New Electrochemical Method of Determining Blood and Blood Fractions Antioxidant Activity

Portable Device for Potentiometric Determination of Antioxidant Capacity

For the first time, a prototype of a portable device for the potentiometric determination of antioxidant capacity based on a new measurement principle is proposed. A feature of the approach is the use of an electrochemical microcell with separated spaces and two identical electrodes with immobilized reagents. An antioxidant solution is introduced into one half-cell, and the antioxidants interact with the reagents. The other half-cell contains only reagents. The potential difference between the electrodes is due to the change in the ratio of the oxidized and reduced form of the reagents, which occurs as a result of the reaction with the antioxidants in one of the half-cells and is related to their concentration. The range of linearity of the microcell with immobilized reagents is 40-4000 μM-eq, and the limit of detection is 20 μM-eq. The device was successfully tested in the analysis of standard antioxidant solutions. The recoveries were (92-113)%, and the relative standard deviation did not exceed 15%. A good correlation was found between the data obtained by the approach and the potentiometric method in a macrocell for fruit juice analysis. Pearson's coefficient for the obtained experimental data was 0.9955. The proposed portable device is promising and can be used in field conditions.

Portable potentiometric device for determining the antioxidant capacity

At present, the development of portable devices for the express assessment of the content of biologically active objects, such as antioxidants, is one of the relevant technological problems of modern chemistry, medicine, and engineering. The main advantages of such devices are the simplicity and rapidity of analysis, small volumes of analyte, as well as miniaturization of equipment, making it possible to carry out the on-site analysis and, thus, to take a step towards the personalized medicine. The potentiometric method using the K3[Fe(CN)6]/K4[Fe(CN)6] system, which in the laboratory-scale version proved to be the most accurate, reproducible, and express, was the basis for the developed prototypes of portable devices. In this study, two versions of prototypes of the portable device are proposed, namely, the open microcell with the 0.2 ml volume and the microfluidic device with flow control. The correctness of the antioxidant capacity (AOC) determination in both systems was confirmed by comparing the results of the "introduced-found" method on model solutions of antioxidants and their mixtures with the AOC results obtained in a standard laboratory electrochemical cell. The relative standard deviation did not exceed 10%. The AOC of some beverage industry was determined using the microfluidic device. The correlation coefficient of the results, obtained in the microfluidic device and the laboratory cell, was 0.90, which indicates good data convergence and the possibility of using the potentiometric method implemented in the microfluidic device to assess the AOC of multicomponent objects.

Electrochemical Hybrid Methods and Sensors for Antioxidant/Oxidant Activity Monitoring and Their Use as a Diagnostic Tool of Oxidative Stress: Future Perspectives and Challenges

The terminology used in electrochemical methods which are used to generate the measured signal in antioxidant/oxidant activity (AOA/OA) sensors is briefly considered. The review presents a hybrid version of electrochemical methods for the determination of AOA/OA. Invasive electrochemical methods/sensors for AOA/OA of blood/serum/plasma, and non-invasive ones for semen, sweat, saliva and skin determination are described. AOA/OA sensors application in health estimation, cosmetology, food and nutrients is presented. Attention is paid to widely described approaches and technologies used in chemical/biochemical sensors. It will be considered as base/prototypes for developing sensors of the kind for AOA/OA determination. Prospects for the development of wearable, written sensors and biosensors are considered. Miniature and wireless sensors will allow for the monitoring of the patient’s state, both at the bedside and far beyond the hospital. The development of wearable self-powered written and printed sensors is an important step towards personalized medicine.

An integrated approach to the investigation of antioxidant properties by potentiometry

An analytical methodology is proposed for a comprehensive study of antioxidant properties of various objects based on the implementation of various mechanisms of antioxidant action. In order to interpret results regarding the action of antioxidants in living organisms it is proposed to adhere to certain requirements for research methods of antioxidant properties, for oxidizing agents of a radical and non-radical nature. The developed integrated approach consists in using the potentiometry method and is based on the antioxidant capacity determination which is founded on the interaction of antioxidants with the К₃[Fe(CN)₆] by the ET-mechanism and the conjugation mechanism and the antiradical capacity determination based on the interaction of antioxidants with peroxyl radicals by the HAT-mechanism. Individual antioxidants of natural origin, plant materials extracts as well as synthesized 6-nitro-1,2,4-triazoloazin containing polyphenols fragments, which are complex conjugated structures, have been investigated. It has been shown that in the antioxidants study it is advisable to use the integrated approach that will allow to evaluate antioxidant properties from the point of view of various antioxidants action mechanisms.

