A Graphene Quantum Dots-Hypochlorite Hybrid System for the Quantitative Fluorescent Determination of Total Antioxidant Capacity

Acetazolamide loaded-silver nanoparticles: A potential treatment for murine trichinellosis

Trichinellosis is a global food-borne disease caused by viviparous parasitic nematodes of the genus Trichinella. Due to the lack of effective, safe therapy and the documented adverse effects of traditional therapy, this study aimed to evaluate the therapeutic effect of acetazolamide-loaded silver nanoparticles (AgNPs) on murine trichinellosis. Fifty male Swiss albino mice were divided into five groups of ten mice each: Group I, normal control group; Group II, infected with T. spiralis and not treated; Group III, infected and given AgNPs; Group IV, infected and treated with acetazolamide; and Group V, infected and treated with acetazolamide-loaded AgNPs. Mice were infected orally with 250 larvae. The efficacy was assessed by counting T. spiralis adults and larvae, measuring serum total antioxidant capacity, and observing the histopathological and ultrastructural alterations. Acetazolamide-loaded AgNPs treatment exhibited the highest percentage of reduction (84.72% and 80.74%) for the intestinal adults and the muscular larvae of T. spiralis-infected animals, respectively. Furthermore, during the intestinal and muscular phases, the serum of the same group had the best free-radical scavenging capacity (antioxidant capacity), which reduced tissue damage induced by oxidative stress. Histopathologically, the normal intestinal and muscular architecture was restored in the group treated with acetazolamide-loaded AgNPs, in addition to the reduced inflammatory infiltrate that alleviated inflammation compared to infected animals. Our results confirmed the marked destruction of the ultrastructural features of T. spiralis adults and larvae. Acetazolamide-loaded AgNPs are a promising therapy against T. spiralis infection.

Synthesis of Graphene Quantum Dot Magnesium Hydroxide Nanocomposites and Investigation of Their Antioxidant and Antimicrobial Activities

In this paper, we synthesized graphene quantum dots magnesium hydroxide nanocomposites (GQDs/Mg(OH)₂). The synthesized nanocomposites were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Malvern Zetasizer. The antimicrobial and antioxidant properties of the obtained GQDs/Mg(OH)₂ nanocomposites were investigated. GQDs/Mg(OH)₂ nanocomposites have MIC values of 15.625 μg/mL against fungi (C. metapsilosis and C. parapsilosis) and 62.5 μg/mL against Gram (+) (S. pneumonia and E. faecalis) and Gram (-) (E. coli). The synthesized GQDs/Mg(OH)₂ nanocomposites showed moderate antioxidant activity. The results showed that at 100-µg/mL GQDs/Mg(OH)₂ nanocomposite concentration, the H₂O₂ scavenging activity was 62.18%.

Real-Time Visualization of the Antioxidative Potency of Drugs for the Prevention of Myocardium Ischemia-Reperfusion Injury by a NIR Fluorescent Nanoprobe

The burst of the reactive oxygen species (ROS) is the culprit of myocardial ischemia-reperfusion injury. As direct ROS scavengers, antioxidants are clinically documented drugs for the prevention of reperfusion injury. However, some drugs give disappointing therapeutic performance despite their good in vitro effects. Therefore, in vivo assessments are necessary to screen the antioxidants before clinical trials. However, traditional methods such as histological study require invasive and complicated preprocessing of the biological samples, which may fail to reflect the actual level of the unstable ROS with a very short lifetime. Peroxynitrite (ONOO^-) is a characteristic endogenous ROS produced during reperfusion. Here, we modified the ONOO^--responsive near-infrared fluorescent probe on a myocardium-targeting silica cross-linked micelle to prepare a nanoprobe for the real-time monitoring of ONOO^- during coronary reperfusion. A ROS-stable cyanine dye was co-labeled as an internal reference to achieve ratiometric sensing. The nanoprobe can passively target the infarcted myocardium and monitor the generation of ONOO^- during reperfusion in real-time. The antioxidants, carvedilol, atorvastatin, and resveratrol, were used as model drugs to demonstrate the capability of the nanoprobe to evaluate the antioxidative potency in situ. The drugs were either loaded and delivered by the nanoprobe to compare their in vivo efficacy under similar concentrations or administered intraperitoneally as a free drug to take their pharmacokinetics into account. The imaging results revealed that pharmacokinetics might be the determinant factor that influences the efficacy of the antioxidants.

