New method of separating particles could lead to improved COVID-19 test

The finding has been hailed as “a fundamentally significant contribution to the field that only comes along every 10-20 years."

By DONNA RACHEL EDMUNDS
Prof. Moran Bercovici, Dr. Federico Paratore, Vesna Bacheva and Dr. Govind Kaigala - Group photo via Zoom. (photo credit: Courtesy)
Prof. Moran Bercovici, Dr. Federico Paratore, Vesna Bacheva and Dr. Govind Kaigala - Group photo via Zoom.
(photo credit: Courtesy)
A groundbreaking study hailed as "fundamentally significant" by colleagues in the field could give rise to a new, rapid and more accurate method of testing for the coronavirus, researchers have said.
In a recent paper published in Angewandte Chemie, researchers at IBM Research Europe in Zurich and at the Technion - Israel Institute of Technology have demonstrated a new method of separating particles according to size, by creating virtual channels within a fluid that effectively sift the molecules.
The study builds upon a concept presented by the same team in a paper published last year in the Proceedings of the National Academy of Sciences, in which the researchers demonstrated that it was possible to set up flow fields within a microfluidic chamber using technology called electric field actuation, in a manner impossible to achieve with traditional pump and valve technology.
In the more recent study, the team used this technology to make the liquid split into bidirectional flows – alternating stripes in which the fluid moved in opposite directions. When particles are introduced into this flow the behave in a somewhat non-intuitive way: the smaller. lighter particles effectively stay still as they rapidly bounce back and forth between the opposing flows, while the larger, heavier particles are carried away by the flow.
“We know that all particles in a fluid move in random directions in a process called Brownian motion” said Vesna Bacheva, a PhD candidate in the Technion Faculty of Mechanical Engineering, and a co-first author of the paper.
“This is the same mechanism that allows us to smell a small drop of perfume from across the room – the molecules simply make their way randomly in a process also known as diffusion.  However, small particles diffuse much faster than large ones, and when placed in the bidirectional flow they move across the opposing flow streams very quickly. Larger molecules or particles diffuse much slower and end up being carried away by the flow.”
“It really is very simple,” added Dr. Federico Paratore, postdoctoral researcher at IBM Research in Zurich, who also co-first authored the paper. “Surprisingly, it hasn’t been done so far, most likely because of technological limitations. Whereas developing the concept certainly took time and iterations, with today’s microfabrication capabilities the final device is rather a simple solid-state device that can be produced on a large scale”.
The team dubbed their method the "bidirectional flow filter" or BFF, and the finding was hailed by one of the paper's reviewers as “a fundamentally significant contribution to the field that only comes along every 10-20 years."
One of the uses for the BFF demonstrated in the paper was the separation of antibodies and particles from small molecules, a use which could lead to a new test for the coronavirus. One of the challenges for testing for a virus is that a positive test relies on probe molecules and target molecules finding each other within the sample, followed by the removal of excess probe molecules which did not encounter their target. When the sample size is very small, this last step can be extremely challenging.
“Our method does this very well, provided that the two reacting elements are of sufficiently different size,” commented Prof. Moran Bercovici.
Dr. Govind Kaigala further explained: “Fortunately, the coronavirus is fairly large – about 100 nm in diameter. This is much larger than antibodies or other probes that can be used to bind to it. Using our method we hope to be able to place a patient’s sample into our chip where it will mix with visible probes, and then see only the viruses flowing out while the unbound probes stay behind."