Direct Electroanalytical Method for Alternative Assessment of Global Antioxidant Capacity Using Microchannel Electrodes

Analytical Capabilities of Coulometric Sensor Systems in the Antioxidants Analysis

The definition of antioxidants (AOs), their classification and properties as well as electrochemical sensor systems for AOs analysis are briefly discussed. The analytical capabilities of coulometric titration with electrogenerated titrants as sensor systems for AOs determination have been considered in detail. The attention focused on the individual AO quantification that was mainly used in the pharmaceutical analysis and estimation of total antioxidant parameters (total antioxidant capacity (TAC), ferric reducing power (FRP) and ceric reducing/antioxidant capacity (CRAC)) allowing the fast screening of the target samples including their quality control. The main advantages of coulometric sensor systems are pointed out. The selective quantification of individual AO in a complex matrix using a combination of chromatography with coulometric or coulometric array detection under potentiostatic mode is discussed. The future development of coulometric sensor systems for AOs analysis is focused on the application of novel coulometric titrants and the application of coulometric detection in flow injection analysis.

Turn-on fluorescent assay for antioxidants based on their inhibiting polymerization of dopamine on graphene quantum dots

We describe a sensitive turn-on fluorescent assay for antioxidants by using fluorescence-tunable graphene quantum dots (GQDs). GQDs exhibited strong fluorescence without dopamine (DA). DA could self-polymerize to a thin polydopamine (PDA) film on the surface of GQDs under alkaline environment, resulting in the fluorescence quenching of GQDs via fluorescence resonance energy transfer (FRET). However, the self-polymerization of DA could be effectively inhibited in the presence of antioxidants including glutathione (GSH), ascorbic acid (AA), cysteine (Cys), and homocysteine (Hcys). Thus, the fluorescence of GQDs restored. The "turn-on" sensing of antioxidants could be achieved with high sensitivity. The detection limit for GSH, AA, Cys, and Hcys could be achieved as low as 2.4 nM, 1.5 nM, 4.2 nM, and 4.4 nM, respectively. Finally, the GQDs@PDA system was applied for monitoring cerebral antioxidants in rat brain microdialysates. This work promises new opportunities to evaluate antioxidant capacity in physiological and pathological fields.

Electrochemical Generation and Detection of Transient Concentration Gradients in Microfluidic Channels. Theoretical and Experimental Investigations

Transient concentration gradients generated and detected electrochemically in continuous flow microchannels were investigated by numerical simulations and amperometric measurements. Operating conditions including device geometry and hydrodynamic regime were theoretically delineated for producing gradients of various profiles with tunable characteristics. Experiments were carried out with microfluidic devices incorporating a dual-channel-electrode configuration. Under these conditions, high electrochemical performance was achieved both to generate concentration gradients and to monitor their dynamics along linear microchannels. Good agreement was observed between simulated and experimental data validating predictions between gradient properties and generation conditions. These results demonstrated the capability of electrochemical microdevices to produce in situ tunable concentration gradients with real-time monitoring. This approach is versatile for the active control in microfluidics of microenvironments or chemical gradients with high spatiotemporal resolution.

The antioxidant capacity of erythrocyte concentrates is increased during the first week of storage and correlated with the uric acid level

BACKGROUND AND OBJECTIVES

Red blood cells (RBCs) suffer from lesions during cold storage, depending in part on their ability to counterbalance oxidative stress by activating their antioxidant defence. The aim of this study was to monitor the antioxidant power (AOP) in erythrocyte concentrates (ECs) during cold storage.

MATERIALS AND METHODS

Six ECs were prepared in saline-adenine-glucose-mannitol (SAGM) additive solution and followed during 43 days. The AOP was quantified electrochemically using disposable electrode strips and compared with results obtained from a colorimetric assay. Haematological data, data on haemolysis and the extracellular concentration of uric acid were also recorded. Additionally, a kinetic model was developed to extract quantitative kinetic data on the AOP behaviour.

