Au-Co nanoparticles-embedded N-doped carbon nanotube hollow polyhedron modified electrode for electrochemical determination of quercetin

Development of a Silver-Based MOF Oxidase-Like nanozyme modified with molecularly imprinted polymer for sensitive and selective colorimetric detection of quercetin

Antioxidants are vital components in various food, plant, and pharmacological products, making their quantitative, selective, and straightforward assessment essential for evaluating product quality and health benefits. Nanozymes, such as metal-organic frameworks (MOFs) with enzyme-like catalytic activity, hold significant potential for developing highly efficient antioxidant sensing platforms. This is due to their large specific surface area, low density, high porosity, structural diversity, and adjustable pore size. In this study, we synthesized a silver-based MOF exhibiting effective oxidase-like activity and modified it with molecularly imprinted polymer (MIP) using radical polymerization. The developed system (Ag-MOF@MIP) was successfully applied for the colorimetric detection of quercetin, achieving a limit of detection of 0.43 μM and a limit of quantification of 1 μM within a detection range of 1 to 132 μM. This combination exhibited improved selectivity and sensitivity towards quercetin and demonstrated high stability after one month of storage. This detection strategy can also be used to detect other analytes using TMB as a probe.

Electrochemical Sensors and Biosensors for the Determination of Food Nutritional and Bioactive Compounds: Recent Advances

The significance of food nutrients and bioactive compounds in human health has driven the development of many methods for their determination in different matrices. Among these, electroanalysis has gained popularity due to its cost-effectiveness, rapidity, and, in many cases, portability and minimal sample treatment. This review highlights key advances in electrochemical sensors and biosensors from 2019 to the present. Given the variability and the challenges of managing food matrices, the focus is limited to methods that have been thoroughly assessed for their applicability to real samples. The technical characteristics and analytical performance of the proposed sensors are discussed, along with breakthrough features and future trends.

Surface modification prepared porous copper oxide/(Cu-S)n metal-organic framework/reduced graphene oxide hierarchical structure for highly selective electrochemical quercetin detection

Electrochemical alkalization of (Cu-S)n metal-organic framework (MOF) and graphene oxide ((Cu-S)n MOF/GO) composite yields a new CuO/(Cu-S)n MOF/RGO (reduced GO) composite with porous morphology on screen printed carbon electrode (SPCE) which facilitated the electron transfer properties in electrochemical quercetin (QUE) detection. A selective QUE detection ability has been demonstrated by the constructed electrochemical sensor (CuO/(Cu-S)n MOF/RGO/SPCE), which also has a broad dynamic range of 0.5 to 115 µM in pH 3 by differential pulse voltammetry. The detection limit is 0.083 µM (S/N = 3). In this study, it was  observed that the real samples contained 0.34 mg mL-1 and 27.7 µg g-1 QUE in wine and onion, respectively.

Portable wireless electrochemical sensing of breviscapine using core-shell ZIFs-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra-modified electrode

A core-shell ZIF-67@ZIF-8-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra (Co/C-NCNP) hybrid nanostructure was prepared by a pyrolysis method. The synthesized Co/C-NCNP was modified on the screen-printed carbon electrode and used for the portable wireless sensitive determination of breviscapine (BVC) by differential pulse voltammetry. The Co/C-NCNP had a large surface area and excellent catalytic activity with increasing Co sites to combine with BVC for selective determination, which led to the improvement of the sensitivity of the electrochemical sensor. Under optimized conditions, the constructed sensor had linear ranges from 0.15 to 20.0 µmol/L and 20.0 to 100.0 µmol/L with the limit of detection of 0.014 µmol/L (3S0/S). The sensor was successfully applied to BVC tablet sample analysis with satisfactory results. This work provided the potential applications of zeolitic imidazolate framework-derived nanomaterials in the fabrication of electrochemical sensors for the sensitive detection of drug samples.

A smartphone-based colorimetric assay using Cu-tannic acid nanosheets (Cu-TA NShs) as a laccase-mimicking nanozyme for visual detection of quercetin in vegetables

The interaction of Cu-tannic acid nanosheets (Cu-TA NShs) as nanozyme in a surfactant solution of CTAB under relatively acidic conditions is shown to exhibit a catalytic effect on quercetin (Qur). This catalytic property of Cu-TA NShs, which mimics laccase enzyme with many advantages, has been applied to developing a selective colorimetric sensor for the determination of trace amounts of Qur in vegetable samples. This strategy presents a desirable linear relationship between the absorbance signal intensity and the concentrations of Qur from 0.350 to 32.09 µM with a detection limit (LOD) of 0.064 µM (S/N = 3). The feasibility of the proposed portable colorimetric sensor for in situ analysis of the real samples has been validated with the high-performance liquid chromatography (HPLC) method as reference method, and two-tailed test (t test) statistical analysis certifies good agreement between the results. This enzyme-free and sensitive naked-eye sensor with the smartphone-based color map is promising to provide technical support for the rapid and visual detection of Qur in vegetables.