Fluorescent-based nanosensors for selective detection of a wide range of biological macromolecules: A comprehensive review

Thanks to their unique attributes, such as good sensitivity, selectivity, high surface-to-volume ratio, and versatile optical and electronic properties, fluorescent-based bioprobes have been used to create highly sensitive nanobiosensors to detect various biological and chemical agents. These sensors are superior to other analytical instrumentation techniques like gas chromatography, high-performance liquid chromatography, and capillary electrophoresis for being biodegradable, eco-friendly, and more economical, operational, and cost-effective. Moreover, several reports have also highlighted their application in the early detection of biomarkers associated with drug-induced organ damage such as liver, kidney, or lungs. In the present work, we comprehensively overviewed the electrochemical sensors that employ nanomaterials (nanoparticles/colloids or quantum dots, carbon dots, or nanoscaled metal-organic frameworks, etc.) to detect a variety of biological macromolecules based on fluorescent emission spectra. In addition, the most important mechanisms and methods to sense amino acids, protein, peptides, enzymes, carbohydrates, neurotransmitters, nucleic acids, vitamins, ions, metals, and electrolytes, blood gases, drugs (i.e., anti-inflammatory agents and antibiotics), toxins, alkaloids, antioxidants, cancer biomarkers, urinary metabolites (i.e., urea, uric acid, and creatinine), and pathogenic microorganisms were outlined and compared in terms of their selectivity and sensitivity. Altogether, the small dimensions and capability of these nanosensors for sensitive, label-free, real-time sensing of chemical, biological, and pharmaceutical agents could be used in array-based screening and in-vitro or in-vivo diagnostics. Although fluorescent nanoprobes are widely applied in determining biological macromolecules, unfortunately, they present many challenges and limitations. Efforts must be made to minimize such limitations in utilizing such nanobiosensors with an emphasis on their commercial developments. We believe that the current review can foster the wider incorporation of nanomedicine and will be of particular interest to researchers working on fluorescence technology, material chemistry, coordination polymers, and related research areas.

One-step synthesis of nitrogen-doped multi-emission carbon dots and their fluorescent sensing in HClO and cellular imaging

Tunable multicolor carbon dots (CDs) with a quantum yield reach up to 35% were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. Transmission electron microscopy images reveal that the as-prepared CDs possess a small size distribution below 10 nm with bright blue, green, and yellow color emission, designated as b-CDs, g-CDs, and y-CDs, respectively. The in-depth investigations reveal that the multicolor emission CDs with different fraction displays fluorescence emission wavelength ranges from 398 nm (b-CDs), 525 nm (g-CDs), to 553 nm (y-CDs) which could be well modulated by controlling the amount of heteroatom nitrogen especially amino nitrogen onto their surface structures. Further experiments verify the important role of nitrogen content by using rhodamine solely or substituting urea with sulfur containing compounds as precursors to produce corresponding CDs since the performance is lower than that of urea incorporation. Theoretical calculation results also reveal that the increasing amount of amino nitrogen into their surface structures of b-CDs, g-CDs to y-CDs is responsible for reduced band gaps energy, which result in the redshifted wavelength. Benefiting from the excellent photoluminescence properties, wide pH variation range, high photo stability, and low toxicity, these CDs were employed for HClO sensing at 553 nm within the range 5 to 140 μM with a limit of detection (LOD) of 0.27 ± 0.025 μM (n = 3) and multicolor cellular imaging in HeLa cells. Tunable multicolor carbon dots (CDs) were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. The as-prepared CDs exhibit bright blue, green, and yellow color emission which could be well modulated by controlling the increasing incorporation of heteroatom nitrogen especially amino nitrogen into their surface structures. These CDs were employed for HClO sensing and demonstrated to multicolor cellular imaging in HeLa cells.

