Sensitive Electrochemical Detection of Caffeic Acid in Wine Based on Fluorine-Doped Graphene Oxide

Fluorinated photoreduced graphene oxide with semi-ionic C-F bonds: An effective carbon based photocatalyst for the removal of volatile organic compounds

There is much interest in developing metal-free halogenated graphene such as fluorinated graphene for various catalytic applications. In this work, a fluorine-doped graphene oxide photocatalyst was investigated for photocatalytic oxidation (PCO) of a volatile organic compound (VOC), namely gaseous methanol. The fluorination process of graphene oxide (GO) was carried out via a novel and facile solution-based photoirradiation method. The fluorine atoms were doped on the surface of the GO in a semi-ionic C-F bond configuration. This presence of the semi-ionic C-F bonds induced a dramatic 7-fold increment of the hole charge carrier density of the photocatalyst. The fluorinated GO photocatalyst exhibited excellent photodegradation up to 93.5% or 0.493 h-1 according pseudo-first order kinetics for methanol. In addition, 91.7% of methanol was mineralized into harmless carbon dioxide (CO2) under UV-A irradiation. Furthermore, the photocatalyst demonstrated good stability in five cycles of methanol PCO. Besides methanol, other VOCs such as acetone and formaldehyde were also photodegraded. This work reveals the potential of fluorination in producing effective graphene-based photocatalyst for VOC removal.

In situ engineering of Au-Ag alloy embedded PEDOT nanohybrids at a solvent/non-solvent interface for the electrochemical enzyme-free detection of histamine

Steadfast efforts have been made to develop novel materials and incorporate them into functional devices for practical applications, pushing the research on electroactive materials to the forefront of nano electronics. Liquid/liquid interface-assisted polymerization offers a scalable methodology to fabricate hybrid materials with multifunctional applications, in contrast to the conventional and ubiquitous routes. Here, we explored this efficient and versatile approach toward the in situ tailoring of Au-Ag alloy nanostructures with a conducting polymer, poly(3,4-ethylene-dioxythiophene) (PEDOT). With the appropriate choice of organic and inorganic phases for the distribution of monomer and oxidant, the miscibility restraints of the reactants in a single phase were alleviated. Effective nanostructure tuning of highly crystalline and electroactive PEDOT/Au-Ag alloy has been achieved by varying the molar ratio of Au³⁺/Ag⁺ in the reaction mixture. The as-synthesized composite is further explored to detect neuromodulator histamine (HA), which displays high sensitivity with a limit of detection (LOD) of 1.5 nM, and selectivity even in the presence of various interfering analogs of 10-fold concentration. Subsequently, density functional theory (DFT) simulations are employed to assess the mode of interaction between HA and the electroactive surfaces. The competency to detect HA in preserved food entails its potential in food spoilage monitoring. Furthermore, the detection of histamine generated by sub-cultured human neuronal cells SH-SY5Y proves its practical viability in health monitoring devices.

Multi-Layer Biosensor for Pre-Symptomatic Detection of Puccinia strifformis, the Causal Agent of Yellow Rust

The yellow rust of wheat (caused by Puccinia striiformis f. sp. tritici) is a devastating fungal infection that is responsible for significant wheat yield losses. The main challenge with the detection of this disease is that it can only be visually detected on the leaf surface between 7 and 10 days after infection, and by this point, counter measures such as the use of fungicides are generally less effective. The hypothesis of this study is to develop and use a compact electrochemical-based biosensor for the early detection of P. striiformis, thus enabling fast countermeasures to be taken. The biosensor that was developed consists of three layers. The first layer mimics the wheat leaf surface morphology. The second layer consists of a sucrose/agar mixture that acts as a substrate and contains a wheat-derived terpene volatile organic compound that stimulates the germination and growth of the spores of the yellow rust pathogen P. s. f. sp. tritici. The third layer consists of a nonenzymatic glucose sensor that produces a signal once invertase is produced by P. striiformis, which comes into contact with the second layer, thereby converting sucrose to glucose. The results show the proof that this innovative biosensor can enable the detection of yellow rust spores in 72 h.

