Review of conventional electronic noses and their possible application to the detection of explosives

During the past twenty years there has been enormous interest in the detection of simple and complex odours by means of electronic instrumentation. This has led to the commercialisation of so-called 'electronic noses' that typically comprise an array of partially selective sensors with suitable pattern recognition software; they have been applied to many different olfactory problems in industry, e.g. from the quality assurance of foodstuffs through to medical diagnostics. Here, the nature of an electronic nose is reviewed and various strategies are suggested to enhance their performance in terms of detection limit and specificity. The general problem of applying a sensor-based electronic nose to the detection of explosive materials is discussed and, the special. requirement to detect very low vapour pressures of compounds, i.e. a limit of detection of at least parts per billion (10(9)) in air and, in some cases, down to parts per trillion (10(12)) in air. Although there is considerable potential to enhance the detection limit of sensor-based electronic noses, the technology is unlikely to displace in the near future the current 'gold standard' of ion mobility spectroscopy for explosives detection. Instead electronic noses could be regarded as a complementary technology used to screen for unknown compounds.