Label-free fluorescent detection of Hg2+ has been realized via quenching of fluorescence of graphene oxide (GO). The water-soluble GO sheets, which are functionalized with single-stranded DNA ...aptamer, exhibit strong fluorescence emission at 600nm under the excitation of 488nm in the absence of Hg2+ ions. When Hg2+ ions appear in the aqueous solution, Hg2+ ions are sandwiched between the hairpin-shaped double-stranded DNA due to the formation of the thymine–Hg2+–thymine complex, which holds the Hg2+ ions in proximity to the surface of GO sheets. As a result, the fluorescence emission of GO is quenched. The present GO-based sensor shows a limit of detection as low as 0.92nM and excellent selectivity toward Hg2+ over a wide range of metal ions. The present work indicates that GO is a promising fluorescent probe for detection of metal ions and biomolecules.
► An aptamer-functionalized graphene oxide shows strong fluorescence. ► The quenching of fluorescence of graphene oxide is due to the charge transfer from graphene oxide to Hg(II) ions. ► The label-free sensor fluorescent shows a limit of detection of 0.92nM and excellent selectivity toward Hg(II) ions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Graphene oxide (GO) sheets are mixed with the aptamer-functionalized CdSe/ZnS quantum dots (QDs). Consequently, the aptamer-conjugated QDs bind to the GO sheets to form a GO/aptamer-QD ensemble, ...which enables the energy transfer from the QDs to the GO sheets, quenching the fluorescence of QDs. The GO/aptamer–QD ensemble assay acts as a “turn-on” fluorescent sensor for Pb2+ detection. When Pb2+ ions are present in the assay, the interaction of Pb2+ with the aptamer induces a conformational change in the aptamer, leading to the formation of a G-quadruplex/Pb2+ complex. As a result, the QDs that are linked to the G-quadruplex/Pb2+ complex are detached from the GO sheet, which “turns on” the fluorescence of the QDs. This sensor exhibits a limit of detection of 90pM and excellent selectivity toward Pb2+ over a wide range of metal ions. The experiments have provided direct evidence that the fluorescence of QDs is quenched by GO via the nano-metal surface energy transfer (NSET) mechanism rather than the conventional Förster resonance energy transfer (FRET) process.
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► An ultra-sensitive fluorescent sensor has been developed for lead (II) detection. ► The fluorescence quenching of QDs is due to the nanometal surface energy transfer. ► This sensor exhibits a limit of detection of 90pM and excellent selectivity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Graphene quantum dots (GQDs) are great promising in various applications owing to the quantum confinement and edge effects in addition to their intrinsic properties of graphene, but the preparation ...of the GQDs in bulk scale is challenging. We demonstrated in this work that the micrometer sized graphene oxide (GO) sheets could react with Fenton reagent (Fe2+/Fe3+/H2O2) efficiently under an UV irradiation, and, as a result, the GQDs with periphery carboxylic groups could be generated with mass scale production. Through a variety of techniques including atomic force microscopy, X-ray photoelectron spectroscopy, gas chromatography, ultraperformance liquid chromatography–mass spectrometry, and total organic carbon measurement, the mechanism of the photo-Fenton reaction of GO was elucidated. The photo-Fenton reaction of GO was initiated at the carbon atoms connected with the oxygen containing groups, and C–C bonds were broken subsequently, therefore, the reaction rate depends strongly on the oxidization extent of the GO. Given the simple and efficient nature of the photo-Fenton reaction of GO, this method should provide a new strategy to prepare GQDs in mass scale. As a proof-of-concept experiment, the novel DNA cleavage system using as-generated GQDs was constructed.
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IJS, KILJ, NUK, PNG, UL, UM
Graphene oxide (GO), having a large specific surface area and abundant functional groups, provides an ideal substrate for study enzyme immobilization. We demonstrated that the enzyme immobilization ...on the GO sheets could take place readily without using any cross-linking reagents and additional surface modification. The atomically flat surface enabled us to observe the immobilized enzyme in the native state directly using atomic force microscopy (AFM). Combining the AFM imaging results of the immobilized enzyme molecules and their catalytic activity, we illustrated that the conformation of the immobilized enzyme is mainly determined by interactions of enzyme molecules with the functional groups of GO.
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IJS, KILJ, NUK, PNG, UL, UM
Herein, we report the effects of graphene oxides on human fibroblast cells and mice with the aim of investigating graphene oxides' biocompatibility. The graphene oxides were prepared by the modified ...Hummers method and characterized by high-resolution transmission electron microscope and atomic force microscopy. The human fibroblast cells were cultured with different doses of graphene oxides for day 1 to day 5. Thirty mice divided into three test groups (low, middle, high dose) and one control group were injected with 0.1, 0.25, and 0.4 mg graphene oxides, respectively, and were raised for 1 day, 7 days, and 30 days, respectively. Results showed that the water-soluble graphene oxides were successfully prepared; graphene oxides with dose less than 20 μg/mL did not exhibit toxicity to human fibroblast cells, and the dose of more than 50 μg/mL exhibits obvious cytotoxicity such as decreasing cell adhesion, inducing cell apoptosis, entering into lysosomes, mitochondrion, endoplasm, and cell nucleus. Graphene oxides under low dose (0.1 mg) and middle dose (0.25 mg) did not exhibit obvious toxicity to mice and under high dose (0.4 mg) exhibited chronic toxicity, such as 4/9 mice death and lung granuloma formation, mainly located in lung, liver, spleen, and kidney, almost could not be cleaned by kidney. In conclusion, graphene oxides exhibit dose-dependent toxicity to cells and animals, such as inducing cell apoptosis and lung granuloma formation, and cannot be cleaned by kidney. When graphene oxides are explored for in vivo applications in animal or human body, its biocompatibility must be considered.