Eco-friendly synthesis of sulphur-doped graphenes with applicability in caffeic acid electrochemical assay

A new electrode based on glassy carbon modified with a sulphur-doped graphene material was successfully developed and applied for caffeic acid (CA) voltammetric detection and quantification. The structural features of sulphur-doped graphene (exfGR-S) characterized by different physicochemical and analytical techniques are presented. Cyclic voltammetry (CV) technique was employed to evaluate the electrochemical behavior of both bare glassy carbon (GCE) and modified GCE/exfGr-S electrodes towards CA oxidation. The study revealed that the modified electrode exhibits superior electrochemical performances compared to the bare electrode, with a broad CA detecting range (from 0.1 to 100.0 µM), a low detection limit 3.03 × 10^-8 M), excellent anti-interference capabilities, as well as good stability and repeatability. The developed electrochemical sensor appears to be a promising candidate for real sample quality control analysis since it successfully displayed its ability to directly detect CA in commercially available coffee product without any pretreatment.

Nanomaterials-based electrochemical sensors for the detection of natural antioxidants in food and biological samples: research progress

Antioxidants are healthy substances that are beneficial to the human body and exist mainly in natural and synthetic forms. Among many kinds of antioxidants, the natural antioxidants have great applications in many fields such as food chemistry, medical care, and clinical application. In recent years, many efforts have been made for the determination of natural antioxidants. Nano-electrochemical sensors combining electrochemistry and nanotechnology have been widely used in the determination of natural antioxidants due to their unique advantages. Therefore, a large number of nanomaterials such as metal oxide, carbon materials, and conducting polymer have attracted much attention in the field of electrochemical sensors due to their good catalytic effect and stable performance. This review mainly introduces the construction of electrochemical sensors based on different nanomaterials, such as metallic nanomaterials, metal oxide nanomaterials, carbon nanomaterials, metal-organic frameworks, polymer nanomaterials, and other nanocomposites, and their application to the detection of natural antioxidants, including ascorbic acid, phenolic acids, flavonoid, tryptophan, citric acid, and other natural antioxidants. In the end, the limitations of the existing nano-sensing technology, the latest development trend, and the application prospect for various natural antioxidant substances are summarized and analyzed. We expect that this review will be helpful to researchers engaged in electrochemical sensors.

Electrochemical Sensing of Vanillin Based on Fluorine-Doped Reduced Graphene Oxide Decorated with Gold Nanoparticles

4-hydroxy-3-methoxybenzaldehyde (vanillin) is a biophenol compound that is relatively abundant in the world’s most popular flavoring ingredient, natural vanilla. As a powerful antioxidant chemical with beneficial antimicrobial properties, vanillin is not only used as a flavoring agent in food, beverages, perfumery, and pharmaceutical products, it may also be employed as a food-preserving agent, and to fight against yeast and molds. The widespread use of vanilla in major industries warrants the need to develop simple and cost-effective strategies for the quantitative determination of its major component, vanillin. Herein, we explore the applications of a selective and sensitive electrochemical sensor (Au electrodeposited on a fluorine-doped reduced-graphene-oxide-modified glassy-carbon electrode (Au/F-rGO/GCE)) for the detection of vanillin. The electrochemical performance and analytical capabilities of this novel electrochemical sensor were investigated using electrochemical techniques including cyclic voltammetry and differential pulse voltammetry. The excellent sensitivity, selectivity, and reproducibility of the proposed electrochemical sensor may be attributed to the high conductivity and surface area of the formed nanocomposite. The high performance of the sensor developed in the present study was further demonstrated with real-sample analysis.

Sensitive electrochemical detection of metabisulphite in gastrointestinal fluids

Electrochemical detection of metabisulphite in simulated gastrointestinal fluids.

Electrochemical paraquat sensor based on lead oxide nanoparticles

1,1-Dimethyl-4,4-bipyridinium dichloride known as paraquat is a popular well-known herbicide that is widely used in agriculture around the world. However, paraquat is a highly toxic chemical causing damage to vital organs including the respiratory system, liver, heart, and kidneys and death. Therefore, detection of paraquat is still necessary to protect life and the environment. In this work, an electrochemical sensor based on lead oxide nanoparticles (PbO-NPs) modified on a screen-printed silver working electrode (SPE) has been fabricated for paraquat detection at room temperature. The PbO-NPs have been synthesized by using a sparking method via two Pb metal wires. The electrochemical paraquat sensors have been prepared by a simple drop-casting of PbO-NPs solution on the surface of the SPE. The PbO-NPs/SPE sensor exhibits a linear response in the range from 1 mM to 5 mM with good reproducibility and high sensitivity (204.85 μA mM⁻¹ cm⁻²) for paraquat detection at room temperature. The PbO-NPs/SPE sensor shows high selectivity to paraquat over other popular herbicides such as glyphosate, glufosinate-ammonium and butachlor-propanil. The application of the PbO-NPs/SPE sensor is also demonstrated via the monitoring of paraquat contamination in juice and milk.

