Graphene sniffs out dangerous chemicals

Researchers at the University of Manchester, UK, have used a one-atom thick gauze of carbon atoms known as graphene to build sensors capable of detecting a single molecule of gasses such as alcohol vapour and carbon monoxide.

Representation of a molecule of nitrogen dioxide on a graphene surface

Single molecule detection is the holy grail of sensing technology, but it has until now been impossible owing to thermal noise swamping the signal. Graphene, however, is an exceptionally low noise material electronically, and the researchers led by Kostya Novoselov have shown that a sensor made from graphene can detect a single gas molecule interacting with its surface.

When gas molecules attach to or detach from a graphene surface, they change the local electron concentration by only a single charge, and do not disrupt the structure of the material. This leads to step-like changes in electrical resistance which can be read off as detection events.

Graphene is not the only nanomaterial used to make sensitive gas detectors. Nanowires and nanotubes have also been employed, though without the impressive results achieved with graphene. “It’s difficult to compare,” says Novoselov, “but in terms of signal-to-noise ratio I would say that the sensitivity of graphene sensors is two orders of magnitude greater than nanotube or nanowire-based sensors, probably more.”

Novoselov believes that graphene-based gas detectors could be produced commercially using the epitaxial graphene wafers grown in many laboratories around the world. Much of the interest in graphene has to do with its potential in electronics, but it is extremely difficult to produce on a large scale material of sufficient quality for this purpose.

“The graphene wafers grown in research labs are not yet good enough quality for electronics, but they could be used for gas sensors,” says Novoselov. “They will probably not have single-molecule sensitivity, but still they would be better than the alternatives. Also, wafers grown on silicon carbide substrates can easily be mass-produced.”

Further reading: Detection of individual gas molecules adsorbed on graphene, Schedin et al., Nature Mat. (2007).

Figure: Representation of a molecule of nitrogen dioxide on a graphene surface. (© Mesoscopic Physics Group/University of Manchester).

Article first published in Nanomaterials News.