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Integrated self-adjusting nano-electronic sensors

Final Report Summary - SANES (Integrated self-adjusting nano-electronic sensors)

Carbon nanotubes demonstrated in the past decade that their exciting electronic and mechanical properties make them one of the most promising materials of the 21st century. The absorption of atoms or molecules on the outer walls of carbon nanotubes can affect their properties, for instance the electrical conductivity of the nanotubes. In this way the nanotubes could act in the long term as sensors to detect (bio)-chemicals in industrial or in medical environments, and proposals of this kind exist in the literature.

The originality of the SANES concept was that by combining single-molecule nanodevices with the signal processing technology necessary to handle their output, we planned to build a nano-electronic sensor device which was not merely a duplication of existing sensors using a host of nanometer sized elements instead of micrometer sized ones. Rather, the SANES module would be able to detect and process very small signal changes occurring in individual single-molecule carbon nanotube sensor elements. Consequently, it would have a tremendously enhanced measurement capacity as compared to currently available sensor modules. The extra capacity would be used to allow the SANES module to dynamically reconfigure itself in order to provide a full characterisation of its environment. Using the new tool comprising micro and nano patterning and combining it with the molecular building blocks of the single-tube sensor elements it would be possible to study the effects on a few molecule scale which is clearly an advantage to the actual state of the art where the integration over a large number of building blocks is averaging and blurring out the interesting molecular phenomena. The combination of measurement and theoretical modelling has to be highlighted as well and is an inherent part of the interdisciplinary approach used in SANES.

The most important goal of SANES was to develop a sensor device with superior multiplexing ability. That is a device which is able to react to changes in its environment and tune its individual sensor elements in such a way that its chemical selectivity remains high. This was the state of the art in 2004 and on this basis we endeavoured to measure three different environmental properties simultaneously.

Advances in the past five years have allowed the SANES consortium to significantly outperform these original expectations. This is made possible by using Fluctuation enhanced sensing (FES). We have proven the by using FES it is possible:
(i) to use a single sensor to measure four different analytes selectively;
(ii) to combine selective qualitative analysis with quantitative information collection;
(iii) to reliably measure gas concentrations that are one order of magnitude smaller than those anticipated originally; and to
(iv) maintain its performance for at least five months.

Since the final SANES prototype device is based on the new Oulu sensor chip design which uses four independent sensors that are all software-switchable, we may conclude that the SANES prototype is capable of: measuring temperature (using the built-in Pt sensor), qualitatively differentiating between 16 different gases (4 gases for each sensor) provided that a suitable calibration is available, quantitatively measuring gas concentrations in the 0.1 ppm - 2000 ppm range.

SANES was a successful project that finished on time and delivered a prototype sensor device which actually surpasses the original project objectives by a factor of five concerning gas selectivity and by an order of magnitude concerning lower detection limit. Perhaps it is even more important to realise that the SANES prototype is the first working device with any mass production prospects which actually uses singe nanotubes as sensing elements. Indeed, each junction between each two CNT pair functions as a selective adsorption site in the printed CNT film, and FES made it possible to actually read out this selectivity information from the film.

In the framework of the SANES project, we developed a complete gas sensing prototype unit with very high selectivity. Since the sensor market today is flooded with cheap semiconductor sensors capable of measuring single analytes, we believe that the best business opportunity for the commercialisation of a SANES device is to aim at niche markets demanding high selectivity, sensor versatility and dynamic sensor reconfiguration possibilities.

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