Femtosecond laser-induced photochemical synthesis of anisotropic gold nanoparticles using geometric focusing

Gold nanoparticles have attracted much attention due to their excellent properties and have been widely applied in various fields. The laser-induced photochemical reduction has been developed as a green synthesis method to produce bare gold nanoparticles without generating hazardous waste. Interaction between femtosecond laser pulses and aqueous media generates plasmas containing hydrated electrons and hydrogen peroxide, which are responsible for the nucleation and growth of gold nanoparticles. Brief laser irradiation on aqueous gold ion solution followed by post-irradiation aging has led to anisotropic growth of gold nanoparticles. In this work, laser irradiation was performed using conventional geometric focusing. After post-irradiation treatment by hydrogen peroxide, the solution was left to age while being monitored using in situ UV-vis spectrometer. The emergence of absorption peaks in the near-infrared range indicated the formation of anisotropic gold nanoparticles, as confirmed by TEM images. It was observed that laser irradiation time significantly affects the growth of AuNPs. It was also demonstrated that the concentration of hydrogen peroxide accelerated nanoparticle growth, although excess hydrogen peroxide can cause backward oxidation on the nanoparticles and reduce the anisotropy.