RESULTS

The AOP of total ECs and their extracellular samples attained a maximum after 1 week of storage prior to decaying and reaching a plateau, as shown by the electrochemical measurements. The observed trend was confirmed with a colorimetric assay. Uric acid had a major contribution to the extracellular AOP. Interestingly, the AOP and uric acid levels were linked to the sex of the donors.

CONCLUSION

The marked increase in AOP during the first week of storage suggests that RBCs are impacted early by the modification of their environment. The AOP behaviour reflects the changes in metabolism activity following the adjustment of the extracellular uric acid level. Knowing the origin, interdonor variability and the effects of the AOP on the RBCs could be beneficial for the storage quality, which will have to be further studied.

Multianalyte Physiological Microanalytical Devices

Advances in scientific instrumentation have allowed experimentalists to evaluate well-known systems in new ways and to gain insight into previously unexplored or poorly understood phenomena. Within the growing field of multianalyte physiometry (MAP), microphysiometers are being developed that are capable of electrochemically measuring changes in the concentration of various metabolites in real time. By simultaneously quantifying multiple analytes, these devices have begun to unravel the complex pathways that govern biological responses to ischemia and oxidative stress while contributing to basic scientific discoveries in bioenergetics and neurology. Patients and clinicians have also benefited from the highly translational nature of MAP, and the continued expansion of the repertoire of analytes that can be measured with multianalyte microphysiometers will undoubtedly play a role in the automation and personalization of medicine. This is perhaps most evident with the recent advent of fully integrated noninvasive sensor arrays that can continuously monitor changes in analytes linked to specific disease states and deliver a therapeutic agent as required without the need for patient action.

A ratiometric nanoprobe consisting of up-conversion nanoparticles functionalized with cobalt oxyhydroxide for detecting and imaging ascorbic acid

A new ratiometric probe based on up-conversion nanoparticles displayed excellent selectivity and pronounced sensitivity in the detection of ascorbic acid.

Electrochemical methods as a tool for determining the antioxidant capacity of food and beverages: A review

The growing interest in functional foods had led to the use of analytical techniques to quantify some properties, among which is the antioxidant capacity (AC). In order to identify and quantify this capacity, some techniques are used, based on synthetic radicals capture; and they are monitored by UV-vis spectrophotometry. Electrochemical techniques are emerging as alternatives, given some of the disadvantages faced by spectrophotometric methods such as the use of expensive reagent not environmentally friendly, undefined reaction time, long sample pretreatment, and low precision and sensitivity. This review focuses on the four most commonly used electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, square wave voltammetry and chronoamperometry). Some of the applications to determine AC in foods and beverages are presented, as well as the correlation between both spectrophotometric and electrochemical techniques that have been reported.

Radical scavenging activity of antioxidants evaluated by means of electrogenerated HO radical

A method is proposed and tested concerning the characterization of antioxidants by means of their reaction with electrogenerated HO radicals in galvanostatic assays with simultaneous O2 evolution, using a Pt anode fairly oxidized. The consumption of a set of species with antioxidant activity, ascorbic acid (AA), caffeic acid (CA), gallic acid (GA) and trolox (T), is described by a first order kinetics. The rate of the processes is limited by the kinetics of reaction with HO radicals and by the kinetics of charge transfer. Information regarding the scavenger activity of antioxidants is obtained by the relative value of the rate constant of the reaction between antioxidants and HO radicals, k(AO,HO)/k(O2). The number of HO radicals scavenged per molecule of antioxidant is also estimated and ranged from 260 (ascorbic acid) to 500 (gallic acid). The method is applied successfully in the characterization of the scavenger activity of ascorbic acid in a green-tea based beverage.

Ultrathin g-C3N4/TiO2composites as photoelectrochemical elements for the real-time evaluation of global antioxidant capacity

Using utg-C₃N₄/TiO₂, a photoelectrochemical platform was designed for the sensing of global antioxidant capacity, which presented a rapid response, and anti-fouling and colour-interference-proof properties.