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Bionic Systems: The "Sensory" Magic of Electronic Nose & Electronic Tongue
Release time:
2025-01-21
Biological sensory systems have evolved over millions of years to excel in versatility, performance, and sensitivity. The real-time processing done by the brain through the five senses (sight, hearing, smell, touch, and taste) still far exceeds the capabilities of artificial cognitive systems. Despite their advantages, biological sensory systems are not suitable for monitoring industrial processes or analyzing unpleasant, harmful, or toxic samples such as drugs, viruses, bacteria, and pollutants. To overcome these challenges, bionic systems based on the principles of biological sensory systems have been developed, including the electronic nose (E-Nose) and electronic tongue (E-Tongue), which mimic the mammalian nose.
Technical Principles
Figure 1: Principle of the Electronic Nose
The electronic nose consists of gas-sensitive sensors, a signal processing system, and a pattern recognition system. Since the odor of food reflects a combination of multiple components, when odor molecules are adsorbed onto the sensor material’s surface, they cause changes such as swelling, charge transfer, ion exchange, or interaction with ionic species, leading to changes in the material’s conductivity or resistance. The electrical signals from the sensors are processed through an analog-to-digital converter (ADC) and converted from analog to digital data. These data are then analyzed using machine learning algorithms such as PCA, LDA, K-NN, ANN, PLSR, and PLS-DA. The result is the creation of an "odor fingerprint" or "odor marker" for each sample, enabling objective analysis of products by the instrument’s "sense of smell." The system simulates a complex nose through a matrix of different types of sensors, allowing for rapid, systematic, and scientific odor monitoring, identification, judgment, and analysis.
Figure 2: Principle of the Electronic Tongue
The electronic tongue consists of a taste sensor array, a signal acquisition system, and a pattern recognition system. The concept behind the electronic tongue is based on the biological mechanism of taste perception. In animals, taste perception occurs when taste buds located in different areas of the tongue detect chemical stimuli from different tastants. These signals are then transmitted through nerves to the brain, which processes the overall characteristics of the signals and provides information about the nature of the substances. In the electronic tongue system, the sensor array acts as the tongue, detecting different chemical substances and generating electrical signals. These signals are converted into digital data, processed using mathematical models, and evaluated via computer simulations to determine the taste or properties of the sample.
Given the advantages of the electronic nose and electronic tongue, these systems have been applied in various fields such as food industry, environmental monitoring, healthcare, and pharmaceuticals, with significant research outcomes reported worldwide.
Application Areas
1、Food Industry
Rice, a major staple food worldwide, is vital to agriculture and consumers. Due to changes in storage conditions and enzyme activity, rice undergoes aging, resulting in a decline in quality. A study explored the application of the electronic nose for detecting rice quality, including the detection of 2-AP, aldehydes, heterocyclic compounds, and alcohols. Compared to traditional methods, the electronic nose offers advantages like simpler operation, faster detection, cost-effectiveness, higher accuracy, and better suitability for large-scale and real-time monitoring.
2、Environmental Monitoring
Figure 3: E-Nose Measuring Pesticides in Soil
A study used the electronic nose to collect pesticide odors from soil. Following a proposed detection framework, the system achieved a 99.55% average recognition rate with a detection time of less than 0.00003 seconds. The recognition rate for pesticide types and brands was 98.13% and 97.40%, respectively. Semi-quantitative analysis of pesticide concentration showed that the recognition rate for four concentration levels reached up to 93.75%. The study proposed a distributed soil pollution detection and pesticide-specific recognition framework, enabling rapid and automatic pesticide detection in soil.
3、Healthcare
Changes in biomarkers, metabolites, cf-mtDNA, and miRNA in urine, combined with the ease of sample collection and non-invasive nature, make urine an effective diagnostic tool for cancer. However, current methods for diagnosing cancer using urine often suffer from complexity or low sensitivity and specificity. Solovieva et al. (2019) used an electronic tongue to analyze urine samples from prostate cancer patients and healthy volunteers. Electrochemical measurements were performed, and the data were processed using logistic regression to construct a classification model with 100% sensitivity, 97% accuracy, and 93% specificity. This method’s advantages include simplicity, low cost, short measurement time, and no need for sample preprocessing, showing the potential of the electronic tongue for prostate cancer diagnosis.
4、Pharmaceutical Industry
Cardamom contains volatile components with both medicinal and culinary value, but commercial products vary in quality, and adulteration is common. The electronic nose and tongue were used to analyze differences in taste and odor between cardamom from different origins. PCA and PLS-DA methods were applied to create qualitative models for identifying the authenticity and origin of cardamom. The PCA-DA model of the electronic nose perfectly distinguished cardamom from other samples with an accuracy of 1.00, while the electronic tongue model achieved an accuracy of 0.91. By combining data from both systems, a more accurate origin identification model was developed, achieving 0.82 accuracy in PCA-DA. These analyses suggest that electronic nose and tongue technologies can effectively assess the variety and quality of cardamom, rapidly distinguishing between different origins and verifying authenticity.
These examples demonstrate the widespread application of electronic noses and tongues, particularly in food research. By examining one particularly interesting paper, we can gain insights into the specific applications and conclusions of these technologies in food research.
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