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Sound waves rotate droplets to concentrate and separate nanoparticles

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Mechanical engineers at Duke University have devised a way to rotate individual droplets of liquid to concentrate and separate nanoparticles for biomedical purposes. This technique is much more efficient than the traditional centrifugation approach, it works magic in less than a minute instead of hours or days, and requires only a small portion of the normal sample size. The present invention can highlight new approaches to applications ranging from precision bioassays to cancer diagnosis.


Results will be displayed online in the journal on December 18th Science Advances..

“This idea stems from a very exciting recent discovery that surface acoustic waves can be used to rotate droplets,” said William Bevan, Special of Mechanical Engineering and Materials Science at Duke University. Professor Tony Jun Huang said. “We decided to investigate whether this method could be used to create a point-of-care system that could quickly and efficiently separate and concentrate nanoparticles.”

Huang and his PhD student, Yuyang Gu, began their research by building a device that could rotate individual droplets. In the center of the piezoelectric surface is a ring of polydimethylsiloxane, a type of silicon commonly used in microfluidic technology, which limits the boundaries of droplets and holds them in place. Researchers then placed sound wave generators called interdigital transducers (IDTs) on each side and tilted them so that sound waves of different frequencies passed through the piezoelectric surface and into the droplets. Did.

When on, IDT produces surface acoustic waves that push the sides of the droplet so that Donald Duck is blown away by a huge pair of speakers. In low power settings, the top of the droplet begins to wobble around the ring like the top of a muffin made of Jell-O. However, when the force rises to 11, the balance between the surface tension of the droplet and its centrifugal force causes the droplet to take the form of a pill and begin to rotate in place.

Researchers at Duke University concentrate and separate small particles by rotating individual droplets with sound waves.Credits: Ken Kingery, Duke University

Next, researchers investigated how fluorescent nanoparticles of different sizes behave in rotating droplets. Due to the rotating droplets, the nanoparticles themselves were dragged in a spiral pattern. Depending on their size and sound frequency, they were pushed towards the center of the droplet due to the incident force and hydrodynamics of the sound waves.

Researchers have discovered that different frequencies can be used to specifically concentrate small particles of tens of nanometers. These sizes correlate with biologically important molecules such as DNA and exosomes. Biological nanoparticles are released from all types of cells in the body, which are thought to play important roles in cell-cell communication and disease transmission.

But they were still facing another problem. While nanoparticles of one size were swarming in the center of the droplet, nanoparticles of other sizes were still randomly flying around, making it difficult to access concentrated prizes.

What is their solution? The second rotating droplet.

“We set two droplets of different sizes side by side to rotate at different speeds,” Gu said. “By connecting them in small channels, nanoparticles that are not concentrated in the first nanoparticles will spin off and be trapped in the second channel.”

To further demonstrate how useful their double-droplet centrifugation system is, researchers have shown that exosome subpopulations can be successfully isolated from samples. Also, unlike common centrifugation methods, which require large volumes of samples and can take overnight to work, those solutions require much smaller sample volumes, such as 5 microliters, and less than a minute. Could not.

“This work is intended to simplify and accelerate sample processing, detection, and reagent reactions in a variety of applications such as point-of-care diagnostics, bioassays, and liquid biopsy,” Gu said. ..

“The ability to separate and concentrate exosome subpopulations and other biological nanoparticles is very important,” Huang added. “For example, the recent discovery of exosome subpopulations has excited biologists and researchers because it could revolutionize the field of non-invasive diagnosis, but exosome subpopulations are still used in clinical practice. Not. This is primarily due to difficulties. Our approach provides a simple and automated approach for isolating exosome subpopulation in a fast and biologically compatible way. As a result, we believe it is important to unleash the clinical utility of exosome subpopulation. ”


Microfluidic systems with cell-separating power have the potential to elucidate how new pathogens attack


For more information:
“Acoustic Fluid Centrifuge for Nanoparticle Concentration and Separation”, Yuyang Gu, Chuyi Chen, Zhangming Mao, Hunter Bachman, Ryan Becker, Joseph Rufo, Zeyu Wang, Peiran Zhang, John Mai, Shujie Yang, Jinxin Zhang, Shuaiguo Zhao, Yingshi Ouyang, David TW Wong, Yoel Sadovsky, Tony Jun Huang Science Advances, December 18, 2020. DOI: sciadv.abc0467

Courtesy of Duke University School of Nursing

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Sound waves rotate droplets to concentrate and separate nanoparticles

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