E-nose uses a single antenna and no specific coatings

An artificial nose with only a single sensor sounds like a dream, but researchers in Norway have got a significant way there, with one that can tell six volatile organic compounds apart 96% of the time, and can tell the difference between grapes bought yesterday and grapes bought last week.

The team, from the Norwegian University of Science and Technology in Gjøvik, have used a small antenna partly coated with a mixture of graphene oxide and the ionic polymer Nafion.

The coating is not specially sensitised for a particular chemical, but a general-purpose coating made from a simple mixture of commercial-grade graphene particles and Nafion, applied with a solvent which later dried to leave the coating.

Made on a 33 x 33mm substrate, the antenna is a microstrip design that works across 1 to 8GHz.

Sensing is through driving the antenna with signal that is swept across the bandwidth, while recording returns reflected by the antenna back down the driving cable using a network analyser.

It is this variable frequency drive that adds an additional dimension to the smell sensing, without needing dozens or hundreds of individual transducers each sensitised to different specific chemicals.

Analysing real and imaginary parts of the reflections allows fingerprints to be built up that allowed four different alcohols (methyl, ethyl, propyl and butyl) to be identified every time.

When isomers (molecules with the same atoms, but re-arranged) of two of those (2-bytyle alcohol and iso propyl alcohol) were added to the list to make six options, differentiation dropped, but was still 96.7%.

Bruised apples (with skin still intact) were clearly identifiable from unblemished apples, strawberries bought one day before were distinguished from those bought five days before, and grapes bought the previous day were distinguished from grapes bought five days before.

In the proof-of-concept, the antenna was inside a 10 litre container and samples needed to be left for several minutes before a sweep could detect any chemicals that were emitted.

A similar antenna coated with graphite instead of graphene also worked, but with almost five times less sensitivity.

While the antenna was sniffing chemicals, it was simultaneously demonstrated transferring data over the 5.8GHz ISM band.

Professor Michael Cheffena (left) and Yu Dang

“We are literally surrounded by technology that communicates using antennas,” said NTNU Professor Michael Cheffena. “By giving the antennas sensor functions, existing infrastructure can be used in new areas of application. This has been one of the main motivations for investigating whether antennas can be used for these purposes.”

Medical applications are also foreseen.

“Volatile organic compounds enable trained dogs to detect health-threatening changes in blood sugar and diseases like cancer, so the principle is largely the same,” said fellow researcher Yu Dang.

For more information, the paper ‘Facile E-nose based on single antenna and graphene oxide for sensing volatile organic compound gases with ultrahigh selectivity and accuracy‘ can be read in full without payment in the journal on ‘Sensors and Actuators B: Chemical’.