Science News
from research organizations

Moving microswimmers using magnetic vortices

March 24, 2016
DOE/Argonne National Laboratory
Scientistshave discovered a way to use a microscopic, swirling flow to rapidly clear a circle of tiny bacteria or swimming robots.

A rotating particle creates a flow that pushes swimming bacteria into a spiral-shaped halo around the center. The discovery helps scientists understand the interaction of microswimmers and could help prevent films from forming in microfluidic devices such as labs-on-a-chip.
Credit: Image courtesy Igor Aronson and Andrey Sokolov.

Scientists at the U.S. Department of Energy's Argonne National Laboratory have discovered a way to use a microscopic, swirling flow to rapidly clear a circle of tiny bacteria or swimming robots.

"This discovery offers a new approach for control and manipulation of microscopic swimmers," said Argonne physicist and co-author Igor Aronson, and it could be useful in tiny microfluidic ("lab-on-a-chip") devices that can quickly run chemical or biological analyses or perform tasks.

In the study, published today in Nature Communications, the researchers placed a magnetic particle in the center of a liquid film filled with swimming bacteria.

Normally the bacteria swim randomly; but when scientists spun the particle by applying a rotating magnetic field, the swimmers shot away from the center, like a school of fish that suddenly realized there's a shark in their midst.

What's actually happening is that the particle is rotating, creating a small vortex around itself. The bacteria swim parallel to the stream lines and are quickly pushed outwards -- except for a few that get sucked in right next to the particle.

They're not pushed out by centrifugal force, said Argonne scientist Andrey Sokolov, who co-authored the paper; dead bacteria, which aren't swimming, are not pushed out with their living companions.

"Because of the curvature of the flow, some swim in and are trapped on the rotating particle, and others are forced to swim out of the curved flow," Sokolov said.

This technique could separate live from dead bacteria, or different species, bacterial strains or mutants from one another. "The shape and swimming rates of different species would mean they separate," Aronson said.

"At certain frequencies of rotation, the bacteria self-organize into a spiral-shaped halo, creating a microscopic galaxy -- similar to our galaxy Milky Way, but trillions of trillions (1024) of times smaller," Sokolov said.

In addition to new understanding of the forces governing microswimmers and their environments, the vortex technique could help prevent biofilms from forming and disrupting microfluidic devices, the authors suggested.

They are particularly interested in creating systems in which microswimmers could assemble gears to build a tiny machine and then power it, Aronson said.

Aronson and Sokolov also modeled the results theoretically and saw good alignment between computer models and observed results, they said.

Story Source:

Materials provided by DOE/Argonne National Laboratory. Note: Content may be edited for style and length.

Journal Reference:

  1. Andrey Sokolov, Igor S. Aranson. Rapid expulsion of microswimmers by a vortical flow. Nature Communications, 2016; 7: 11114 DOI: 10.1038/ncomms11114

Cite This Page:

DOE/Argonne National Laboratory. "Moving microswimmers using magnetic vortices." ScienceDaily. ScienceDaily, 24 March 2016. <>.
DOE/Argonne National Laboratory. (2016, March 24). Moving microswimmers using magnetic vortices. ScienceDaily. Retrieved April 30, 2017 from
DOE/Argonne National Laboratory. "Moving microswimmers using magnetic vortices." ScienceDaily. (accessed April 30, 2017).