Single-layer Graphene Oxide Sheets Research Articles

Enhancing Radiosensitization of Non-Small Cell Lung Cancer with Graphene Oxide@AgPt Nanocomposites: A Bioinformatics Study

In this study, we employed bioinformatics techniques to investigate the radiosensitization mechanisms of graphene oxide (GO) and silver-platinum (AgPt) nanocomposites (NCs) on microRNAs (miRNAs) in non-small cell lung cancer (NSCLC). The GO@AgPt nanocomposites were synthesized through a hydrothermal method involving graphene oxide. Characterization and structural analysis were performed using transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Our experimental model was A549 cells, categorized into three groups: the blank group, control group, and GO@AgPt group. The blank group remained untreated, while the control group was exposed to 4Gy X-ray irradiation. The GO@AgPt group received 15 μg/mL GO@AgPt for 4 hours before exposure to 4Gy X-ray irradiation. Cellular RNA was extracted from each group, and a transcriptome sequencing library was constructed. Subsequent analysis identified differential genes, followed by gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway assessments. Our results revealed the uniform attachment of AgPt spherical nanoparticles (NPs) with an approximate diameter of 10 nm to the GO surface. The GO@AgPt nanocomposites comprised four single-layer GO sheets, each approximately 4 nm in thickness, with the Ag peak area being about six times that of the Pt peak area. A total of 197 miRNAs exhibited differential expression between the GO@AgPt and control groups, with 94 up-regulated and 103 down-regulatedmiRNAs. These miRNAs were associated with biological processes such as positive regulation of gene expression, cell surface interactions, and growth factor binding. Furthermore, they were implicated in various pathways, including microRNAs in cancer, fatty acid metabolism, human T-cell leukemia virus 1 infection, FoxO signaling, and alcoholic liver disease. Our findings demonstrate that GO@AgPt nanocomposites enhance the radio-sensitization effect in NSCLC, with 197 differentialmiRNAs participating in the process.

Structure and Property Evolution of Graphene Oxide Sheets during Low-Temperature Reduction on a Solid Substrate

The structure and property evolution of graphene oxide (GO) during low-temperature (≤200 °C) reduction is related to the economically effective production and many behaviors of graphene-based materials, such as property tuning and long-term stability at high working temperatures. The interfacial effects on the physiochemical processes are yet to be quantified experimentally. Here, combining scanning polarization force microscopy with UV–vis absorption spectra, the formation and expansion of sp2 domains on individual single-layered GO sheets and the opto-electronic behaviors of GO films on average at low temperatures are in situ monitored. Kinetics of the interfacial evolutions are examined. Surprisingly, unexpected faster evolution of GO sheets at interfaces than that in bulk water is observed. We find this discrepancy can be addressed if the water atmosphere is taken into account and the humidity dependence of evolution is verified. Environmental water and asymmetric moisturizing of GO are believed to play important roles in the process. Based on this, the evolution rate is modulated via adjusting the humidity. The findings shed light on the interfacial structure and property evolution processes of GO and open a new avenue to manipulate the evolution rates at low temperatures.

The ionized graphene oxide membranes for water-ethanol separation

Nanoporous graphene oxide (GO) membranes have shown great promise in separating water and ethanol with high flux and selectivity. The current design of these membranes focuses on tuning the pore sizes in GO sheets to achieve superior selectivity. In this paper, using molecular dynamics simulations, we study the feasibility of achieving effective water-ethanol separation by tuning the ionization of the functional groups on the periphery of pores in single-layer GO sheets. For pores featuring neutral carboxyl (COOH) groups, the water-to-ethanol selectivity coefficient is ∼7 when the pore diameter is 0.68 nm but decays to ∼1.5 when the pore diameter increases to ∼1.12 nm. However, our simulations suggest that through the ionization (deprotonation) of the COOH groups of the 1.12 nm-wide pores, we can achieve a water-to-ethanol selectivity coefficient of ∼7 in these pores. This improvement is mainly attributed to the enhanced (suppressed) accessibility of water (ethanol) molecules to the pore induced by the ionization of the functional groups.

