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Chapter 6 – Production of Few Layer Graphene in Aqueous Media for Biological Studies biological and toxicity studies. Aqueous dispersions were first prepared by solvent exchange method of graphene originally in NMP or DMF by dialysis. Aqueous graphene dispersions were then prepared directly, by exfoliating graphite in in biocompatible surfactant and biomolecule (phospholipids and albumin protein) solutions. Cell culture experiments by my collaborators found that the solvent-exchanged and biocompatible surfactant-exfoliated pristine FLG displayed minimal cytotoxicity and albumin-exfoliated FLG hardly any cytotoxicity, whereas GO and phospholipid-exfoliated FLG were particularly cytotoxic (Appendix 9.6.1). 6.2. SOLVENT EXCHANGE OF GRAPHENE 6.2.1. Why solvent exchange is needed? The direct LPE of graphite in organic solvents using sonication produces pristine graphene (SLG to FLG) at high concentrations.3 The hydrophobic nature of graphene makes it unstable in aqueous media without it being stabilized by a surfactant. The organic solvents NMP and DMF are among the most effective solvents for direct exfoliation due to similar surface tension to that of graphite.3 However, these organic solvents have high boiling points and, due to their incompatibility/toxicity, they are unsuitable for biological studies. Whereas, so far, the aqueous media stability of GO, rGO and functionalised-GO makes them a favourable candidates for the biological investigations.5 NMP and DMF however are miscible with water, so it may be possible to dilute the dispersions. As a part of a control experiment, the metabolic activity of a Breast Cancer cells line (MCF-7) were investigated against different concentrations of NMP and DMF in water (see Appendix 9.6.1 and Figure 9.12a). It was found that at least 90 % of cells survived when the organic solvent level was reduced up to 0.1 v/v% (99.9 v/v% water). 163PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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