We demonstrate phototoxicity generated by silicon quantum dot nanoparticles (SiQDNPs) using zebrafish as an animal model. Having long exciton lifetime, the SiQDNPs can function as photosensitizers which absorb incident optical light and transfer the energy to oxygen molecules in close proximity, generating cytotoxic singlet oxygens. First, the zebrafish embryos were soaked in the SiQDNP suspension in E3 medium, while being illuminated under blue light or kept in the dark for 6 h. Through neutral red staining immediately afterward, the illuminated embryos showed more prominent injuries at their head, yolk sac and tail parts than those in the dark. Furthermore, prolonged observation after the treatment revealed that the illuminated embryos had mortality rates significantly higher than those without illumination, clearly showing the phototoxicity effect generated by the SiQDNPs. However, adverse effect due to the immersion of whole embryos in the SiQDNP suspension was also observed. To alleviate this issue, minute amounts of the SiQDNPs were microinjected to the embryos, followed by blue light illumination. By acridine orange staining subsequently, cell apoptosis localized near the microinjection site was revealed, whereas no apoptosis was found for those also microinjected with the SiQDNPs but without illumination. The phototoxicity effect demonstrated on zebrafish embryos in this work manifests the potential of using the SiQDNPs as a photosensitizer for photodynamic therapy.
Keywords: photodynamic therapy; phototoxicity; silicon quantum dot; singlet oxygen; zebrafish embryo.