Molecular simulation of permeation behaviour of ethanol/water molecules with single-layer graphene oxide membranes

Graphene oxide (GO)-based materials have shown promise as water-permeating membranes in pervaporation separation. However, the feed permeation and surface affinity of single-layer nanoporous GO sheet for liquid mixtures remain unresolved. Here, the pressure-driven molecular transport of pure ethanol and pure water, as well ethanol-water mixtures, crossing through single-layer nanoporous GO sheet was studied by non-equilibrium molecular dynamics simulations. We show that single-layer GO sheet with controlled pore sizes can effectively reject ethanol and allow water permeation with high permeability. This means that porous GO sheets could act as an effective dehydration membrane, therefore providing the initial barrier for ethanol passage in GO-based membrane. The pore size effect was considered as the separation mechanism. Both ethanol and water molecules in the mixture show comparable affinity with GO surfaces. The hydrogen-bonding coupling interaction between mixture and surface functional groups provide addition influence on the molecular transport through GO pores.

Mechanical and Tribological Properties of Graphene Reinforced Natural Rubber Composites: A Molecular Dynamics Study

ABSTRACTGraphene reinforced natural rubber composites are developed to study the improvement in mechanical and tribological properties of natural rubber by the introduction of graphene as reinforcement. Constant strain minimization method has been applied to calculate Young’s and shear modulus of developed structures. A three-layer model containing Fe (Iron) atoms at the top and bottom and polymer matrices in the middle has been constructed to calculate the tribological properties. A shear loading is applied to the top iron nanorod by sliding it to the surface of the polymer matrices for 600 ps with a velocity of 0.01 nm/ps. The results show the increase of 185% in Young’s modulus, 32% in shear modulus and 48% in hardness by reinforcing natural rubber with single-layer graphene oxide sheet, respectively. Also, reduction of 28% and 36% in the friction coefficient and abrasion rate obtained by the introduction of graphene oxide sheet in natural rubber matrix. Also, interaction energy between graphene and natural rubber, the angle, bond and kinetic energy of the polymer and composites has been calculated and discussed.

Formation of Graphene Oxide Nanoscrolls in Organic Solvents: Toward Scalable Device Fabrication

In this work, formation of graphene oxide (GO) nanoscrolls in organic solvents was investigated upon dispersing GO nanosheets in organic solvents by sonication. It was found that, in some of the organic solvents, the single-layer GO sheets can effectively curl onto themselves to form the nanoscrolls that then sediment under gravity from the dispersion media. The sedimentation was monitored by UV–vis spectroscopy when the GO suspensions were left aside for different time periods after the sonication. The nanoscrolls were separated and characterized by transmission electron microscopy (TEM) and electron diffraction (ED). A typical solvent with such scroll-forming function is pyridine, where 82% of the GO sheets form the GO nanoscrolls and undergo the sedimentation. Scroll formation is also observed for N,N-dimethylformamide (DMF), methanol, ethanol, isopropyl alcohol, acetic acid, and isobutyric acid, but the yields vary with the solvents. The scrolls formed in pyridine suspension show the average length ov...

PH-controlled drug release of radiation synthesized graphene oxide/(acrylic acid-co-sodium alginate) interpenetrating network

Hydrogel biocomposites containing a combination of graphene oxide (GO) and natural polymer-based copolymer of sodium alginate (Alg) and acrylic acid (AAc) were prepared by radiation-induced copolymerization and crosslinking. FTIR, XRD, and AFM analyses revealed the successful preparation of single-layered graphene oxide sheets. FTIR and TGA data confirmed the incorporation of GO within the (AAc-co-Alg) copolymer hydrogel. The effect of GO content, as interpenetrating network, on the swelling behavior of (AAc-co-Alg) copolymer hydrogel was investigated. The results of the pH-dependent swelling showed the presence of GO within the prepared hydrogel improve the ability of the GO/(AAc-co-Alg) nanocomposite hydrogel to bypass the acidity of the simulated stomach medium (pH 1) without significant swelling and regulate it for longer period in simulated intestine medium (pH 7). Moreover, the swelling kinetics showed that all the samples under investigation possess Fickian at pH 1 and non-Fickian at pH 7. The evaluation of the prepared GO/(AAc-co-Alg) nanocomposite hydrogel as drug carrier was carried out in either simulated stomach and intestine media using cefadroxil as a model drug. The drug release profile came in a good agreement with swelling results which recommend the GO/(AAc-co-Alg) nanocomposite hydrogel as potential targeted drug delivery system.

