Unlike Zen koans, such as “What’s the sound of one hand clapping?” this question actually has an answer—one that could change the way we conduct medical research.
A newly developed microfluidic device can quickly distinguish cells by their size, deformability and electrical properties according to their acoustical properties. This is because the compressibility and denseness of cells determines their response to sound waves. This method can be used to separate cell types of similar size, making chemical labels unnecessary.
How to Sort Cells by Sound
The microfluidic channel vibrates at a low frequency. As cells flow through the channel, they are pushed to a certain position depending on how they interact with the acoustic forces generated by the vibration.
If the cells flow through water in the channel, nearly all of them cluster at the channel center because they are denser than water. Adding a compound called iodixanol creates a density gradient medium in the channel to prevent these clusters.
When small vibrations are applied, the resulting acoustic forces maintain the gradient position. The density gradient forces the cells to move sideways as they flow along the channel until they reach the correct zone.
“If we make the liquid super dense in the middle and less dense at the edges, the particles or cells will move until their acoustic properties match whatever the local environment is,” explained Joel Voldman, an MIT professor of electrical engineering and computer science.
Applications for Acoustic Cell Sorting
This technique could lead to the development of a handheld device capable of providing fast test results for a complete blood count. This test, which requires blood samples to be sent to a lab for analysis, is used to determine how many red blood cells and different types of white blood cells are present in a patient’s bloodstream.
“You could do a complete blood count that doesn’t require any labeling of the cells,” said Voldman.
Using this method, the three different types of white blood cells—monocytes, lymphocytes and neutrophils—can be distinguished from each other. Monocytes and neutrophils are similar in size, which normally makes them more difficult to distinguish, however this is not a problem for the microfluidic device.
The device could also make it possible to isolate tumor cells from a patient’s blood sample and monitor cancer progression as a result. Thus far, research has shown that this method could distinguish different types of tumor cells based on their acoustic properties; therefore, the application could be quite useful in the medical field to identify diseases and types of cancers.
For another example of microfluidic sorting, check out this record-breaking particle sorting method.