Nano-tetherball biosensor precisely detects glucose
Researchers have created a precise biosensor for detecting blood glucose, and potentially many other biological molecules, by using single-wall carbon nanotubes anchored to gold-coated nanocubes, according to research published in the January issue of the American Chemical Society (ACS) journal, ACS Nano.

The device, which resembles a tiny cube-shaped tetherball, is a sensor anchored to electronic circuitry by a nanotube, which acts as both a tether and ultrathin wire to conduct electrical signals, according to Timothy Fisher, a professor of mechanical engineering at Purdue University in West Lafayette, Ind.

The technology detects glucose more precisely than any biosensors in development, and might be used in medicine to detect other types of biological molecules and in future biosensors for scientific research, said Marshall Porterfield, an associate professor of agricultural and biological engineering at Purdue.

The nanotubes have a diameter of about two nanometers, or billionths of a meter, roughly 25,000 times thinner than a human hair. Other sensors require at least five times more glucose to generate a signal, and the new sensor also can operate over a wider range of glucose concentration, which means it could be used for many purposes.

The single-wall nanotubes are especially suited for electronic sensors because electricity flows more efficiently through wires only a few nanometers in diameter than it does through ordinary wires.

The engineers have developed a technique to grow individual carbon nanotubes vertically on top of a silicon wafer, a step toward making advanced electronics, wireless devices and sensors using nanotubes.

The nanotubes grow out of tiny holes in a "porous anodic alumina template,” and then then palladium metal is deposited inside the pores, eventually forming cube-shaped caps at the top of each pore. This palladium nanocube is then coated with gold, which is compatible with biological molecules, according to the paper’s authors.

Then, the protein streptavidin is attached to the gold-coated palladium nanocubes and another protein called biotin, is added to the streptavidin.

The researchers used fluorescent-dyed streptavidin molecules to prove that the molecule attached specifically to the nanocube tetherballs and not broadly to all materials. After verifying the tetherball portion of the device could be used as a sensor, the researchers turned the device into a glucose sensor by replacing the biotin with an enzyme called glucose oxidase. The enzyme causes an electrochemical reaction in the presence of glucose and oxygen, generating an electrical signal.

"This is the first time researchers have assembled from the atomic to the biomolecular level all the components you need for a biosensor," Porterfield said. "It's like Tinker Toys at the biomolecular level."

The research was conducted at the Birck Nanotechnology Center and the Bindley Bioscience Center in Purdue's Discovery Park.

The researchers have filed a patent application for the system.