Humidity induced charge migration on single layer graphene oxide sheets

The charge migration on the surface of single layer graphene oxide (GO) sheets was investigated by scanning polarization force microscopy. Electrostatic charges were observed to transfer over 1 μm across the insulating single layer GO sheets surface with the help of water molecules condensed from the environment. Humidity-dependent charge migration on GO sheets was visualized on the nanometer scale and the migration velocity was plotted at a relative humidity range of 10%–40%. When the relative humidity reached 50% or higher, water film would form on the whole GO sheet surface, which made the GO sheet conductive to the electrostatic charges.

Bacteriorhodopsin as a superior substitute for hydrazine in chemical reduction of single-layer graphene oxide sheets

Bacteriorhodopsin (bR) molecules were utilized as light-driven proton pumps for green as well as effective reduction of single-layer graphene oxide (GO) sheets. The bR molecules and graphene sheets were separated from each other in an aqueous environment by using a polytetrafluoroethylene membrane filter, in order to prevent their direct interactions (including attachment of the bR molecules onto the GO). Although reduction of GO using hydrazine or bR showed similar deoxygenation levels (based on X-ray photoelectron spectroscopy), the former resulted in formation of CN bonds which can substantially decrease the electrical conductivity of the reduced sheets. The electrical characteristics of the single-layer graphene sheets were studied by recording current–voltage curves of the sheets located between two Au electrodes on a SiO2 (300nm)/Si (100) substrate. The electrical conductivity of the bR-reduced graphene oxide (rGO) sheets was found about one order of magnitude better than that of hydrazine-rGO sheets. The excellent electrical conductivity of the bR-rGO sheets (with sheet resistance of ∼7.1×104Ω/sq) was assigned to the effective deoxygenation (without formation of any CN bonds) and better restoration of the graphitic structure of the GO sheets, using the protons pumped by the bR molecules.

Gelation of graphene oxides induced by different types of amino acids

We have investigated gelation of graphene oxide (GO) sheets induced by amino acids. For gelation of single layer GO sheets, six different types of amino acids were added to GO suspension as gelators. To understand gelation mechanism, we varied the concentration and type of amino acids as well as the pH of suspension, and monitored the morphology and rheological properties of reaction mixtures. Gelation was observed in acidic pH only with three types of amino acids (arginine, tryptophan, and cysteine) whereas no gel was formed at other pH values (neutral and basic). As the type of amino acid was varied, both the binding strength between amino acid and GO and the moduli (G′ and G′′) of reaction mixtures followed the same order, arginine>cysteine>tryptophan>asparagine>aspartic acid>glycine. To rationalize these results, we considered interactions between amino acid side chains and GO sheets (i.e., electrostatic interaction, π–π stacking, and hydrogen bonding), and found that the hydrogel formed by electrostatic attraction with arginine exhibited shorter gel time and larger moduli than the other samples. Finally, synthesis of GO hydrogel at physiological pH was demonstrated by increasing the concentration of GO sheets.

Direct Observation of Spatially Heterogeneous Single-Layer Graphene Oxide Reduction Kinetics

Graphene oxide (GO) is an important precursor in the production of chemically derived graphene. During reduction, GO's electrical conductivity and band gap change gradually. Doping and chemical functionalization are also possible, illustrating GO's immense potential in creating functional devices through control of its local hybridization. Here we show that laser-induced photolysis controllably reduces individual single-layer GO sheets. The reaction can be followed in real time through sizable decreases in GO's photoluminescence efficiency along with spectral blueshifts. As-produced reduced graphene oxide (rGO) sheets undergo additional photolysis, characterized by dramatic emission enhancements and spectral redshifts. Both GO's reduction and subsequent conversion to photobrightened rGO are captured through movies of their photoluminescence kinetics. Rate maps illustrate sizable spatial and temporal heterogeneities in sp(2) domain growth and reveal how reduction "flows" across GO and rGO sheets. The observed heterogeneous reduction kinetics provides mechanistic insight into GO's conversion to chemically derived graphene and highlights opportunities for overcoming its dynamic, chemical disorder.

