Graphene derivatives-based electrodes for the electrochemical determination of carbamate pesticides in food products: A review.

Graphene (GR) composites have great potential for the determination of carbamates pesticides (CPs) by electrochemical methods. Since the beginning of the 20th century, GR has shown remarkable promise as electrode material for various sensors. The contamination of food products with harmful CPs is a major problem as they do not always damage human health immediately, but can be harmful after prolonged exposure. A range of advantages can be gained from their electrochemical determination, such as high sensitivity, reasonably selectivity, rapid detection, low limit of detection, and easy electrode fabrication. Furthermore, these electrochemical techniques are robust, reproducible, user-friendly, and conform to both "green" and "white" analytical chemistry. This review is focused on results published in the last ten years in the field of electrochemical determination of CPs in food products using GR and its derivatives.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review.

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

A review of surface-enhanced Raman spectroscopy in pathological processes.

With the continuous growth of the human population and new challenges in the quality of life, it is more important than ever to diagnose diseases and pathologies with high accuracy, sensitivity and in different scenarios from medical implants to the operation room. Although conventional methods of diagnosis revolutionized healthcare, alternative analytical methods are making their way out of academic labs into clinics. In this regard, surface-enhanced Raman spectroscopy (SERS) developed immensely with its capability to achieve single-molecule sensitivity and high-specificity in the last two decades, and now it is well on its way to join the arsenal of physicians. This review discusses how SERS is becoming an essential tool for the clinical investigation of pathologies including inflammation, infections, necrosis/apoptosis, hypoxia, and tumors. We critically discuss the strategies reported so far in nanoparticle assembly, functionalization, non-metallic substrates, colloidal solutions and how these techniques improve SERS characteristics during pathology diagnoses like sensitivity, selectivity, and detection limit. Moreover, it is crucial to introduce the most recent developments and future perspectives of SERS as a biomedical analytical method. We finally discuss the challenges that remain as bottlenecks for a routine SERS implementation in the medical room from in vitro to in vivo applications. The review showcases the adaptability and versatility of SERS to resolve pathological processes by covering various experimental and analytical methods and the specific spectral features and analysis results achieved by these methods.

Quantitative determination of new anti-inflammatory drug indomenthyl and its metabolite in rabbit plasma by HPLC-MS/MS.

Background: Indomenthyl is an innovative anti-inflammatory drug with a high analgesic activity. Indomenthyl releases indomethacin under the influence of neutrophil esterases in the inflammation focus. Methodology/results: This research is aimed at developing a highly sensitive method for the quantitative determination of indomenthyl and its active metabolite indomethacin in rabbit plasma by HPLC-MS/MS. Protein precipitation and extraction with acetonitrile were used for analyte isolation from plasma according to the QuEChERS principle. The target quantitative ion pairs m/z were respectively 496.4 → 358.0 for indomenthyl, 358.0 → 139.5 for indomethacin, and 340.1 → 202.1 for the IS. Conclusion: The calibration curve was linear over the range 0.1-1000 ng mL-1. The technique was applied to the pharmacokinetic study at a dose of 25 mg kg-1 to rabbits.

A Laser Reduced Graphene Oxide Grid Electrode for the Voltammetric Determination of Carbaryl.

Laser-reduced graphene oxide (LRGO) on a polyethylene terephthalate (PET) substrate was prepared in one step to obtain the LRGO grid electrode for sensitive carbaryl determination. The grid form results in a grid distribution of different electrochemically active zones affecting the electroactive substance diffusion towards the electrode surface and increasing the electrochemical sensitivity for carbaryl determination. Carbaryl is electrochemically irreversibly oxidized at the secondary amine moiety of the molecule with the loss of one proton and one electron in the pH range from 5 to 7 by linear scan voltammetry (LSV) on the LRGO grid electrode with a scan rate of 300 mV/s. Some interference of the juice matrix molecules does not significantly affect the LSV oxidation current of carbaryl on the LRGO grid electrode after adsorptive accumulation without applied potential. The LRGO grid electrode can be used for LSV determination of carbaryl in fruit juices in the concentration range from 0.25 to 128 mg/L with LOD of 0.1 mg/L. The fabrication of the LRGO grid electrode opens up possibilities for further inexpensive monitoring of carbaryl in other fruit juices and fruits.

