Synthesis and Physicochemical Transformations of Size-Sorted Graphene Oxide during Simulated Digestion and Its Toxicological Assessment against an In Vitro Model of the Human Intestinal Epithelium.

In the last decade, along with the increasing use of graphene oxide (GO) in various applications, there is also considerable interest in understanding its effects on human health. Only a few experimental approaches can simulate common routes of exposure, such as ingestion, due to the inherent complexity of the digestive tract. This study presents the synthesis of size-sorted GO of sub-micrometer- or micrometer-sized lateral dimensions, its physicochemical transformations across mouth, gastric, and small intestinal simulated digestions, and its toxicological assessment against a physiologically relevant, in vitro cellular model of the human intestinal epithelium. Results from real-time characterization of the simulated digestas of the gastrointestinal tract using multi-angle laser diffraction and field-emission scanning electron microscopy show that GO agglomerates in the gastric and small intestinal phase. Extensive morphological changes, such as folding, are also observed on GO following simulated digestion. Furthermore, X-ray photoelectron spectroscopy reveals that GO presents covalently bound N-containing groups on its surface. It is shown that the GO employed in this study undergoes reduction. Toxicological assessment of the GO small intestinal digesta over 24 h does not point to acute cytotoxicity, and examination of the intestinal epithelium under electron microscopy does not reveal histological alterations. Both sub-micrometer- and micrometer-sized GO variants elicit a 20% statistically significant increase in reactive oxygen species generation compared to the untreated control after a 6 h exposure.

Coagulation Behavior of Graphene Oxide on Nanocrystallined Mg/Al Layered Double Hydroxides: Batch Experimental and Theoretical Calculation Study.

Graphene oxide (GO) has attracted considerable attention because of its remarkable enhanced adsorption and multifunctional properties. However, the toxic properties of GO nanosheets released into the environment could lead to the instability of biological system. In aqueous phase, GO may interact with fine mineral particles, such as chloridion intercalated nanocrystallined Mg/Al layered double hydroxides (LDH-Cl) and nanocrystallined Mg/Al LDHs (LDH-CO3), which are considered as coagulant molecules for the coagulation and removal of GO from aqueous solutions. Herein the coagulation of GO on LDHs were studied as a function of solution pH, ionic strength, contact time, temperature and coagulant concentration. The presence of LDH-Cl and LDH-CO3 improved the coagulation of GO in solution efficiently, which was mainly attributed to the surface oxygen-containing functional groups of LDH-Cl and LDH-CO3 occupying the binding sites of GO. The coagulation of GO by LDH-Cl and LDH-CO3 was strongly dependent on pH and ionic strength. Results of theoretical DFT calculations indicated that the coagulation of GO on LDHs was energetically favored by electrostatic interactions and hydrogen bonds, which was further evidenced by FTIR and XPS analysis. By integrating the experimental results, it was clear that LDH-Cl could be potentially used as a cost-effective coagulant for the elimination of GO from aqueous solutions, which could efficiently decrease the potential toxicity of GO in the natural environment.

Chemically reduced graphene contains inherent metallic impurities present in parent natural and synthetic graphite.

Graphene-related materials are in the forefront of nanomaterial research. One of the most common ways to prepare graphenes is to oxidize graphite (natural or synthetic) to graphite oxide and exfoliate it to graphene oxide with consequent chemical reduction to chemically reduced graphene. Here, we show that both natural and synthetic graphite contain a large amount of metallic impurities that persist in the samples of graphite oxide after the oxidative treatment, and chemically reduced graphene after the chemical reduction. We demonstrate that, despite a substantial elimination during the oxidative treatment of graphite samples, a significant amount of impurities associated to the chemically reduced graphene materials still remain and alter their electrochemical properties dramatically. We propose a method for the purification of graphenes based on thermal treatment at 1,000 °C in chlorine atmosphere to reduce the effect of such impurities on the electrochemical properties. Our findings have important implications on the whole field of graphene research.

Rice husk-derived graphene with nano-sized domains and clean edges.

