Nanocarbon Toxicity (Version-1; 2012.03.09)
László P. Biró
Nanocarbons: fullerenes , carbon nanotubes (CNTs) , and graphene  in the past twenty five years have been continuously at the forefront of research and applications efforts of nanotechnology. More recently graphene has generated an exponential increase of scientific interest (Fig. 1 in ). Given the very wide range of applications envisaged for this one single atom thick, honeycomb lattice of carbon [5, 6, 7], its potential toxicological implications should be investigated very carefully, before the material will become widespread in consumer goods. Moreover, graphene may prove to be a very convenient model material - for extant and hypothetical sp2 type carbon nanoarchitectures  - which can also help in elucidating discrepancies in the sometimes contradictory results published so far regarding the toxicological effects of nanocarbons like fullerenes and CNTs . The physical and chemical properties of such nanocarbons exhibit a strong dependence on their nanostructure. For example, the incorporation of non-hexagonal rings into straight CNTs transforms these in randomly curved nanoobjects, the typical example being the CNTs produced by chemical vapor deposition (CVD), or eventually in regularly coiled CNTs if the non-hexagonal rings are incorporated in a regular way.[10 ,11].
In fact graphenes are already a wider class of material from the point of view of toxicology, too. This class includes graphene itself, few layer graphite (FLG), ultrathin graphite (more than atomic10 layers thick, but thinner than 100 nm) graphene oxide (GO), reduced graphene oxide (r-GO) .
The fact that both the physical and chemical properties of graphenes are strongly dependent on structure , crystallographic orientation of the edges and lateral feature size , atomic scale structural defects , insofar has been somewhat disregarded from the point of view of toxicology. The differences of physical and chemical properties will be translated into differences of biological activity.
The variety of graphene most intensely investigated for applications, is the graphene produced by CVD . This kind of material in fact is a patchwork of small two dimensional (2D) crystallites with a random distribution of orientations with respect to each other . The individual crystallites are separated by grain boundaries which have different structural and electronic properties as compared with crystalline grains which they separate .
The group of Prof. Biró has developed several methods based on the use of scanning probe microscopes (SPM) for the production of graphene nanoarchitectures with a precise control of the crystallographic orientation of the edges and of the lateral dimensions of the features in the nanometer range [Error: Reference source not found, 19, 20].
Despite its thickness of one single atom, graphene, and FLG can be observed by optical microscopy, too . On a properly chosen substrate, coated with graphene type materials, this will allow simultaneous, or sequential observation of cell proliferation by conventional optical microscopy, fluorescence microscopy and atomic resolution structural characterization by SPM complemented by other global characterization techniques (SFG, SAXS, XPS) which may provide information on the chemical functionalization of the substrate. A special marker system will be developed which will allow the precise relocation of investigated regions when using different microscopic methods.
The following major scientific questions should be addressed using a multidisciplinary approach:
The differences of cell behavior on mechanically exfoliated graphene of high crystallinity and on CVD graphene with small grains
The effects on cell proliferation of controlled amounts of structural disorder in graphene of high crystallinity, the structural disorder may be induced in controlable way by ion irradiation [Error: Reference source not found].
The effect of graphene edges of particular orientation, for example of zig-zag edges [Error: Reference source not found] on cell proliferation
The effect of the number of graphene edges in a certain area on cell adhesion and cell mortality.
Atomic scale characterization of the grapehene edges which have negative effects on cell viability
Graphene and FLG dispersion may be used in cell cultures to investigate the endocytosis of these materials. Cell mortality shoul be monitored.
The AFM investigation of the outer cell membrane of cells exposed to graphene/FLG suspensions.
Tailor made bent graphene nanoribbon junction. The two joined nanoribbons have armchair, respectively zig-zag edges. The graphene nanoribbon junction was produced in the group of Prof. Biró by atomic resolution Scanning Tunneling Lithography (STL) .
8 M. Terrones, A. R. Botello-Méndez, J. Campos-Delgado, F. López-Urías, Y. I. Vega-Cantú, F. J. Rodríguez-Macías, A. L. Elías, E. Muñoz-Sandoval, A. G. Cano-Márquez, and J.-christophe Charlier, Nano Today, 2010, 5, 351-372.