Tech

IT'S harder than finding a needle in a haystack. Unusual or rare cells, such as those that cause the spread of cancer, are difficult to isolate from thousands of other cells in a sample.

Now a new device has been developed which can direct and focus streams of cells in a liquid, and even separate them out according to size. "We can take a stream of cells and focus, defocus and reflect it as if it's a light beam," says Robert Austin of Princeton University, who developed the device with colleagues from Princeton and Boston University, Massachusetts.

The device is a silicon wafer studded with rows of tiny pillars through which a liquid containing particles of various sizes is made to flow. Due to friction, the liquid flows more slowly close to the pillars than midway between them. Small particles are unaffected by this, but those above a critical size tend to pass close to the pillars and are deflected. Using rows of pillars with an offset from one row to the next, different sizes of particle can be collected into streams following diverging paths, an effect akin to a prism separating a beam of white light into its constituent colours.

Changing the positions and sizes of the pillars allowed the team to create chips with different capabilities. By varying the separation of the pillars from just 200 nanometres to hundreds of micrometres, the team was able to separate a wide range of particles, including red and white blood cells and platelets, based on their size (Proceedings of the National Academy of Sciences, DOI: 10.173/pnas.0712398105).

The chip should even be able to separate out the contents of single cells, making it easier to isolate and sequence genes or proteins. This could be particularly useful when studying rare or abnormal cells, such as metastatic cancer cells.

The team have also developed a silicon "lens" that focuses particles of a certain size into a single intense stream. This could help isolate particles that occur at low concentrations, such as fetal blood cells in a mother's bloodstream. It may have applications outside medicine, too, in areas such as water purification and desalination.

Jon Cooper, professor of bioengineering at the University of Glasgow, UK, thinks the device will prove highly versatile. "As a platform, it could pave the way for a wide variety of technologies in the future," he says.

Cancer - Learn more about one of the world's biggest killers in our comprehensive special report.

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