A new synthetic method is demonstrated for transforming rice husks into bulk amounts of graphene through its calcination and chemical activation. The bulk sample consists of crystalline nano-sized graphene and corrugated individual graphene sheets; the material generally contains one, two, or a few layers, and corrugated graphene domains are typically observed in monolayers containing topological defects within the hexagonal lattice and edges. Both types of graphenes exhibit atomically smooth surfaces and edges.

Sensitive detection of ketamine with an electrochemical sensor based on UV-induced polymerized molecularly imprinted membranes at graphene and MOFs modified electrode.

Ketamine is one of the most widely abused drugs in the world and poses a serious threat to human health and social stability; therefore, the ability to accurately monitor the substance in real-time is necessary. However, several problems still exists towards this goal, such as the generally low concentration of the target molecules disturbed in the complex samples that undergo analysis during criminal investigations. In this work, the sensitive and selective detection of ketamine was accomplished by molecularly imprinted electrochemical sensor. The molecularly imprinted membrane as a biomimetic recognition element was fabricated by the UV-induced polymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) on a metal-organic framework/graphene nanocomposite (MOFs@G) modified screen-printed electrode. The screen printed electrode (SPE) provided good adhesion for the formation of the imprinted membranes and increased the stability of the sensor. The morphology and performance of the imprinted films were characterized in detail by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The experimental results demonstrated that the imprinted sensor had excellent sensitivity, selectivity, and long-term stability. It offered a low detection limit (4.0 × 10-11 mol L-1) and had a dynamic range from 1.0 × 10-10 mol L-1 to 4.0 × 10-5 mol L-1. Furthermore, the established method was successfully applied for the determination of ketamine in urine and saliva samples.

Two photon excitable graphene quantum dots for structured illumination microscopy and imaging applications: lysosome specificity and tissue-dependent imaging.

Biocompatible graphene quantum dots (GQDs), obtained from extracts of neem root, are found to be suitable for structured illumination microscopy and two-photon microscopy (TPM). Results of TPM and confocal luminescence microscopy ensure lysosome specificity in live cells and tissue-dependent localization in zebrafish, respectively, of GQDs.

Steam purification for the removal of graphitic shells coating catalytic particles and the shortening of single-walled carbon nanotubes.

Purification and shortening of single-walled carbon nanotubes (SWNTs) is carried out by treatment with steam. During the steam purification the graphitic shells coating the catalytic metal particles are removed. Consequently, the exposed catalytic particles can be easily dissolved by treatment with hydrochloric acid. No damage to the carbon nanotube tubular structure is observed, even after prolonged treatment with steam. Samples are characterized by HRTEM, TGA, magnetic measurements, Raman spectroscopy, AFM, and XPS.

The pristine graphene produced by liquid exfoliation of graphite in mixed solvent and its application to determination of dopamine.

The pristine graphene can be easily prepared in isopropanol-water mixture with salts as assistant via liquid-phase exfoliation method. The concentration of graphene dispersion reaches as high as 0.565 mg/mL. The graphene film prepared by drop-casting method shows an excellent electrical conductivity (7.095 × 104 S/m). Furthermore, an electrochemical biosensor based on the pristine graphene shows high selectivity and sensitivity for the determination of dopamine. The linear detection range for dopamine is 2.5-1500 µM with detection limit of 1.5 µM. This method provides a potential process for preparing high-quality graphene ready-to-use in low-boiling point solvent.

Direct electrodeposition of Graphene enhanced conductive polymer on microelectrode for biosensing application.

Engineering of neural interface with nanomaterials for high spatial resolution neural recording and stimulation is still hindered by materials properties and modification methods. Recently, poly(3,4-ethylene-dioxythiophene) (PEDOT) has been widely used as an electrode-tissue interface material for its good electrochemical property. However, cracks and delamination of PEDOT film under pulse stimulation are found which restrict its long-term applications. This paper develops a flexible electrochemical method about the co-deposition of graphene with PEDOT on microelectrode sites to enhance the long-term stability and improve the electrochemical properties of microelectrode. This method is unique and profound because it co-deposits graphene with PEDOT on microelectrode sites directly and avoids the harmful post reduction process. And, most importantly, significantly improved electrochemical performances of the modified microelectrodes (compared to PEDOT-GO) are demonstrated due to the large effective surface area, good conductivity and excellent mechanical property of graphene. Furthermore, the good mechanical stability of the composites is verified by ultrasonication and CV scanning tests. In-vivo acute implantation of the microelectrodes reveals the modified microelectrodes show higher recording performance than the unmodified ones. These findings suggest the composites are excellent candidates for the applications of neural interface.