An Overview of Optical and Electrochemical Sensors and Biosensors for Analysis of Antioxidants in Food during the Last 5 Years

Antioxidants are a group of healthy substances which are useful to human health because of their antihistaminic, anticancer, anti-inflammatory activity and inhibitory effect on the formation and the actions of reactive oxygen species. Generally, they are phenolic complexes present in plant-derived foods. Due to the valuable nutritional role of these mixtures, analysis and determining their amount in food is of particular importance. In recent years, many attempts have been made to supply uncomplicated, rapid, economical and user-friendly analytical approaches for the on-site detection and antioxidant capacity (AOC) determination of food antioxidants. In this regards, sensors and biosensors are regarded as favorable tools for antioxidant analysis because of their special features like high sensitivity, rapid detection time, ease of use, and ease of miniaturization. In this review, current five-year progresses in different types of optical and electrochemical sensors/biosensors for the analysis of antioxidants in foods are discussed and evaluated well. Moreover, advantages, limitations, and the potential for practical applications of each type of sensors/biosensors have been discussed. This review aims to prove how sensors/biosensors represent reliable alternatives to conventional methods for antioxidant analysis.

Carbon-based nanomaterials for viral infection management

Carbon-based nanomaterials such as graphene and nanodiamonds have demonstrated impressive physical and chemical properties, such as remarkable strength, corrosion resistance, and excellent electrical and thermal conductivity, and stability. Because of these unique characteristics, carbon nanomaterials are explored in a wide range of fields, including the diagnosis and treatment of viruses. As there are emerging concerns about the control of virus including Middle East respiratory syndrome virus (MERS), severe acute respiratory syndrome coronavirus (SARS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), this review highlights the recent development of carbon based-nanomaterials for the management of viral infections.

Colorimetric sensors and nanoprobes for characterizing antioxidant and energetic substances

The development of analytical techniques for antioxidant compounds is important, because antioxidants that can inactivate reactive species and radicals are health-beneficial compounds, also used in the preservation of food and protection of almost every kind of organic substance from oxidation. Energetic substances include explosives, pyrotechnics, propellants and fuels, and their determination at bulk/trace levels is important for the safety and well-being of modern societies exposed to various security threats. Most of the time, in field/on site detection of these important analytes necessitates the use of colorimetric sensors and probes enabling naked-eye detection, or low-cost and easy-to-use fluorometric sensors. The use of nanosensors brings important advantages to this field of analytical chemistry due to their various physico-chemical advantages of increased surface area, surface plasmon resonance absorption of noble metal nanoparticles, and superior enzyme-mimic catalytic properties. Thus, this critical review focuses on the design strategies for colorimetric sensors and nanoprobes in characterizing antioxidant and energetic substances. In this regard, the main themes and properties in optical sensor design are defined and classified. Nanomaterial-based optical sensors/probes are discussed with respect to their mechanisms of operation, namely formation and growth of noble metal nanoparticles, their aggregation and disaggregation, displacement of active constituents by complexation or electrostatic interaction, miscellaneous mechanisms, and the choice of metallic oxide nanoparticles taking part in such formulations.

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.

Antioxidant Activity of Graphene Quantum Dots Prepared in Different Electrolyte Environments

Antioxidants can reduce or inhibit damage such as oxidative decay caused by elevated levels of free radicals. Therefore, pursuing antioxidants with excellent properties has attracted more and more attention. Graphene quantum dots (GQDs) are considered a promising material because of their good free radical scavenging activity, low toxicity, and excellent water solubility. However, their scavenging efficiency, antioxidant mechanism, and effective control methods need to be improved. Herein, in order to further reveal the antioxidant mechanism of GQDs, the role of electrolytes in improving the antioxidant activity of GQDs is explored. In addition, 1,1-diphenyl-2-picrazine (DPPH∙), hydroxyl (∙OH), and superoxide (∙O₂⁻) free radicals are used to evaluate the antioxidant activity of the as-prepared GQDs. Combined with transmission electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and cyclic volt–ampere characteristic curves, the effects of an electrolytic environment on the surface functional groups, charge transfer capability, and defect states of GQDs are obtained. The antioxidant mechanism of GQDs and how to improve their antioxidant activity are further elucidated.