A copper nanoparticle-based electrochemical immunosensor for carbaryl detection.

A hapten-protein conjugate with copper nanoparticles (Hap-Car-BSA@CuNPs) was first synthesized in the present work for the determination of carbaryl. The copper nanoparticles (CuNPs) of the conjugate were used as electrochemical labels in the direct solid-phase competitive determination of carbaryl residues in flour from different crops. The signal was read by linear sweep anodic stripping voltammetry (LSASV) of copper (through the electrochemical stripping of accumulated elemental copper) on a gold-graphite electrode (GGE). To form a recognition receptor layer of monoclonal antibodies against the carbaryl on the surface of the GGE, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 1-hydroxy-2,5-pyrrolidinedione (NHS) were used as the best covalent cross-linkers. The concentrations of the antibodies and the Hap-Car-BSA@CuNPs conjugate were optimized for carbaryl detection by the electrochemical immunosensor. The electrochemical immunosensor can be used for highly sensitive determination of carbaryl residues in flour samples in the concentration range 0.8-32.3 µg·kg-1, with a limit of detection 0.08 µg·kg-1. The present work paves the path for a novel method for monitoring carbaryl in other food products, drinks, and soil samples.

An electrochemical sensor for detecting selenium in biological fluids on an arenediazonium tosylate-modified metal electrode.

This article presents the results on using a new electrochemical sensor modified with arenediazonium salts (MGE-Cu-COOH) to determine selenium in biological fluids (blood serum). It was shown that the sensitivity of the determination of selenite ions using this modified electrode is higher compared to that of the unmodified one (MGE-Cu). The effect of the concentration of arenediazonium tosylates on various substituents was studied, and the conditions for the production of the electrochemical sensor were developed. The surface of the modified electrode was investigated using SEM. The increase in the effective surface area of the electrode was found to be due to the formation of a system of ultramicroelectrodes. In biological samples, the LOD and LOQ of selenium were established at the levels of 0.057 and 0.166 µg l-1, respectively. Finally, the correctness of the results on selenium determination in real samples by the "input-found" method, which correlates well with the known value, was verified.

Label-Free Electrochemical Biosensors for the Determination of Flaviviruses: Dengue, Zika, and Japanese Encephalitis.

A highly effective way to improve prognosis of viral infectious diseases and to determine the outcome of infection is early, fast, simple, and efficient diagnosis of viral pathogens in biological fluids. Among a wide range of viral pathogens, Flaviviruses attract a special attention. Flavivirus genus includes more than 70 viruses, the most familiar being dengue virus (DENV), Zika virus (ZIKV), and Japanese encephalitis virus (JEV). Haemorrhagic and encephalitis diseases are the most common severe consequences of flaviviral infection. Currently, increasing attention is being paid to the development of electrochemical immunological methods for the determination of Flaviviruses. This review critically compares and evaluates recent research progress in electrochemical biosensing of DENV, ZIKV, and JEV without labelling. Specific attention is paid to comparison of detection strategies, electrode materials, and analytical characteristics. The potential of so far developed biosensors is discussed together with an outlook for further development in this field.

Electrochemical immunoassay for the detection of antibodies to tick-borne encephalitis virus by using various types of bioconjugates based on silver nanoparticles.

