University of Illinois researchers led by Michael S. Strano have fabricated a glucose sensor out of single-walled carbon nanotubes. The technology could prove a blessing to diabetics and others who need to pay close attention to their blood chemistry.
Carbon nanotubes were a logical choice for the sensor because they characteristically fluoresce in the NIR spectral region, where human tissue and biological fluids are particularly transparent. The tubes are first suspended in water and then coated with a monolayer of glucose oxidase, an enzyme that prevents the tubes from cohering to one another and also forms a selective site on which glucose can bind and generate hydrogen peroxide. The tubes are then exposed to ferricyanide, an ion sensitive to hydrogen peroxide, which passes through the porous monolayer and attaches to the tube surface. In the presence of glucose, the glucose oxidase produces hydrogen peroxide that quickly reacts with the ferricyanide. The resulting changes in the nanotubes' electron density and optical properties affect their fluorescent qualities—the more glucose, the greater the fluorescence.
Single-walled carbon nanotubes were encased in a permeable capillary for insertion into the body.
To demonstrate the practicality of using the treated nanotubes as biomedical indicators, the investigators secured some of them in a capillary permeable to glucose and inserted it into human tissue. The sensor's fluorescent behavior corresponded to the local glucose concentration.
According to Strano, the new surface chemistry technique permits electrons to be moved into and out of the nanotubes without damaging their structural bonds. And the sensor could be adapted to respond to other analytes, permitting it to detect a wide range of chemical components in blood and tissue.
The research team also included Seunghyun Baik, Paul Barone, and Daniel Heller. The work was supported by the National Science Foundation.