Silicon chip filters out cancer cells

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 ...