Electrochemical characterization of in situ functionalized gold organosulfur self-assembled monolayer with conducting polymer and carbon nanotubes for determination of rutin

Electrochemistry of Flavonoids: A Comprehensive Review

Flavonoids represent a large group of aromatic amino acids that are extensively disseminated in plants. More than six thousand different flavonoids have been isolated and identified. They are important components of the human diet, presenting a broad spectrum of health benefits, including antibacterial, antiviral, antimicrobial, antineoplastic, anti-mutagenic, anti-inflammatory, anti-allergic, immunomodulatory, vasodilatory and cardioprotective properties. They are now considered indispensable compounds in the healthcare, food, pharmaceutical, cosmetic and biotechnology industries. All flavonoids are electroactive, and a relationship between their electron-transfer properties and radical-scavenging activity has been highlighted. This review seeks to provide a comprehensive overview concerning the electron-transfer reactions in flavonoids, from the point of view of their in-vitro antioxidant mode of action. Flavonoid redox behavior is related to the oxidation of the phenolic hydroxy groups present in their structures. The fundamental principles concerning the redox behavior of flavonoids will be described, and the phenol moiety oxidation pathways and the effect of substituents and experimental conditions on flavonoid electrochemical behavior will be discussed. The final sections will focus on the electroanalysis of flavonoids in natural products and their identification in highly complex matrixes, such as fruits, vegetables, beverages, food supplements, pharmaceutical compounds and human body fluids, relevant for food quality control, nutrition, and healthcare research.

Ultrasensitive Determination of Natural Flavonoid Rutin Using an Electrochemical Sensor Based on Metal-Organic Framework CAU-1/Acidified Carbon Nanotubes Composites

Rutin, a natural flavonol glycoside, is widely present in plants and foods, such as black tea and wheat tea. The antioxidant and anti-inflammatory effects of flavonoids are well known. In this study, a new electrochemical rutin sensor was developed using multiwalled carbon nanotubes/aluminum-based metal-organic frameworks (MWCNT/CAU-1) (CAU-1, a type of Al-MOF) as the electrode modification material. The suspension of multiwalled carbon tubes was dropped on the surface of the GCE electrode to make MWCNT/GCEs, and CAU-1 was then attached to the electrode surface by electrodeposition. MWCNTs and CAU-1 were characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Due to the synergistic effect of CAU-1 and MWCNT-COOH, the prepared sensor showed an ultrasensitive electrochemical response to rutin. Under optimized conditions, the sensor showed a linear relationship between 1.0 × 10^-9~3.0 × 10^-6 M with a detection limit of 6.7 × 10^-10 M (S/N = 3). The sensor also showed satisfactory stability and accuracy in the detection of real samples.

Bioactive Flavonoids: A Comprehensive Review on Pharmacokinetics and Analytical Aspects

Flavonoids are a diversified group of natural substances which were discovered to provide a variety of health benefits in human beings. Vegetables, fruits, wine and tea are the primary flavonoid dietary sources for humans and as the flavonoids are so closely connected to human dietary items and health, it is vital to explore the structural-activity connection. The arrangement, replacement of functional groups, and total number of hydroxyl groups around flavonoid's nucleus structure affect their biological activity, metabolism, and bioavailability. Various flavonoids have been proven to have hepatoprotective properties, that help in the prevention of coronary heart disease. Similarly, these flavonoids also possess anticancer, and anti-inflammatory activities. Flavonoids have been found to have a functional and structural link with their enzyme inhibitory action, that appears to have antiviral effect through acting as antioxidants, damaging cell membranes, blocking enzymes, activating mechanisms of host self-defense, and limiting virus penetration and attaching to cells. Identification, characterization, isolation, and biological role of flavonoids, as well as their uses on health advantages, are all major topics in research and development currently. This review represents a summary of various sources of flavonoids, class, subclass, their chemical structures, biological activities, the pharmacokinetics of flavonoids and various analytical, bioanalytical and electrochemical methods for determination of flavonoids from different matrices.

A Comprehensive Review on the Electrochemical Sensing of Flavonoids

Flavonoids are bioactive polyphenolic compounds, widespread in the plant kingdom. Flavonoids possess broad-spectrum pharmacological effects due to their antioxidant, anti-tumor, anti-neoplastic, anti-mutagenic, anti-microbial, anti-inflammatory, anti-allergic, immunomodulatory, and vasodilatory properties. Care must be taken, since excessive consumption of flavonoids may have adverse effects. Therefore, proper identification, quantification and quality evaluations of flavonoids in edible samples are necessary. Electroanalytical approaches have gained much interest for the analysis of redox behavior and quantification of different flavonoids. Compared to various conventional methods, electrochemical techniques for the analysis of flavonoids offer advantages of high sensitivity, selectivity, low cost, simplicity, biocompatibility, easy on-site evaluation, high accuracy, reproducibility, wide linearity of detection, and low detection limits. This review article focuses on the developments in electrochemical sensing of different flavonoids with emphasis on electrode modification strategies to boost the electrocatalytic activity and analytical efficiency.