XRD and Spectroscopic Investigations of ZIF-Microchannel Glass Plates Composites

In this study, new composite materials comprising zeolitic imidazolate framework (ZIF) structures and microchannel glass (MCG) plates were fabricated using the hydrothermal method and their morphological and spectral properties were investigated using XRD, SEM, FTIR, and Raman spectroscopy. XRD studies of powder samples revealed the presence of an additional phase for a ZIF-8 sample, whereas ZIF-67 samples, which were prepared through two different chemical routes, showed no additional phases. A detailed analysis of the FTIR and micro-Raman spectra of the composite samples revealed the formation of stable ZIF structures inside the macropores of the MCG substrate. The hydrophilic nature of the MCG substrate and its interaction with the ZIF structure resulted in the formation of stable ZIF-MCG composites. We believe that these composite materials may find a wide range of important applications in the field of sensors, molecular sieving.

Electrochemical Characterization of the Antioxidant Properties of Medicinal Plants and Products: A Review

Medicinal plants are an important source of bioactive compounds with a wide spectrum of practically useful properties. Various types of antioxidants synthesized in plants are the reasons for their application in medicine, phytotherapy, and aromatherapy. Therefore, reliable, simple, cost-effective, eco-friendly, and rapid methods for the evaluation of antioxidant properties of medicinal plants and products on their basis are required. Electrochemical methods based on electron transfer reactions are promising tools to solve this problem. Total antioxidant parameters and individual antioxidant quantification can be achieved using suitable electrochemical techniques. The analytical capabilities of constant-current coulometry, potentiometry, various types of voltammetry, and chrono methods in the evaluation of total antioxidant parameters of medicinal plants and plant-derived products are presented. The advantages and limitations of methods in comparison to each other and traditional spectroscopic methods are discussed. The possibility to use electrochemical detection of the antioxidants via reactions with oxidants or radicals (N- and O-centered) in solution, with stable radicals immobilized on the electrode surface, via oxidation of antioxidants on a suitable electrode, allows the study of various mechanisms of antioxidant actions occurring in living systems. Attention is also paid to the individual or simultaneous electrochemical determination of antioxidants in medicinal plants using chemically modified electrodes.

Doped metal clusters as bimetallic AuCo nanocatalysts: insights into structural dynamics and correlation with catalytic activity by in situ spectroscopy

Co-doped Au25 nanoclusters with different numbers of doping atoms were synthesized and supported on CeO2. The catalytic properties were studied in the CO oxidation reaction. In all cases, an enhancement in catalytic activity was observed compared to the pure Au25 nanocluster catalyst. Interestingly, a different catalytic performance was obtained depending on the number of Co atoms within the cluster. This was related to the mobility of atoms within the cluster's structure under pretreatment and reaction conditions, resulting in active CoAu nanoalloy sites. The evolution of the doped Au clusters into nanoalloys with well-distributed Co atoms within the Au cluster structure was revealed by combined XAFS, DRIFTS, and XPS studies. Overall, these studies contribute to a better understanding of the dynamics of doped nanoclusters on supports upon pretreatment and reaction, which is key information for the future development and application of bimetallic nanocluster (nanoalloy) catalysts.

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.

Three-dimensional MoS2-graphene aerogel nanocomposites for electrochemical sensing of quercetin

A facile and novel electrochemical sensing platform is reported for quercetin determination with MoS₂ nanoflowers-3D graphene aerogel (3D MoS₂-GA) nanocomposite as signal amplified material. The 3D MoS₂-GA nanocomposite was synthesized through a two-step hydrothermal method, in which MoS₂ nanoflowers were prepared in advance. Characterizations of 3D MoS₂-GA were performed by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The 3D MoS₂-GA-modified glassy carbon electrode (3D MoS₂-GA/GCE) was used to investigate the electrochemical behaviors of quercetin with electrochemical parameters calculated, reaction mechanism discussed, and experimental conditions optimized. Notably, the redox peak current densities of quercetin on 3D MoS₂-GA/GCE raised 5.14 and 6.40 times compared with those on a bare GCE. Furthermore, a novel electroanalytical approach was proposed for the sensitive determination of quercetin within the concentration range 0.01 ~ 5.0 μmol/L, accompanied by a low detection limit of 0.0026 μmol/L (at a working potential of 0.38 V vs. Ag/AgCl). The recovery for practical sample analysis ranges from 97.0 to 105%, and the relative standard deviation is less than 4.2%. This established method shows reliable performance in determination of quercetin in tablets and urine samples.

Gold Nanomaterials-Based Electrochemical Sensors and Biosensors for Phenolic Antioxidants Detection: Recent Advances

Antioxidants play a central role in the development and production of food, cosmetics, and pharmaceuticals, to reduce oxidative processes in the human body. Among them, phenolic antioxidants are considered even more efficient than other antioxidants. They are divided into natural and synthetic. The natural antioxidants are generally found in plants and their synthetic counterparts are generally added as preventing agents of lipid oxidation during the processing and storage of fats, oils, and lipid-containing foods: All of them can exhibit different effects on human health, which are not always beneficial. Because of their relevant bioactivity and importance in several sectors, such as agro-food, pharmaceutical, and cosmetic, it is crucial to have fast and reliable analysis Rmethods available. In this review, different examples of gold nanomaterial-based electrochemical (bio)sensors used for the rapid and selective detection of phenolic compounds are analyzed and discussed, evidencing the important role of gold nanomaterials, and including systems with or without specific recognition elements, such as biomolecules, enzymes, etc. Moreover, a selection of gold nanomaterials involved in the designing of this kind of (bio)sensor is reported and critically analyzed. Finally, advantages, limitations, and potentialities for practical applications of gold nanomaterial-based electrochemical (bio)sensors for detecting phenolic antioxidants are discussed.