Khiena Z. Brainina

Noninvasive Potentiometric Method of Determination of Skin Oxidant/Antioxidant Activity

A noninvasive potentiometric method of determining skin oxidant/antioxidant activity is proposed that allows to measure, the shift of the potential of the mediator system applied to the skin in a mixture with a conductive gel. Direct correlation between the concentration of oxidants or antioxidants in the skin and related compounds, extracted from the skin to gel is proved mathematically. The possibility of using characteristics of skin OA/AOA as a criterion for assessing human health is discussed.

Antioxidant Activity Evaluation Assay Based on Peroxide Radicals Generation and Potentiometric Measurement

A new version of potentiometric evaluation of antioxidant activity in biological liquids, food, drinks, and so forth, based on the mediator system combined with the free radicals generation has been proposed. A radical initiator, 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), and K3[Fe(CN)6]/K4[Fe(CN)6] as a mediator system were used. Interactions of the mediator system with radicals, radicals with antioxidants, and erythrocytes have been investigated. The correlation coefficient between the data obtained in the presence and the absence of AAPH equals 0.98. In addition, the possibility to determine a free radical generation rate by using the mediator system has been demonstrated.

Chapter 27 Screen-printed enzyme-free electrochemical sensors for clinical and food analysis

Publisher Summary Problems with the use of electrochemical methods arise from attempts to create reliable, convenient and user-friendly non-toxic sensors. New technologies and materials enable the development of new sensors with unique properties, which has become possible because of the application of nanomaterials as transducers, catalytic constituent of enzyme-free sensors, and labels for immunosensors. Examples of using nanoparticles in accordance with the points mentioned are presented in this chapter. They are electrochemical immunosensor, enzyme-free urea sensor, and sensor for angle of arrival (AOA) measurement. The proposed potentiometric method of measuring AOA presents a good and prospective alternative to the existing methods, which is confirmed by close correlation among the data obtained with the use of potentiometric and traditional methods. The advantages of the proposed method are its simplicity, cost effectiveness and possibility to be used for on-site and on-line analysis. Correlation between the results, obtained by using the known sensors and methods and the proposed sensors, is very good. The approach demonstrates perspectives for creating enzyme-free chemical/biochemical sensors. It also allows the elimination of disadvantages of enzyme containing sensors—in particular, their time and thermal instability, high cost, and necessity to use substrate in the analyzed solution. Integration of electrochemistry, nanotechnology, mimetic synthesis and bioanalysis makes it possible to create new sensors. It can significantly broaden the area of electroanalysis application with regard to developing smaller as well as quite new instruments and information sources for clinical and food analysis.

A Nanostructured Sensor Based on Gold Nanoparticles and Nafion for Determination of Uric Acid

The paper discusses the mechanism of uric acid (UA) electrooxidation occurring on the surface of gold nanoparticles. It has been shown that the electrode process is purely electrochemical, uncomplicated with catalytic stages. The nanoeffects observed as the reduction of overvoltage and increased current of UA oxidation have been described. These nanoeffects are determined by the size of particles and do not depend on the method of particle preparation (citrate and “green” synthesis). The findings of these studies have been used to select a modifier for carbon screen-printed electrode (CSPE). It has been stated that CSPE modified with gold nanoparticles (5 nm) and 2.5% Nafion (Nf) may serve as non-enzymatic sensor for UA determination. The combination of the properties of nanoparticles and Nafion as a molecular sieve at the selected pH 5 phosphate buffer solution has significantly improved the resolution of the sensor compared to unmodified CSPE. A nanostructured sensor has demonstrated good selectivity in determining UA in the presence of ascorbic acid. The detection limit of UA is 0.25 μM. A linear calibration curve has been obtained over a range of 0.5–600 μM. The 2.5%Nf/Au(5nm)/CSPE has been successfully applied to determining UA in blood serum and milk samples. The accuracy and reliability of the obtained results have been confirmed by a good correlation with the enzymatic spectrophotometric analysis (R2 = 0.9938) and the “added−found” technique (recovery close to 100%).

Sensors Based on Bio and Biomimetic Receptors in Medical Diagnostic, Environment, and Food Analysis

Analytical chemistry is now developing mainly in two areas: automation and the creation of complexes that allow, on the one hand, for simultaneously analyzing a large number of samples without the participation of an operator, and on the other, the development of portable miniature devices for personalized medicine and the monitoring of a human habitat. The sensor devices, the great majority of which are biosensors and chemical sensors, perform the role of the latter. That last line is considered in the proposed review. Attention is paid to transducers, receptors, techniques of immobilization of the receptor layer on the transducer surface, processes of signal generation and detection, and methods for increasing sensitivity and accuracy. The features of sensors based on synthetic receptors and additional components (aptamers, molecular imprinted polymers, biomimetics) are discussed. Examples of bio- and chemical sensors’ application are given. Miniaturization paths, new power supply means, and wearable and printed sensors are described. Progress in this area opens a revolutionary era in the development of methods of on-site and in-situ monitoring, that is, paving the way from the “test-tube to the smartphone”.

Procedure 40 Potentiometric determination of antioxidant activity of food and herbal extracts

Publisher Summary Food and herbs are main natural sources of antioxidants. In this connection, antioxidant activity (AOA) of these products is essential for planning right diet as well as for sound therapy. Screen-printed platinum sensor and potentiometric method of measuring AOA of food and herbal extracts are presented in this chapter. The study of extract AOA allows concluding that AOA of water–ethanol extracts is higher than AOA of water extracts. It results from the fact that polyphenols, main antioxidants in plants, are better extracted by ethanol than by water. To sum up, potentiometric determination of AOA with the use of screen-printed platinum sensor provides the possibility to analyze foodstuff and herbal extracts. The method is easy to use, express and reliable. Information on AOA of foodstuff can be applied for quality monitoring of the product and raw materials. It can be realized in onsite and on-line formats for production processes control.

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

Abstract 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.

Procedure 39 Non-enzymatic urea sensor

Publisher Summary This chapter describes a new non-enzymatic urea sensor based on catalytic chemical reaction. The sensor consists of screen-printed transducer and catalytic system which is immobilized on the transducer surface as a mixture with carbon ink. The sensor is used for measuring concentration of urea in blood serum, dialysis liquid. Detection limit is 0.007mM, while the correlation coefficient is 0.99. Some analysis data of serum samples using the proposed sensor and urease-containing sensor are presented. Comparison of blood serum samples analysis data confirms that using anion-exchange column provides good separation of the interfering compounds and analyte. The results confirm accuracy and reliability of the proposed analysis