A facile fabrication of a hierarchical ZIF-8/MWCNT nanocomposite for the sensitive determination of rutin

In this paper, a novel type of zeolitic imidazolate framework-8 (ZIF-8) polyhedron/multi-walled carbon nanotube (MWCNT) modified electrode was successfully prepared for effective on-site detection of rutin. The morphology and microstructure of the ZIF-8/MWCNT nanocomposite were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The electrochemical performance of the ZIF-8/MWCNT based electrode for the determination of rutin was studied by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPV). The as-prepared sensor illustrates better electrocatalytic activity and lower background current than the MWCNT modified electrode for the oxidation of rutin. Besides, the ZIF-8/MWCNTs sensor offers a remarkable linear response for rutin concentrations from 0.1 to 15 μM. The detection limit (LOD) was calculated to be 0.26 nM (S/N = 3). Also, the ZIF-8/MWCNT electrode showed high anti-interference ability towards common interfering species. More importantly, the fabricated electrode was quickly evaluated for determination of rutin in medicine tablets with satisfactory recoveries and the obtained results successfully achieved good consistency with the data from high performance liquid chromatography (HPLC). Finally, the method shows an enhanced electrocatalytic property and sensitivity for the analysis of rutin, which may provide an economical and promising electrochemical sensor for practical on-site detection of rutin.

Surfactant-free solvothermal synthesis of Cu-MOF via protonation-deprotonation approach: A morphological dependent electrocatalytic activity for therapeutic drugs

A copper-1,4-naphthalenedicarboxylic acid-based organic framework (Cu-NDCA MOF) with different morphologies was synthesized by solvothermal synthetic route via a simple protonation-deprotonation approach. The synthesized Cu-NDCA MOFs were analyzed by diverse microscopic and spectral techniques. The FE-SEM and TEM image results exhibited the flake-like (FL), partial anisotropic (PAT), and anisotropic (AT)-Cu-NDCA MOFs formation obtained at different pH (3.0, 7.0, and 9.0) of the reaction medium. The AT-Cu-NDCA MOF/GC electrode not only increases the electroactive surface area but also boosts the electron transfer rate reaction compared to other modified electrodes (PAT- and FL-Cu-NDCA MOFs/GCEs). Under the optimized conditions, the modified electrode (AT-Cu-NDCA MOF) exhibited a sharp oxidation peak (+ 0.46 V vs. Ag/AgCl) and higher current response for rutin. The electrode provides a wide linear range from 1 × 10^-9 to 50 × 10^-6 M, a low detection limit of 1.21 × 10^-10 M, LOQ of 0.001 μM, and sensitivity of 0.149 μA μM^-1 cm^-2. The AT-Cu-NDCA MOF/GC electrode exhibited good stability (RSD = 3.52 ± 0.02% over 8 days of storage), and excellent reproducibility (RSD = 2.62 ± 0.02% (n = 3)). The modified electrode was applied to the determination of rutin in apple, orange, and lemon samples with good recoveries (99.79-99.91, 99.24-99.69, and 99.53-99.83, respectively). Graphical abstract Anisotropic structure of Cu-NDCA MOFs and its modification on glassy carbon electrode for ultra-sensitive determination of rutin in fruit samples.

Electrochemical Voltammogram Recording for Identifying Varieties of Ornamental Plants

An electrochemical voltammogram recording method for plant variety identification is proposed. Electrochemical voltammograms of Vistula, Andromeda, Danuta, Armandii 'Apple Blossom,' Proteus, Hagley Hybrid, Violet Elizabeth, Kiri Te Kanawa, Regina, and Veronica's Choice were recorded using leaf extracts with two solvents under buffer solutions. The voltametric data recorded under different conditions were derived as scatter plots, 2D density patterns, and hot maps for variety identification. In addition, the voltametric data were further used for genetic relationship studies. The dendrogram deduced from the voltammograms was used as evidence for relationship study. The dendrogram deduced from voltametric data suggested the Andromeda, Danuta, Proteus, Regina, and Hagley Hybrid were closely related, while Violet Elizabeth and Veronica's Choice were closely related. In addition, Vistula and Armandii 'Apple Blossom' could be considered outliers among the varieties.