Graphene quantum dots: Synthesis, characterization, cell viability, genotoxicity for biomedical applications

We report the synthesis and applications of a novel N-doped graphene quantum dots (GQDs) using hydrothermal reaction between citric acid and p-aminophenol. The synthesized N-doped GQDs have been characterized physico-chemically and evaluated its antioxidant, antimicrobial, DNA binding and cleavage activities. siRNA loading studies were performed and their effects on cells were evaluated. Obtained results indicate that monodisperse solution of N-doped GQDs has been obtained with particles size ca. ∼10.9 ± 1.3 nm. UV–Vis spectroscopy studies of the interactions between the N-doped GQDs and calf thymus DNA (CT-DNA) showed that the compound interact with CT-DNA via both intercalative and electrostatic binding. The DNA cleavage study showed that the N-doped GQDs cleaved DNA without any external agents. The antioxidant activity of N-doped GQDS was very active when compared to BHT. As the concentration of the compound increased, the antioxidant activity also increased. Cell viability assay demonstrated that the Ndoped GQDs showed cell viability (70%) when the concentration reached 200 μg/mL for A549 and also MDA-MB-231, 150 μg/mL for NIH-3T3 cell lines at 24 h incubation. N-doped GQDs were coated with Eudragit RS 100 and EphA2-siRNA was loaded. As a result of the studies on these formulations, it was concluded that there may be significant effects on A549 cells. The microscopy results revealed that N-doped GQDs was quickly internalized into the cell. Our novel N-doped-GQDs with siRNA are candidate for in situ tumor suppression via DNA and mRNA breakage.

Nanoscaled luminescent terbium metal–organic frameworks for measuring and scavenging reactive oxygen species in living cells

A nanosized Tb-MOF with a boronic acid ligand can be used for the highly sensitive detection and scavenging of ROS in living cells.

Optimizing oxygen functional groups in graphene quantum dots for improved antioxidant mechanism

The development of new antioxidants with quick absorbance of free radicals and excellent biocompatibility has drawn intensive attention in recent years. Graphene quantum dots (GQDs) seemed to be one of the most promising antioxidants because of their appropriate antioxidant activity, unique structure, excellent biocompatibility, and low toxicity. However, the relatively low antioxidant activity in comparison with inorganic semiconductor materials and unclear antioxidant mechanism limited their application in cells. In this paper, we further explored their antioxidant mechanism by focusing on the relationship between antioxidant activity and surface oxygen functional groups. The total oxygen fraction was controlled by post-preparation reduction using NaBH₄ and the type of oxygen functional groups was adjusted by free radicals during the preparation of GQDs. The degree of reduction and content of surface oxygen groups were determined by X-ray photoelectron spectroscopy (XPS), and the antioxidant activity was obtained by scavenging of 1,1-diphenyl-2-picryl-hydrazyl (DPPH˙) and hydroxyl (˙OH) free radicals. Based on the analysis of XPS, Raman, and Fourier-transform infrared (FT-IR) spectra, the relationship between antioxidant activity and the surface oxygen groups of GQDs was obtained, and the antioxidant mechanism of GQDs was revealed with a particular specification of each oxygen group in the antioxidant activity of GQDs, meanwhile, the biocompatibility of GQDs has been demonstrated by cytotoxicity tests. We hope that our results will provide a new insight into a complete antioxidant mechanism of GQDs.

Label-free fluorescence imaging of cytochrome c in living systems and anti-cancer drug screening with nitrogen doped carbon quantum dots

As an important biomarker for the early stage of apoptosis, cytochrome c (Cyt c) has been recognized as a key component of the intrinsic apoptotic pathway. Fluorescence imaging tools enabling detection of Cyt c in apoptotic signaling have been rarely explored, though they are critical for cell biology and clinical theranostics. Here, we designed a novel label-free N-doped carbon dot (N-doped CD)-based nanosensor that enables fluorescence activation imaging of Cyt c release in cell apoptosis. The inner filter effect of Cyt c towards N-doped CDs enabled quantitative Cyt c measurement. The nanosensor exhibited high sensitivity and selectivity, rapid response, good cell-membrane permeability and low cytotoxicity. All these features are favorable for in situ visualization of Cyt c for apoptosis research. Notably, the developed nanosensor was successfully applied to monitor intracellular release of Cyt c, and to visualize Cyt c in living zebrafish for the first time. Moreover, it also provided a viable platform for cell-based screening of apoptosis-inducing compounds. In virtue of these advantages and potential, the developed assay not only holds great significance for the better understanding of certain diseases at the cellular level, but also provides an invaluable platform for apoptotic studies and screening of anti-cancer drugs toward drug development.