The PbO nanoparticles-based electrochemical sensor can be integrated into a smartphone for on-site field testing of paraquat with high sensitivity and selectivity.

The Importance of Developing Electrochemical Sensors Based on Molecularly Imprinted Polymers for a Rapid Detection of Antioxidants

This review aims to pin out the importance of developing a technique for rapid detection of antioxidants, based on molecular imprinting techniques. It covers three major areas that have made great progress over the years in the field of research, namely: antioxidants characterization, molecular imprinting and electrochemistry, alone or combined. It also reveals the importance of bringing these three areas together for a good evaluation of antioxidants in a simple or complex medium, based on selectivity and specificity. Although numerous studies have associated antioxidants with molecular imprinting, or antioxidants with electrochemistry, but even electrochemistry with molecular imprinting to valorize different compounds, the growing prominence of antioxidants in the food, medical, and paramedical sectors deserves to combine the three areas, which may lead to innovative industrial applications with satisfactory results for both manufacturers and consumers.

Preparation and Applications of Fluorinated Graphenes

The present review focuses on the numerous routes for the preparation of fluorinated graphene (FG) according to the starting materials. Two strategies are considered: (i) addition of fluorine atoms on graphenes of various nature and quality and (ii) exfoliation of graphite fluoride. Chemical bonding in fluorinated graphene, related properties and a selection of applications for lubrication, energy storage, and gas sensing will then be discussed.

Nanomaterials in Electrochemical Sensing Area: Applications and Challenges in Food Analysis

Recently, nanomaterials have received increasing attention due to their unique physical and chemical properties, which make them of considerable interest for applications in many fields, such as biotechnology, optics, electronics, and catalysis. The development of nanomaterials has proven fundamental for the development of smart electrochemical sensors to be used in different application fields such, as biomedical, environmental, and food analysis. In fact, they showed high performances in terms of sensitivity and selectivity. In this report, we present a survey of the application of different nanomaterials and nanocomposites with tailored morphological properties as sensing platforms for food analysis. Particular attention has been devoted to the sensors developed with nanomaterials such as carbon-based nanomaterials, metallic nanomaterials, and related nanocomposites. Finally, several examples of sensors for the detection of some analytes present in food and beverages, such as some hydroxycinnamic acids (caffeic acid, chlorogenic acid, and rosmarinic acid), caffeine (CAF), ascorbic acid (AA), and nitrite are reported and evidenced.

Voltamperometric Sensors and Biosensors Based on Carbon Nanomaterials Used for Detecting Caffeic Acid-A Review

Caffeic acid is one of the most important hydroxycinnamic acids found in various foods and plant products. It has multiple beneficial effects in the human body such as antioxidant, antibacterial, anti-inflammatory, and antineoplastic. Since overdoses of caffeic acid may have negative effects, the quality and quantity of this acid in foods, pharmaceuticals, food supplements, etc., needs to be accurately determined. The present paper analyzes the most representative scientific papers published mostly in the last 10 years which describe the development and characterization of voltamperometric sensors or biosensors based on carbon nanomaterials and/or enzyme commonly used for detecting caffeic acid and a series of methods which may improve the performance characteristics of such sensors.

Effect of surface properties on the electrochemical response of cynarin by electro-synthesized functionalized-polybithiophene/MWCNT/GNP

