Multimodal gold nanostars as SERS tags for optically-driven doxorubicin release study in cancer cells

Surface Enhanced Raman Scattering (SERS) active gold nanostars represent an opportunity in the field of bioimaging and drug delivery. The combination of gold surface chemical versatility with the possibility to tune the optical properties changing the nanoparticles shape constitutes a multimodal approach for the investigation of the behavior of these carriers inside living cells. In this work, SERS active star-shaped nanoparticles were functionalized with doxorubicin molecules and covered with immuno-mimetic thiolated polyethylene glycol (PEG). Doxorubicin-conjugate gold nanoparticles show an intense Raman enhancement, a good stability in physiological conditions, and a low cytotoxicity. The strong adsorption of the anticancer drug doxorubicin in close contact with the gold nanostars surface enables their use as SERS tag imaging probes in vivo. Upon laser irradiation of the nanoparticles, a strong SERS signal is generated by the doxorubicin molecules close to the nanostars surface, enabling the localization of the nanoparticles inside the cells. After long time irradiation, the SERS signal drops, indicating the thermally driven delivery of the drug inside the cell. Therefore, the combination of SERS and laser scanning confocal microscopy is a powerful technique for the real-time analysis of drug release in living cells.