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 plasmonic resonance modes, which make them an attractive candidate for biomedical applications in drug and gene delivery, biological imaging, and cancer treatment. 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 with respect to cellular uptake and cellular viability 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 the shorter aspect ratios and a lower cytotoxicity simply because of the lower concentration of CTAB used during the synthesis, and a gentler purification method, such as sedimentation, also appeared to be a factor. Overall, the synthesis protocols, functionalization, purification processes, and the stability of GNRs in media have a major effect on cellular uptake and viability. Our results suggest that perhaps AR does play a role in endocytosis although an overall trend could not be unequivocally established, and sedimentation, contact time, and internalization kinetics need to be probed further using more biocompatible ligands in future studies.