Understanding the electronic nose: principles, progress, and future directions

At the core of e-nose technology is a fascinating attempt to replicate how our own sense of smell works. Figure 1 illustrates how e-nose technology bears interesting analogies to the biological olfactory system [2]. Much like the human nose uses millions of olfactory receptors to detect odors, the e-nose relies on an array of highly sensitive sensors that interact with gases in the air. In the human body, the signals picked up by the olfactory receptors are transmitted to the olfactory bulbs, which process the odor into a stimulus for recognition in the brain. In the e-nose counterpart, the interaction of the different sensors with the gaseous mixture creates complex signal patterns, which travel through a circuit where they are amplified and digitized. The signal is analyzed by powerful software that acts as the system's “brain” and uses algorithms to distinguish specific gases from a gaseous mixture based on their individual digital fingerprints.

With the ability to discriminate individual target gases from complex gaseous mixtures, e-noses are unlocking new possibilities across a wide variety of application fields (Figure 2) [4]. In healthcare, they are being developed for non-invasive disease diagnostics by detecting volatile biomarkers in breath. In the food and beverage industry, e-noses could assist in quality control, freshness monitoring, and even flavour profiling. Environmental monitoring is another key area, where e-noses could help track air pollution, detect hazardous gases, and support early warning systems in industrial settings. Additionally, e-nose devices are promising for applications in agriculture for soil analysis, crop monitoring, and early detection of plant diseases.

While the initial excitement around electronic noses (e-noses) were huge, their widespread use in everyday technology still hasn't materialized, even after a few decades of research. Although the number of publications on e-noses has been steadily rising, their commercial availability and practical applications remain limited. 

Looking at the publication trends over time, we see a clear picture. As shown in Figure 3, the purple line represents a steady increase in e-nose research since the first paper in 1987, showing that interest in the field hasn't waned. In fact, from 2000 to 2010, when nanomaterials were gaining traction, e-nose research was growing faster than the broader sensor field – the boom in nanomaterials research appears to have given e-noses a significant push forward in this time period. However, in more recent years, e-nose research has made up a smaller slice of the overall sensor research pie, signalling that momentum in the field may have slowed.