  We developed a simple way to generate binary patterns based on spectral
slopes in different frequency ranges at fluctuation-enhanced sensing. Such
patterns can be considered as binary "fingerprints" of odors. The method has
experimentally been demonstrated with a commercial semiconducting metal oxide
(Taguchi) sensor exposed to bacterial odors (Escherichia coli and
Anthrax-surrogate Bacillus subtilis) and processing their stochastic signals.
With a single Taguchi sensor, the situations of empty chamber, tryptic soy agar
(TSA) medium, or TSA with bacteria could be distinguished with 100%
reproducibility. The bacterium numbers were in the range of 25 thousands to 1
million. To illustrate the relevance for ultra-low power consumption, we show
that this new type of signal processing and pattern recognition task can be
implemented by a simple analog circuitry and a few logic gates with total power
consumption in the microWatts range.
