams to trap and mani­pulate particles, essentially acting as micro­scopic hands for scientists.

New type of optical tweezers: Micro-rotors are used for single target control. (Source: U. Exeter)

The first optical tweezers were developed in the 1970s by Arthur Ashkin. Since then, a series of break­throughs have allowed scientists to manipulate complex objects such as viruses and cells. However, this existing technique has limi­tations – the high inten­sities of light required by optical tweezers can damage live biological specimens, and also restrict the types of objects that can be held.

Now, the research team have developed a new technique that enables optical trapping without focussing any laser light onto the trapped particles. To do this they have developed optically trapped micro-rotors, which are placed in the liquid surroun­ding the particle, and used to mani­pulate its movement using fluid flow. As the micro-rotors are rotated, they create a wave in the liquid that exerts a force on the particle – much in the same way that a jet of water in a Jacuzzi can push away anything that floats past.

By control­ling the directions of each micro-rotor, scientists can either move the particle to a specific location or hold it in one spot – allowing particles to be sorted or imaged at high reso­lution. Crucially, this new technique allows scientists to use flow to pinpoint one specific particle at a time, and not affect others in close proximity. David Phillips, part of the University of Exeter’s Physics department, said: “This research expands the applications of optical tweezers to trap particles of any material in a liquid environment, and without risk of photo-damage, and adds to the toolbox of techniques that allow us develop new nano­technologies.” (Source: U. Exeter)

Reference: U. G. Būtaitė et al.: Indirect optical trapping using light driven micro-rotors for reconfigurable hydrodynamic manipulation, Nat. Commun. 10, 1215 (2019): DOI: 10.1038/s41467-019-08968-7

Link: School of Physics and Astronomy, University of Exeter, Exeter, UK

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