Two-step femtosecond laser ablation-based method for the synthesis of stable and ultra-pure gold nanoparticles in water

A two-step laser-assisted method for the synthesis of small and low-dispersed colloidal gold nanoparticles in deionized water is reported. As the first step, laser ablation from a gold target is used to fabricate relatively large (few tens of nanometers) and size-dispersed colloids. As the second step, self-modification of the femtosecond laser pulse into a white-light supercontinuum is used to perform the secondary ablation of colloids. We show that the latter treatment leads to a drastic reduction of both the mean nanoparticles size and size dispersion as well as to the enhancement of the solution stability. Being prepared in pure deionized water, the colloidal nanoparticles are stable and free of any impurities, making them unique for surface enhanced Raman scattering (SERS) and bio-imaging in vivo applications.