## 3 Results
Figure 6: SEM images of PECVD grown graphene nanowalls at different magnifications at (**a**) \(\times\)65, (**b**) \(\times\)100, and (**c**) \(\times\)150. Figure 7: Cell viability (%) of _Escherichia coli_ ATCC 35218. Figure 8: Cell viability (%) of _Staphylococcus aureus_ ATCC 25923. Figure 10: Antibacterial activity of _Staphylococcus aureus_ ATCC 25923 ((**A**) glass control; (**B**) CVD-1; (**C**) CVD-2; (**D**) CVD-3; (**E**) Ni Control; (**F**) CVD-1-Ni). Figure 9: Antibacterial activity of _Escherichia coli_ ATCC 35218 ((**A**) glass control; (**B**) CVD-1; (**C**) CVD-2; (**D**) CVD-3; (**E**) Ni Control; (**F**) CVD-1-Ni). For CVD Gr nanosheets transferred onto G substrates, as the number of layers of GrNs decreased, the cell viability (%) of _E. coli_ decreased from 100% to 51.4%. Additionally, the antibacterial effect of CVD monolayer GrN synthesized onto Ni substrate has been studied. In the case of CVD graphene nanosheets synthesized onto Ni substrate, the cell viability (%) of _E. coli_ decreased from 100% to 38.18%. It is also concluded that the antibacterial activity against _E. coli_ CVD monolayer Gr nanosheets synthesized onto Ni substrate was better than CVD monolayer graphene nanosheets onto G substrate. It has been observed that the antibacterial activity of _S. aureus_ was extremely weak (from 100% to 84.3%) for the samples grown on Ni substrate. [PERSON] et al. [23] showed the antibacterial activity of monolayer Gr films on Cu, Ge, and SiO\({}_{2}\). In particular, the growth of _E. coli_ and _S. aureus_ were inhibited by graphene films on Cu and Ge. [PERSON] et al. [24] examined the antibacterial activity of Gr nanosheets that can be applied in the development of biomedical devices. They observed that Gr nanosheets have antibacterial activities against _E. coli_. It is seen that the findings are compatible with the literature. As can be seen from the experimental results, PECVD Gr nanowalls synthesized onto G substrates, particularly at 200 W, exhibited stronger antibacterial activity against _E. coli_ and _S. aureus_, and the cell viabilities of _E. coli_ and _S. aureus_ decreased from 100% to 25.19% and 100% to 9.02%, respectively. The data obtained in the present study were also subjected to variance analysis. PCA was applied to illustrate the differences between the samples by evaluation of cell viabilities (%) of _E. coli_ and _S. aureus_. The score scatterplot, loading scatter plot, and biplot for the samples are shown in Figure 10(a)-c, respectively. Using PCA analysis, we examined the experimental results. The first two principal components (PC1 = 86.8% and PC2 = 13.2%) accounted for 100.0% of the variance. PECVD-2 and PECVD-3 were clustered together, and they were well separated from the other samples (Figure 10(a)), indicating that they had some differences. On the other hand, as can be seen from Figure 10(a), no other treatment was included in the same group. Both cell viabilities (%) of _E. coli_ and _S. aureus_ were positioned at the right side of the plot (Figure 10(b),c), while PECVD-2 and PECVD-3 were located at the left part of PC1 (Figure 10(c)). This result showed that PECVD-2 and PECVD-3 treatments were the treatments where the most inhibition on the cell viabilities (%) of _E. coli_ and _S. aureus_ was achieved (Figure 10(c)). In the current study, it was determined that the graphene treatments had a significant (\(p<0.01\)) effect on the cell viability (%) of _E. coli_. The effect of graphene treatments on the cell viability (%) of _E. coli_ is shown in Table 1. While the treatments of CVD-3 and PECVD-1 were not statistically different from the control groups (G-control and Ni-control), the highest inhibition on the cell viability (%) of _E. coli_ was statistically found in the treatments of PECVD-3, PECVD-2, CVD-1-Ni, and CVD-1. Figure 5.0 Score scatter plot (**a**), loading scatter plot (**b**), and biplot (**c**) of principal component analysis (PCA) (PC1 versus PC2) for the attributes in the samples.