An in vitro study investigating the effects of functional groups on the toxicity of gold nanoparticles

Abstract

The thesis provides a comprehensive investigation on the interaction and toxicity effects of newly synthesized gold nanoparticles in human embryonic kidney (HEK 293) and human hepatocellular carcinoma (HepG2) cell lines. The citrate stabilized AuNPs with increasing diameter and polyethylene glycol modified AuNPs presenting various functional groups were synthesized. The synthesis of AuNPs was achieved using the citrate reduction and the Brust–Schiffrin methods. The AuNPs were further characterized in cell growth medium using TEM, UV-vis, Zetasizer and FTIR. Cellular uptake and sub-cellular localization of AuNPs was studied with dark field microscopy and field emission electron microscope fitted with an energy dispersive X-ray spectrometer. TEM was further used to show the exocytosis of the AuNPs following long term exposure. Cytotoxicity of AuNPs was assessed using real-time cell analyzer impedance technology to monitor cell viability and cell proliferation. Furthermore, the genotoxicity, cytokine induction and the effect of AuNPs on the generation of free radicals was investigated using chromosome aberration test; flow cytometer and electron spin resonance. TEM micrographs confirmed that AuNPs were taken up by the cells. The AuNPs were deposited in the cytoplasm and in endosomal and lysosomal vesicles of cells. Furthermore, TEM revealed that AuNPs are depleted from cells after 4 weeks of culture through excretion of the nanoparticles filled vesicles to the medium. AuNPs deposited in the cell cytoplasm are removed by diffusion through the plasma membrane. Quantification of intracellular AuNPs revealed a high uptake of citrate stabilized AuNPs in the two cell lines when compared to the PEG-coated AuNPs. The cytotoxicity profiles of the nanoparticles revealed a size and surface chemistry dependent effect on cells, with HEK 293 cells as the most sensitive cell type. AuNPs with the azide, nitriloacetic acid, carboxyl, biotin, hydroxyl, and the methoxy functional groups showed genotoxicity effects in HEK 293 cells. In addition, the carboxyl and the nitriloacetic acid functionalized AuNPs showed catalytic activity in free radical generation. In conclusion, the functional groups on AuNPs surface may induce adverse effects in cells through interaction with cellular components. The results will have implication in hazard identification of newly synthesized AuNPs and safety evaluation of AuNPs in future studies.