The biological parallel
Smell is the sense that allows us to perceive volatile compounds as odours. Thanks to a complex biological system, air enters the nostrils and reaches the olfactory epithelium, where specialised neurons equipped with cilia act as receptors. When an odour molecule binds to these cilia, a signal is sent to the brain, which interprets it as a specific scent.
The electronic nose was developed as an objective alternative to the human sense of smell for the characterisation of odours, overcoming physiological limits, subjective judgement, and the risks associated with exposure to hazardous substances.
More than a simple substitute, it serves as an advanced analytical tool that combines a sensor array with pattern recognition software. Thanks to this architecture, the system can be trained to identify individual gases or mixtures, much like the human brain learns to distinguish the aroma of coffee from the scent of rain.
Electronic noses are characterised by a non-destructive analytical capability applicable across multiple sectors. The PEN3, for instance, is widely employed in the food and pharmaceutical industries, among many other sectors, to optimise quality control processes by accurately detecting contamination or sensory defects. In the medical field, the same system is used as a cutting-edge diagnostic support for identifying specific pathologies through the analysis of volatile compounds. Simultaneously, in the fields of security and environmental protection, the OlfoSense system ensures constant and reliable monitoring of toxic gases or pollutant emissions.
The heart of the system: MOS (Metal Oxide Semiconductor) sensors
While the receptors of the nasal epithelium represent the biological sensor, in electronic noses, these are replaced by MOS sensors: a set of ten units in the PEN3 and four in the OlfoSense.
MOS sensors, or metal oxide semiconductors, detect the presence of gases by recording changes in the electrical conductivity of the metal oxide when it interacts with volatile molecules. MOS sensors are non-specific; however, depending on the doping material and the temperature to which they are heated, they exhibit greater sensitivity towards different classes of volatile compounds.
The collective responses provided by the ten MOS sensors generate a ‘map’ of signals that defines the odour profile, or “olfactory fingerprint”, unique to each substance. These sensors constitute the technological heart and the fundamental element of the entire device.
From analysis to data
Once the sensors have recorded the set of signals, the crucial step in transforming these signals into useful information occurs through digital processing. The recognition and classification of samples are performed using dedicated statistical software and chemometric analysis techniques.
Through specific algorithms, such as Principal Component Analysis (PCA), the system compares the newly detected olfactory fingerprint with a database of previously recorded models. It is precisely this analysis that allows the instrument to accurately discriminate one odour profile from another. Thanks to its high sensitivity, the system can operate with objective repeatability, eliminating the margins of error arising from human subjectivity.
