Separating circulating cancer cells from blood cells for diagnostic, prognostic and treatment purposes may become much easier using an acoustic separation method and an inexpensive, disposable chip, according to a team of engineers. "Looking for circulating tumor cells in a blood sample is like looking for a needle in a haystack," said Tony Jun Huang, professor of engineering science and mechanics. "Typically, the CTCs are about one in every one billion blood cells in the sample."

Existing methods of separation use tumor-specific antibodies to bind with the cancer cells and isolate them, but require that the appropriate antibodies be known in advance. Other methods rely on size, deformability or electrical properties. Unlike conventional separation methods that centrifuge for 10 minutes at 3000 revolutions per minute, surface acoustic waves can separate cells in a much gentler way with a simple, low-cost device.

Acoustic-based separations are potentially important because they are non-invasive and do not alter or damage cells. However, in order to be effective for clinical use, they also need to be rapidly and easily applicable.

"In order to significantly increase the throughput for capturing those rare CTCs, device design has to be optimized for much higher flow rates and longer acoustic working length," said Ming Dao, principal research scientist, materials science and engineering, Massachusetts Institute of Technology. "With an integrated experimental/modeling approach, the new generation of the device has improved cell sorting throughput more than 20 times higher than previously achieved and made it possible for us to work with patient samples."

The researchers worked both experimentally and with models to optimize the separation of CTCs from blood. They used an acoustic-based microfluidic device so that the stream of blood could continuously pass through the device for separation. Using the differential size and weight of the different cells they chose appropriate acoustic pressures that would push the CTCs out of the fluid stream and into a separate channel for collection. They report their results in the Proceedings of the National Academy of Sciences.