Coated nanotubes make biosensors

A good sensor should be able to sense extremely small changes and should be able to transmit this information about its environment consistently.

Researchers working to make sensors that indicate a given chemical or biological agent after sensing only a few or even a single molecule of that substance are turning to the minuscule tools of nanotechnology.

Researchers from the University of Illinois at Urbana-Champaign are using carbon nanotubes to sense single molecules, and are tapping the way carbon nanotubes give off near-infrared light in order to read what the sensors have detected.

Carbon nanotubes are rolled-up sheets of carbon atoms that can be narrower than 1 nanometer in diameter. A nanometer is one millionth of a millimeter, or the span of 10 hydrogen atoms.

The sensors could eventually be used to monitor biochemical changes in biological fluids and tissue in real time, according to the researchers.

Carbon nanotubes floresce, or emit light after absorbing light, at a wavelength in the near infrared region. This is useful because near infrared wavelengths are not blocked by human tissue or biological fluids; this allows for sensors that can transmit information from inside the body. Unlike quantum dots and organic molecules, which are also being studied for use as biological sensors and markers, nanotubes do not lose their ability to fluorese over time. This consistency makes it possible to derive information from the wavelength and intensity of the fluorescence.

The researchers modified carbon nanotubes so they stick to a target molecule; when they do so their fluorescence diminishes, which indicates that the molecule is present. The researchers proof-of-concept system detected glucose levels in a sample of blood.

The method could be used practically in 5 to 10 years, according to the researchers. The work appeared in the December 12, 2004 issue of Nature Materials.