PEGylated gold nanorods as optical trackers for biomedical applications: an in vivo and in vitro comparative study.

Gold nanorods (AuNRs) are eligible for a variety of biological applications including cell imaging, sensing, and photothermal therapy thanks to their optical properties. The aim of this work is to show how AuNRs could be employed as non-photobleachable optical contrast agents for biomedical applications. In order to demonstrate the feasibility of their use as optical trackers, we employed two-photon emission confocal microscopy on cells incubated with PEGylated AuNRs. Remarkably, AuNRs were localized mostly in the perinuclear zone and microscopy characterization showed the presence of a considerable number of rods inside cell nuclei. Furthermore, we estimated the toxicity and the efficiency of cellular uptake of the PEGylated AuNRs as a function of administered dose on HeLa/3T3 cell lines and on zebrafish during development, employed as an in vivo model. Eventually, we observed good agreement between in vivo and in vitro experiments. The employed AuNRs were prepared through a photochemical protocol here improved by tuning the amount of the cationic surfactant cetyltrimethylammonium bromide for the achievement of AuNRs at two different aspect ratios. Furthermore we also investigated if the AuNR aspect ratio influenced the toxicity and the efficiency of cellular uptake of the PEGylated AuNRs in HeLa/3T3 cell lines and in zebrafish embryos.