Synthetic Microswimmers: Inanimate Microparticles Display Complex Behavior

Janus Particles

Janus particles under the electron microscope. The titanium dioxide microswimmers are barely larger than one micrometer. Copyright: Simmchen Group

TU Dresden Freigeist fellow Dr Juliane Simmchen is investigating with her multidisciplinary junior research group the motion of synthetic microswimmers in liquids. Her goal is to enable these inanimate microparticles to move in a certain direction of their own accord and thus, in future, to be used in sensor technology or biological cleaning. “Actually, it’s a bit like playing computer games in the laboratory,” the chemist describes her extraordinary research work in an interview with the Volkswagen Foundation.

The Simmchen group is working with the so-called “Janus particles.” These consist of a body of titanium dioxide with two differently coated sides: one side with a catalytically active layer of nickel and gold, the other side remains untreated. Titanium dioxide is used as a whitening agent, for example in wall paint, but it also reacts with light. As a result, Janus particles are photocatalytic, which means that as soon as light hits them, chemical reactions occur that set off a movement.

The group has now observed and analyzed an extremely unusual phenomenon in the motion of Janus particles: as soon as the particles leave an illuminated zone in the microscope, they turn around by themselves and swim back – a behavior that is actually only known from microorganisms. But how can such complex behavior be triggered in synthetic microswimmers?

First author Lukas Niese and Dr. Simmchen were able to show that as long as the particles are active in the light, their swimming direction is stabilized by a combination of physicochemical effects. As soon as the particles are no longer exposed to light, there is no energy conversion and the direction of movement is no longer stable. “In this case,” explains Lukas Niese, “the natural thermal movement (Brownian Motion) sets in. This causes the particles to virtually flip, and then they swim back into the exposed area.”

“The fact that such simple effects as the Brownian Motion can lead to such complex behavior was quite astonishing and impressive, especially in terms of the evolution and the development of abilities. We could make use of this property for the targeted control of microrobots. Applications are conceivable in which the particles filter and remove pollutants from liquids or transport medicine through the body, and perhaps even transport information,” says Dr. Simmchen, explaining the significance of the discovery.

Reference: “Apparent phototaxis enabled by Brownian motion” by Lukas Niese, Linlin Wang, Sayan Das and Juliane Simmchen, 20 October 2020, Soft Matter.
DOI: 10.1039/D0SM01603A

1 Comment on "Synthetic Microswimmers: Inanimate Microparticles Display Complex Behavior"

  1. Sekar Vedaraman | December 13, 2020 at 12:47 pm | Reply

    Interesting.

    Nano appears to be the half-way house between the real and quantum world. Light seems to be playing a very important part. The dual nature of light (Wave & Particle) and Bohr’s uncertainty Principle as well as Schrodingers( dead cat both inside the room and existing at the same time in the room, one alive and one dead may have a role — Janus – the two faced god from ancient Human “Mythology” is a good way to represent the gold plated—-tool coated on one side. By the way , other ancient “Mythology” in other parts of the world have Gods with infinite Number of Faces!!

    From a Scientists perspective it is best to —Question every assumption of the past centuries and also the mathematics developed over the previous centurries, and understand what is the root cause of brownian motion. I suspet not just Light but Sound too may have role to play in this phenomenon, though I may be wrong about this intuitive guess. However many phenomenon in the Gross world are affected by sound which could be cacophony or “wonderful” music depending on the genetic and concious being involved . Why —Even Plants which are not supposed to have any consciousness grow better with beautiful music, Wondered why the Flowers always sway towards the sunlight — maybet in search of solar energy. Or Maybe, instinctively.

    Next level expperiments may require further exploration, of which part of the spectrum of the light besides the UV light have a similar or antagonist effect . Especially interested in the wide spectrum 0f visible and infra-red spectrum. Especially as darkness appears to result in chaos and Illya Prigogene theory of Irreversible thermodynamics and reducing entropy coming into play.

    Next level experiments with Sound can also be meaningful and valuable for understanding the growth and development of the fetus in the womb of the mother and the impact of the same on the development of the baby yet to make an appearance on the world stage and what types of music, and other such information is being aborbed by the new life growing in the womb of the mother and the development of the brain and other senses and intuition and higher levels of the sense specctrum ,beyond the five known and sixth sense!.

    Never been able to figure out why in the race to fertilize the Egg there is rarely more than one winner in humans , except when we use artifical means to impregnate the female whereas in other mammals like Dogs there is litter. The fastest swimmer explanation is as incomplete as is the “theory of everything” by the great “Stephen Hawkinngs!”

    We need mathematics which connects the Gross Universe to the Quantum Universe.

    I susppect even if we get answers to all these questions we will not find an answer to how life actaully originates! The more you search the greater the frustration as
    (1) 95 % of experiments fail and the 5% which succeed which gives only partial insight. Direted Research based on the newer tools being invented by Humanity may help in the future to undertake more focused research. This may help improve the success rate from 5% to higher levels.
    (2) Many aspeccts of Human existence and phenomenon is dismissed as Pseuodo Science!

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