Graphene Oxide Scrolls on Hydrophobic Substrates Fabricated by Molecular Combing and Their Application in Gas Sensing

Well-aligned graphene oxide (GO) scrolls are prepared through the controlled folding/scrolling of single-layer GO sheets using molecular combing on hydrophobic substrates, such as aged gold substrate, polydimethylsiloxane film, poly(L-lactic acid) film, and octadecyltrimethoxysilane-modified silicon dioxide. As a proof of concept, the gas sensor fabricated with a single reduced GO scroll is used to detect NO(2) gas with a concentration as low as 0.4 ppm.

Purified Graphene Oxide Dispersions Lack In Vitro Cytotoxicity and In Vivo Pathogenicity

Prompted by the excitement from the description of single layer graphene, increased attention for potential applications in the biomedical field has been recently placed on graphene oxide (GO). Determination of the opportunities and limitations that GO offers in biomedicine are particularly prone to inaccuracies due to wide variability in the preparation methodologies of GO material in different laboratories, that results in significant variation in the purity of the material and the yield of the oxidation reactions, primarily the Hummers method used. Herein, the fabrication of highly pure, colloidally stable, and evenly dispersed GO in physiologically-relevant aqueous buffers in comparison to conventional GO is investigated. The purified GO material is thoroughly characterized by a battery of techniques, and is shown to consist of single layer GO sheets of lateral dimensions below 500 nm. The cytotoxic impact of the GO in vitro and its inflammation profile in vivo is investigated. The purified GO prepared and characterized here does not induce significant cytotoxic responses in vitro, or inflammation and granuloma formation in vivo following intraperitoneal injection. This is one of the initial steps towards determination of the safety risks associated with GO material that may be interacting with living tissue.

Driving Forces of Conformational Changes in Single-Layer Graphene Oxide

The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance.

Interfacial Microstructure and Properties of Carbon Fiber Composites Modified with Graphene Oxide

The performance of carbon fiber-reinforced composites is dependent to a great extent on the properties of fiber-matrix interface. To improve the interfacial properties in carbon fiber/epoxy composites, we directly introduced graphene oxide (GO) sheets dispersed in the fiber sizing onto the surface of individual carbon fibers. The applied graphite oxide, which could be exfoliated to single-layer GO sheets, was verified by atomic force microscope (AFM). The surface topography of modified carbon fibers and the distribution of GO sheets in the interfacial region of carbon fibers were detected by scanning electron microscopy (SEM). The interfacial properties between carbon fiber and matrix were investigated by microbond test and three-point short beam shear test. The tensile properties of unidirectional (UD) composites were investigated in accordance with ASTM standards. The results of the tests reveal an improved interfacial and tensile properties in GO-modified carbon fiber composites. Furthermore, significant enhancement of interfacial shear strength (IFSS), interlaminar shear strength (ILSS), and tensile properties was achieved in the composites when only 5 wt % of GO sheets introduced in the fiber sizing. This means that an alternative method for improving the interfacial and tensile properties of carbon fiber composites by controlling the fiber-matrix interface was developed. Such multiscale reinforced composites show great potential with their improved mechanical performance to be likely applied in the aerospace and automotive industries.

