Sensors for the analysis of redox reactions

Figure 1 Schematic diagram of a biosensor

Biosensors, regardless of their type, can function either in stationary or in kinetic modes. The kinetic mode of operation of the bio selector is realized under conditions when the sensitivity of the analysis depends on the activity of biological material, i.e. from a biochemical reaction. The biochemical reaction rate is limited by the process of substrate transformation, and not by its transport to the bio selector.

Depending on the characteristics of the chemical reaction, a converter is selected. In potentiometric converters, the potential difference between the working electrode and the reference electrode is determined under conditions when the current is zero.
The improvement of bioselective membranes is mainly carried out not only by searching for new biological materials, but also by modifying existing ones.
The design of systems with enzymatic properties is one of the most important areas of modern biotechnology. Already today, environmental monitoring issues occupy a significant place in the development of biosensor technologies.
Biosensors are successfully used to control environmental pollution, in medical diagnostics, in industry for the production of a wide class of products, as well as for the qualitative and quantitative determination of lower aliphatic alcohols, in particular a mixture of methanol and ethanol. The active components of biosensors are enzymes. The use of biosensors has a number of undoubted advantages: preliminary separation of the components of the analyzed sample is not required; they have high selectivity, sensitivity and expressiveness, as well as the simplicity of the hardware design and, in some cases, the relative cost-effectiveness of the tools used. Modern biosensor technology is developing at an exceptionally high speed. Currently, biosensors of over 100 different substances have been created. The growing interest in biosensors is proved by the increase in their sales on a growing schedule.
Depending on the substances being determined, biosensors can be divided into 2 groups: sensors for inorganic analysis and sensors for determining organic substances. In the chemical industry, in medicine, as well as in biology, one of the most important inorganic substances requiring special determination is hydrogen peroxide.
Hydrogen peroxide is probably the only product that produces so many diverse reactions. This can be attributed to the fact that it occupies an intermediate position between the states of oxygen oxidation in water and in molecular oxygen, as well as the widespread occurrence of redox reactions involving oxygen. However, at some point in this chain, a reaction involving molecular oxygen must occur, which favors the formation of hydrogen peroxide in such processes. These reactions are strongly influenced by "biological catalysts" - enzymes.
The formation of hydrogen peroxide was found in a number of enzyme and biological systems, but only if the system does not contain heavy metals or catalase and peroxidase enzymes that decompose hydrogen peroxide.
Recently, the use of hydrogen peroxide for well-known organic synthesis reactions has increased, for example, for epoxidation, hydroxylation, quinone formation, ring opening, polymerization, and peroxidation. Such reactions are used in the production of waxes, resins, polymers, plasticizers, pharmaceutical and medical preparations, insecticides, and many organic products.
The widespread use of hydrogen peroxide in biology and the chemical industry, and its significant effect on substances and processes, requires a more accurate and precise analysis of it. Many amperometric catalase biosensors have been developed for the determination of hydrogen peroxide.
Many chemical sensors of various types have also been developed for detecting hydrogen peroxide.
Chemical sensors are sensors that give a direct, i.e. without a fixed sampling and its preparation. Information on the chemical composition of the environment is usually continuous and with a short response time. As you know, one of the most important analytical parameters that chemical sensors must have is their selectivity.
However, on the basis of biological objects (enzymes, cells, tissues, antibodies, receptors, nucleic acids, etc.), sensors have significant disadvantages, as a rule, limiting their use: high sensitivity to environmental influences, short term of operation, high cost, use sometimes complex enzyme systems, multi-step determination, etc.
Chemical sensors, in contrast to biosensors, are inert to environmental influences, but as a rule, their sensitivity is not high enough. In connection with the above, the need arises to create new systems capable of synthesizing all of above advantages characteristic of both sensors.
Based on successes in the field of imitation catalysis, it is possible to synthesize biomimetic analogs of the corresponding enzymes, the use of which in sensors will help to get rid of many of the above disadvantages.
The purpose of this work was studying of the physicochemical foundations of the design of a catalase - biomimetic sensor for determining H₂O₂. A feature of this work is the development of a new type of catalase - imitation sensor and the study of its physical and chemical properties, based on chemical modeling of certain functions of catalase biosensors.
Sensors synthesizing positive signs are biomimetic sensors, obtained because of an electrochemical system developed by us, which occupies an intermediate position between bio - and chemosensors, which allows you to selectively combine a number of advantages of their positive qualities: high sensitivity threshold, quick response, and affordable design.
The penetration of biosensors and their mimetic analogs into the analytical market is determined by their price and ease of use. For the competitiveness of biosensors with existing methods of analysis, the price of disposable biosensors should be low, and for reusable use another four times lower for a single determination. Undoubtedly, the introduction of sensory technologies will continue contribute the improving of quality of medical tests, and, therefore, the diagnosis, monitoring of food products, the environment, and technological processes.
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