CANCER and other diseases may one day be diagnosed by chemical sensors implanted inside a sick person's cells, according to researchers at the University of Michigan.
Raoul Kopelman and his colleagues have made tiny sensors out of polymer balls just 20 nanometres across, 10 times the width of a DNA helix. The balls, nicknamed "pebbles", are impregnated with a dye that glows when it binds to a particular chemical. They take up only one-billionth of the volume of a cell, so they can be inserted into living cells without upsetting their biochemical machinery.
The amount of light produced by the dye depends on the concentration of the target chemical. Many different pebbles can be put into the same cell, containing dyes that glow a characteristic colour in response to their particular targets.
So far the team has developed pebbles that detect calcium, oxygen,
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