January 19, 2009: In a recent paper, researchers at the National Institute of Standards and Technology (NIST) have described a new method for creating gas detectors so sensitive that some day they may be able to register tiny emissions from a single cell. The research could provide a new way to determine if drugs or nanoparticles harm cells or to study how cells communicate with one another.

Based on metal oxide nanotubes, the new sensors are a hundred to 1,000× more sensitive than current devices based on thin films and are able to act as multiple sensors simultaneously.

To address these problems, the NIST group built upon another design using a sheet of aluminum oxide about the thickness of a human hair and perforated with millions of holes about 200nm wide. With the nanosized pores serving as a mold, the researchers dipped the aluminum oxide sheet in a solution of tungsten ions, coating the interior of the pores and casting the nanotubes in place. After the nanotubes were formed, the team deposited thin layers of gold on the top and bottom of the aluminum oxide membrane to act as electrical contacts.

NIST researchers have developed a new technique to form nanotubes for use in gas sensing applications. One hundred to 1000× more sensitive than comparable sensors, their device could be used to study biological cell stress and cell communication. (Source: NIST)

The sensor’s high sensitivity derives from its design, which ensures that any sensor response is the result of the gas interacting with the interior of the nanotube. The researchers also note that this same technique can easily be adapted to form nanotubes of other semiconductors and metal oxides so long as the ends of the nanotubes remain open.

A schematic diagram (not to scale) of the preparation and application of a nanotube gas sensor based on tungsten oxide deposited on a substrate of nanoporous aluminum oxide. Perforated with millions of nanoscale holes, the aluminum oxide sheet served as a template or mold for the creation of the nanotubes. Researchers dipped the sheet in a solution of tungsten ions, allowed the sheet to dry, and sintered (a baking process characterized by incremental temperature increases used to ensure that a coating will stick) it four times, building up a thin film of tungsten oxide on the walls of the pores. (Source: NIST)