This work reports for the first time a significantly improved and simplified electrochemical immunoassay to detect antibodies to tick-borne encephalitis virus (TBEV) using a 96-well microtiter plate as a platform for immobilization and silver nanoparticles (AgNPs) as electrochemical labels. The electrochemical assay is performed by detecting the elemental silver oxidation signal where the electroactive signalling silver species are released from the bioconjugates (Ab@AgNP, AbS@AgNP, and ProteinA@AgNP). For this purpose, AgNPs were synthesized and further tagged with biomolecules (antibodies to TBEV, cleaved antibodies to TBEV, and protein A). Signal is read by linear sweep anodic stripping voltammetry (LSASV) of silver ions (through the electrochemical stripping of accumulated elemental silver) on a graphite electrode (GE). AbS@AgNP was chosen as the best option for the new electrochemical immunoassay. The results of electrochemical measurements demonstrated that voltammetric signal increased with the increasing concentration of target antibodies to TBEV within the range from 100 to 1600 IU mL-1, with a detection limit of 90 IU mL-1. To verify the practical application of the novel electrochemical immunosensor, the quantity of immunoglobulins against TBEV in human serum was checked. The results may contribute to the development of alternative methods for monitoring TBEV in biological fluids.

Preparation and Investigation of Silver Nanoparticle⁻Antibody Bioconjugates for Electrochemical Immunoassay of Tick-Borne Encephalitis.

A new simple electrochemical immunosensor approach for the determination of antibodies to tick-borne encephalitis virus (TBEV) in immunological products was developed and tested. The assay is performed by detecting the silver reduction signal in the bioconjugates with antibodies (Ab@AgNP). Here, signal is read by cathodic linear sweep voltammetry (CLSV) through the detection of silver chloride reduction on a gold-carbon composite electrode (GCCE). Covalent immobilization of the antigen on the electrode surface was performed after thiolation and glutarization of the GCCE. Specific attention has been paid to the selection of conditions for stabilizing both the silver nanoparticles and their Ab@AgNP. A simple flocculation test with NaCl was used to select the concentration of antibodies, and the additional stabilizer bovine serum albumin (BSA) was used for Ab@AgNP preparation. The antibodies to TBEV were quantified in the range from 50 IU·mL-1 to 1600 IU·mL-1, with a detection limit of 50 IU·mL-1. The coefficient of determination (r2) is 0.989. The electrochemical immunosensor was successfully applied to check the quality of immunological products containing IgG antibodies to TBEV. The present work paves the path for a novel method for monitoring TBEV in biological fluids.

Flexible plasmonic graphene oxide/heterostructures for dual-channel detection.

Graphene oxide (GO) films are deposited on flexible Kapton substrates and selectively modified to conductive reduced graphene oxide (rGO) electrodes using laser patterning. Based on this, we design, fabricate, and test a flexible sensor integrating laser-reduced GO with silver plasmonic nanostructures. The fabricated device results in dual transduction channels: for electrochemical and plasmonic nanostructure-based surface-enhanced Raman spectroscopy (SERS) detection. The spectroscopic analysis verifying the formation of rGO and the modification by silver nanostructures is performed by Raman, energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The morphological investigation is followed by optical and scanning electron microscopy imaging. In addition to pristine silver nanostructures, the Raman spectroscopy results show the formation of species such as Ag2O, Ag2CO3, and Ag2SOx. A dual-channel sensor device based on electrochemical and plasmonic detection is fabricated as a demonstration of our Ag-rGO flexible concept architecture. The dual-channel device performance is successfully demonstrated in the electrochemical and SERS detection of 4-nitrobenzenethiol (4-NBT) using the same device. Our results show that without Ag nanostructures the sensitivity in the electrochemical and optical channels is not sufficient to detect 4-NBT. The performance and stability of the silver modified device are also verified. This work demonstrates an inexpensive, highly efficient, and greener way that is compatible with solution-processing technology for the production of flexible GO-based electrochemical and SERS detection devices integrated with plasmonic nanostructures.

Electrochemical Oxidability of Antioxidants: Synergism and Antagonism in Mixes.

