الفهرس 
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Abstract
In the last decades. nanotechnology has become a key word in scientific research as well as in the public interest and it is considered as the critical research technology of the 21 SI century. Gold nanoparticles have been proven to be powerful tools in various nanornedicinal applications. Consequently. the study of cytotoxicity and genotoxicity of gold nanoparticles has been emerged as an important issue. In this study, we have studied the cytotoxicity (using MTT assay) and genotoxicity (using comet assay) of gold nanospheres and nanorods in human hepatocellular carcinoma cell line (HepG2). The experimental conditions such as nanoparticles preparation (surface modification). laser power, time of exposure, and concentration of the gold nanoparticles have been studied. Non-PEGylated and PEGylated Au nanospheres with Poly (ethylene glycol) methyl ether thiol (m-PEG-SH), were synthesized by citrate reduction method. Also, Au nanorods were prepared using the seed-mediated method and modified with m-PEG-SH. The prepared nanoparticles were characterized using UV-Vis. spectroscopy. dynamic light scattering (DLS) and transmission electron microscopy (TEM). The synthesized Au nanoparticles before and after the PEGylation showed very good stability for both after different types of low intensity laser exposure and in the cell culture supplementary media (RPM I). The potential cytotoxicity of the synthesized Au nanoparticles before and after PEGylation in dark conditions showed that there is no significant difference in cell viability between non-PEGylated and PEGylated Au nanospheres at the same concentration. Also, the results shwed that the non-PEGylated Au nanorods had significant cytotoxicity. In contrast. the PEGylated Au nanorods showed no significant cytotoxicity regardless of incubation period. Under irradiation conditions using low power 532 nm DPSS laser and 780 nrn diode laser for different exposure times, only non-PEGylated Au nanospheres had phototoxicity on cell viability upon exposure to 532 nm DPSS laser at longer exposure time (120 min) and for all concentrations used, while no significant effects were observed with other preparations. Non-PEGylated Au nanorods showed no significant decrease in cell viability at all concentrations used after 5 min exposure. Longer laser exposure times up to 30 min resulted in slight decrease in cell viability while PEGylated Au nanorods only had effects after 30 min of exposure. The genotoxicity of synthesized Au nanoparticles demonstrated that non-PEGylated Au nanospheres and nanorods induced DNA damage while PEGylated Au nanosphere and nanorods did not show remarkable increase of DNA damage compared to untreated cells. The present study demonstrated that the PEGylated Au nanoparticles reduced cytotoxicity and genotoxicity effects on HepG2 cells compared to non-PEGylated Au nanoparticlcs, This makes this system safer to use in several important biomedical applications.