Graphene nanosheets were prepared by the direct exfoliation of graphite in an aqueous lysozyme solution using ultrasonication. Atomic force microscopy studies indicated that the nanosheets possessed small lateral dimensions of less than three layers. Raman spectroscopy suggested that defects were introduced by the sonication process. These defects were primarily edge defects, not basal-plane defects. Cytotoxicity studies revealed that the lysozyme-supported nanosheets possessed anticancer activity at certain micromolar concentrations. Three other proteins and gold nanoparticles prepared with those proteins were examined as aids in graphene exfoliation. The overall protein or nanoparticle charge played an important role in the graphite exfoliation to graphene. All of the graphene dispersions were sensitive to pH. Changing the pH reversibly converted the graphene from a highly dispersed state to an aggregated state and vice versa. Although no lateral dimension differences were observed in the nanosheets prepared using the nanoparticles, their cell viability percentages varied depending on the particular protein used.
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