CANCER and other diseases may one day be diagnosed by chemical sensors
implanted inside a sick person鈥檚 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 鈥減ebbles鈥�, 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.
Advertisement
So far the team has developed pebbles that detect calcium, oxygen, pH
level and potassium. 鈥淲e can recognise chemical patterns and changes, and
correlate them with the presence of a disease or toxin,鈥� says Kopelman.
It is even possible to use dyes that would normally be toxic, says team
member Jonathan Aylott. 鈥淭he polymer matrix protects the dye so it isn鈥檛
affected by what is going on in the cell,鈥� he says.
One way of getting the pebbles into the cells is to inject them using tiny
syringes. A faster option uses a 鈥済ene gun鈥� to fire the pebbles into cells on a
burst of helium.
Kopelman鈥檚 pebbles 鈥渄on鈥檛 require any external connection or penetration
through the cell membrane to any external readout device鈥�, says David Walt, a
biochemist at Tufts University in Medford, Massachusetts. But he points out that
Kopelman has yet to prove the pebbles don鈥檛 create inflammation or trigger an
immune reaction.
Kopelman is now working on a new generation of biosensors containing dyes
linked to enzymes, enabling them to detect a wider range of substances. When the
enzymes bind to chemicals such as glucose, the amount of light the pebble emits
changes. 鈥淭he advantage is you can detect a wider range of things,鈥� says Walt.
Kopelman will report progress on his sensors to the Federation of Analytical
Chemistry and Spectroscopy Society in Nashville, Tennessee, next month.
So far the researchers have been imaging light from the pebbles by putting
the cells under a microscope. Now they plan to put the sensors into living
animals. Kopelman hopes that the pebbles could eventually be useful for
diagnosis. 鈥淭his could be for single cells under a microscope, on a chip, or
even within the body,鈥� he says.