Carbon nanotubes yield a new class of biological sensors

Nanotechnology researchers at the University of Illinois in Urbana-Champaign have demonstrated a tiny, implantable detector that could one day allow diabetics to monitor their glucose levels continuously-without ever having to draw a blood sample.

The work, which is the first application of a whole new class of biological sensors, was funded by the National Science Foundation (NSF) and announced December 12 in the online edition of the journal Nature Materials.

Principal investigator Michael Strano, a professor of chemical and biomolecular engineering at Illinois, explains that the new sensors are based on single-walled carbon nanotubes: cylindrical molecules whose sides are formed from a lattice of carbon atoms. The idea is to exploit the nanotubes’ ability to fluoresce, or glow, when illuminated by certain wavelengths of infrared light-“a region of the spectrum where human tissue and biological fluids are particularly transparent,” says Strano.

To make a sensor, Strano and his collaborators first coat the nanotubes with a “molecular sheath”: a one-molecule-thick layer of compounds that react strongly with a particular chemical-in this case, glucose. The mix of compounds is chosen so that the reaction also changes the nanotubes’ fluorescent response. Then the researchers load the coated nanotubes into a needle-thin capillary tube that can safely be implanted into the body. The capillary keeps the nanotubes from directly touching living cells but still allows glucose to enter.

The Illinois researchers tested their glucose sensor by inserting it into a human tissue sample. Then they illuminated the sample with an infrared laser and verified that the strength of the fluorescence from the buried sensor was directly related to the glucose concentrations in the tissue.