## 3 Results and Discussion
### Cytotoxicity Assay of AuNPs  
The development of therapeutic nanotechnology using nanogold, especially in diagnosis and treatment in oncology, requires numerous toxicological examinations to detect the appropriate dosing for patient safety [104; 105]. Herein, an MTT assay was used to evaluate the nanotoxicological properties of _Z. officinal_-induced AuNPs against normal and tumor cell lines. Consistent with previous studies, AuNPs displayed powerful cytotoxicity against cancerous and normal cells in a dose-dependent mode [106]. These findings can be correlated to the microscopic changes and cytotoxic effects of AuNPs toward the PC12 cancer cell line, which were both concentration-dependent [107]. The cancer cell lines HepG2 and MCF7 lose approximately 94.8% and 70% of their viability, respectively, after treatment with 500 \(\upmu\)g mL\({}^{-1}\), whereas the normal OEC cell line only loses about 50% of its viability at the same concentration (Figure 7). On the other hand, the normal and cancer cell lines recover their viability percentages with concentrations reduced to 99.4 \(\pm\) 1.8%, 51.8 \(\pm\) 0.9, and 83.9 \(\pm\) 0.5% for OEC, HepG2, and MCF7, respectively, at a concentration of 125 \(\upmu\)g mL\({}^{-1}\). This indicates that the phytosynthesized AuNPs are more active against hepatocellular carcinoma (HepG2) than adenocarcinoma (MCF7), with negligible activity against normal oral epithelial cells at concentrations of 250 and 125 \(\upmu\)g mL\({}^{-1}\) (Figure 7). Analysis of variance showed that the maximum antiproliferative effect was observed for the hepatocellular carcinoma HepG2 cells, with an IC\({}_{50}\) value of 131.9 \(\pm\) 9.34 \(\upmu\)g mL\({}^{-1}\), whereas the AuNP concentration required for 50% morbidity (IC\({}_{50}\)) of adenocarcinoma Mcf7 cells reached 288.23 \(\pm\) 31.39 \(\upmu\)g mL\({}^{-1}\). In contrast, the value of IC\({}_{50}\) for the normal oral epithelial OEC cells was 487.612 \(\pm\) 3.53 \(\upmu\)g/mL (Figure 7). The significant difference in IC\({}_{50}\) values between tested cancerous and normal cells may represent a safe therapeutic window to determine doses and spare patients from harmful side effects. Figure 6: Antioxidant activity of plant-based AuNPs measured by DPPH method at different concentrations compared to ascorbic acid. Data show average values \(\pm\) SD (n = 3). Different letters on the bars at the same concentration indicate that the mean values are significantly different (at \(p\leq\) 0.05). Similarly, [PERSON] et al. [108] reported the efficient toxicological properties of phytofabricated AuNPs against the lymphoblastic leukemia cell lines Molt-3 and TALL-104, with IC\({}_{50}\) values of 329 and 381 ug/mL, respectively. On the other hand, AuNPs derived from Parsley leaf extract reduced the viability of the human colorectal cell line (CO-II) at a low concentration (IC\({}_{50}\) = 56.83 g/mL); this enhanced cytotoxicity could be attributed to the free radicals generated by nanoparticles. In addition, the tiny size of nanoparticles contributes to the destruction of the membrane of cancer cells [109]. Biogenic gold nanoparticles were found to be excellent candidates for biomedical applications and safe for a normal cell line but toxic to cancer cells (MDA-MB-231) [110]. [PERSON] et al. correlated observed morphological changes with cell apoptosis induced by AuNPs. [PERSON] et al. [105] commented that AuNPs reduced the viability of breast adenocarcinoma and hepatocellular carcinoma. The characteristic nanotoxicological potential was attributed to several possible mechanisms and causes associated with the shape of AuNPs, incubation time, size, concentration, surface functionalization, fabrication method, and the type of treated cells. Figure 8 depicts the microscopic observation of normal and cancer cell lines after treatment with various concentrations of AuNPs.