report
2.3.3.1.3 Measuring quality with electronic noses and tongues

While it is important to detect and identify contaminants, it is equally important to manufacturers (particularly of high value foods) to measure the quality of their produce: primarily colour, smell, taste, and mouth-feel.  Traditionally such quality control would have been performed by experienced individuals; however this is not always appropriate, especially for high volume foodstuffs.  Developments over the last two decades based on semiconductor and polymer materials are going some way to automate the quality control procedures as far as taste and smell are concerned.  These are commonly known as electronic tongues and noses[i].  The presence of specific chemicals within a sample (gas or liquid) can be quantified through changes in the electronic properties of the detector material as a result of binding that chemical species.  By using different materials, or by doping the detection material, variable sensitivities to different chemicals can be engineered.  These different detector materials are then arranged within the electronic nose or tongue; each constituting a separate electronic address.  The detection profile (or fingerprint) from a sample can be used to determine the chemical composition and distinguish between different but related products.

Microtechnology-based systems are mature, for example commercially available electronic noses have been used to detect the presence of microbial contamination (indirectly, through the measurement of volatile metabolites)[ii].  However, nanotechnology advances are expected to increase sensitivity and breadth of chemicals that can be measured, thereby giving greater discrimination between different chemical species over a wider range of concentrations.  Recent work has demonstrated the potential for greater sensitivity, with electronic noses based on doped tin oxide thin films discriminating between two different red wines[iii], and doped zinc oxide nanoparticulates discriminating between different vinegars[iv]^,[v].