AIMS: To investigate electrochemical oxidability of antioxidants to reveal synergistic and antagonistic effects in mixes. MATERIALS AND METHODS: Electrochemical oxidability of some widely used antioxidants, including uric acid, glutathione, trolox, ascorbic acid, gallic acid, Mexidol, and potassium fenozan, was investigated by the amperometric approach. RESULTS: All obtained electrochemical oxidability values correlate well with antioxidant activity parameters of the same compounds measured by other methods. The measurements of the electrochemical oxidability for binary mixes of substances were tested to reveal any synergistic actions. The experimental results and calculated values overlap for various combinations of tested mixes. It testifies to the absence of interaction between them (both synergism and antagonism) in the oxidation process. CONCLUSIONS: The constants of oxidation were defined for different antioxidants and mixes by amperometric approach. Most mixes of probed compounds revealed absence of interaction between them in oxidation process. In some cases (mainly with glutathione and ascorbic acid), antagonism takes place, deteriorating effects of their joint application. Apparently, a partial reduction of glutathione by ascorbic acid leads to excess of the measured value over calculated value.

Comparative investigation of antioxidant activity of human serum blood by amperometric, voltammetric and chemiluminescent methods.

INTRODUCTION: A blood test can provide important information about the functional state of the antioxidant system. Malfunction of this system increases the concentration of free radicals and can cause oxidative stress. A difficulty in assessing oxidative stress is the lack of a universal method for determining the antioxidant activity (AOA) of blood components, because of their different nature. MATERIAL AND METHODS: The objects of investigation were sera of 30 male patients with a diagnosis of alcohol dependence syndrome and healthy donors. Comparative investigation of total antioxidant activity (TAA) of human serum blood was carried out by voltammetric (VA), amperometric (AM) and chemiluminescent (HL) methods. RESULTS: All applied methods revealed that serum TAA of the patients with alcoholism is lower than TAA of healthy donors (control group); according to amperometric method the average value of serum TAA was 850 ±210 nA × s, and 660 ±150 nA × s for healthy donors and alcoholics respectively (p < 0.05). Similar trend was revealed by chemiluminescence and voltammetry methods. The results confirm that thiol compounds make a significant contribution to the antioxidant activity of serum. The average thiol concentrations were 0.94 ±0.34 mmol/l and 1.21 ±0.36 mmol/l (p < 0.05) for alcoholics and healthy donors respectively. Decreasing thiol concentration in blood of alcoholics leads to depletion of antioxidant systems of blood. However, the differences between the results of AM, VA and HL methods were significant, because they reflected different aspects of antioxidant activity. CONCLUSIONS: For objective assessment of antioxidant activity of biological objects, we suggest using methods based on different model systems.

Study of total antioxidant activity of human serum blood in the pathology of alcoholism.

The total antioxidant activity (TAA) of human serum blood of patients suffering from alcoholism was tested by cathode voltammetry with a model process of oxygen electroreduction. A known spectrophotometrical method was used for comparison. As results the total antioxidant activity of serum blood of patients with alcoholism was estimated by voltammetry during therapy in hospital. It was shown the TAA of serum blood of patients in pathology before and after treatment is lower than that one of healthy people. However, during the process of 10 days of alcoholism treatment the TAA coefficient increases. The relationship between the coefficient of total antioxidant activity of human serum blood and the stage of treatment was detected.

Study of OH radicals in human serum blood of healthy individuals and those with pathological schizophrenia.

The human body is constantly under attack from free radicals that occur as part of normal cell metabolism, and by exposure to environmental factors such as UV light, cigarette smoke, environmental pollutants and gamma radiation. The resulting "Reactive Oxygen Species" (ROS) circulate freely in the body with access to all organs and tissues, which can have serious repercussions throughout the body. The body possesses a number of mechanisms both to control the production of ROS and to cope with free radicals in order to limit or repair damage to tissues. Overproduction of ROS or insufficient defense mechanisms leads to a dangerous disbalance in the organism. Thereby several pathomechanisms implicated in over 100 human diseases, e.g., cardiovascular disease, cancer, diabetes mellitus, physiological disease, aging, etc., can be induced. Thus, a detailed investigation on the quantity of oxygen radicals, such as hydroxyl radicals (OH(•)) in human serum blood, and its possible correlation with antioxidant therapy effects, is highly topical. The subject of this study was the influence of schizophrenia on the amount of OH(•) in human serum blood. The radicals were detected by fluorimetry, using terephthalic acid as a chemical trap. For all experiments the serum blood of healthy people was used as a control group.