Andrey Ipatov

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.

Application of an E-Tongue to the Analysis of Monovarietal and Blends of White Wines

This work presents a multiparametric system capable of characterizing and classifying white wines according to the grape variety and geographical origin. Besides, it quantifies specific parameters of interest for quality control in wine. The system, known as a hybrid electronic tongue, consists of an array of electrochemical microsensors—six ISFET based sensors, a conductivity sensor, a redox potential sensor and two amperometric electrodes, a gold microelectrode and a microelectrode for sensing electrochemical oxygen demand—and a miniaturized optofluidic system. The test sample set comprised eighteen Catalan monovarietal white wines from four different grape varieties, two Croatian monovarietal white wines and seven bi- and trivarietal mixtures prepared from the Catalan varieties. Different chemometric tools were used to characterize (i.e., Principal Component Analysis), classify (i.e., Soft Independent Modeling Class Analogy) and quantify (i.e., Partial-Least Squares) some parameters of interest. The results demonstrate the usefulness of the multisensor system for analysis of wine.

Determination of cyanide using flow-injection multisensor system

A flow-injection multisensor system (FIMS) comprising potentiometric sensors of different types for determination of free cyanide activity in basic solutions for extraction of noble metals was developed. The solvent polymeric membrane sensors based on metalloporphyrin and crystalline sensors were combined in the sensor system. The system allowed determination of cyanide activity in the range 10(-4)-1 mol l(-1) with an error less than 5% in individual cyanide solutions and acceptable precision (about 20%) in process liquids. The system was able to analyse up to 20 samples per h. The FIMS was also applied to detecting of silver ions in the presence of cyanide. Chalcogenide glass sensor was used as the detector that ensured the precision of 20%.

Integrated multi-sensor chip with photocured polymer membranes containing copolymerised plasticizer for direct pH, potassium, sodium and chloride ions determination in blood serum

An analytical system based on a sensor array with ion-selective field effect transistors (ISFETs) monolithically integrated in one chip covered with photocured polymer membranes containing copolymerized plasticizer and a sequential injection analysis (SIA) is shown to offer an automation of the analysis of blood serum components. For sequential injection system a custom made dual channel flow cell for the sensor array was developed. Optimisation of ion-sensitive membrane characteristics and calibration solution compositions were carried out. The system was used to analyze sodium, potassium, chloride ion contents in blood serum samples. The precision of the ion determination in samples was typical for potentiometric method with standard deviation of about 3-5%.

Integrated Multisensor for FIA-Based Electronic Tongue Applications

The design, fabrication, and application of a monolithically integrated array of chemical sensors is presented. The multisensor chip includes six independent ion selective field effect transistors (ISFETs), a pair of interdigitated platinum electrodes, and a diode temperature sensor. Simultaneous polarization of multiple ISFETs is enabled by electrical isolation of the devices using two different approaches: by trenches and by p-n junction. The degradation of ISFET parameters by the fabrication steps of the interdigitated electrodes has been also studied and solutions consisting of additional annealing steps proposed. The multisensor chip has been assembled within a flow cell and applied as an electronic tongue to the measurement of bottled drinking water. Sensitivity to different ions has been achieved by deposition of organic membranes on top of the ISFET devices. Discrimination of different commercial waters by means of principal component analysis (PCA) of the data is demonstrated.

An impedimetric chemical sensor for determination of detergents residues.

A new impedimetric sensor based on an interdigitated electrode array with electrode digits located at the bottom of microcapillaries formed in silicon dioxide is presented. Microcapillaries are opened at the top, so that in contact with an electrolyte solution the ac current flows close to the surface of the capillary wall from one electrode to another and is significantly affected by changes in the surface conductance at the SiO2/electrolyte interface. Adsorption of detergents on the sensor surface affects the charge distribution in the electrical double layer and thus the surface conductance. These changes are registered by measuring impedance. Effect of surface adsorption of ionic and non-ionic surfactants on the sensor impedance is studied. The sensor is shown to be able to measure commercial detergents residues in a tap water starting from 5 ppm even in solutions with high electrolyte conductivity.

New flow-through analytical system based on ion-selective field effect transistors with optimised calcium selective photocurable membrane for bovine serum analysis

An analytical system based on ion-selective field effect transistors (ISFETs) with Ca(2+) ion selective photocurable membranes is developed to offer a semiautomatic analysis of serum calcium concentration of ruminants. Optimisation of ion-sensitive membrane composition containing different copolymerised plasticizers was performed to minimise the effect of a highly lipophilic samples on sensors characteristics. To improve the system reliability the set of calibration solutions and measurement sequence were also optimised. The system was used to determine total calcium concentration in bovine sera. The precision of the ion determination was higher than reported for double charge ions with a standard deviation of about 3-7%. It is shown that the presence of coagulant in blood serum samples does not affect the determined total calcium concentration.