Cynarin is one of the biologically active functional components present a wide range of pharmacological applications. Herein, we reported the fabrication and surface properties investigation of a new highly sensitive electrochemical sensor for the detection of cynarin. The electrochemical sensors were fabricated in several steps; the first being the synthesis of bi-thiophene derivatives-based monomers 3,3'-bithiophen (M1); 2-methoxy-5-carbaldehyde-[3,3'-bithiophene] (M2) and 2-((2-methoxy-[3,3'-bithiophen]-5-yl)methylene)malononitrile) (M3) followed by electrochemical polymerization on a glassy carbon electrode after which multi-walled carbon nanotube (MWCNT) and gold nanoparticles (GNP's) were electrodeposited layer-by-layer on the polymer coating to obtain multilayer electrochemical sensors. The morphological properties of the formed polymers were evaluated using SEM analysis and the apparent contact angles to preview the changes in surface properties after the functionalization of monomers and therefore their effects on the detection of cynarin. Analytical parameters such as the accumulation time and pH of the PBS solution which influence the sensitivity of the electrochemical sensors were optimized. Under the optimal conditions the GCE/P3/MWCNT/GNP's showed a wide range of analyte concentrations (1 to 100 μM and 0.01 to 1 μM) and detection limit of 0.0095 using pulse differential voltammetry. In addition, the electrochemical sensors showed good reproducibility, stability and selectivity and they were used successfully for the determination of cynarin in real solutions.

Biosensors and Sensing Systems for Rapid Analysis of Phenolic Compounds from Plants: A Comprehensive Review

Phenolic compounds are secondary metabolites frequently found in plants that exhibit many different effects on human health. Because of the relevant bioactivity, their identification and quantification in agro-food matrices as well as in biological samples are a fundamental issue in the field of quality control of food and food supplements, and clinical analysis. In this review, a critical selection of sensors and biosensors for rapid and selective detection of phenolic compounds is discussed. Sensors based on electrochemistry, photoelectrochemistry, fluorescence, and colorimetry are discussed including devices with or without specific recognition elements, such as biomolecules, enzymes and molecularly imprinted materials. Systems that have been tested on real matrices are prevalently considered but also techniques that show potential development in the field.

Electrochemical Sodium Ion Sensor Based on Silver Nanoparticles/Graphene Oxide Nanocomposite for Food Application

High sodium ion (Na+) consumption leads to high blood pressure which causes many health issues. Real-time determination of Na+ content in food is still important to limit Na+ intake and control the taste of food. In this work, we have developed an electrochemical sensor based on agglomeration of silver nanoparticles (AgNPs) and graphene oxide (GO) modified on a screen-printed silver electrode (SPE) for Na+ detection at room temperature by using cyclic voltammetry (CV). The AgNPs were synthesized through a simple green route using Pistia stratiotes extract as a reducing agent under blue light illumination and mixed with the GO to be a Na+ selective sensing nanocomposite. The AgNPs/GO/SPE sensor showed high sensitivity (0.269 mA/mM/cm2), high selectivity, linear relationship (0–100 mM), good stability, and excellent reproducibility to Na+ detection as well as low limit of detection (9.344 mM) for food application. The interfering species such as K+, Zn2+, Na+, Mg2+, glucose, and ascorbic acid did not have any influence on the Na+ determination. The AgNPs/GO/SPE sensor was successfully applied to determine Na+ in real samples such as fish sauce and seasoning powder of instant noodle.

Synthesis and Electrochemical Study of Three-Dimensional Graphene-Based Nanomaterials for Energy Applications

Graphene is an attractive soft material for various applications due to its unique and exclusive properties. The processing and preservation of 2D graphene at large scales is challenging due to its inherent propensity for layer restacking. Three-dimensional graphene-based nanomaterials (3D-GNMs) preserve their structures while improving processability along with providing enhanced characteristics, which exhibit some notable advantages over 2D graphene. This feature article presents recent trends in the fabrication and characterization of 3D-GNMs toward the study of their morphologies, structures, functional groups, and chemical compositions using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Owing to the attractive properties of 3D-GNMs, which include high surface areas, porous structures, improved electrical conductivity, high mechanical strength, and robust structures, they have generated tremendous interest for various applications such as energy storage, sensors, and energy conversion. This article summarizes the most recent advances in electrochemical applications of 3D-GNMs, pertaining to energy storage, where they can serve as supercapacitor electrode materials and energy conversion as oxygen reduction reaction catalysts, along with an outlook.

