Cellular Uptake and Cytotoxicity of Varying Aspect Ratios of Gold Nanorods in HeLa Cells

Gold nanorods (GNRs) have received broad attention due to their tunable surface plasmon modes, which make them attractive candidates for applications in drug and gene delivery, biological imaging, and cancer treatments. In this study, we highlight the interactions of four different aspect ratios (ARs), 2.6, 3.2, 5.4 and 11.5, of GNRs with HeLa cells. Specifically, we study the uptake of the particles by HeLa cells while also considering the effects of other parameters such as the surface stabilizer, supernatant, and serum proteins present in the medium. From this work, it was determined that the cell viability depended on the chemical composition of the supernatant especially the amount of excess surfactant, hexadecyltrimethylammonium bromide (CTAB), used for the synthesis of GNRs; thus, the effect of aspect ratio of GNRs on endocytosis could not be directly discerned. For example, when exposed to GNRs of aspect ratio 11.5, HeLa cells showed higher cellular uptake compared to smaller aspect ratios, and also exhibited lower cytotoxicity due to the lower concentration of CTAB used in their synthesis. Gentler purification methods (sedimentation) appeared to be a factor in lowering the free CTAB concentration for experiments containing GNRs of aspect ratio 11.5. Overall, the synthesis protocols functionalization, purification processes, and the stability of GNRs in media have an effect on cellular uptake and viability. Our results suggest that the AR of GNRs may a role in endocytosis when mPEG, instead of CTAB, is used as a stabilizing ligand although an overall trend could not be unequivocally established. In future studies, sedimentation, contact time, and internalization kinetics need to be probed further using more biocompatible ligands and less inert ligands (mPEG) to determine the effect of AR on GNR internalization in HeLa cells.