Random walk of single gold nanoparticles in zebrafish embryos leading to stochastic toxic effects on embryonic developments

We have synthesized and characterized stable (non-aggregating, non-photobleaching and non-blinking), nearly monodisperse and highly-pure Au nanoparticles, and used them to probe nanoparticle transport and diffusion in cleavage-stage zebrafish embryos and to study their effects on embryonic development in real-time. We found that single Au nanoparticles (11.6 ± 0.9 nm in diameter) passively diffused into the chorionic space of the embryos via their chorionic pore canals and continued their random-walk through chorionic space and into the inner mass of embryos. Diffusion coefficients of single nanoparticles vary dramatically (2.8 × 10⁻¹¹ to 1.3 × 10⁻⁸ cm² s⁻¹) as nanoparticles diffuse through the various parts of embryos, suggesting highly diverse transport barriers and viscosity gradients in the embryos. The amount of Au nanoparticles accumulated in embryos increases with nanoparticle concentration increases. Interestingly, however, their effects on embryonic development are not proportionally related to their concentration. The majority of embryos (74% on average) chronically incubated with 0.025–1.2 nM Au nanoparticles for 120 h developed to normal zebrafish, with some (24%) being dead and few (2%) deformed. We have developed a new approach to image and characterize individual Au nanoparticles embedded in tissues using histology sample preparation methods and localized surface plasmon resonance spectra of single nanoparticles. We found Au nanoparticles in various parts of normally developed and deformed zebrafish, suggesting that the random-walk of nanoparticles in embryos during their development might have led to stochastic effects on embryonic development. These results show that Au nanoparticles are much more biocompatible with (less toxic to) the embryos than the Ag nanoparticles that we reported previously, suggesting that they are better suited as biocompatible probes for imaging embryos in vivo. The results provide powerful evidences that the biocompatibility and toxicity of nanoparticles is highly dependent on their chemical properties, and that the embryos can serve as effective in vivo assays to screen their biocompatibility.