Application of Electrochemical Sensors Based on Carbon Nanomaterials for Detection of Flavonoids

Flavonoids have a variety of physiological activities such as anti-free radicals, regulating hormone levels, antibacterial factors, and anti-cancer factors, which are widely present in edible and medicinal plants. Real-time detection of flavonoids is a key step in the quality control of diverse matrices closely related to social, economic, and health issues. Traditional detection methods are time-consuming and require expensive equipment and complicated working conditions. Therefore, electrochemical sensors with high sensitivity and fast detection speed have aroused extensive research interest. Carbon nanomaterials are preferred material in improving the performance of electrochemical sensing. In this paper, we review the progress of electrochemical sensors based on carbon nanomaterials including carbon nanotubes, graphene, carbon and graphene quantum dots, mesoporous carbon, and carbon black for detecting flavonoids in food and drug homologous substances in the last four years. In addition, we look forward to the prospects and challenges of this research field.

Electrochemical Detection of Curcumin in Food with a Carbon Nanotube-Carboxymethylcellulose Electrode

Herein, an electrochemical method is presented for the detection of curcumin in food using a carbon nanotube (CNT)-carboxymethylcellulose (CMC) electrode. The CNT-CMC electrode exhibited ideal characteristics for curcumin detection, namely, a high response current and adequate peak separation toward curcumin oxidation. Cyclic voltammetry revealed two oxidation peaks. In the first scan, only the irreversible peak (Peak I) was observed at a higher potential. In the second scan, the reversible redox peak pairs (Peaks II and II') appeared at lower potentials, and the potential of Peak I was decreased. Peak I corresponded to oxidation of the hydroxyl groups of the benzene ring to the catechol group via a phenoxy radical, while Peaks II and II' indicated the redox loop system of the generated catechol group. The current at Peak II was used to quantify the concentration of curcumin in the linear range of 1 - 48 μM and detection limit of 0.084 μM. The concentrations of curcumin determined by the CNT-CMC electrode in real food samples were consistent with those determined by high-performance liquid chromatography.

A magnetic nanocomposite prepared from electrospun CoFe2O4 nanofibers and graphene oxide as a material for highly sensitive determination of rutin

A magnetic bar carbon paste electrode (MBCPE) modified with cobalt ferrite magnetic electrospun nanofibers (NFs) and graphene oxide (GO) is described for the electrochemical determination of rutin. The NFs were prepared by electrospinning using a solution that contains poly(vinyl pyrrolidone) (PVP) and Co(II) and Fe(III) nitrates as metal sources. Carbon paste was prepared by hand mixing GO, CoFe₂O₄ NFs and graphite. This paste was then packed into the end of a glass tube and a very small magnetic bar was inserted into the tube to be coated with the carbon paste to provide a magnetic field. The MBCPE was used to attract the magnetic nanofibers to the electrode surface. Cyclic voltammetry and differential pulse voltammetry techniques were used to study the electrochemical behavior of rutin on the modified MBCPE at pH 2.5. The electrocatalytic current, best measured at a potential of around 0.5 V (vs. Ag/AgCl), varies with the rutin concentration in two linear ranges, viz. from 0.001-0.1 nM and from 1.0-100 nM, with a 0.94 pM detection limit. The electrode was successfully applied to the determination of rutin in lemon, red apple, lime and orange juices. Graphical abstractSchematic representation of a modified magnetic bar carbon paste electrode for detection of rutin. To achieve the modified electrode, electrospun CoFe₂O₄ nanofibers, graphene oxide and a very small magnetic bar are packed into the end of a glass tube.

Recent developments in conducting polymers: applications for electrochemistry

Scientists have categorized conductive polymers as materials having strongly reversible redox behavior and uncommon combined features of plastics and metal. Because of their multifunctional characteristics, e.g., simplistic synthesis, acceptable environmental stability, beneficial optical, electronic, and mechanical features, researchers have largely considered them for diverse applications. Therefore, their capability of catalyzing several electrode reactions has been introduced as one of their significant features. A thin layer of the conducting polymer deposited on the substrate electrode surface can augment the electrode process kinetics of several solution species. Such electrocatalytic procedures with modified conducting polymer electrodes can create beneficial utilization in diverse fields of applied electrochemistry. This review article explores typical recent applications of conductive polymers (2016–2020) as active electrode materials for energy storage applications, electrochemical sensing, and conversion fields such as electrochemical supercapacitors, lithium-ion batteries, fuel cells, and solar cells.

Scientists have categorized conductive polymers as materials having strongly reversible redox behavior and uncommon combined features of plastics and metal.