A novel biosensing strategy for screening G-quadruplex ligands based on graphene oxide sheets

A novel fluorescence biosensing strategy for simple, rapid and sensitive selecting quadruplex-binding ligands was reported by using graphene oxide (GO) as the fluorescence quencher. Data from transmission electron microscopy (TEM), atomic force microscopy (AFM) image, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy demonstrated that single-layered GO sheets were successfully prepared with well dispersion in aqueous solution. The fluorescein amidite (FAM)-labeled signal probe first adsorbed onto the surface of GO through π-stacking interaction between the ring structure in the nucleobases and the hexagonal cells of GO, and the fluorescence of the dye was quenched. When the quadruplex-binding ligands were introduced, the signal probe folded to form intramolecular G-quadruplex structure, which led to the releasing of FAM-labeled signal probe from the surface of GO and the fluorescence intensity recovered. Three series of Chinese medicine monomers were investigated by the proposed method, and the flavonoids were demonstrated to be the potential quadruplex-binding ligands by fluorescence measurement and melting temperature analysis. The results indicated that this strategy offers a simple, rapid and sensitive method for screening G-quadruplex ligands and it could find wide applications in the discovery of new antitumor drugs.

Fabrication of nanoelectrode ensembles by electrodepositon of Au nanoparticles on single-layer graphene oxide sheets

Nanoelectrode ensembles (NEEs) have been fabricated by the electrodeposition of Au nanoparticles (AuNPs) on single-layer graphene oxide (GO) sheets coated on a glassy carbon electrode (GCE). The fabricated NEEs show a typical sigmoidal shaped voltammetric profile, arising from the low coverage density of AuNPs on GCE and large distance among them, which can be easily controlled by varying the electrodeposition time. As a proof of concept, after the probe HS-DNA is immobilized on the NEEs through the Au-S bonding, the target DNA is detected with the methylene blue intercalator. Our results show that the target DNA can be detected as low as 100 fM, i.e. 0.5 amol DNA in 5 μL solution.

Dielectrophoretic assembly and atomic force microscopy modification of reduced graphene oxide

A simple and controllable method is developed to experimentally study the effects of defects on reduced graphene oxide (RGO) sheets for nanoelectronics application. First, a deterministic technique is developed to assemble a single layer graphene oxide sheet onto the gaps of microelectrodes by optimizing the dielectrophoretic parameters (10 Vpp at 1 MHz for 5 s). This is followed by the utilization of atomic force microscopy–based mechanical cutting method to form line defects on RGO sheets. Based on these two procedures, the experimental studies of the effects of line defects on RGO are investigated, which provides an alternative approach to study the influence of defects on graphene. The electric transport measurement results show that the electrical performance of the defected RGO devices generally decrease due to Anderson localization, which supports the theoretical studies of the influence of defects on the electrical properties of RGO.

Aqueous Liquid Crystals of Graphene Oxide

The formation of liquid crystals (LCs) is the most viable approach to produce macroscopic, periodic self-assembled materials from oriented graphene sheets. Herein, we have discovered that well-soluble and single-layered graphene oxide (GO) sheets can exhibit nematic liquid crystallinity in water and first established their isotropic-nematic solid phase diagram versus mass fraction and salt concentration. The zeta potential of GO dispersion is around -64 mV, and its absolute value decreases with increasing salt concentration, implying that the electrostatic repulsive force between negatively charged GO sheets is the dominant interaction in the system of GOLCs and also explaining the salt-dependent phase behavior. For single-layer GO sheets with average diameter of 2.1 μm and polydispersity index of 83%, the isotropic-nematic phase transition occurs at a mass concentration of ∼0.025%, and a stable nematic phase forms at ∼0.5%. Rheological measurements showed that GO aqueous dispersions performed as typical shear flows and confirmed the isotropic-nematic transition. The ordering of GO sheets in aqueous dispersions and the solid state is demonstrated by the characterizations of polarized-light optical microscopy, small-angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The direct, real-time fluorescent inspections by confocal laser microscopy further reveal that the individually dispersed fluorescent GO sheets align with orientational directions along their long axes. These novel findings shed light on the phase behaviors of diversely topological graphenes and lay the foundation for fabrication of long-range, ordered nano-objects and macroscopically assembled graphene-based functional materials.

Single-layer graphene oxide sheet: a novel substrate for dip-pen nanolithography

Graphene oxide (GO) sheet is used as a novel substrate for dip-pen nanolithography (DPN). After GO is transferred onto SiO(2) using the Langmuir-Blodgett technique, CoCl(2) is patterned on both GO and exposed SiO(2) substrates simultaneously by DPN, which is used for growth of different structured carbon nanotubes.