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Metal-organic frameworks (MOFs) offer a unique variety of properties and morphology of the structure that make it possible to extend the performance of existing and design new electrochemical biosensors. High porosity, variable size and morphology, compatibility with common components of electrochemical sensors, and easy combination with bioreceptors make MOFs very attractive for application in the assembly of electrochemical aptasensors. In this review, the progress in the synthesis and application of the MOFs in electrochemical aptasensors are considered with an emphasis on the role of the MOF materials in aptamer immobilization and signal generation. The literature information of the use of MOFs in electrochemical aptasensors is classified in accordance with the nature and role of MOFs and a signal mode. In conclusion, future trends in the application of MOFs in electrochemical aptasensors are briefly discussed. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. A.P. acknowledges support of the Russian Science Foundation (grant No 17-73-20024) in part related to the analysis of the reaction conditions and operation of the MOF aptasensors. T.H. acknowledges funding from the Science Grant Agency VEGA, project No.: 1/0419/20.

Biomimetic approaches to the assembling of regular layers of electrochemical sensors make it possible to extend their performance because of the tuning shape and charge of the lipid analogs and implementation of artificial receptors in the lipid layers. The role of artificial components in modification of the properties of the surface layers and application of the nanopore devices are of particular interest. In review, recent trends in assembling modified lipid membranes and their artificial analogs with nanopores have been considered with particular emphasis on their use in electrochemical sensors.

The article analyzes the current state of the metal processing industry and the secondary raw materials market, considers the problems and identifies prospects for its development. The relevance of the article is due to the rapid development of new information and communication technologies, thanks to which there is a new way to manage the processes of collection and processing of secondary raw materials, which is based on fundamentally different rules than the traditional one. To create conditions, it is advisable to work on improving the reliability and international comparability of data, the development of quality standards of secondary raw materials, the creation of an information platform of common access, which will not only monitor the development of the economic system, but also to share information with all participants in the sector. The results of the study can be used to improve the methodology for the formation of mechanisms for the effective use of secondary raw materials by processing companies.

Synthesis and application of nanostructured materials applicable in the assembly of electrochemical sensors is one of the important trends in material sciences and analytical chemistry. In this work, we have proposed and implemented simple non-template method for assembling nanofibers from the polyaniline ultrasonicated with phenyliminophenothiazine in aqueous media. Two-step procedure including association with emeraldine dispersion and reorganization under ultrasonication led to formation of nanofibrillar structures with average diameter of 20 nm. UV-spectroscopy confirms that association of phenyliminophenothiazine and polyaniline in acidic medium resulted in an intense absorption band at 900–910 nm due to donor-acceptor interaction between the reactants. The material combined emeraldine charge transmission with redox activity of phenyliminophenothiazine was found promising for electrochemical sensing. It was confirmed by comparison of characteristics of appropriate solid-contact sensors based on emeraldine and phenyliminophenothiazine toward Fe(III) ions, ascorbic acid and hydroquinone. In all the cases, the use of phenyliminophenothiazine results in a wider concentration range and more reproducible signal against characteristics of similar sensor based on polyaniline. The applicability of the sensor was confirmed by determination of iron content in commercial medication.

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.

Potentiometric sensors based on glassy carbon electrode covered with polyaniline and thiacalix[4]arenes containing amidopyridine, morpholide, pyrrolidide and hydrazide functional groups in cone, partial cone and 1,3-alternate conformations have been developed and applied for determination of Ag(+) ions in the range from 1.0 x 10(-2) to 4.0 x 10(-7)M and limits of detection from 1 x 10(-7) to 3.5 x 10(-8)M. The sensitivity of Ag(+) detection decreases in the following range of thiacalix[4]arene substituents: morpholide>pyrrolidide>amidopyridine>hydrazide. Potentiometric selectivity coefficients predominantly showed binding of Ag(+), Hg(II) and Fe(III) ions over other transient and alkali metals. The influence of functional groups and conformation of receptor on the selectivity of the sensor response was investigated. As shown, selectivity and sensitivity of Ag(+) determination depends on the steric accessibility of the binding site and flexibility of the receptor structure. For Fe(III) ions, changes of the sensor potential are also determined by their implementation in redox reactions of polyaniline.

The inhibitory effect of 1,3-substituted p-tert-butylcalix[4]arenes on butyrylcholinesterase from horse serum has been discovered and kinetically investigated with photometric microassay techniques. The interaction of calix[4]arene with the enzyme is described in accordance with the formal kinetics of competitive reversible inhibition. The inhibition constants calculated depend on the substituent in the lower rim of the calix[4]arene and vary in the range of (5–110) × 10-6 M. The proposed mechanism of inhibition involves the cooperative interaction of indophenyl acetate used as a substrate, calix[4]arene and the enzyme without any covalent or electrostatic binding of the functional groups in the active site of cholinesterase. This results in the coordination of the calixarene on the enzyme surface in the proximity of the enzyme active site. Such interaction prevents the substrate from entering the enzyme active site.

Solid-contact ion-selective electrodes based on glassy carbon electrode covered with electropolymerized polyaniline and tetrasubstituted thiacalix[4]arene ionophores with hexyl and o-pyridylamido functional groups at the lower rim have been developed and examined in the discrimination of the brands of apple juices and herbal liqueurs. For this purpose, the liquids tested were diluted and spiked with a constant amount of Fe3+ ions. The variation of the signal toward Fe3+ ions was achieved due to their involvement in the reactions with the organic ligands and the antioxidants present. As was shown, the combination of the three electrodes with various receptors makes it possible to predict the brand of apple juices and herbal liqueurs using linear discriminant analysis in 95–100% cases. The discrimination procedure makes it possible to discriminate liquids within 20 min. Besides, the electrodes developed make it possible to detect individual antioxidants (ascorbic, malic, oxalic acids, hydroquinone, and quercetin) in the range from 5.0 × 10−6 to 1.0 × 10−2 M in direct potentiometric measurements and redox titration.