Cytotoxicity of graphene oxide and graphene in human erythrocytes and skin fibroblasts

Two-dimensional carbon-based nanomaterials, including graphene oxide and graphene, are potential candidates for biomedical applications such as sensors, cell labeling, bacterial inhibition, and drug delivery. Herein, we explore the biocompatibility of graphene-related materials with controlled physical and chemical properties. The size and extent of exfoliation of graphene oxide sheets was varied by sonication intensity and time. Graphene sheets were obtained from graphene oxide by a simple (hydrazine-free) hydrothermal route. The particle size, morphology, exfoliation extent, oxygen content, and surface charge of graphene oxide and graphene were characterized by wide-angle powder X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, dynamic light scattering, and zeta-potential. One method of toxicity assessment was based on measurement of the efflux of hemoglobin from suspended red blood cells. At the smallest size, graphene oxide showed the greatest hemolytic activity, whereas aggregated graphene sheets exhibited the lowest hemolytic activity. Coating graphene oxide with chitosan nearly eliminated hemolytic activity. Together, these results demonstrate that particle size, particulate state, and oxygen content/surface charge of graphene have a strong impact on biological/toxicological responses to red blood cells. In addition, the cytotoxicity of graphene oxide and graphene sheets was investigated by measuring mitochondrial activity in adherent human skin fibroblasts using two assays. The methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, a typical nanotoxicity assay, fails to predict the toxicity of graphene oxide and graphene toxicity because of the spontaneous reduction of MTT by graphene and graphene oxide, resulting in a false positive signal. However, appropriate alternate assessments, using the water-soluble tetrazolium salt (WST-8), trypan blue exclusion, and reactive oxygen species assay reveal that the compacted graphene sheets are more damaging to mammalian fibroblasts than the less densely packed graphene oxide. Clearly, the toxicity of graphene and graphene oxide depends on the exposure environment (i.e., whether or not aggregation occurs) and mode of interaction with cells (i.e., suspension versus adherent cell types).     

氧化石墨烯在生物医学领域的应用

氧化石墨烯(GO)是石墨烯的衍生物,具有较高的比表面积和丰富的官能团:底面含羟基和环氧基,边缘含羧基。这些官能团赋予了氧化石墨烯良好的亲水性、分散性和生物相容性,易于修饰和功能化,加之其优良的光学性质,使得氧化石墨烯在生物医学领域具有广阔的应用前景。着重介绍了氧化石墨烯在生物传感器、生物成像、药物/基因传送、光热/光动力治疗、抗菌材料、生物安全性方面的研究现状和进展。     

Collective magnetic behavior of graphene nanohole superlattices

We predict a new class of 2-D crystalline “bulk” magnets—the graphene nanohole (GNH) superlattices with each GNH acting like a “super” magnetic atom, using first principles calculations. We show that such superlattices can exhibit long-range magnetic order above room temperature, with a collective magnetic behavior governed by inter-NH spin spin interactions in additional to intra-NH spin ordering. Furthermore, magnetic semiconductors can be made by doping magnetic NHs into semiconducting NH superlattices. The possibility of engineering magnetic GNHs for storage media and spintronics applications is discussed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

氧化石墨烯的制备及结构研究进展

氧化石墨烯是一种表面含有丰富的含氧官能团石墨烯衍生物.氧化石墨烯拥有较大的比表面积、良好的亲水性和生物亲和性,被广泛应用于传感器、储能材料、药物载体、催化等领域.本文介绍了近几年氧化石墨烯的制备方法,简述了由Hummers法制备氧化石墨烯的生成机理,主要概括了氧化石墨烯新的结构模型,提出寻找高效绿色的氧化剂是制备氧化石墨烯的关键,确定氧化石墨烯的结构对其表面改性及在复合材料的应用和发展有重要的影响.     

Highly conducting graphene sheets and Langmuir-Blodgett films

Graphene is an intriguing material with properties that are distinct from those of other graphitic systems. The first samples of pristine graphene were obtained by 'peeling off' and epitaxial growth. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation-reintercalation-expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solvents. The graphene sheets exhibit high electrical conductance at room and cryogenic temperatures. Large amounts of graphene sheets in organic solvents are made into large transparent conducting films by Langmuir-Blodgett assembly in a layer-by-layer manner. The chemically derived, high-quality graphene sheets could lead to future scalable graphene devices.     

