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      The toxicity of graphene quantum dots

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          Abstract

          This review provides a comprehensive account on the current research status regarding the toxicity of graphene quantum dots (GQDs) – a new nano material with profound potential in various advanced applications.

          Abstract

          Recently, there has been a rapidly expanding interest in a new nano material, graphene quantum dots, owing to its profound potential in various advanced applications. Despite its exciting application outlook, the toxicology of the material has to be well addressed before its practical use in the highly prospective areas – especially for bio-applications such as bio-sensing, bio-imaging and nanomedicine ( e.g. drug delivery). This review provides a comprehensive account of the current research status regarding the toxicity of graphene quantum dots (GQDs), including raw GQDs, chemically doped GQDs and chemically functionalized GQDs. It summarises the existing tests on both in vivo and in vitro toxicity. Important topics including the uptake mechanism by cells and parameters governing the toxicity of GQDs (such as concentration, methods of synthesis, particle size, surface chemistry and chemical doping) are discussed. It also covers demonstrations on toxicity regulation of GQDs via chemical modification, as a toxicity mechanism via generation of reactive oxygen species (ROS) by some GQDs is also evident. Based on the evaluation of the current research status, possible future perspectives are also suggested.

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          Edge state in graphene ribbons: Nanometer size effect and edge shape dependence

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            Chaotic Dirac billiard in graphene quantum dots

            We report on transport characteristics of quantum dot devices etched entirely in graphene. At large sizes, they behave as conventional single-electron transistors, exhibiting periodic Coulomb blockade peaks. For quantum dots smaller than 100 nm, the peaks become strongly non-periodic indicating a major contribution of quantum confinement. Random peak spacing and its statistics are well described by the theory of chaotic neutrino (Dirac) billiards. Short constrictions of only a few nm in width remain conductive and reveal a confinement gap of up to 0.5eV, which demonstrates the in-principle possibility of molecular-scale electronics based on graphene.
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              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).
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                Author and article information

                Journal
                RSCACL
                RSC Advances
                RSC Adv.
                Royal Society of Chemistry (RSC)
                2046-2069
                2016
                2016
                : 6
                : 92
                : 89867-89878
                Affiliations
                [1 ]Environmental Engineering & Queensland Miro- and Nanotechnology Centre
                [2 ]Griffith University
                [3 ]Nathan Campus
                [4 ]Brisbane
                [5 ]Australia
                [6 ]CSIRO Materials Science and Engineering – Clayton
                [7 ]Clayton
                Article
                10.1039/C6RA16516H
                7b62337b-c684-4147-b5a4-064b24c4f24c
                © 2016
                History

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