## 3 Results and Discussion
### Effects of Amount of Zinc Citrate on Antibacterial Efficacy of PVA/Zinc Citrate Nanofiber Mats  
Antibacterial efficacy against _S. aureus_ of PVA/zinc citrate nanofiber mats is indicated in Figure 7A. The pure PVA nanofiber mats are not bacteriostatic. In contrast, the addition of different amounts of zinc citrate (0.5, 1, 3, or 5 wt %) results in significant inhibition zones against _S. aureus_, and the diameter of the inhibition zone that PVA/zinc citrate nanofiber mats created is proportional to the amount of zinc citrate, as indicated in Table 3. The diameter of the inhibition zone of PVA/Zinc citrate nanofiber mats with the corresponding amount of zinc citrate are 5 mm (0.5 wt %), 7 mm (1 wt %), 11.8 mm (3 wt %), and 13.5 mm (5 wt %). In comparison to the inhibition zone caused by 0.5 wt % zinc citrate, the inhibition zone is increased by 1.4 times (1 wt %), 2.36 times (3 wt %), and 2.7 times (5 wt %). Adding 0.5 wt % zinc citrate has a significant antibacterial efficacy, and adding 5 wt % zinc citrate yields the maximum inhibition zone of 13.5 mm, which has only a slight 1.7 mm increase, in comparison to the inhibition zone caused by 3 wt % zinc citrate. This mild increase in the diameter of inhibition zone also suggests that 3 wt % zinc citrate is the optimal parameter.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Element**} & \multicolumn{4}{c}{**Zinc Citrate Content (wt \%)**} \\ \cline{2-5}  & **0.5 wt \%** & **1 wt \%** & **3 wt \%** & **5 wt \%** \\ \hline
**C K** & 56.23\% & 55.52\% & 53.85\% & 52.74\% \\
**O K** & 43.02\% & 42.93\% & 42.97\% & 42.57\% \\
**Zn L** & 0.74\% & 1.56\% & 3.18\% & 4.69\% \\ \hline
**Totals** & & & 100 & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Element content of PVA/zinc citrate nanofiber mats as related to various amounts of zinc citrate.  
Figure 6: EDS charts of PVA/zinc citrate nanofiber mats that contain (**a**) 0 wt %; (**b**) 0.5 wt %; (**c**) 1 wt %; (**d**) 3 wt %; and (**e**) 5 wt % zinc citrate.  
Zinc ions have antibacterial properties due to their positive charges, which interact with the negative charges of the cell wall of bacteria. The imbalance between positive and negative charges in turn causes damages to cell walls. The bacteria thus fail to regenerate their cell walls and then stop their proliferation. [PERSON] _et al._ indicate that zinc compound has antibacterial efficacy against _S. aureus_[42]. The antibacterial efficacy against _E. coli_ is indicated in Figure 7B. Regardless of the amount of zinc citrate, the PVA/zinc citrate nanofiber mats do not cause any inhibition zones, and _E. coli_ is absent over the PVA/zinc citrate nanofiber mats. This phenomenon indicates that PVA/zinc citrate nanofiber mats have only bacteriostatic, rather than antibacterial efficacy. Figure 7C indicates that a high content of zinc citrate causes a lower optical density of the suspension, which is composed of PVA/zinc citrate nanofiber mats and _S. aureus solution_, which exemplifies that the nanofiber mats possess a satisfactory antibacterial effect against _S. aureus_. In contrast, the optical density remains constant when PVA/zinc citrate nanofiber mat is cultured with _E. coli_ is administered, indicating a mere bacteriostatic effect. These results are in conformity with Figure 7A,B.