Researchers develop device that uses sound waves to separate blood-based nanoparticles

Duke University engineers have created a gadget that employs sound waves to separate and sort the smallest particles found in the blood in a couple of minutes. The technique is based on a concept known as "virtual pillars," and it has the potential to benefit both scientific research and medicinal applications.

Small extracellular vesicles (SEVs) are tiny biological nanoparticles generated by all types of cells in the body and are thought to play an important role in cell-to-cell communication and disease transmission. Acoustic Nanoscale Separation by Wave-pillar Excitation Resonance, or ANSWER for short, is a revolutionary technology that not only extracts nanoparticles from biofluids in under 10 minutes but also separates them into size categories thought to have unique biological roles.

The findings were published online in the journal Science Advances.

"These nanoparticles have significant potential in medical diagnosis and treatment, but the current technologies for separating and sorting them take several hours or days, are inconsistent, produce low yield or purity, suffer from contamination and sometimes damage the nanoparticles," said Tony Jun Huang, the William Bevan Distinguished Professor of Mechanical Engineering and Materials Science at Duke.

"We want to make extracting and sorting high-quality sEVs as simple as pushing a button and getting the desired samples faster than it takes to take a shower," Huang said.

According to a recent study, sEVs are divided into various subgroups of varying sizes (e.g., smaller than 50 nanometers, between 60 and 80 nanometers, and between 90 and 150 nanometers). Each size is thought to have unique biological features.

Researchers are thrilled by the recent finding of sEV subpopulations because of their potential to transform the field of non-invasive diagnostics, such as the early identification of cancer and Alzheimer's disease. However, the particles have not yet made their way into therapeutic settings.

Huang attributes this to the challenges in identifying and isolating these nano-sized sEV subpopulations. Huang, his doctoral student Jinxin Zhang, and collaborators from UCLA, Harvard, and the Magee-Women's Research Institute created the ANSWER platform to solve this problem.

A single pair of transducers generates a standing sound wave that envelops a narrow, enclosed fluid-filled channel. Through the channel walls, the sound wave "leaks" into the liquid core and interacts with the original standing sound wave. This interaction causes a resonance that forms "virtual pillars" throughout the middle of the channel with proper design of the wall thickness, channel size, and sound frequency.

Each of these virtual pillars is effectively a half-egg-shaped high-pressure zone. Particles that attempt to cross the pillars are forced toward the channel's boundaries. And the greater the particle size, the greater the push.

By tuning the series of virtual pillars to create nuanced forces on the travelling nanoparticles, the researchers can precisely sort them by size into a variety of groups determined by the needs of the experiments at hand.

"The ANSWER EV fractionation technology is the most advanced capability for precise EV fractionation, and it will significantly impact the horizon of EV diagnostics, prognostics and liquid biopsy," said David Wong, director of UCLA Center for Oral/Head & Neck Oncology Research.

In the new paper, the researchers demonstrate that their ANSWER platform can successfully sort sEVs into three subgroups with 96 per cent accuracy for nanoparticles on the larger end of the spectrum and 80 per cent accuracy for the smallest. They also show flexibility in their system, adjusting the number of groupings and ranges of sizes with simple updates to the sound wave parameters. Each of the experiments only took 10 minutes to complete, whereas other methods such as ultra-centrifugation can take several hours or days.

"Due to its contact-free nature, ANSWER offers a biocompatible approach for the separation of biological nanoparticles," Zhang said. "Unlike mechanical filtration methods, which have fixed separation cutoff diameters, ANSWER offers a tunable approach to nanoscale separation, and the cutoff diameter can be precisely modified by varying the input acoustic power."

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