The Janus Particle: How These Two-Faced ‘Nanoswimmers’ Could Improve Drug Delivery, Waste Recovery

A new form of nanorobots, fast and self-propelled nanoswimmers, could soon help in a wide variety of applications, from drug delivery to industrial waste recovery.

Researchers from the University of Colorado Boulder were able to prove that a swarm of these synthetic nanorobots could escape mazes and cavities by as much as 20 times faster compared to other existing materials. Details and results of testing these nanoswimmers are presented in the latest PNAS article, "Mechanisms of transport enhancement for self-propelled nanoswimmers in a porous matrix."

Taking Inspiration from Living Microorganisms

In their paper, researchers explain that several real-world applications of these synthetic nanorobots are similar to living microorganisms - dependent on transport mechanisms in complex environments. Furthermore, the exact environment and mechanisms that allow these movements remain poorly understood. They then presented a case of the nanoswimmers capable of escaping enclosures at rates more than a magnitude of order compared to other materials they tested. Researchers noted that the nanoswimmers have potential applications in cleaning contaminated water and soil and waste recovery, or even in drug delivery requirements to specific parts of the body without risking other uninvolved parts and tissues.

"This is the discovery of an entirely new phenomenon that points to a broad potential range of applications," shares Daniel Schwartz, senior author in the published study and the Glenn L. Murphy Endowed Professor of Chemical and Biological Engineering at CU Boulder in a news release from the university.

Schwarz also recalls in the CU Boulder release how nanoswimmers first gained interest from the theoretical physics community some twenty years ago, with the community thinking of a vast array of potential applications for these materials. One hurdle that limited advancements in understanding these particles are the lack of equipment and setup to model and observe these particles in the context of their respective environment.

Janus Particles and Brownian Motion, and How They Made These Nanorobots

The nanoswimmers are based on a particle known as "Janus particle," a spherical particle whose two faces or halves each have different properties. The unique particle was named after the two-faced god in Roman mythology and was first used in a 1989 scientific study to describe a glass particle whose one face was hydrophobic (repels water) while the other was hydrophilic (water absorbing/ retaining).

In the new CU Boulder research, the fast-moving nanorobots are also spherical particles but made with silica or polymer and treated with different engineering methods to achieve a different property for each of its faces. One hemisphere is a catalytic surface that encourages chemical reactions while the other does not. Having one side actively react allows the entire Janus particle to take energy from its environment and cause it to move independently, an ability known as self-propulsion.

On the other hand, particles such as dust and other passive materials that move randomly are known as Brownian particles - the particles involved in the phenomenon known as Brownian motion. These are the same materials that the researchers used to create their Janus particle.

Researchers then used these Brownian particles turned into nanoswimmers in a "maze" made from a porous material, observing the speed and efficiency with which a Janus particle passed through.

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