In the know…December 2011
Julia Varet, SAFENANO Toxicologist
In our December in the know article, SAFENANO's Julia Varet outlines why graphene is exciting to the nano world and the importance of EHS testing for its novel applications.
...on graphene
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Scientific interest in graphene has been catalysed by the award of the 2010 Nobel Prize in Physics for ground-breaking experiments regarding the two-dimensional material. As with many novel materials, applications of graphene and its derivatives offer many technological opportunities and to ensure safe development of graphene, the potential impact on health and environment is being studied.
Graphene is a 2-dimensional allotrope of carbon and is defined as a one atom thick sheet of carbons atoms hexagonally arranged (sp2 hybridization). By contrast, graphite, carbon nanotubes and fullerenes are respectively 3-, 2- and 0-dimensional nanomaterials essentially based on the from the graphene moiety. There are two main ways to synthesise graphene: bottom up (chemical vapour deposition, arc discharge etc) and top down by exfoliation of graphite (e.g. mechanical exfoliation, electrochemical synthesis etc).
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Graphene and its derivatives such as graphene oxide display interesting electrical, thermal, mechanical and optical properties. The uses for the graphene family of nanomaterials are extensive, covering applications as diverse as battery electrodes, super-capacitors, nano-electronics (e.g. transistors and sensors), inks, anti-bacterial paper, and many biomedical uses for imaging, drug delivery, tissue engineering, and biosensors. A detailed review on methods of synthesis, properties, and applications of graphene and related nanomaterials has been published by Singh et al. (2011).
Recent research has shown that…
In relation to the biological aspects of graphene, Ren et al. (2010) using in vitro acellular assays, directly mixed together graphene oxide and DNA, the genetic material of the cells. The results indicated that the planar physical structure of graphene oxide favoured its interactions with DNA. Moreover, in presence of both graphene oxide and transition metal ions, the authors observed breakages of the DNA. It was therefore suggested that the physico-chemical characteristics of graphene oxide favoured its interaction with DNA and could lead to DNA breakages, if they come in contact together. This raises concerns about the potential genotoxicity of graphene oxide upon exposure but also promises in terms of development of new chemotherapeutic agents.
Recently, Sanchez et al. (2011) published an extensive review on the physico-chemical characteristics and biological effects of the graphene-family of nanomaterials. The authors first highlighted the importance of in-depth physico-chemical characterisation and then classification of the materials according to the definitions in use. Parameters such as size, surface area, layer number, edges, surface chemistry and structural defects, and purity are key aspects to consider in order to give a comprehensive characterisation of these materials. Moreover, the authors described specific difficulties related to the study of these materials in terms of characterisation and biological impact and stressed out the potential for interference in assays. Crucially, the authors presented some work estimating the deposition of such graphene sheets in the respiratory tract. Their data showed that these graphene nanomaterials could deposit along the respiratory tract and that factors such as size and layer number would strongly influence the deposition patterns. A scope on the biological effects and biomedical applications of graphene nanomaterials was also presented.
The numerous potential applications of graphene and related materials make them very attractive, not only to the scientific community but also to the business community in general who are keen to capitalise on the benefits that the product offers. Further studies on the potential exposure and hazard are required in order to ensure that these materials are developed in a safe and responsible manner to help ensure their long term sustainability.
SAFENANO scientists are researching the health and environmental aspects associated with the synthesis and use of graphene and related materials, in two FP7 projects: Electrograph and NanoMaster.
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References
Singh V, Joung D, Zhai L, Das S, Khondaker S, Seal S. 2011, “Graphene based materials: Past, present and future.” Prog. Mater Sci. vol 56, no. 8, pp. 1178-1271.
Ren H, Wang C, Zhang J, Zhou X, Xu D, Zheng J, Guo S, Zhang J. 2010, “DNA cleavage system of nanosized graphene oxide sheets and copper ions.” ACS Nano. vol. 4, no. 12, pp. 7169-74.
Sanchez VC, Jachak A, Hurt RH, Kane AB. 2011, “Biological Interactions of Graphene-Family Nanomaterials: An Interdisciplinary Review.” Chem Res Toxicol. [Epub ahead of print]