Electronic tongue based on an array of metallic potentiometric sensors

An electronic tongue for simultaneous determination of Ca2+, Mg2+, K+ and NH4+ in water samples by multivariate calibration methods

In this study, a multi ion-selective electrode system was developed for simultaneous determination of Ca²⁺, Mg²⁺, K⁺ and NH₄⁺ ions. The system, called electronic tongue, was used for the quantitative determination of these ions in different water samples. The measurement system was comprised of sixteen ion-selective electrodes, an Ag/AgCl double-junction reference electrode, and a sixteen-channel multi-potentiometer. In the fabrication process of the electronic tongue, an electrode body, which comprised eight ion-selective electrodes together on it, was designed. The obtained data were evaluated by using multivariate calibration methods such as Classical Least Squares (CLS), Principal Component Regression (PCR) and Partial Least Squares (PLS1). The parameters that influence the electronic tongue performance were investigated. Analyses were conducted in synthetic water samples and real water samples. Percentage recovery values in synthetic samples, which were calculated via PLS1, were found 101.35%, 102.41%, 100.04% and 99.23% for Ca²⁺, Mg²⁺, K⁺ and NH₄⁺ respectively. The results, obtained from the electronic tongue and other analytical techniques, were compared and no significant difference was found between the results at 95% confidence level.

Voltammetric electronic tongue for vinegar fingerprinting

The application of a voltammetric electronic tongue (ET) towards the classification and authentication of vinegar is reported. Vinegar samples of different varieties were analysed with a three-sensor array, without performing any sample pre-treatment, but only an electrochemical cleaning stage between sample measurements to avoid fouling onto the electrode surfaces. Next, the use of discrete cosine transform (DCT) for the compression and reduction of signal complexity in voltammetric measurements was explored, and the number of coefficients was optimized through its inverse transform. Finally, the obtained coefficients were analysed by principal component analysis (PCA) to attempt the discrimination of the different vinegars and by linear discriminant analysis (LDA) to build a model that allows its categorization. Satisfactory results were obtained overall, with a classification rate of 100% for the external test subset (n = 15).

Solid-Contact Potentiometric Sensors and Multisensors Based on Polyaniline and Thiacalixarene Receptors for the Analysis of Some Beverages and Alcoholic Drinks

Electronic tongue is a sensor array that aims to discriminate and analyze complex media like food and beverages on the base of chemometrics approaches for data mining and pattern recognition. In this review, the concept of electronic tongue comprising of solid-contact potentiometric sensors with polyaniline and thacalix[4]arene derivatives is described. The electrochemical reactions of polyaniline as a background of solid-contact sensors and the characteristics of thiacalixarenes and pillararenes as neutral ionophores are briefly considered. The electronic tongue systems described were successfully applied for assessment of fruit juices, green tea, beer, and alcoholic drinks They were classified in accordance with the origination, brands and styles. Variation of the sensor response resulted from the reactions between Fe(III) ions added and sample components, i.e., antioxidants and complexing agents. The use of principal component analysis and discriminant analysis is shown for multisensor signal treatment and visualization. The discrimination conditions can be optimized by variation of the ionophores, Fe(III) concentration, and sample dilution. The results obtained were compared with other electronic tongue systems reported for the same subjects.

Discrimination of different white chrysanthemum by electronic tongue

This paper describes the application of the electronic tongue (E-tongue) in the Discrimination of different white chrysanthemum. Three grade samples, two brands of samples and the samples adulterated were measured by the E-tongue. It was found the samples with different grades or brands could be clearly discriminated and the samples adulterated were separated from the authentic samples using PCA. The results of DFA and BPNN showed the total predicted accuracy of three grades samples were 86.7% and 93.3%. A strong positive correlation was observed between the sensory score and the predicted score (correlation coefficient is 0.9768) using PLS, and the samples were correctly classified. These results suggest the E-tongue may be useful for quality control of white chrysanthemum.

Recent trends in potentiometric sensor arrays--a review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.

Recent advances in electronic tongues

This minireview describes the main developments of electronic tongues (e-tongues) and taste sensors in recent years, with a summary of the principles of detection and materials used in the sensing units. E-tongues are sensor arrays capable of distinguishing very similar liquids employing the concept of global selectivity, where the difference in the electrical response of different materials serves as a fingerprint for the analysed sample. They have been widely used for the analysis of wines, fruit juices, coffee, milk and beverages, in addition to the detection of trace amounts of impurities or pollutants in waters. Among the various principles of detection, electrochemical measurements and impedance spectroscopy are the most prominent. With regard to the materials for the sensing units, in most cases use is made of ultrathin films produced in a layer-by-layer fashion to yield higher sensitivity with the advantage of control of the film molecular architecture. The concept of e-tongues has been extended to biosensing by using sensing units capable of molecular recognition, as in films with immobilized antigens or enzymes with specific recognition for clinical diagnosis. Because the identification of samples is basically a classification task, there has been a trend to use artificial intelligence and information visualization methods to enhance the performance of e-tongues.

Optimization of Sensor Array Data with Various Pattern Recognition Techniques

An electronic tongue which composed of selective electrodes is applied to mineral water recognition (optimization of sensor array). The task of the system is to distinguish among five brands of mineral water. For this purpose, various pattern recognition (PARC) procedures are employed: principle components analysis (PCA), independent component analysis, linked-like adaptive genetic algorithm (LAGA), et al. LAGA networks are proved to exhibit the best performance both in array optimization and mineral water recognition. Their further advantages, such as fast training and robustness, make them the suggested pattern classifiers for sensor array data.