Biochemical and biomedical applications of graphene oxide (GO) critically rely on the interaction of biomolecules with it. It has been previously reported that the biological activity of the ...GO–enzyme conjugate decreases due to electrostatic interaction between the enzymes and GO. Herein, the immobilization of horseradish peroxidase (HRP) and oxalate oxidase (OxOx) on chemically reduced graphene oxide (CRGO) are reported. The enzymes can be adsorbed onto CRGO directly with a tenfold higher enzyme loading than that on GO, and maximum enzyme loadings reach 1.3 and 12 mg mg−1 for HRP and OxOx, respectively. Significantly, the more CRGO is reduced, the higher the enzyme loading. The CRGO–HRP conjugates also exhibit higher enzyme activity and stability than GO–HRP. Excellent properties of the CRGO–enzyme conjugates are attributed to hydrophobic interaction between the enzymes and the CRGO. The hydrophobic interaction mode of the CRGO–enzyme conjugates can be applied to other hydrophobic proteins, and thus could dramatically improve the performance of immobilized proteins. The results indicate that CRGO is a potential substrate for efficient enzyme immobilization, and is an ideal candidate as a macromolecule carrier and biosensor.
The enzyme loadings on chemically reduced graphene oxide (CRGO) increase with the hydrophobicity of the CRGO surface, thus suggesting that hydrophobic interaction is a driving force for the enzyme immobilization. These results indicate that CRGO is an ideal candidate as a macromolecule carrier and biosensor.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
This review selectively describes the recent progress in the interactions of proteins (enzymes) and short-chain peptides with graphene and graphene oxide (GO). Particularly, the advances of ...the immobilization mechanisms of enzymes on graphene and GO, the catalytic properties of the immobilized enzymes, and their applications are summarized in detail. The interfacings of the peptides with graphene and GO, the as assembled conjugates, and their potential applications are discussed briefly. The possible ongoing development for the assembly of conjugates of graphene and GO with proteins and peptides in a controlled manner is speculated upon.
Owing to its large capacity and high average potential, the structure and reversible O‐redox compensation mechanism of Na2Mn3O7 have recently been analyzed. However, capacity fade and low coulombic ...efficiency over multiple cycles have also been found to be a problem, which result from oxygen evolution at high charge voltages. Herein, a Na0.44MnO2⋅Na2Mn3O7 heterojunction of primary nanosheets was prepared by a sol‐gel‐assisted high‐temperature sintering method. In the nanodomain regions, the close contact of Na0.44MnO2 not only supplies multidimensional channels to improve the rate performance of the composite, but also plays the role of pillars for enhancing the cycling stability and coulombic efficiency; this is accomplished by suppressing oxygen evolution, which is confirmed by high‐resolution (HR)TEM, cyclic voltammetry, and charge/discharge curves. As the cathode of a Na‐ion battery, at 200 mA g−1 after 100 cycles, the Na0.44MnO2⋅Na2Mn3O7 heterojunction retains an 88 % capacity and the coulombic efficiency approaches 100 % during the cycles. At 1000 mA g−1, the Na0.44MnO2⋅Na2Mn3O7 heterojunction has a discharge capacity of 72 mAh g−1. In addition, the average potential is as high as 2.7 V in the range 1.5–4.6 V. The above good performances indicate that heterojunctions are an effective strategy for addressing oxygen evolution by disturbing the long‐range order distribution of manganese vacancies in the Mn‐O layer.
Pillar of strength: In the heterojunction of primary nanosheets, Na0.44MnO2 plays the role of pillars for suppressing oxygen evolution of Na2Mn3O7 during the sodiation/desodiation process, which allows the composite to display good cycle stability (after 100 cycles, 88 % capacity is maintained) and high coulombic efficiency (approaches 100 % during the cycles).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Composition, morphology, and surface characteristics of solid substrates play critical roles in regulating immobilized enzyme activity. Grapheme oxide (GO), a novel nanostructured material, has been ...illustrated as an ideal enzyme immobilization substrate due to its unique chemical and structural properties. Physical properties and catalytic activity of GO immobilized horseradish peroxidase (HRP) and its application in phenolic compound removal are described in the present study. HRP loading on GO was found to be much higher than that on reported substrates. The GO immobilized HRP showed improved thermal stability and a wide active pH range, attractive for practical applications. The removal of phenolic compounds from aqueous solution using the GO immobilized HRP was explored with seven phenolic compounds as model substrates. The GO immobilized HRP exhibited overall a high removal efficiency to several phenolic compounds in comparison to soluble HRP, especially for 2,4-dimetheoxyphenol and 2-chlorphenol, the latter a major component of industrial wastewater.
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IJS, KILJ, NUK, PNG, UL, UM
Photodynamic therapy (PDT) has emerged as an alternative and promising noninvasive treatment for cancer as well as non-cancer diseases, which involves the uptake of photosensitizers (PSs) by cancer ...cells followed by irradiation. The use of nanomaterials as carriers of PSs is a very promising approach to improve the development of PDT in clinical medicine. In this study, a novel folic acid-conjugated graphene oxide (GO) was strategically designed and prepared as targeting drug delivery system to achieve higher specificity. The second generation photosensitizer (PS) Chlorin e6 (Ce6) was effectively loaded into the system via hydrophobic interactions and π-π stacking. The nanocarriers can significantly increase the accumulation of Ce6 in tumor cells and lead to a remarkable photodynamic efficacy on MGC803 cells upon irradiation. These suggested that folic acid-conjugated GO loaded Ce6 had great potential as effective drug delivery system in targeting PDT.
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