In the last ten years or so electronic noses have become commercially available, based on a detection device known as a Taguchi sensor. These are heated semiconductor oxide films that change their resistance when they absorb gases. The gases break down inside the film and the various molecular species gather at grain boundaries within the film changing its resistance.
Electronic noses consist of an array of Taguchi sensors designed to spot different molecular species. These are connected to a computer that analyses the pattern of signals they produce to identify the gases present in a mixture. These can work with fairly complex volatiles and some electronic noses are capable of evaluating various foods .
Now Hung-Chih Chang at Texas A&M University and a few pals say it is possible to use the tools to identify bacteria by their smell alone.
This requires a slightly different mode of sensing in which the random variations in the signal from the sensor are analysed. These variations are the result of molecular species migrating from one grain boundary to another, a process that is intimately linked to their chemical environment. So a decent analysis of these fluctuations can pin down odours even more precisely, a technique knonw as fluctuation-enhanced sensing.
The team says it is possibel to spot the bacteria responsible for food poisoning such as E. coli and the bacterai used in biological attacks such as anthrax.
Many of the current ways of identifying bacteria require the suspect to be cultured first, a time-consuming process. Not so for electronic noses. That and the fact that the hardware is commercially available now should mean we’ll see alot more of them in the next few years.
Ref: arxiv.org/abs/0901.3100: Fluctuation-Enhanced Sensing of Bacterium Odors