AFM study Atomic force microscopy (AFM) is an important technique for the morphological characterization of GO and graphene materials and is also capable of imaging and evaluating the surface morphology and properties [54–58]. Figure 7A,B is a typical AFM image of GO and graphene dispersion in water after their deposition
on a freshly cleaned glass surface. The average thickness of as-prepared graphene, measured from the height profile of the AFM image, is about 23.81 nm. Compared with the well-exfoliated GO sheets, with a thickness of about 8.09 nm (Figure 7A), the thickness of graphene is larger than that of GO (Figure 7B). The height profile diagram of the AFM image indicates that the thickness of the sheets is around ICG-001 nmr 23.81 nm, comparable to the typical thickness of single-layer GO sheets (8.09 nm). Akhavan et al. [29] used glucose as a reducing agent for the synthesis of
graphene and suggested that the increase in thickness of the reduced sheets can be assigned to adsorption of reductant molecules such as glucose-based molecules on both sides of the reduced sheets. Esfandiar et al. [32] observed increased thickness of graphene due to the attachment of the oxidized melatonin molecules on both sides of the reduced GO. Similarly, Zhu et al. [33] suggested that the capping selleck inhibitor reagent plays an important role in increasing the thickness of the as-prepared GNS, though most of the oxygen-containing functional groups were removed after the reduction. Su et al. [62] demonstrated that dispersed molecules with large aromatic structures and extra negative charges are noncovalently immobilized on the basal plane of graphene sheets via strong interactions. Figure 7 AFM images of GO (A) and S-rGO (B). Biocompatibility of S-rGO Measuring the biocompatibility of graphene is complex and depends on the techniques used for synthesis and the selection of the biological model
system for study. In order to evaluate the biocompatibility of as-prepared S-rGO, the cytotoxic effect of GO and S-rGO against PMEF cells was investigated. As shown in Figure 8, the second viability of PMEF cells which were incubated with S-rGO was always around 100% under the used concentrations (10 to 100 μg/mL) after a 24-h exposure. This result indicated that S-rGO was significantly biocompatible even if relatively high concentrations were used; interestingly, cell viability was not compromised when concentrations of S-rGO were increased, whereas when concentrations of GO were increased, the viability decreased to about 40%, which was distinct to S-rGO. Taken together, these results suggested that S-rGO is more compatible than GO which is due to the functionalization of GO by spinach leaf extract. Previous studies demonstrated that hydrazine-rGO was highly toxic to cells [7]. Therefore, it was considered that the surface chemistry was the primary contributor to the difference of toxicity selleck products between S-rGO and GO.