MIT researchers found a way to separate cells by exposing them to sounds waves; the dime-sized device could help locate tumor cells circulating in patients' blood.

Separating cells through this method would be a gentler alternative to current technologies that help predict whether or not a tumor is going to spread; many of today's methods require tagging the cells with harsh chemicals.

"Acoustic pressure is very mild and much smaller in terms of forces and disturbance to the cell. This is a most gentle way to separate cells, and there's no artificial labeling necessary," said Ming Dao, a principal research scientist in MIT's Department of Materials Science and Engineering and one of the senior authors of the paper, which appears this week in the Proceedings of the National Academy of Sciences.

To sort the cells using sound waves in the past researchers have used microfluidic devices with two acoustic transducers to produce sounds on either side of a micro channel; when these two waves meet they forma standing wave which produces a line of low pressure that runs parallel to the direction of cell flow. Cells that encounter the node are pushed to the side, and their movement depends on their shape and size. The problem with this method is it can only push cells aside at short distances.

This new device tilts sound waves so they run across the micro channel at an angle, this causes each cell to encounter several pressure nodes along the way. The new method makes it easier to capture cells of different sizes as they reach the end of the channel.

The team tried to separate breast cancer cells known as MCF-7 from white blood cells using the device. The two cells differ in size, density, and compressibility. The device proved to be able to recover 71 percent of the cancer cells. In the future the researchers plan to test the method on samples from cancer patients.

"If you can detect these rare circulating tumor cells, it's a good way to study cancer biology and diagnose whether the primary cancer has moved to a new site to generate metastatic tumors," Dao said.

"This method is a step forward for detection of circulating tumor cells in the body. It has the potential to offer a safe and effective new tool for cancer researchers, clinicians and patients," said Subra Suresh, president of Carnegie Mellon.