Research Highlight

Subject Category: Biomaterials and biosensors

NPG Asia Materials research highlight; doi:10.1038/asiamat.2009.229
Published online 6 July 2009

Nanoelectronics: Odor assessment

The first field-effect transistor-based bioelectronic nose to specifically detect odor molecules.

Human and animal noses are low-power, rapid-response organs that can sense and distinguish a multitude of odor and flavor molecules with exceptional sensitivity and selectivity. Designed to mimic these sensing abilities, electronic noses are devices used to detect food contamination or spoilage, monitor air and water quality, and to identify toxic substances and explosives. Jyongsik Jang and Tai Hun Park at Seoul National University and collaborators1 have now designed the first field-effect transistor (FET) based bioelectronic nose by combining human odorant-binding proteins (hOR2AG1) with nanotubes prepared from polypyrrole — a conducting polymer. FETs are particularly useful in such sensor applications because of their high sensitivity and fast response.

“Polypyrrole is a conducting polymer with superior conductivity and biocompatibility,” says Jang. “It is considered that organic polymer nanomaterials have higher affinity for bioreceptors compared to carbon nanotubes or other inorganic nanomaterials. In addition, useful functional groups were readily incorporated into the conducting polymer nanotubes through the polymerisation process.”

The researchers first expressed the hOR2AG1 proteins in E. coli cell membranes and synthesized nanotubes by templated polymerization using inert cylinders. They then patterned an interdigitated array of gold microelectrodes by lithography, treated the electrode array with a silicon-based coupling reagent, and laid out the conducting polymer nanotubes (CPNTs). The proteins were finally anchored to the nanotubes to afford an hOR2AG1-conjugated CPNT FET device (Fig. 1).

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Fig. 1: Schematic representation of FET-based bioelectronic nose system showing the source electrode (S), drain electrode (D) and liquid-ion gate (G).

“Most FETs are fabricated by conventional lithographic techniques. However, in our study, the chemical binding approach offered better stability for sensing analytes in liquid phase and highly reliable contact between the nanotubes and the electrodes,” says Jang.

To evaluate the performance of their FET-based bioelectronic nose, the researchers monitored the source–drain current of the devices at low voltage in real time during exposure to various odorants. They found that the current increased linearly with the concentration of amyl butyrate — an apricot-smelling compound that responds specifically to hOR2AG1. Exposure to other odorants did not produce such a marked increase in current, suggesting that the bioelectronic nose is highly odorant specific. The researchers are planning to build systems capable of detecting complex odors by FET-based devices containing mixtures of different odorant-binding proteins. They also plan to study the interactions and interference effects in these systems.

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References

  1. Yoon, H., Lee, S.H, Kwon, O.S, Song, H.S, Oh, E.H, Park, T.H & Jang, J. Polypyrrole nanotubes conjugated with human olfactory receptors: high-performance transducers for FET-type bioelectronic noses. Angew. Chem. Int. Ed. 48, 2755 (2009). | Article | ChemPort |

This research highlight has been approved by the author of the original article and all empirical data contained within has been provided by said author.

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