The role of polymeric coatings for a safe-by-design development of biomedical gold nanoparticles assessed in zebrafish embryo

In the biomedical field, gold nanoparticles (GNPs) have attracted the attention of the scientific community thanks to their high potential in both diagnostic and therapeutic applications. The extensive use of GNPs led researchers to investigate their toxicity, identifying stability, size, shape, and surface charge as key properties determining their impact on biological systems, with possible strategies defined to reduce it according to a Safe-by-Design (SbD) approach. The purpose of the present work was to analyze the toxicity of GNPs of various sizes and with different coating polymers on the developing vertebrate model, zebrafish. In particular, increasing concentrations (from 0.001 to 1 nM) of 6 or 15 nm poly-(isobutylene-alt-maleic anhydride)-graft-dodecyl polymer (PMA)-or polyethylene glycol (PEG)-coated GNPs were tested on zebrafish embryos using the fish embryo test (FET). While GNP@PMA did not exert significant toxicity on zebrafish embryos, GNP@PEG induced a significant inhibition of embryo viability, a delay of hatching (with the smaller size NPs), and a higher incidence of malformations, in terms of tail morphology and eye development. Transmission electron microscope analysis evidenced that the more negatively charged GNP@PMA was sequestered by the positive charges of chorion proteins, with a consequent reduction in the amount of NPs able to reach the developing embryo and exert toxicological activity. The mild toxic response observed on embryos directly exposed to GNP@PMA suggest that these NPs are promising in terms of SbD development of gold-based biomedical nanodevices. On the other hand, the almost neutral GNP@PEG, which did not interact with the chorion surface and was free to cross chorion pores, significantly impacted the developing zebrafish. The present study raises concerns about the safety of PEGylated gold nanoparticles and contributes to the debated issue of the free use of this nanotool in medicine and nano-biotechnologies.