Microrotors Trap Tiny Objects Without Exposing Them to Light

A team of researchers from the Universities of Glasgow, Bristol, and Exeter have developed a technique that optically traps microscopic objects by using hydrodynamics to exert nanoscale-precision control over aqueous particles, without directly illuminating them. This novel approach could lead to optical tweezers that will be able to trap and manipulate complex objects without exposing them to the risks of high-intensity light.

Researchers from the Universities of Glasgow, Bristol, and Exeter have developed a new technique that enables optical trapping without focusing any laser light onto the trapped particles. Courtesy of David Phillips et al/University of Exeter.

The researchers used light-driven microrobotics to move microscopic objects. They placed optically trapped microrotors in liquid surrounding the object; and the microrotors used the flow of the liquid to manipulate the movement of the object. Closed-loop control enabled the researchers to create highly localized flow-fields by precisely piloting the motion of the microrotors. When the microrotors were rotated, they created a wave in the liquid that exerted a force on the object, similar to a jet of water in a Jacuzzi pushing away an object floating past it.

By controlling the directions of each microrotor, the researchers could either move the object to a specific location or hold it in one spot, allowing objects to be sorted or imaged at high resolution. The new technique also allows the researchers to use fluid flow to pinpoint one particle at a time, without impacting other particles in close proximity.

The research team demonstrated 2D trapping of absorbing particles that cannot be optically trapped directly; stabilized the position and orientation of yeast cells; and demonstrated independent control over multiple objects simultaneously.

Researcher David Phillips 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.”

The first optical tweezers were developed in the 1970s by Dr. Arthur Ashkin, who was awarded the Nobel Prize in Physics in 2018 for his pioneering work. Optical tweezers have allowed scientists to manipulate complex objects such as viruses and cells; but the high intensities of light required by optical tweezers can damage live specimens and restrict the types of objects that can be held. The new work could expand the capabilities of optical tweezers platforms and introduce a new paradigm for manipulation of aqueous mesoscopic systems.

The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-08968-7).

These are micro-robotics used to move of moving microscopic objects around. Courtesy of David Phillips/University of Exeter.