Nano World: Nanowires help spot cancer

"It's easy, quick, with low cost. The patient and the doctor can get blood test results within a few minutes," said researcher Charles Lieber, a Harvard chemist. "All you need is a drop of blood."

The microchip the researchers developed can hold up to 200 silicon wires, each 20 nanometers wide and roughly a micron long. The nanowires are coated with antibodies and nucleotides that latch onto compounds unique to cancers. The diameter of the nanowire is roughly that of these markers, so when a cancer molecule binds to a wire, the resulting change in conductivity across the nanowire is significant enough for researchers to detect.

The array is sensitive enough to spot cancer telltales making up just one-hundredth-billionth of the amount of protein in a drop of blood. For instance, in tests of extracts from as few as 10 tumor cells, the nanowire sensors could in real time monitor the activity of telomerase, an enzyme normally inactive in most of the body's cells but active in at least 80 percent of known human cancers.

The new device is 1,000 to 1 million times more sensitive than other devices using carbon nanotubes or prior devices made with silicon nanowires from Lieber's team by improving electrical connections with the nanowires. Lieber and his colleagues report their findings in the October issue of Nature Biotechnology.

"It could be available for everyday use with patients in the next two to five years without problem," Lieber said.

Current tests for cancer molecules require multiple, time-consuming steps for each marker. "Many tests performed today take up to a week or more, and not less than a day to get results," Lieber said. "We can detect multiple markers from a tiny blood sample in a single step."

So far, conventional tests for cancer identify only whether or not cancer is present, and not what type is there. Still, different types of cancer each have different molecular fingerprints. By plugging in the right cancer markers, nanowire arrays could pinpoint which exact type of cancer a patient has, Lieber said.

"Silicon nanowires have been developed to a level of reproducibility -- in structure, size and electronic properties -- far beyond other nanomaterials, and thus it is possible to make highly reproducible sensor elements en masse as required for commercialization," Lieber added.

These findings mark "the first demonstration of using a nanowire based sensor that works using electric signal, which offers the great potential of real-time and wireless detection of cancers at cell level. This technology will have a huge impact to the diagnostics of cancers," said nanotechnologist Zhong Lin Wang at the Georgia Institute of Technology in Atlanta. "The next goal may be to develop this technology into an integrated and implantable device for in-situ sensing of cancer markers."

Copyright 2005 by United Press International