An international team of researchers has achieved the ultimate in sensitivity - a gas sensor capable of detecting a single molecule. The sensor is based on graphene, a sheet of carbon a single atom thick.

Kostya Novoselov from the University of Manchester, UK, and colleagues from Russia and The Netherlands, created micrometre-sized flakes of graphene by micromechanical cleavage of graphite at the surface of oxidised silicon wafers. The researchers then used electron beam lithography to make electrical contacts on the flake. A single flake, around 10 micrometres across, was placed in a chamber and its electrical resistance measured as dilute nitrogen dioxide was slowly leaked in. The researchers observed distinct and discrete step changes in resistance, corresponding to single molecules of the gas adsorbing to and desorbing from the graphene flake.

’Graphene has few intrinsic charge carriers but remains conductive,’ team member Andre Geim, of the University of Manchester, told Chemistry World. ’So when you add just a single electron it changes the resistivity significantly.’ Geim said that it should be possible to functionalise the surface of graphene to detect defined species.

’We are talking about the possibility of increasing the sensitivity of gas sensors by orders of magnitude,’ Geim said. ’Graphene has the ultimate sensitivity because in principle it cannot be beaten - you cannot get more sensitive than a single molecule.’

David Williams, a gas sensor expert from the University of Auckland in New Zealand, told Chemistry World: ’To count gas molecules on and off a surface using a simple, robust and stable device operating at room temperature is a major achievement.’ He added, ’Whilst practical application of the results is some way off, the device appears to be very robust, simple and stable.’

"Graphene has the ultimate sensitivity because in principle it cannot be beaten - you cannot get more sensitive than a single molecule" - Andre Geim, University of Manchester

Rob White, Product Marketing Manager of UK-based City Technology Ltd, a company that manufactures gas sensors, described the research as ’potentially very interesting.’ White said, ’There is considerable legislative drive to reduce the measurement limit of sensors in line with reducing exposure limits and any technology seeking to achieve this has significance for us. In addition, the gas species characterised in the paper is a molecule of concern in the markets we address.’

Simon Hadlington

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