## 4 Conclusions  
This paper presents the successful synthesis of ZnO NPs from _P. ostreatus_ mushrooms, and characterization of ZnO NPs on UV-Vis spectra confirmed the peaks of ZnO NPs at  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Cell Lines** & **IC25 (mg/mL)** & **IC50 (mg/mL)** \\ \hline \multirow{2}{*}{Mushroom extract} & Hek293 & 0.074 (74 \(\mathrm{\SIUnitSymbolMicro g}\)/mL) & 0.335 (335 \(\mathrm{\SIUnitSymbolMicro g}\)/mL) \\  & HepG2 & - & - \\ \multirow{2}{*}{Mushroom ZnO NPs} & Hek293 & 0.034 (34 \(\mathrm{\SIUnitSymbolMicro g}\)/mL) & 0.056 (56 \(\mathrm{\SIUnitSymbolMicro g}\)/mL) \\  & HepG2 & 0.037 (37 \(\mathrm{\SIUnitSymbolMicro g}\)/mL) & 0.055 (55 \(\mathrm{\SIUnitSymbolMicro g}\)/mL) \\ \hline \hline \end{tabular}
\end{table}
Table 2: The extrapolated IC25 and IC50 concentrations for HepG2 and Hek293 cells.  
340 and 400 nm. The synthesized ZnO NPs were observed to be spherical and agglomerated with high stability. Thus, the mushroom was able to act as a reducing, capping, and stabilizing agent in the synthesis of ZnO NPs. The green-synthesis method proved beneficial in fighting against Gram-positive and Gram-negative bacteria, which are a major concern in the health sector. This is the first report of ZnO NP biosynthesis using the edible _P. ostreatus_ mushroom. Hence, an alternative safe, cost-effective, and ecofriendly biosynthesis method to produce ZnO NPs can be achieved through mushroom-mediated synthesis. Further research can be conducted on other nanoparticles using the _P. ostreatus_-mediated biosynthesis method. Overall, minimal cytotoxicity to HepG2 cells (cell viability above 75% in accordance with the ISO standard) was observed for the _P. ostreatus_ mushroom extract. Thus, the liver function of xenobiotic metabolism possibly resulted in the detoxification of the cytotoxic compounds in the mushroom extract. However, cell viability below the ISO standard at MIC above 0.160 mg/mL indicates that the mushroom extract should be used with caution due to its potential cytotoxicity to kidney cells. The mushroom-synthesized ZnO NPs were acutely cytotoxic to both Hek293 and HepG2 cells. Further studies should investigate the cytotoxic effects of the _P. ostreatus_ mushroom extracts in vivo using a rat or mouse model, since metabolism in the liver may reduce the toxic effects in kidney cells that were elucidated in this study. The cytotoxicity data also demonstrate antiproliferative activity of the mushroom-synthesized ZnO NPs in HepG2 cells. Thus, further investigation of potential anticancer effects of the _P. ostreatus_ mushroom extract and mushroom-synthesized ZnO NPs is warranted and recommended.  
The manuscript was written and read by all the authors who were mentioned on title page. The authors [PERSON], [PERSON] and O.J.P. structured and designed the experiments, and wrote and proofread the paper for possible corrections. [PERSON], I.N.M. and R.K. conducted the laboratory experiments, and collected and analyzed data; S.K. also proofread the paper, and analyzed and interpreted part of the data. All authors have read and agreed to the published version of the manuscript.  
This work was supported and funded by the National Research Foundation (NRF) of South African [grant number: 138414] to M.B.C. and [grant number: 145396] awarded to O.J.P. Some of the work reported herein was made possible through funding by the South African Medical Research Council through its Division of Research Capacity Development under the Early Investigators Programme awarded to O.J.P. from funding received from the South African National Treasury.  
Not applicable.  
All the authors declare no conflict of interest for this work. There is no known competing financial interest and personal relationship that could influence this paper's reported work.