Researchers compare the processing of biological fluid samples with searching for a needle in a haystack — only in this case, the haystack could be diagnostic samples, and the needle might be tumor cells present in just parts-per-million concentrations. Now, a new way of processing these samples could make such detections possible in real time, according to a team from MIT, Massachusetts General Hospital (MGH), and Harvard Medical School.

The team’s surprising discovery is described in a paper in the journal Nature Communications. The technique could allow cells to be sorted while hurtling through the channels of a microfluidic device at speeds faster than those of race cars, the authors say — at least 100 times faster than any existing system

Normally, fluid flowing through a narrow channel at such high velocity would break up into a chaotic, turbulent flow, making any sorting or identification of cells impossible. But the research team found ways of eliminating this turbulence and even focusing the flow, driving the particles into single file within the channel.

“If you’re trying to find a needle in a haystack, it’s a lot easier if the needle is right in the middle of the haystack,” says co-author Gareth McKinley, the School of Engineering Professor of Teaching Innovation in MIT’s Department of Mechanical Engineering. With this method, that’s essentially what you get: In a process the team calls “inertio-elastic flow focusing,” McKinley says, the flow itself helps concentrate the particles that are of interest. “The bigger particles go to the center first,” he says.

In searching for tumor cells in a large volume of fluid — for example, in a fluid sample drained from a patient’s lungs, or in peritoneal fluid — there may be millions of cells, including those from the tumor, in a volume of up to a few liters; these cells’ shapes, numbers, and biophysical characteristics could make them indicators of cancer.

The researchers showed that by adjusting the flow properties of the fluid sample, they could concentrate all of the larger particles at the center of the flow. They adapted a high-speed, pulsed-laser imaging system to take snapshots of the shapes, sizes, and orientations of the particles as they fly through the device.

Ultimately, the researchers say, the work might lead to a compact, bedside device that could take a blood sample from a patient and provide diagnostic information immediately, rather than requiring processing at a lab, which can take hours or even days.