Voltammetric Sensors Based on Nanomaterials for Detection of Caffeic Acid in Food Supplements

Caffeic acid may be accurately detected in food supplements by using cyclic voltammetry and carbon screen-printed sensors modified with various nanomaterials. Sensor characterization by cyclic voltammetry in reference solutions has shown that carbon nanotubes or carbon nanofibers significantly improve the sensor response in terms of sensitivity and reversibility. Screen-printed sensors were then used in order to study the electrochemical behavior of caffeic acid in aqueous solution at pH 3.6. A redox process was observed in all cases, which corresponds to a reversible redox process involving the transfer of two electrons and two protons. The role of nanomaterials in the increment of sensor performance characteristics was evidenced. Calibration curves were developed for each sensor, and the detection (LOD) and quantification (LOQ) limits were calculated. Low LOD and LOQ values were obtained, in the 10−7 to 10−9 M range, which demonstrates that the method is feasible for quantification of caffeic acid in real samples. Caffeic acid was quantitatively determined in three food supplements using the most sensitive sensor, namely the carbon nanofiber sensor. The Folin–Ciocalteu spectrophotometric assay was used to validate the results obtained with the sensor. The results obtained by using the voltammetric method were consistent with those obtained by using the spectrophotometric method, with no statistically significant differences between the results obtained at 95% confidence level.

Heteroatom-doped graphene as sensing materials: a mini review

Graphene is one of the astounding recent advancements in current science and one of the most encouraging materials for application in cutting-edge electronic gadgets. Graphene and its derivatives like graphene oxide and reduced graphene oxide have emerged as significant nanomaterials in the area of sensors. Furthermore, doping of graphene and its derivatives with heteroatoms (B, N, P, S, I, Br, Cl and F) alters their electronic and chemical properties which are best suited for the construction of economical sensors of practical utility. This review recapitulates the developments in graphene materials as emerging electrochemical, ultrasensitive explosive, gas, glucose and biological sensors for various molecules with greater sensitivity, selectivity and a low limit of detection. Apart from the most important turn of events, the properties and incipient utilization of the ever evolving family of heteroatom-doped graphene are also discussed. This review article encompasses a wide range of heteroatom-doped graphene materials as sensors for the detection of NH₃, NO₂, H₂O₂, heavy metal ions, dopamine, bleomycinsulphate, acetaminophen, caffeic acid, chloramphenicol and trinitrotoluene. In addition, heteroatom-doped graphene materials were also explored for sensitivity and selectivity with respect to interfering analytes present in the system. Finally, the review article concludes with future perspectives for the advancement of heteroatom-doped graphene materials.

Graphene is one of the astounding recent advancements in current science and one of the most encouraging materials for application in cutting-edge electronic gadgets.

Progress in Electrochemical (Bio)Sensors for Monitoring Wine Production

Electrochemical sensors and biosensors have been proposed as fast and cost effective analytical tools, meeting the robustness and performance requirements for industrial process monitoring. In wine production, electrochemical biosensors have proven useful for monitoring critical parameters related to alcoholic fermentation (AF), malolactic fermentation (MLF), determining the impact of the various technological steps and treatments on wine quality, or assessing the differences due to wine age, grape variety, vineyard or geographical region. This review summarizes the current information on the voltamperometric biosensors developed for monitoring wine production with a focus on sensing concepts tested in industry-like settings and on the main quality parameters such as glucose, alcohol, malic and lactic acids, phenolic compounds and allergens. Recent progress featuring nanomaterial-enabled enhancement of sensor performance and applications based on screen-printed electrodes is emphasized. A case study presents the monitoring of alcoholic fermentation based on commercial biosensors adapted with minimal method development for the detection of glucose and phenolic compounds in wine and included in an automated monitoring system. The current challenges and perspectives for the wider application of electrochemical sensors in monitoring industrial processes such as wine production are discussed.

Deep Learning for Industrial Computer Vision Quality Control in the Printing Industry 4.0

Rapid and accurate industrial inspection to ensure the highest quality standards at a competitive price is one of the biggest challenges in the manufacturing industry. This paper shows an application of how a Deep Learning soft sensor application can be combined with a high-resolution optical quality control camera to increase the accuracy and reduce the cost of an industrial visual inspection process in the Printing Industry 4.0. During the process of producing gravure cylinders, mistakes like holes in the printing cylinder are inevitable. In order to improve the defect detection performance and reduce quality inspection costs by process automation, this paper proposes a deep neural network (DNN) soft sensor that compares the scanned surface to the used engraving file and performs an automatic quality control process by learning features through exposure to training data. The DNN sensor developed achieved a fully automated classification accuracy rate of 98.4%. Further research aims to use these results to three ends. Firstly, to predict the amount of errors a cylinder has, to further support the human operation by showing the error probability to the operator, and finally to decide autonomously about product quality without human involvement.