Silver Chloride/Ferricyanide-Based Quasi-Reference Electrode for Potentiometric Sensing Applications

Processes’ occurring at the Ag/AgCl/Cl–, ([Fe(CN)6]3–/4–) ions interface study results are presented. Conditions are selected for the mixed salts’ precipitate formation on the silver surface. It has been shown that the potential of a silver screen-printed electrode (AgSPE) coated with a mixed precipitate containing silver chloride/ferricyanide is stable in the presence of [Fe(CN)6]3–/4–. The electrode can serve as a quasi-reference electrode (QRE) in electrochemical measurements in media containing ions [Fe(CN)6]3−/4−. The electrode is formed during polarization of AgSPE (0.325 V vs. Ag/AgCl/KCl, 3.5 M) in a solution containing chloride- and ferri/ferrocyanides ions. The results of the obtained QRE study by potentiometry, scanning electron microscopy and cyclic voltammetry are presented. The proposed QRE was used in a sensor system to evaluate the antioxidant activity (AOA) of solutions by hybrid potentiometric method (HPM). The results of AOA assessment of fruit juices and biofluids obtained using new QRE and commercial Ag/AgCl RE with separated spaces do not differ.

Potentiometry as a Tool for Monitoring of Antioxidant Activity and Oxidative Stress Estimation in Medicine

The complexity of biological objects and the rapid change in their composition after sampling, the variety of compounds of different chemical nature, possessing oxidative and antioxidant properties, make the task of its estimating extremely nontrivial and important for food, nutrients and human health characterization. The paper discusses the use of potentiometry in determining integral antioxidant/oxidant activity mainly of biological fluids and human skin. The source of information is the electrode potential shift that occurs when the analyzed object is inserted in the solution of the mediator system or when the mediator system is exposed to human skin. The experimental approaches, protocols, calculations are described. A number of examples of antioxidant activity and oxidative stress estimation in medicine are presented. The works show lower levels of antioxidant activity (AOA) of plasma and blood serum in patients with cardiovascular diseases, obesity, and malignant neoplasms as compared with the healthy volunteers. It was found out that antioxidant activity of fertile men semen is higher than AOA of infertile patients. Using the method discussed have shown that in some infertile male patients antioxidant activity of semen has been accompanied by oxidant activity. It has been found, that antioxidant activity of skin increases after intake of ascorbic acid and vitamin-enriched juices. The described approach holds considerable promise for monitoring oxidative stress of the whole organism and its systems, and for selecting effective and safe therapy. Thus, it opens up new opportunities in expanding the use of analytical chemistry in such an important field as medicine.

Nanomaterials: Electrochemical Properties and Application in Sensors

The unique properties of nanoparticles make them an extremely valuable modifying material, being used in electrochemical sensors. The features of nanoparticles affect the kinetics and thermodynamics of electrode processes of both nanoparticles and redox reactions occurring on their surface. The paper describes theoretical background and experimental studies of these processes. During the transition from macro- to micro- and nanostructures, the analytical characteristics of sensors modify. These features of metal nanoparticles are related to their size and energy effects, which affects the analytical characteristics of developed sensors. Modification of the macroelectrode with nanoparticles and other nanomaterials reduces the detection limit and improves the degree of sensitivity and selectivity of measurements. The use of nanoparticles as transducers, catalytic constituents, parts of electrochemical sensors for antioxidant detection, adsorbents, analyte transporters, and labels in electrochemical immunosensors and signal-generating elements is described.

Potentiometric study of antioxidant activity: development and prospects

The increasing interest in the study of the antioxidant activity of different objects is caused by an unbalance between the formation of reactive oxygen species (ROS) and the performance of the antioxidant system in humans under certain conditions, which leads to oxidative stress and pathological states of the organism. This article presents a brief critical review of the methods that are used to measure integrated antioxidant activity (AOA). It is shown that the most promising methods for measuring AOA are electrochemical ones, particularly potentiometry, as it best fits the nature of the processes causing oxidative stress. The article gives the theoretical rational for requirements that an oxidizer of antioxidants (AO) should meet. The work presents the thermodynamic grounds for the use of an earlier proposed mediator system, kinetics of chemical reactions between AO and the mediator system. In order to confirm reliability and accuracy of the results, numerous correlation studies were conducted, aiming to compare the data obtained with the use the proposed method and independent analytical methods. The article presents the results of the potentiometric study of AOA for a variety of objects, including individual antioxidant → nutritional supplements → food → blood and blood fractions.