## 3 Results and Discussion
These data are comparable with the results obtained with the MitoSOX assay, thus confirming that GO sheets cause mitochondrial dysfunctions, which lead to ROS species generation. The treatment with hybrids GO-AuNP increases significantly more the total ROS generation with respect to the AuNPs and GO alone. Figure 8 shows the representative confocal microscopy images and optical imaging of the neuroblastoma cells after incubation for 2 h with the different samples. The staining of the nuclei (in blue) and lysosomes (in red) allows one to display the more effective cellular uptake of GO-AuNP  
Figure 6: MitoSOX experiment on neuroblastoma SH-SYSY cell line. Cells were incubated for 24 h with AuNPs, GO-AuNP, and free GO nanosheets, at different concentrations: 5, 10, 15 nM of AuNPs; 5, 10, 20 \(\mu\)g/mL of GO into the hybrids; 5, 10, 20 \(\mu\)g/mL of GO alone. Results are presented as mean \(\pm\) SEM from experiments in triplicate and normalized with respect to the control untreated cells. Asterisk (**) represents the correlation significant at the \(p\leq 0.01\) and (***) at the \(p\leq 0.001\) level with respect to the control; (§) represents the correlation significant at the \(p\leq 0.05\) and (§§) at the \(p\leq 0.001\) level with respect to the GO. nanocomposites in comparison with the bare GO nanosheets. In fact, in the bright field micrographs, are visible several dark features, corresponding to the aggregated nanomaterials, for the cells treated with AuNPs and GO-AuNP but not those incubated with GO. Moreover, an extra red fluorescence, due to the scattering by the AuNPs aggregates [59] is clearly visible intracellularly, even at the nuclear level, for the cells incubated with GO-AuNP. These findings are very promising for future research directions of these nanoplatforms in the theranostic field of nanomedicine. Figure 8: Laser scanning confocal microscopy (LSM) micrographs of SH-SYSY neuroblastoma cells after 2 h treatment with the various samples: (**a**) untreated, (**b**) 5 nM AuNP, (**c**) 20 \(\mathrm{\SIUnitSymbolMicro}\)/mL GO, (**d**) 20 \(\mathrm{\SIUnitSymbolMicro}\)/mL GO-AuNP. Left: merged channels of blue (nuclear staining with Hoechst, \(\lambda_{\mathrm{ex/em}}=\) 405/425–475) and red (LysoTracker Deep Red, \(\lambda_{\mathrm{ex/em}}=\) 633/650–700); right: merged channels of blue and grey (bright field images). Scale bar = 20 \(\mathrm{\SIUnitSymbolMicro}\). Figure 7: The 2′,7′-dichlorofluorescein (DCF) experiment on neuroblastoma SH-SYSY cell line. Cells were incubated for 24 with AuNPs, GO-AuNP, and free GO nanosheets, at different concentrations: 5, 10, 15 nM of AuNPs; 5, 10, 20 \(\mathrm{\SIUnitSymbolMicro}\)/mL of GO into the hybrids; 5, 10, 20 \(\mathrm{\SIUnitSymbolMicro}\)/mL of GO alone. Results are presented as mean \(\pm\) SEM from experiments in triplicate and normalized with respect to the control untreated cells. Asterisk (*) represents the correlation significant at the \(p\leq\) 0.05 and (***) at the \(p\leq\) 0.001 level with respect to the control; (**#) represents the correlation significant at the \(p\leq\) 0.01 and (***#) at the \(p\leq\) 0.001 level with respect to the AuNPs; (SSSS) represents the correlation significant at the \(p\leq\) 0.001 level with respect to the GO.