Potential Nanotoxicity of Pegylated Gold Nanorods having Different Sizes and Shapes as a Biocompatible Contrast Agent for 2PE Imaging

Gold nanoparticles (AuNPs) entices the attention last years in nanobiotechnology. Different methodologies were designed to produce AuNPs with tunable sizes and shapes. Gold nanorods (AuNRs) are candidates for different applications including cell imaging, smart drug delivery and photothermal therapy. AuNRs dispersion is characterized by two surface plasmonic resonances referring to the interaction of incident light with the free electrons of the transversal and longitudinal axes atoms. The absorption wavelength of the longitudinal surface plasmonic resonance is highly sensitive to the aspect ratio of the NRs and the medium dielectric resonance. Regarding to these spectacular properties and by tuning the aspect ratio of the NRs, AuNRs can be useful as contrast agent for cell imaging through controlling the wavelength of the excitation light. Here we report about AuNRs with two different aspect ratios, photochemically synthesized using CTAB as cationic surfactant. Functionalization was performed on the NRs surface to exchange cytotoxic CTAB molecules with thio methoxypolyethylene glycol (mPEG-SH). In order to evaluate the cellular uptake of the AuNRs and the potential nanotoxicity we used cell line, namely: HeLa. The viability of the cells after nanorods uptake was evaluated by colorimetric assay to reveal the percentage of dead and apoptotic cells after exposure. Furthermore, due to the fact that oxidative stress is one of the mechanisms responsible of toxicity of nanoparticles, we investigated the levels of reduced gluthation (GSH) of treated versus control cells by using a second colorimetric assay. 2PE microscopy at different laser wavelengths has been used to estimate the effectiveness of AuNRs as contrasting agent for cell imaging. Occasionally, TEM images were acquired for cells after exposure to NRs to quantify NRs inside the cells and in which specific regions.