Size and time dependent internalization of label-free nano-graphene oxide in human macrophages

Graphene oxide shows great promise as a material for biomedical applications,e.g.,as a multi-drug delivery platform.With this in view,reports of studies on the interaction between nanosized graphene oxide flakes and biological cells are beginning to emerge.However,the number of studies remains limited,and most used labeled graphene oxide samples to track the material upon endocytosis.Unfortunately,the labeling process alters the surface functionality of the graphene oxide,and this additional functionalization has been shown to alter the cellular response.Hence,in this work we used label-free graphene oxide.We carefully tracked the uptake of three different nanoscale graphene oxide flake size distributions using scanning/transmission electron microscopy.Uptake was investigated in undifferentiated human monocyte cells (THP-1) and differentiated macrophage cells.The data show clear size dependence for uptake,such that larger graphene oxide flakes (and clusters) are more easily taken up by the cells compared to smaller flakes.Moreover,uptake is shown to occur very rapidly,within two min of incubation with THP-1 cells.The data highlights a crucial need for cellular incubation studies with nanoparticles,to be conducted for short incubation periods as certain dependencies (e.g.,size and concentration) are lost with longer incubation periods.     

A hybrid material of graphene and poly (3,4-ethyldioxythiophene) with high conductivity, flexibility, and transparency

A novel hybrid material prepared from graphene and poly (3,4-ethyldioxythiophene) (PEDOT) shows excellent transparency, electrical conductivity, and good flexibility, together with high thermal stability and is easily processed in both water and organic solvents. Conductivities of the order of 0.2 S/cm and light transmittance of greater than 80% in the 400–1800 nm wavelength range were observed for films with thickness of tens of nm. Practical applications in a variety of optoelectronic devices are thus expected for this transparent and flexible conducting graphene-based hybrid material. Electronic Supplementary Material  Supplementary material is available in the online version of this article at http://dx.doi.org/ and is accessible free of charge.     

Graphene Oxide: Surface Activity and Two‐Dimensional Assembly

Graphene oxide (GO) is a promising precursor for preparing graphene‐based composites and electronics applications. Like graphene, GO is essentially one‐atom thick but can be as wide as tens of micrometers, resulting in a unique type of material building block, characterized by two very different length scales. Due to this highly anisotropic structure, the collective material properties are highly dependent on how these sheets are assembled. Therefore, understanding and controlling the assembly behavior of GO has become an important subject of research. In this Research News article the surface activity of GO and how it can be employed to create two‐dimensional assemblies over large areas is discussed.     

Preparation and characterization of graphene/NiO nanocomposites

Graphene-based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this article, we present a facile approach for the preparation of graphene/NiO nanocomposites using graphite oxide and nickel chloride as starting materials. The as-synthesized composites were characterized using X-ray diffraction, Fourier transform-Infrared spectroscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, thermogravimetry, and differential scanning calorimetry analyses. It was shown that graphene sheets were decorated by the in situ-formed NiO nanoparticles to form a film-like composite structure and as a result, the restacking of the as-reduced graphene sheets was effectively prevented. The NiO-coated graphene nanocomposites can be expected to remarkably improve the electrochemical properties of NiO and would be the promising candidates for a variety of applications in future nanotechnology.     

A facile approach to the synthesis of graphene nanosheets under ultra-low exfoliation temperature

High specific surface area graphene nanosheets have been obtained from graphite oxide by using an effective modified exfoliation method under vacuum, the exfoliation temperature (135 degrees C) is much lower than that conventionally applied (1050 degrees C) to obtain monolayer graphene sheets via rapid thermal shock. These products have fluffy and highly porous structure and with a lateral size typically of a few micrometers. Transmission electron microscopy (TEM) observation shows that it looks like a wrinkled transparent ultrathin film consisting of single or few-layer graphene sheets, and their Brunauer-Emmett-Teller surface area is as large as 750 m2/g. Simultaneously, X-ray photoelectron spectroscopy analysis revealed that considerable amount of oxygen-containing groups (C/O ratio, 5:1) retained on the graphene sheets after exfoliation process, which would provide convenience for further modification of the surface properties and chemistry of graphene sheets. This work offers a facile and scalable approach to fabricate graphene oxide and opens up a new vista of various potential applications electronics and composite materials.