Graphene oxide decorated monolithic column as stationary phase for capillary electrochromatography.

In this work, GO bonded monolith (pAS-GO@PS-DVB) as the stationary phase for capillary electrochromatography was fabricated, which was achieved by a simple one-step in-situ copolymerization of styrene and vinylized GO in the presence of divinylbenzene as a cross-linker. GO functionalization was primarily completed using p-aminostyrene based on condensation reaction between amino and carboxyl groups. The characterization by infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy proved the covalent bonding of GO on the monolith. The average pore diameter via Barrett-Joyner-Halenda, specific surface area and pore volume via Brunauer-Emmett-Teller equation by nitrogen adsorption/desorption were determined to be 112.4nm, 485.8m(2)g(-1) and 1.4cm(3)g(-1), respectively. The pAS-GO@PS-DVB monolithic column gave effective separation for a wide range of aromatic compounds, which was based on hydrogen bonding and π-π interactions of GO with polar and/or non-polar organic compounds. The reproducibility in terms of the precisions of migration time, peak height and peak area was estimated below 6% using thiourea and other aromatic compounds. Furthermore, the differences of migration time, peak height and peak area between the first-week analysis and the forth-week analysis were less than 19%, indicating good stability of the proposed monolithic column in one month. The applicability of the pAS-GO@PS-DVB monolith was also demonstrated by baseline separation of three phenols and three anilines.

Ginkgo biloba: a natural reducing agent for the synthesis of cytocompatible graphene.

BACKGROUND: Graphene is a novel two-dimensional planar nanocomposite material consisting of rings of carbon atoms with a hexagonal lattice structure. Graphene exhibits unique physical, chemical, mechanical, electrical, elasticity, and cytocompatible properties that lead to many potential biomedical applications. Nevertheless, the water-insoluble property of graphene restricts its application in various aspects of biomedical fields. Therefore, the objective of this work was to find a novel biological approach for an efficient method to synthesize water-soluble and cytocompatible graphene using Ginkgo biloba extract (GbE) as a reducing and stabilizing agent. In addition, we investigated the biocompatibility effects of graphene in MDA-MB-231 human breast cancer cells. MATERIALS AND METHODS: Synthesized graphene oxide (GO) and GbE-reduced GO (Gb-rGO) were characterized using various sequences of techniques: ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. Biocompatibility of GO and Gb-rGO was assessed in human breast cancer cells using a series of assays, including cell viability, apoptosis, and alkaline phosphatase (ALP) activity. RESULTS: The successful synthesis of graphene was confirmed by UV-vis spectroscopy and FTIR. DLS analysis was performed to determine the average size of GO and Gb-rGO. X-ray diffraction studies confirmed the crystalline nature of graphene. SEM was used to investigate the surface morphologies of GO and Gb-rGO. AFM was employed to investigate the morphologies of prepared graphene and the height profile of GO and Gb-rGO. The formation of defects in Gb-rGO was confirmed by Raman spectroscopy. The biocompatibility of the prepared GO and Gb-rGO was investigated using a water-soluble tetrazolium 8 assay on human breast cancer cells. GO exhibited a dose-dependent toxicity, whereas Gb-rGO-treated cells showed significant biocompatibility and increased ALP activity compared to GO. CONCLUSION: In this work, a nontoxic natural reducing agent of GbE was used to prepare soluble graphene. The as-prepared Gb-rGO showed significant biocompatibility with human cancer cells. This simple, cost-effective, and green procedure offers an alternative route for large-scale production of rGO, and could be used for various biomedical applications, such as tissue engineering, drug delivery, biosensing, and molecular imaging.

Efficient inkjet printing of graphene.