Highly sensitive simultaneous electrochemical determination of myricetin and rutin via solid phase extraction on a ternary Pt@r-GO@MWCNTs nanocomposite

The simultaneous electrochemical determination of myricetin and rutin remains a challenge due to their indistinguishable potentials. To solve this problem, we constructed a ternary platinum nanoparticle, reduced graphene oxide, multi-walled carbon nanotubes (Pt@r-GO@MWCNTs) nanocomposite via a facile one-pot synthetic method. Under the optimized conditions, the ternary Pt@r-GO@MWCNTs nanocomposite exhibited good electrocatalytic activity toward myricetin and rutin via solid phase extraction and excellent performance for the simultaneous determination of myricetin and rutin. The oxidation peak current of myricetin was proportional to its concentrations in the range of 0.05–50 μM with a detection limit of 0.01 μM (S/N = 3). The linear range for rutin was 0.05–50 μM with a detection limit of 0.005 μM (S/N = 3). The ternary nanocomposite sensor also exhibited good reproducibility and stability, and was successfully used for the simultaneous determination of myricetin and rutin in real orange juice samples with recoveries ranging between 100.57% and 108.46%.

Label-free detection of pepsinogen 1 and 2 by polyethylene coating Lamb microfluidic device

Early screening of gastric cancer is a critical importance for the improvement of patients' survival rate. Here, a polyethylene coating Lamb (PE-Lamb) microfluidic device with immune layer for gastric cancer label-free detection was constructed. Two serum pepsinogen 1 (PG1) and pepsinogen 2 (PG2) biomarkers were applied to screen and predict the appearance of gastric cancer. Compared with enzyme-linked immunosorbent assay (ELISA), this method achieved a higher sensitivity and less time (40 min vs 120 min). The limit of detections (LOD) were reached 60 pg/mL for PG1 and 30 pg/mL for PG2, which have two orders of magnitude lower than traditional ELISA. The linearity coefficient indexes (R²) for PG1 and PG2 were 0.992 and 0.953 respectively, which is similar to that of ELISA. In addition, PG1 and PG2 mixed antigens sample with human serum was detected by PE-Lamb approach, and the frequency response showed high reproducibility and specificity. The results indicate that PE-lamb diagnostic technique is a novel and promising method for high-throughput screening and early diagnosis of gastric cancer.

Electrochemistry Study of Permselectivity and Interfacial Electron Transfers of a Branch-Tailed Fluorosurfactant Self-Assembled Monolayer on Gold

We investigated the permselectivity and interfacial electron transfers of an amphiphilic branch-tailed fluorosurfactant self-assembled monolayer (FS-SAM) on a gold electrode by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The FS-SAM was prepared by a self-assembly technique and a "click" reaction. The barrier property and interfacial electron transfers of the FS-SAM were also evaluated using various probes with different features. The FS-SAM allowed a higher degree of permeation by small hydrophilic (Cl^- and F^-) electrolyte ions than large hydrophobic (ClO₄^- and PF₆^-) ones. Meanwhile, the redox reaction of the Fe(CN)₆^3- couple was nearly completely blocked by the FS-SAM, whereas the electron transfer of Ru(NH₃)₆³⁺ was easier than that of Fe(CN)₆^3-, which may be due to the underlying tunneling mechanism. For hydrophobic dopamine, the hydrophobic bonding between the FS-SAM exterior fluoroalkyl moieties and the hydrophobic probes, as well as the hydration resistance from the interior hydration shell around the oligo (ethylene glycol) moieties, hindered the transport of hydrophobic probes into the FS-SAM. These results may have profound implications for understanding the permselectivity and electron transfers of amphiphilic surfaces consisting of molecules containing aromatic groups and branch-tailed fluorosurfactants in their structures.

Palladium Supported on an Amphiphilic Triazine-Urea-Functionalized Porous Organic Polymer as a Highly Efficient Electrocatalyst for Electrochemical Sensing of Rutin in Human Plasma

Metal nanoparticle-containing porous organic polymers have gained great interest in chemical and pharmaceutical applications owing to their high reactivity and good recyclability. In the present work, a palladium nanoparticle-decorated triazine-urea-based porous organic polymer (Pd@TU-POP) was designed and synthesized using 1,3-bis(4-aminophenyl)urea with cyanuric chloride and palladium acetate. The porous structure and physicochemical properties of the electrode material Pd@TU-POP were observed using a range of standard techniques. The Pd@TU-POP material on the electrode surface showed superior sensing ability for rutin (RT) because the Pd dispersion facilitated the electrocatalytic performance of TU-POP by reducing the overpotential of RT oxidation dramatically and improving the stability significantly. Furthermore, TU-POP provides excellent structural features for loading Pd nanoparticles, and the resulting Pd@TU-POP exhibited enhanced electron transfer and outstanding sensing capability in a linear range between 2 and 200 pM having a low detection value of 5.92 × 10^-12 M (S/N = 3). The abundant porous structure of Pd@TU-POP not only provides electron transport channels for RT diffusion but also offers a facile route for quantification sensing of RT with satisfactory recoveries in aqueous electrolyte containing human plasma and red wine. These data reveal that the synthetic Pd@TU-POP is an excellent potential platform for the detection of RT in biological samples.