An efficient and mature inkjet printing technology is introduced for mass production of coffee-ring-free patterns of high-quality graphene at high resolution (unmarked scale bars are 100 µm). Typically, several passes of printing and a simple baking allow fabricating a variety of good-performance electronic devices, including transparent conductors, embedded resistors, thin film transistors, and micro-supercapacitors.

Synthesis of magnetic ß-cyclodextrin-chitosan/graphene oxide as nanoadsorbent and its application in dye adsorption and removal.

Magnetic ß-cyclodextrin-chitosan/graphene oxide materials (MCCG) were fabricated through a facile chemical route and their application as excellent adsorbents for dye removal were also demonstrated. The characteristics results of FTIR, SEM, TEM and XRD showed that MCCG was successfully prepared. The results showed that, benefiting from the surface property of graphene oxide, hydrophobicity of ß-cyclodextrin, the abundant amino and hydroxyl functional groups of chitosan, and from the magnetic property of Fe(3)O(4), the adsorbent possesses quite a good and versatile adsorption capacity to the dye under investigation, and can be easily and rapidly extracted from water by magnetic attraction. Most importantly, the adsorbent can be easily and efficiently regenerated for reuse with hardly any compromise of the adsorption capacity. The adsorption kinetics, isotherms and thermodynamics were investigated to indicate that the kinetics and equilibrium adsorptions were well-described by pseudo-second-order kinetic and Langmuir isotherm model, respectively. The thermodynamic parameters suggested that the adsorption process was spontaneous and endothermic in nature. The inherent advantages of the nano-structured adsorbent, such as adsorption capacity, easy, handy operation, rapid extraction, and regeneration, may pave a new, efficient and sustainable way towards highly-efficient dye pollutant removal in water and wastewater treatment.

A facile route to recover intrinsic graphene over large scale.

The intrinsic properties of initially p-type doped graphene (grown by chemical vapor deposition (CVD)) can be recovered by buffered oxide etch (BOE) treatment, and the dominant factor governing p-type doping is identified as the H(2)O/O(2) redox system. Semi-ionic C-F bonding prevents the reaction between the products of the H(2)O/O(2) redox system and graphene. BOE-treated graphene field effect transistors (FETs) subsequently exposed to air, became p-type doped due to recovery of the H(2)O/O(2) redox system. In comparison, poly(methyl methacrylate) (PMMA)-coated graphene FETs had improved stability for maintaining the intrinsic graphene electronic properties.

Clean transfer of graphene for isolation and suspension.

Fabrication of large-area clean graphene sheets is the first step toward the development of high-performance applications in surface chemistry and biotechnology as well as in high-mobility electronics. Here we demonstrate the clean transfer of graphene grown by chemical vapor deposition on Cu foil, with surface cleanness defined by transmission electron microscopy (TEM) in combination with Raman scattering on the same position of suspended graphene sheets. For clean graphene, the Raman spectra exhibit distinctive features that can explicitly discriminate from that of graphene covered with a thin layer of amorphous carbon such as residual poly(methyl methacrylate) (PMMA). By applying this technique to graphene sheets with various degrees of surface cleanness, we show that the quantitative characterization of the thickness of surface contaminants is possible based on multiple reflections and interference of light in samples.

Beneficiation of graphite fines from moulding factory wastes.

As the costs of waste disposal increase, more attention is being placed upon the re-use and recycling of valuable minerals contained within the waste streams. In this article, the waste streams from a moulding factory were treated by physical methods to obtain a re-usable graphite fraction. Multi-gravity separators (MGS) and shaking tables (ST) are being used in coal processing and heavy minerals beneficiation. In the present study, the possibility of using an MGS and ST to separate graphite from moulding sand was analysed as part of such investigations. The effects of changes in different process variables on the concentrate sand content and graphite recovery values were studied. Several parameters, thought to have an effect on the separation were tested. After the ST experiments, a graphite concentrate was obtained having 4.5% sand content with 60.8% recovery. After the investigations carried out by MGS, a graphite concentrate was obtained having 0.95% sand content with 68.0% recovery. The results demonstrated that recovered graphite fractions can be re-used in the factory, thus reducing the quantity of waste and costs.